Subjects -> PHYSICS (Total: 857 journals)
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SOUND (25 journals)

Showing 1 - 22 of 22 Journals sorted alphabetically
Acoustical Physics     Hybrid Journal   (Followers: 13)
Acoustics     Open Access   (Followers: 4)
Acoustics Australia     Hybrid Journal   (Followers: 1)
Acoustics Today     Hybrid Journal   (Followers: 9)
Acta Acustica     Open Access   (Followers: 4)
Advances in Acoustics and Vibration     Open Access   (Followers: 48)
Applied Acoustics     Hybrid Journal   (Followers: 36)
Archives of Acoustics     Open Access   (Followers: 22)
Australasian Journal of Ultrasound in Medicine (AJUM)     Hybrid Journal   (Followers: 2)
Bioacoustics : The International Journal of Animal Sound and its Recording     Partially Free   (Followers: 5)
Building Acoustics     Hybrid Journal   (Followers: 4)
Bulletin de l'AFAS     Open Access   (Followers: 1)
Journal of Sound and Vibration     Hybrid Journal   (Followers: 161)
Journal of the Acoustical Society of America     Full-text available via subscription   (Followers: 58)
Journal of Ultrasonography     Open Access   (Followers: 1)
Journal of Ultrasound in Medicine     Full-text available via subscription   (Followers: 12)
Open Journal of Acoustics     Open Access   (Followers: 23)
Phonica     Open Access  
Proceedings of Meetings on Acoustics     Open Access   (Followers: 14)
Sonography     Hybrid Journal   (Followers: 1)
SoundEffects - An Interdisciplinary Journal of Sound and Sound Experience     Open Access   (Followers: 4)
Ultrasound International Open     Open Access   (Followers: 2)
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Number of Followers: 4  

  This is an Open Access Journal Open Access journal
ISSN (Online) 2624-599X
Published by MDPI Homepage  [249 journals]
  • Acoustics, Vol. 5, Pages 57-71: Study of Tire–Pavement Noise
           Acoustic Performance in Resilient Road Pavement Made of Strain-Hardening
           Cementitious Composites

    • Authors: Bawono, NguyenDinh, Thangaraj, Ertsey-Bayer, Simon, Lechner, Freudenstein, Yang
      First page: 57
      Abstract: A modified strain-hardening cementitious composite (SHCC) material, fabricated using corundum aggregates (SHCC-Cor), has been proposed for roadway applications as it offers high structural performance and high skid resistance. However, the acoustic performance of SHCC is unclear and has not been well studied in the past. Theoretically, SHCC may not provide the optimum solution in acoustic performance as it provides a low texture profile, high density, and low porosity. In this study, the acoustic performance of pavement slabs made of SHCC and modified SHCC-Cor are investigated using a nondestructive method to determine the surface roughness (macro texture) of slab surfaces. The pavement–tire noise level was then simulated using SPERoN software. As result, the noise level coming from the pavement made of SHCC could be up to 65 dB(A), while the noise level for SHCC-Cor increased up to 69.2 dB(A) because of the lower shape factor (G) due to a rougher surface as a result of the existence of corundum aggregate on the SHCC surface. The aeroacoustics were also increased compared to the SHCC slab. The modification of SHCC-Cor by introducing grooves (SHCC-Cor-Gro) successfully reduced the sound level coming from the vibration.
      Citation: Acoustics
      PubDate: 2023-01-09
      DOI: 10.3390/acoustics5010004
      Issue No: Vol. 5, No. 1 (2023)
  • Acoustics, Vol. 5, Pages 72-86: The Effect of Stimuli Level on Distortion
           Product Otoacoustic Emission in Normal Hearing Adults

    • Authors: Maryam Naghibolhosseini
      First page: 72
      Abstract: The goal of this study is to compare three of the most commonly used primary-level relation paradigms (i.e., Scissors, Boys Town ‘Optimal’, and Equal-Level) in generation of distortion product otoacoustic emissions (DPOAEs) in normal hearing adults. The generator and reflection components were extracted from DPOAEs in each paradigm. The generator and reflection component levels and input/output (I/O) functions were compared across paradigms and primary-tone levels. The results showed a different I/O function growth behavior across frequency and levels among paradigms. The Optimal paradigm showed a systematic change in the generator and reflection component levels and I/O slopes across primary levels among subjects. Moreover, the levels and slopes in the Optimal paradigm were more distinct across levels with less variations across frequency leading to a systematic change in the DPOAE fine structure across levels. The I/O functions were found to be more sensitive to the selected paradigm; especially the I/O function for the reflection component. The I/O functions of the reflection components showed large variability across frequencies due to different frequency shifts in their microstructure depending on the paradigm. The findings of this study suggested the Optimal paradigm as the proper primary-level relation to study cochlear amplification/compression. The findings of this study shows that care needs to be taken in comparing the findings of different studies that generated DPOAEs with a different level-relation paradigm.
      Citation: Acoustics
      PubDate: 2023-01-10
      DOI: 10.3390/acoustics5010005
      Issue No: Vol. 5, No. 1 (2023)
  • Acoustics, Vol. 5, Pages 87-119: GIS Based Road Traffic Noise Mapping and
           Assessment of Health Hazards for a Developing Urban Intersection

    • Authors: Md Iltaf Zafar, Rakesh Dubey, Shruti Bharadwaj, Alok Kumar, Karan Kumar Paswan, Anubhav Srivastava, Saurabh Kr Tiwary, Susham Biswas
      First page: 87
      Abstract: Determination of health hazards of noise pollution is a challenge for any developing city intersection. The people working at roadside open-air shops or near the congested roads of any intersection face intense noise pollution. It becomes very difficult to efficiently determine the hazards of noise on the health of people living near the intersection. An attempt was made to determine the noise-induced health hazards of the developing city of Bahadurpur, UP, India. The noise levels were monitored over 17 station points of the intersection for three months at different times of the day. Equivalent noise level (Leq) maps were determined within an accuracy of ±4dB. Areas adjacent to intersections indicated noise exposure levels close to 100 dB. Health hazards for the people of the intersection were determined through the testing of auditory and non-auditory health parameters for 100 people. A total of 75–92% of the people who work/live near the noisy intersection were found to be suffering from hearing impairment, tinnitus, sleep disturbance, cardiovascular diseases, hypertension, etc. Whether the recorded health hazards were indeed related to noise exposure was confirmed by testing the health parameters of people from the nearby and less noisy area of Pure Ganga. The nearby site reported mild hazards to the health of the population. An alarming level of hearing impairment was prevalent in the noisy Bahadurpur intersection (79–95%) compared to the same in Pure Ganga (13–30%). The estimated noise-induced health hazards were also compared for noisy and less-noisy study sites using ANOVA statistics. The results suggested that the health hazards reported in the two sites are not similar. Further, the severe hazards to people’s health at the underdeveloped intersection were found to be primarily caused by the intense exposure to noise.
      Citation: Acoustics
      PubDate: 2023-01-13
      DOI: 10.3390/acoustics5010006
      Issue No: Vol. 5, No. 1 (2023)
  • Acoustics, Vol. 5, Pages 120-121: Acknowledgment to the Reviewers of
           Acoustics in 2022

    • Authors: Acoustics Editorial Office Acoustics Editorial Office
      First page: 120
      Abstract: High-quality academic publishing is built on rigorous peer review [...]
      Citation: Acoustics
      PubDate: 2023-01-20
      DOI: 10.3390/acoustics5010007
      Issue No: Vol. 5, No. 1 (2023)
  • Acoustics, Vol. 5, Pages 1-27: A Hybrid Multistep Procedure for the
           Vibroacoustic Simulation of Noise Emission from Wind Turbines

    • Authors: Marc Zarnekow, Thomas Grätsch, Frank Ihlenburg
      First page: 1
      Abstract: This paper proposes an efficient hybrid analytical-computational approach for the simulation of mechanical vibrations and sound radiation in wind turbine drive trains.The computational procedure encompasses the detailed modeling of vibrational sources and structural sound paths as well as the major panels of airborne noise radiation. The angle-varying mesh stiffness is obtained from a series of quasi-static finite element simulations. A novel procedure is proposed to obtain the time-varying mesh stiffness at fluctuating speed. The varying mesh stiffness is introduced as a parametric excitation in an analytical gear model, and the Fourier-transformed results are used as vibrational sources in a finite-element-based harmonic response analysis of the drive train. The present paper focuses on the modeling of gear contact and gearbox vibrations. The models and procedures are outlined, and computational results are compared to physical measurements on a 2.5 MW wind turbine. The results are in good qualitative agreement at tonal frequencies. This is particularly the case at fluctuating speed, where both the simulation and the measurement show the characteristic effect of frequency modulation. The computational procedure has been expanded to the whole drive train and is effectively applied in the conception and evaluation of design measures for the reduction of tonal amplitudes.
      Citation: Acoustics
      PubDate: 2022-12-22
      DOI: 10.3390/acoustics5010001
      Issue No: Vol. 5, No. 1 (2022)
  • Acoustics, Vol. 5, Pages 28-45: Intangible Mosaic of Sacred Soundscapes in
           Medieval Serbia

    • Authors: Zorana Đorđević, Dragan Novković, Marija Dragišić
      First page: 28
      Abstract: Religious practice in Serbia has taken place using both indoors and outdoors sacred sites ever since the adoption of Christianity in medieval times. However, previous archaeoacoustic research was focused on historic church acoustics, excluding the open-air soundscapes of sacred sites. The goal of this review paper is to shed light on the varieties of sacred soundscapes that have supported the various needs of Orthodox Christian practice in medieval Serbia. First, in relation to the acoustic requirements of the religious service, we compare the acoustic properties of masonry and wooden churches based on the published archaeoacoustic studies of medieval churches and musicological studies of the medieval art of chanting. Second, we provide an overview of the ethnological and historical studies that address the outdoor sacred soundscapes and investigate the religious sound markers of large percussion instruments, such as bells and semantra, the open-air litany procession that has been practiced during the annual celebration of a patron saint’s day in rural areas, and the medieval assemblies that took place on the sacred sites. This paper finally points out that the archaeoacoustic studies of sacred soundscapes should not be limited to church acoustics but also include open-air sacred sites to provide a complete analysis of the aural environment of religious practice and thus contribute to understanding the acoustic intention of medieval builders, as well as the aural experience of both clergy and laity.
      Citation: Acoustics
      PubDate: 2022-12-27
      DOI: 10.3390/acoustics5010002
      Issue No: Vol. 5, No. 1 (2022)
  • Acoustics, Vol. 5, Pages 46-56: Investigation of the Change of Acoustic
           Pressure in an Element of Acoustic Barrier with an Elliptical Shape

    • Authors: Krasimir Nedelchev, Elitsa Gieva, Ivan Kralov, Ivelina Ruskova
      First page: 46
      Abstract: In the presented article we have investigated the variation of the sound pressure level in characteristic areas around an element of an acoustic barrier with an elliptical shape at different frequencies (from 100 Hz to 2000 Hz). The variation of the sound pressure level in four characteristic areas located on the axis of symmetry of the acoustic barrier element is investigated. The purpose of the research is to determine in which of the areas it is most efficient to place devices for generating electrical energy from acoustic noise. The results were analyzed and relevant conclusions were drawn.
      Citation: Acoustics
      PubDate: 2022-12-31
      DOI: 10.3390/acoustics5010003
      Issue No: Vol. 5, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 821-833: The Importance of Noise Attenuation
           Levels in Neonatal Incubators

    • Authors: Fernández-Zacarías, Puyana‐Romero, Hernández-Molina
      First page: 821
      Abstract: Background: It is known that high noise levels can be harmful to preterm infants, causing physiological and psychological disorders. It is also known that premature babies spend a lot of time in an incubator. In this sense, many studies show that incubator noise levels can range from 45 to 70 dB. However, these differences in noise levels depend, fundamentally, on the wide range of methodology that can be used. This study aims to know the levels of noise from a fan in the incubator itself and how much it can isolate the noises coming from the outside. Methods: For this purpose, the noise levels of three incubators were measured within a sound-dampened booth for free-field audiometry. For the emission of acoustic energy, a pink noise generator was used; likewise, two microphones were placed, one inside the incubator cabin and the other outside, to determine the acoustic insulation levels of the tested incubators. Results: The incubators produced equivalent continuous sound pressure levels between 53.5 and 58 dB. Acoustic insulation analysis showed that levels varied from one incubator to another, between 5.2 and 10.4 dB. Conclusions: It is necessary to improve the acoustic insulation inside the incubator cabin and to reduce the noise levels of the motor fan. On the other hand, although the incubators are meeting the noise criteria set out in the IEC60601-2-19: 2009 standard of 60 dBA, under normal use conditions, they are still far from the limit recommended by the American Academy of Pediatrics (45 dBA).
      Citation: Acoustics
      PubDate: 2022-09-21
      DOI: 10.3390/acoustics4040049
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 834-848: Compensation of Modeling Errors for the
           Aeroacoustic Inverse Problem with Tools from Deep Learning

    • Authors: Hans-Georg Raumer, Daniel Ernst, Carsten Spehr
      First page: 834
      Abstract: In the field of aeroacoustic source imaging, one seeks to reconstruct acoustic source powers from microphone array measurements. For most setups, one cannot expect a perfect reconstruction. The main effects that contribute to this reconstruction error are data noise and modeling errors. While the data noise is accounted for in most advanced reconstruction methods, e.g., by a proper regularization strategy, the modeling error is usually neglected. This article proposes an approach that extends regularized inverse methods with a mechanism that takes the modeling error into account. The presented algorithmic framework utilizes the representation of the Fast Iterative Shrinkage Thresholding Algorithm (FISTA) algorithm by a neural network and uses standard gradient schemes from the field of deep learning. It is directly applicable to a single measurement, i.e., a prior training phase on previously generated data is not required. The capabilities of the method are illustrated by several numerical examples.
      Citation: Acoustics
      PubDate: 2022-09-27
      DOI: 10.3390/acoustics4040050
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 849-866: Horizontal and Vertical Voice
           Directivity Characteristics of Sung Vowels in Classical Singing

    • Authors: Manuel Brandner, Matthias Frank, Alois Sontacchi
      First page: 849
      Abstract: Singing voice directivity for five sustained German vowels /a:/, /e:/, /i:/, /o:/, /u:/ over a wide pitch range was investigated using a multichannel microphone array with high spatial resolution along the horizontal and vertical axes. A newly created dataset allows to examine voice directivity in classical singing with high resolution in angle and frequency. Three voice production modes (phonation modes) modal, breathy, and pressed that could affect the used mouth opening and voice directivity were investigated. We present detailed results for singing voice directivity and introduce metrics to discuss the differences of complex voice directivity patterns of the whole data in a more compact form. Differences were found between vowels, pitch, and gender (voice types with corresponding vocal range). Differences between the vowels /a:, e:, i:/ and /o:, u:/ and pitch can be addressed by simplified metrics up to about d2/D5/587 Hz, but we found that voice directivity generally depends strongly on pitch. Minor differences were found between voice production modes and found to be more pronounced for female singers. Voice directivity differs at low pitch between vowels with front vowels being most directional. We found that which of the front vowels is most directional depends on the evaluated pitch. This seems to be related to the complex radiation pattern of the human voice, which involves a large inter-subjective variability strongly influenced by the shape of the torso, head, and mouth. All recorded classical sung vowels at high pitches exhibit similar high directionality.
      Citation: Acoustics
      PubDate: 2022-10-01
      DOI: 10.3390/acoustics4040051
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 867-884: A Time-Domain Finite-Difference Method
           for Bending Waves on Infinite Beams on an Elastic Foundation

    • Authors: Katja Stampka, Ennes Sarradj
      First page: 867
      Abstract: To model the vibration and structure-borne sound excitation and propagation of a railway rail, it can be modeled as an infinite beam on an elastic foundation. Existing analytical or numerical models are either formulated in the frequency domain or consider only finite beams in the time domain. Therefore, a time-domain approach for bending wave propagation on an effectively infinite beam on an elastic foundation is proposed. The approach makes use of an implicit finite-difference method that allows for varying properties of the beam and the foundation along the length of the beam. Strategies for an efficient discretization are discussed. The method is validated against existing analytical models for a single layer and two layers, as well as continuous and discrete support. The results show very good agreement, and it can be concluded that the proposed method can be seen as a versatile method for simulating the behavior of a beam on different kinds of elastic foundations.
      Citation: Acoustics
      PubDate: 2022-10-05
      DOI: 10.3390/acoustics4040052
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 885-893: One-Way Wave Operator

    • Authors: Hans-Joachim Raida
      First page: 885
      Abstract: The second-order partial differential wave Equation (Cauchy’s first equation of motion), derived from Newton’s force equilibrium, describes a standing wave field consisting of two waves propagating in opposite directions, and is, therefore, a “two-way wave equation”. Due to the second order differentials analytical solutions only exist in a few cases. The “binomial factorization” of the linear second-order two-way wave operator into two first-order one-way wave operatoras has been known for decades and used in geophysics. When the binomial factorization approach is applied to the spatial second-order wave operator, this results in complex mathematical terms containing the so-called “Dirac operator” for which only particular solutions exist. In 2014, a hypothetical “impulse flow equilibrium” led to a spatial first-order “one-way wave equation” which, due to its first order differentials, can be more easily solved than the spatial two-way wave equation. To date the conversion of the spatial two-way wave operator into spatial one-way wave operators is unsolved. By considering the one-way wave operator containing a vector wave velocity, a “synthesis” approach leads to a “general vector two-way wave operator” and the “general one-way/two-way equivalence”. For a constant vector wave velocity the equivalence with the d’Alembert operator can be achieved. The findings are transferred to commonly used mechanical and electromagnetic wave types. The one-way wave theory and the spatial one-way wave operators offer new opportunities in science and engineering for advanced wave and wave field calculations.
      Citation: Acoustics
      PubDate: 2022-10-10
      DOI: 10.3390/acoustics4040053
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 894-902: Experimental Study of the Acoustic
           Cavitation Threshold in Sunflower Oil Depending on Different Impact Regime

    • Authors: Natalia Mikhailova, Ivan Smirnov, Bulat Yakupov
      First page: 894
      Abstract: In engineering problems associated with acoustic wave propagation in a liquid, cavitation onset could be an adverse phenomenon, or, conversely, a required process. In both cases, knowledge of the ultrasonic parameters that lead to cavitation onset under given external conditions is relevant and necessary for solving both fundamental and practical problems. The present work proposes experimental results of studying the threshold of acoustic cavitation, which was implemented at different ultrasound frequencies with a change in external pressure, power of transducer and temperature of the liquid. The experiments were carried out for sunflower oil. The test findings demonstrated how the cavitation threshold changes with varying the power of ultrasound exposure in time. In addition, the effect of external pressure fluctuations on cavitation onset was investigated. The obtained results contribute to the understanding of cavitation processes and could be necessary for verification of theoretical models.
      Citation: Acoustics
      PubDate: 2022-10-17
      DOI: 10.3390/acoustics4040054
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 903-914: Resonant Metasurfaces with a Tangential

    • Authors: Nikolay Kanev
      First page: 903
      Abstract: Metasurfaces formed by monopole and dipole resonators are studied theoretically. The monopole resonators are Helmholtz resonators or membranes vibrating on the first eigenfrequency; the dipole ones are spheres on springs or membranes vibrating on the second eigenfrequency. It is shown that acoustic properties of the metasurface formed by the built-in monopole resonators can be described by an equivalent impedance, which characterizes a normal forcing to the surface, whereas this impedance is not suitable for the metasurface formed by the dipole resonators, because motion of the metasurface is excited by a forcing tangential to the surface. For such boundaries, a new characteristic named “tangential impedance” is proposed. This is a ratio of the second derivative of the sound pressure along a coordinate tangential to the boundary to the normal velocity of the boundary. The dipole metasurface can be described by the equivalent tangential impedance. Reflection and absorption coefficients of the surface with the tangential impedance are found for a harmonic plane wave in dependance of an incidence angle. It is found that the angular dependences of the coefficients are very different for the monopole and dipole metasurfaces.
      Citation: Acoustics
      PubDate: 2022-10-21
      DOI: 10.3390/acoustics4040055
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 915-933: Flow Dynamics and Acoustics from Glottal
           Vibrations at Different Frequencies

    • Authors: Jinxiang Xi, Mohamed Talaat, Xiuhua Si, Haibo Dong
      First page: 915
      Abstract: Glottal vibration is fundamental to breathing-related disorders and respiratory sound generation. However, responses of the flow and acoustics to glottal vibrations of different frequencies are unclear. The objective of this study is to numerically evaluate the influences of glottal vibration frequencies on inspiratory airflow dynamics and flow-induced sound signals; this is different from normal phonation that is driven by controlled expiratory flows. A computational model was developed that comprised an image-based mouth–throat–lung model and a dynamic glottis expanding/contracting following a sinusoidal waveform. Large Eddy simulations were used to solve the temporal and spatial flow evolutions, and pressure signals were analyzed using different transform algorithms (wavelet, Hilbert, Fourier, etc.). Results show that glottal vibrations significantly altered the flows in the glottis and trachea, especially at high frequencies. With increasing vibration frequencies, the vortices decreased in scale and moved from the main flow to the walls. Phase shifts occurred between the glottis motion and glottal flow rates for all frequencies considered. Due to this phase shift, the pressure forces resisted the glottal motion in the first half of contraction/expansion and assisted the glottal motion in the second half of contraction/expansion. The magnitude of the glottal flow fluctuation was approximately linear with the vibration frequency (~f0), while the normal pressure force increased nonlinearly with the frequency (~f01.85). Instantaneous pressure signals were irregular at low vibration frequencies (10 and 20 Hz) but became more regular with increasing frequencies in the pressure profile, periodicity, and wavelet-transformed parameters. The acoustic characteristics specific to the glottal vibration frequency were explored in temporal and frequency domains, which may be used individually or as a combination in diagnosing vocal fold dysfunction, snoring, sleep apnea, or other breathing-related diseases.
      Citation: Acoustics
      PubDate: 2022-10-28
      DOI: 10.3390/acoustics4040056
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 934-947: Correlation between Seismic Waves
           Velocity Changes and the Occurrence of Moderate Earthquakes at the Bending
           of the Eastern Carpathians (Vrancea)

    • Authors: Anica-Otilia Placinta, Felix Borleanu, Iren-Adelina Moldovan, Alina Coman
      First page: 934
      Abstract: Seismic velocity is the geophysical property that has a key role in characterizing dynamic processes and the state of the stress around the faults, providing valuable information regarding the change in the tectonic regime. The stress in the crust is an important indicator of the possible occurrence of a major earthquake, and the variation of seismic velocities, in time, can provide a clearer picture on the tectonic processes taking place in the region. In the crust, velocities change before, during, and after earthquakes through several mechanisms related to fault deformations, pore pressure, stress changes, and recovery processes. In this study, we investigate the possible correlation between the changes of seismic velocities (Vp/Vs) in time and the occurrence of moderate size crustal and intermediate depth earthquakes from the Vrancea region. Our findings show that there are no significant variations in Vp/Vs for the intermediate depth earthquakes, while crustal events have decreased seismic activity prior to the main earthquake and no high Vp/Vs anomalies. Our results indicate key aspects, and such analyses should be carried out in real-time to continuously explore any unusual pattern pointed out by the seismic velocity changes. Vp/Vs and their standard errors can also be used to describe seismic activity patterns that shape the tectonic evolution of the area.
      Citation: Acoustics
      PubDate: 2022-11-01
      DOI: 10.3390/acoustics4040057
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 948-957: Accelerated Conjugate Gradient for
           Second-Order Blind Signal Separation

    • Authors: Hai Huyen Dam, Sven Nordholm
      First page: 948
      Abstract: This paper proposes a new adaptive algorithm for the second-order blind signal separation (BSS) problem with convolutive mixtures by utilising a combination of an accelerated gradient and a conjugate gradient method. For each iteration of the adaptive algorithm, the search point and the search direction are obtained based on the current and the previous iterations. The algorithm efficiently calculates the step size for the accelerated conjugate gradient algorithm in each iteration. Simulation results show that the proposed accelerated conjugate gradient algorithm with optimal step size converges faster than the accelerated descent algorithm and the steepest descent algorithm with optimal step size while having lower computational complexity. In particular, the number of iterations required for convergence of the accelerated conjugate gradient algorithm is significantly lower than the accelerated descent algorithm and the steepest descent algorithm. In addition, the proposed system achieves improvement in terms of the signal to interference ratio and signal to noise ratio for the dominant speech outputs.
      Citation: Acoustics
      PubDate: 2022-11-11
      DOI: 10.3390/acoustics4040058
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 958-966: The Spherical Harmonic Family of

    • Authors: Kevin J. Parker, Miguel A. Alonso
      First page: 958
      Abstract: The free space solution to the wave equation in spherical coordinates is well known as a separable product of functions. Re-examination of these functions, particularly the sums of spherical Bessel and harmonic functions, reveals behaviors which can produce a range of useful beampatterns from radially symmetric sources. These functions can be modified by several key parameters which can be adjusted to produce a wide-ranging family of beampatterns, from the axicon Bessel beam to a variety of unique axial and lateral forms. We demonstrate that several special properties of the simple sum over integer orders of spherical Bessel functions, and then the sum of their product with spherical harmonic functions specifying the free space solution, lead to a family of useful beampatterns and a unique framework for designing them. Examples from a simulation of a pure tone 5 MHz ultrasound configuration demonstrate strong central axis concentration, and the ability to modulate or localize the axial intensity with simple adjustment of the integer orders and other key parameters related to the weights and arguments of the spherical Bessel functions.
      Citation: Acoustics
      PubDate: 2022-11-15
      DOI: 10.3390/acoustics4040059
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 967-995: Temporal Howling Detector for Speech
           Reinforcement Systems

    • Authors: Yehav Alkaher, Israel Cohen
      First page: 967
      Abstract: In this paper, we address the problem of howling detection in speech reinforcement system applications for utilization in howling control mechanisms. A general speech reinforcement system acquires speech from a speaker’s microphone, and delivers a reinforced speech to other listeners in the same room, or another room, through loudspeakers. The amount of gain that can be applied to the acquired speech in the closed-loop system is constrained by electro-acoustic coupling in the system, manifested in howling noises appearing as a result of acoustic feedback. A howling detection algorithm aims to early detect frequency-howls in the system, before the human ear notices. The proposed algorithm includes two cascaded stages: Soft Howling Detection and Howling False-Alarm Detection. The Soft Howling Detection is based on the temporal magnitude-slope-deviation measure, identifying potential candidate frequency-howls. Inspired by the temporal approach, the Howling False-Alarm Detection stage considers the understanding of speech-signal frequency components’ magnitude behavior under different levels of acoustic feedback. A comprehensive howling detection performance evaluation process is designed, examining the proposed algorithm in terms of detection accuracy and the time it takes for detection, under a devised set of howling scenarios. The performance improvement of the proposed algorithm, with respect to a plain magnitude-slope-deviation-based method, is demonstrated by showing faster detection response times over a set of howling change-rate configurations. The two-staged proposed algorithm also provides a significant recall improvement, while improving the precision decrease via the Howling False-Alarm Detection stage.
      Citation: Acoustics
      PubDate: 2022-11-15
      DOI: 10.3390/acoustics4040060
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 996-1012: Enhancement of Guided Wave Detection
           and Measurement in Buried Layers of Multilayered Structures Using a New
           Design of V(z) Acoustic Transducers

    • Authors: Michaël Lematre, Marc Lethiecq
      First page: 996
      Abstract: This paper presents the possibility of enhancement of the generation and detection of poorly energetic acoustic-guided waves in multilayered structures using a new design for a V(z) transducer. By defining a modified V(z) transducer composed of segmented piezoelectric elements, the acoustical energy can be directed towards specific angles in such a way as to generate guided waves that are poorly energetic. By comparing the results using this new design to those obtained with a classical V(z) transducer, it is shown that the generation and detection of such waves is greatly improved, especially for poorly energetic waves that belong to a buried layer in a multilayered structure. This is especially seen on the components of the spectra of V(z). The modeling of the modified V(z) signature for a multi-element focused transducer is widely detailed first. Then, in order to illustrate the advantages of our proposed method, a three-layer structure (aluminum/epoxy/steel) is discussed. The interest of this method for the characterization of elastic properties of “buried” layers through specific guided waves that are detected with great difficulty—or even not at all—with a classical V(z) transducer is demonstrated, especially for the A0 and S0 modes corresponding to the steel layer inside the three-layer structure. In this study, we also develop a specific tracking method for particular guided waves possessing large phase velocity variations over the considered frequency range, as is the case for the S0 mode of the steel sub-layer.
      Citation: Acoustics
      PubDate: 2022-11-15
      DOI: 10.3390/acoustics4040061
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 1013-1027: Impact of Damping on Oscillation
           Patterns on the Plain Piano Soundboard

    • Authors: Rolf Bader, Niko Plath
      First page: 1013
      Abstract: The influence of internal damping on the vibration of a piano soundboard is investigated using a Finite-Difference Time Domain (FDTD) physical model and experimental measurements. The damping constant of the model is varied according to a range similar to those found with measurements on a real grand piano at different production stages. With strong damping, a clear driving-point dependency of the forced string oscillation on the oscillation pattern of the soundboard is found. When decreasing the damping, this driving-point dependency is decreasing, nevertheless, it is still present. High damping, therefore, decreases soundboard vibration when strings drive the soundboard at the soundboard’s eigenfrequencies. However, such large damping increases soundboard vibrations when strings drive the soundboard at frequencies which are not eigenfrequencies. Therefore, strong damping smooths out the frequency response spectrum of an instrument. Extreme damping without any presence of distinct eigenmodes leads to a radiation of the strings sound spectrum without soundboard filtering. Low damping leads to a strong influence of the soundboard on the string’s radiated sound. Therefore, the amount of soundboard characteristics can be designed to alter internal damping process by choice of materials, including wood or varnish, and geometry. Additionally, damping reduces the presence of ’dead spots’, notes which are considerably lower in volume compared to other notes.
      Citation: Acoustics
      PubDate: 2022-12-02
      DOI: 10.3390/acoustics4040062
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 1028-1044: A Modification of the Monte Carlo
           Filtering Approach for Correcting Negative SEA Loss Factors

    • Authors: Paweł Nieradka, Andrzej Dobrucki
      First page: 1028
      Abstract: Monte Carlo Filtering (MCF) is one of the methods of Experimental Statistical Energy Analysis (E-SEA), which allows the correction of negative LFs (Loss Factors). In this article, a modification of the MCF method, called DESA (Diagonal Expansion of the Search Area), is proposed. The technique applies a non-uniform extension of the search area when generating a population of normalized energy matrices. The degree of expansion of the search area is controlled by the Diagonal Penalty Factor (DPF). The authors demonstrated the method’s effectiveness on a system that could not be identified in several frequency bands by the classical MCF method. After applying DESA, it was possible to fill in the problematic bands that were missing CLF (coupling loss factor) and DLF (damping loss factor) values. The paper also proposes a way to minimize the errors introduced by using overly high DPF values.
      Citation: Acoustics
      PubDate: 2022-12-16
      DOI: 10.3390/acoustics4040063
      Issue No: Vol. 4, No. 4 (2022)
  • Acoustics, Vol. 4, Pages 517-537: Numerical Analysis of the Main Wave
           Propagation Characteristics in a Steel-CFRP Laminate Including Model Order

    • Authors: Andrey Mikhaylenko, Natalie Rauter, Nanda Kishore Bellam Bellam Muralidhar, Tilmann Barth, Dirk A. Lorenz, Rolf Lammering
      First page: 517
      Abstract: Guided ultrasonic waves are suitable for use in the context of structural health monitoring of thin-walled, plate-like structures. Hence, observing the wave propagation in the plates can provide an indication of whether damage has occurred in the structure. In this work, the wave propagation in fiber metal laminate consisting of thin steel foils and layers of carbon fiber-reinforced polymer is studied, focusing on the main propagation characteristics like dispersion diagrams and displacement fields. For this purpose, the dispersion diagrams derived from the analytical framework and numerical simulations are first determined and compared to each other. Next, the displacement fields are computed using the global matrix method for two excitation frequencies. The results derived from the analytical framework is used to validate the numerically determined displacement fields based on a 2D and a 3D modeling approach. For both investigations the results of the analytical treatment and the numerical simulation show good agreement. Furthermore, the displacement field reveals the typical and well-known characteristics of the propagation of guided waves in thin-walled structures. Since the use of full 3D models involves a very high computational cost, this work also successfully investigates the possibility for model order reduction to decrease the computational time and costs of the simulation without the loss of accuracy.
      Citation: Acoustics
      PubDate: 2022-06-25
      DOI: 10.3390/acoustics4030032
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 538-553: Audio Denoising Coprocessor Based on
           RISC-V Custom Instruction Set Extension

    • Authors: Jun Yuan, Qiang Zhao, Wei Wang, Xiangsheng Meng, Jun Li, Qin Li
      First page: 538
      Abstract: As a typical active noise control algorithm, Filtered-x Least Mean Square (FxLMS) is widely used in the field of audio denoising. In this study, an audio denoising coprocessor based on Retrenched Injunction System Computer-V (RISC-V), a custom instruction set extension was designed and a software and hardware co-design was adopted; based on the traditional pure hardware implementation, the accelerator optimization design was carried out, and the accelerator was connected to the RISC-V core in the form of coprocessor. Meanwhile, the corresponding custom instructions were designed, the compiling environment was established, and the library function of coprocessor acceleration instructions was established by embedded inline assembly. Finally, the active noise control (ANC) system was built and tested based on Hbird E203-Core, and the test data were collected through an audio analyzer. The results showed that the audio denoising algorithm can be realized by combining a heterogeneous System on Chip (SoC) with a hardware accelerator, and the denoising effect was approximately 8 dB. The number of instructions consumed by testing custom instructions for specific operations was reduced by approximately 60%, and the operation acceleration effect was significant.
      Citation: Acoustics
      PubDate: 2022-06-29
      DOI: 10.3390/acoustics4030033
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 554-563: One-Way Vibration Absorber

    • Authors: Oskar Bschorr, Hans-Joachim Raida
      First page: 554
      Abstract: A vibration absorber consisting of a one-dimensional waveguide with a reflectionless termination extracts vibrational energy from a structure that is to be damped. An optimum energy dissipation occurs for the so-called power adjustment, i.e, the same level of resistance and the opposite reactance of structure and absorber. The dimensioning of these impedance parameters on the base of the classic second order “two-way” wave equation provides analytical solutions for a few simple waveguide shapes; solutions for all other waveguides are only accessible via numerical finite-element computation. However, the competing first order “one-way” wave equation allows for an analytical conception of both the known broadband vibration absorber and the “Acoustic Black Hole” absorber. For example, for an exponential waveguide, the two-way calculation shows no resistance (and hence no real wave propagation) below a cut-off frequency, while the one-way wave equation predicts absorption in the whole frequency range.
      Citation: Acoustics
      PubDate: 2022-07-13
      DOI: 10.3390/acoustics4030034
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 564-573: Evaluation of the Oscillation Velocity
           in the Neck of the Helmholtz Resonator in Nonlinear Regimes

    • Authors: Alexandr Komkin, Aleksei Bykov, Olga Saulkina
      First page: 564
      Abstract: Methods for measuring the acoustic characteristics of orifices have been reviewed. Comparison of three methods for evaluating of oscillation velocity in the neck of the Helmholtz resonator are presented. The first method is measurements in an impedance tube with the two-microphone method, the second is based on measuring the sound pressure in the resonator chamber, and the third is based on direct measurements of bias flow with a Pitot tube. The results of measuring the oscillation velocity in the neck of the Helmholtz resonator are presented, and show that these methods are in good agreement only within linear acoustics, but they lead to different results in nonlinear regimes characterized by high sound pressure levels.
      Citation: Acoustics
      PubDate: 2022-07-19
      DOI: 10.3390/acoustics4030035
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 574-587: Locating Sources of Vibration with
           Harmonics and Pulse Signals in Industrial Machines

    • Authors: Anvar Valeev, Bulat Kharrasov
      First page: 574
      Abstract: This paper is devoted to a new approach to condition monitoring. The main feature is an application of strain gauge analysis for geometrical locating of vibrating defects. Information about the exact geometrical location of a defect, intensity of excitation and its frequency provides accurate diagnostics. The research contains theoretical and experimental parts. Three types of defects are analyzed: defects with harmonic parameters, defects with non-harmonic periodical parameters (pulse periodic signal) and defects with non-periodical parameters (pulse non-periodical signal). For the first type, analysis of micro movements in the equipment is used. The others use triangulation; for detecting time lag of signal approaching in each sensor, an analysis of phase spectrum is used. This method can find sources of vibration/defects with pulse-like signals. An electronic board and computer program for implementation of the proposed method are developed. The electronics measure strain gauge data in real time and transmit it to a computer program. Such an approach gives new information for diagnostics and provides new opportunities for effective defect detection and condition monitoring of various machines and equipment.
      Citation: Acoustics
      PubDate: 2022-07-29
      DOI: 10.3390/acoustics4030036
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 588-608: A Basic Study on the Design of
           Dotted-Art Heterogeneous MPP Sound Absorbers

    • Authors: Kimihiro Sakagami, Midori Kusaka, Takeshi Okuzono
      First page: 588
      Abstract: Recently, dotted-art MPPs have been proposed in which a designed pattern is made with the holes. In such a case, the MPP becomes heterogeneous in general. However, existing theories used for the prediction of the absorption characteristics of MPPs assume homogeneity. Therefore, the elaboration of a method for heterogeneous MPPs needs to be performed. In previous work, the authors proposed a method to predict the absorption characteristics of a heterogeneous MPP by using synthesized impedances of each part with different parameters; this is called the synthetic impedance method (SIM) in the present paper. The SIM can potentially be used for various heterogeneous MPPs; however, its scope of applicability needs to be clarified. Furthermore, in proposing a design concept of dotted-art heterogeneous MPPs, the condition that would make the designed MPPs fall within the scope of the SIM needs to be determined. Therefore, in this study, in order to clarify the scope of the applicability of the SIM, twelve samples are first prepared, and then measured sound absorption characteristics and predicted ones are compared and examined in terms of prediction errors. The results show that there are two conditions that should be met to produce predictable heterogeneous MPPs: (1) holes are distributed over the entire surface of the specimen, and (2) the hole spacing is constant. Considering these conditions, a design concept for a dotted-art heterogeneous MPP is proposed: two types of holes, larger holes for the pattern and smaller holes for the background, should be used to meet the above two conditions. Case studies with nine prototypes show that the SIM can make predictions for dotted-art heterogeneous MPPs fabricated according to the concept described above.
      Citation: Acoustics
      PubDate: 2022-07-31
      DOI: 10.3390/acoustics4030037
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 609-636: Control of Acoustic Energy Input for
           Cleaning of Industrial Boilers

    • Authors: Thabang Mafokwane, Daramy Vandi Von Kallon
      First page: 609
      Abstract: A non-intrusive cleaning method for boiler tubes at Sasol Synfuels power station at Secunda, in the Mpumalanga province of South Africa, is preferred over conventional methods that require boiler shutdown. The elected non-intrusive cleaning method utilizes sound energy waves, produced by an acoustic horn. Due to the nature of sound propagation and the effectiveness required, there is a requisite to control and operate the sonic horn. If the acoustic horn’s sound frequency is too low, it will produce higher sound energy waves that will resonate with the plant’s harmonious frequency and cause structural damage. Conversely, if the sonic horn’s sound frequency is too high, excessive noise levels may be reached and annoy plant personnel. To prevent these undesirable outcomes posed by adopting acoustic cleaning, there needs to be a regulatory system incorporated into the configuration to mitigate vibrations and limit noise. The regulatory system comprises a control system that drives the acoustic horn’s sound frequency as intended through a set point. The designed control system meets the anticipated requirements, such that it has an ideal transient response of 0.562 s, a steady-state error achieved in 1.05 s, with 0.201% overshoot, and most importantly the closed-loop system is stable.
      Citation: Acoustics
      PubDate: 2022-07-31
      DOI: 10.3390/acoustics4030038
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 637-655: Double-Talk Detection-Aided Residual
           Echo Suppression via Spectrogram Masking and Refinement

    • Authors: Eran Shachar, Israel Cohen, Baruch Berdugo
      First page: 637
      Abstract: Acoustic echo in full-duplex telecommunication systems is a common problem that may cause desired-speech quality degradation during double-talk periods. This problem is especially challenging in low signal-to-echo ratio (SER) scenarios, such as hands-free conversations over mobile phones when the loudspeaker volume is high. This paper proposes a two-stage deep-learning approach to residual echo suppression focused on the low SER scenario. The first stage consists of a speech spectrogram masking model integrated with a double-talk detector (DTD). The second stage consists of a spectrogram refinement model optimized for speech quality by minimizing a perceptual evaluation of speech quality (PESQ) related loss function. The proposed integration of DTD with the masking model outperforms several other configurations based on previous studies. We conduct an ablation study that shows the contribution of each part of the proposed system. We evaluate the proposed system in several SERs and demonstrate its efficiency in the challenging setting of a very low SER. Finally, the proposed approach outperforms competing methods in several residual echo suppression metrics. We conclude that the proposed system is well-suited for the task of low SER residual echo suppression.
      Citation: Acoustics
      PubDate: 2022-08-25
      DOI: 10.3390/acoustics4030039
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 656-678: BDREA Betta and Dolphin Pods Routing via
           Energy Scarcity Aware Protocol for Underwater Acoustic Wireless Sensor
           Networks (UAWSNs)

    • Authors: Hamza Zradgui, Khalil Ibrahimi
      First page: 656
      Abstract: There exist numerous applications for deploying Underwater Wireless Sensor Networks (UWSNs), including submarine detection, disaster prevention, oil and gas monitoring, off-shore exploration, and military target tracking. The acoustic sensor nodes are deployed to monitor the underwater environment, considering the area under observation. This research work proposes an energy scarcity-aware routing protocol for energy efficient UWSNs. Moreover, it aims to find the feasible region on the basis of the objective function, in order to minimize the energy tax and extend the network life. There are three different sensors nodes in the network environment, i.e., anchor nodes, relay nodes, and the centralized station. Anchor nodes originate data packets, while relay nodes process them and broadcast between each other until the packets reach the centralized station. The underline base scheme Weighting Depth and Forwarding Area Division Depth-Based Routing (WDFAD-DBR) for routing is based on the depth differences of the first- and second-hop nodes of the source node. The propose work, Betta and Dolphin Pods Routing via Energy Scarcity Aware protocol (BDREA) for packet forwarding from the forwarding nodes considers the first and second hops of the source node, i.e., the packet advancement, the network traffic, the distance to the centralized station, and the inverse normalized energy of the forwarding zone. It is observed that the proposed work improves the performance parameters by approximately 50% in terms of energy efficiency, and prolongs the network life compared to Dolphin and Whale Pod (DOW-PR) protocols. Furthermore, the energy efficiency directly relates to the other parameters, and its enhancement can be seen in terms of an 18.02% reduction in end-to-end delay when compared with the Weighting Depth and Forwarding Area Division Depth-Based Routing (WDFAD-DBR) protocol. Furthermore, BDREA improves the Packet Delivery Ratio (PDR) by approximately 8.71%, compared to DOW-PR, and by 10% compared with the benchmark, WDFAD-DBR, the energy tax by 50% in comparison to DOW-PR, the end-to-end delay by 18%, and the APD by 5% in comparison to WDFAD-DBR.
      Citation: Acoustics
      PubDate: 2022-08-26
      DOI: 10.3390/acoustics4030040
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 679-703: Sound Scattering by Gothic Piers and
           Columns of the Cathédrale Notre-Dame de Paris

    • Authors: Antoine Weber, Brian F. G. Katz
      First page: 679
      Abstract: Although the acoustics of Gothic cathedrals are of interest to researchers, the acoustic impact of their many columns is often neglected. The construction of the Cathédrale Notre-Dame de Paris spanned several centuries, including a wide variety of architectonic elements. This study investigates the sound scattering of a selection of seven designs that are relevant to this building as well as to the architectural style itself. These were measured on scale models (1:8.5 to 1:12), using a subtraction method, for receivers at about 3 m at full scale and a far-field source. They were also numerically simulated using a finite-difference time-domain method in two-dimensional space with an incident plane wave. The method integrates a finite volume framework to employ an unstructured mesh conforming to the complex geometries of interest. The two methods are in strong agreement for the considered configurations. Relative levels to the direct sound of backscattered reflections between −10 dB and 2 dB and between −15 dB and −6 dB in the transverse directions were estimated for the dimensions considered, relative to reported reflection audibility thresholds. Cross-sections with smaller scale geometrical elements on their perimeter can produce diffuse reflections similar to those of surface diffusers.
      Citation: Acoustics
      PubDate: 2022-08-26
      DOI: 10.3390/acoustics4030041
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 704-719: Effectiveness of MP3 Coding Depends on
           the Music Genre: Evaluation Using Semantic Differential Scales

    • Authors: Nikolaos M. Papadakis, Ioanna Aroni, Georgios E. Stavroulakis
      First page: 704
      Abstract: MPEG-1 Layer 3 (MP3) is one of the most popular compression formats used for sound and especially for music. However, during the coding process, the MP3 algorithm negatively affects the spectral and dynamic characteristics of the audio file being compressed. The aim of this study is to evaluate the effect the MP3 coding format for different music genres and different bitrates via listening tests in which the original uncompressed files and the compressed files are compared. For this purpose, five different music genres were selected (rock, jazz, electronic, classical and solo instrument), and the files were compressed in three different bitrates (96 kbps, 160 kbps and 320 kbps). The semantic differential method was used, and ten bipolar scales were selected for the listening tests (e.g., better–worse, more distortion–less distortion, etc.). The following are the most important findings of this study: classical music was negatively affected the most among the genres due to the MP3 compression (lowest ratings in 8 out of 10 bipolar scales), the solo instrument was least affected among the genres (highest rating in 7 out of 10 bipolar scales), and for higher bit rates, the differences in ratings were small for all music genres. The findings of this study could be used to optimize and adapt the standard, depending on the music genre and the musical piece that needs to be encoded.
      Citation: Acoustics
      PubDate: 2022-08-27
      DOI: 10.3390/acoustics4030042
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 720-732: Numerical and Experimental Validation of
           Active Vibration Control Logic Performance of a Hybrid Noise Control-Based

    • Authors: Ilaria Ronconi, Roberta Salierno, Ling Liu, Andrea Giglio, Francesco Ripamonti, Ingrid Paoletti
      First page: 720
      Abstract: The limitations of active noise control (ANC) in coping with low frequencies and of passive noise control (PNC) in coping with middle-high frequencies are objects of research that present the potentialities of hybrid noise control (HBC). It aims at combining both of the behaviours by broadening the range of absorbed frequencies. Among the several application fields, the AEC (architecture, engineering, and construction) market can take advantage for those applications in which the noise conditions are caused by sound sources that tune in a broad frequencies range. In this frame, the paper describes the numerical and experimental validation of the active behaviour of an under-development project of a hybrid noise control-based acoustic bricks. The latter intends to embed the potentialities of active vibrational noise control (AVC) and passive destructive interference (PDI) in a unique design of an easy-to-mount, 3D-printed, customisable smart acoustic blocks. Active vibration control, the object of this paper, is provided by a 5-mm thick aluminium circular plate with an attached piezoelectric patch. The vibration of the latter, depending on a specific control law, defines the vibration of the plate itself achieving an abatement of the reflection coefficient. Through mathematical modelling and tests in an impedance tube, the results show that the control logic can reach an average abatement of the reflection coefficient of 82% in the frequency range 144–1007 Hz.
      Citation: Acoustics
      PubDate: 2022-08-28
      DOI: 10.3390/acoustics4030043
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 733-745: Effects of Industrial Noise on
           Physiological Responses

    • Authors: Massimiliano Masullo, Roxana Adina Toma, Luigi Maffei
      First page: 733
      Abstract: Noise pollution is one of the most common workplace hazards. Noise exposure may induce auditory and extra-auditory physiological and psychological alterations that affect job performance, safety, comfort, and wellbeing. Recent research showed a connection between frequency components of noise and health outcomes, annoyance, physiological and psychological changes. This study investigated whether and how the activation of different typologies of industrial noises set at three different sound levels induced increases in electrodermal activity (EDA) and the heart rate variations differently. A laboratory listening test was performed for the study, in which 24 subjects were exposed to the activation of different industrial noises: Low Frequency, High Frequency, and Modulated noises at Low, Medium, and High sound levels, while some physiological responses were recorded. The noise stimuli were also evaluated based on a self-report questionnaire. Results show that the EDA variation increases as the Sound Level increases and is higher at HF. In contrast, no relevant changes have been found in RR variation. EDA changes are also related to the perception of the Valence dimension of the noise environment, while RR variations not. The findings of this study emphasized that the changes in EDA depend on the sound levels and frequency content of industrial noise typologies, as well as on the perception of their Valence.
      Citation: Acoustics
      PubDate: 2022-08-31
      DOI: 10.3390/acoustics4030044
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 746-763: The Influence of Listeners’ Mood
           on Equalization-Based Listening Experience

    • Authors: Nefeli Dourou, Valeria Bruschi, Susanna Spinsante, Stefania Cecchi
      First page: 746
      Abstract: Using equalization to improve sound listening experience is a well-established topic among the audio society. Finding a general equalization curve is a difficult task because of spectral content influenced by the reproduction system (loudspeakers and room environment) and personal preference diversity. Listeners’ mood is said to be a factor that affects the individual equalization preference. In this study, the effect of a listener’s mood on equalization preference is tried to be investigated. Starting from an experiment with fifty-two listeners, considering five predefined equalization curves and a database of ten music excerpts, the relationship between listeners’ mood and preferred sound equalization has been studied. The main findings of this study showed that the “High-frequency boosting” equalization was the most preferred among participants. However, the “High-frequency boosting” preference of low-aroused people was slightly lower than the high aroused listeners, increasing the preference of the “Low-frequency boosting”.
      Citation: Acoustics
      PubDate: 2022-09-01
      DOI: 10.3390/acoustics4030045
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 764-782: Spatial Coherence Comparisons between
           the Acoustic Field and Its Frequency-Difference and Frequency-Sum
           Autoproducts in the Ocean

    • Authors: Nicholas J. Joslyn, Alexander S. Douglass, David R. Dowling
      First page: 764
      Abstract: The frequency-difference and frequency-sum autoproducts, quadratic products of complex acoustic field amplitudes at two frequencies, may mimic genuine acoustic fields at the difference and sum frequencies of the constituent fields, respectively. Autoproducts have proven useful in extending the useable frequency range for acoustic remote sensing to frequencies outside a recorded field’s bandwidth. In array signal processing applications, the spatial coherence of the field often sets performance limits. This paper presents results for the spatial coherence of the genuine field, the frequency-difference autoproduct, and the frequency-sum autoproduct as determined from data collected during the Cascadia Open-Access Seismic Transects (COAST 2012) experiment. In this experiment, an airgun array providing a 10 to 200 Hz signal was repeatedly fired off the coast of Washington state, and the resulting acoustic fields were recorded by a nominal 8 km long, 636-element towed horizontal array. Based on hundreds of airgun firings from a primarily shore-parallel transect, both autoproducts were found to extend field coherence to frequencies outside the genuine field’s bandwidth and to produce longer coherence lengths than genuine fields, in most cases. When used for matched-field processing, the same data illustrate the benefits of the autoproducts’ extended coherence.
      Citation: Acoustics
      PubDate: 2022-09-07
      DOI: 10.3390/acoustics4030046
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 783-799: Measuring the Acoustical Properties of
           the BBC Maida Vale Recording Studios for Virtual Reality

    • Authors: Gavin Kearney, Helena Daffern, Patrick Cairns, Anthony Hunt, Ben Lee, Jacob Cooper, Panos Tsagkarakis, Tomasz Rudzki, Daniel Johnston
      First page: 783
      Abstract: In this paper we present a complete acoustic survey of the British Broadcasting Corporation Maida Vale recording studios. The paper outlines a fast room acoustic measurement framework for capture of spatial impulse response measurements for use in three or six degrees of freedom Virtual Reality rendering. Binaural recordings from a KEMAR dummy head as well as higher order Ambisonic spatial room impulse response measurements taken using a higher order Ambisonic microphone are presented. An acoustic comparison of the studios is discussed, highlighting remarkable similarities across three of the recording spaces despite significant differences in geometry. Finally, a database of the measurements, housing the raw impulse response captures as well as processed spatial room impulse responses is presented.
      Citation: Acoustics
      PubDate: 2022-09-14
      DOI: 10.3390/acoustics4030047
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 800-821: The Acoustics of the Palace of Charles V
           as a Cultural Heritage Concert Hall

    • Authors: Jose A. Almagro-Pastor, Rafael García-Quesada, Jerónimo Vida-Manzano, Francisco J. Martínez-Irureta, Ángel F. Ramos-Ridao
      First page: 800
      Abstract: This paper analyses the acoustic behaviour of the Palace of Charles V from a room acoustics perspective but also ponders the uniqueness of the space and its ability to engage and enhance the audience experience. The Palace of Charles V is a relevant part of the historical heritage of Granada. It has an architectural but also an acoustic uniqueness that deserves research. A measurement campaign was made to calculate parameters such as T30, IACC, C80 or Gm, and to explain the behaviour of the Palace. The BQI is quite high, but the late part of the impulse response (t > 80 ms) has strong unwanted reflections causing low clarity (C80) and listener envelopment (LEV). Nevertheless, the Palace is a successful concert venue with good feedback from musicians and the audience.
      Citation: Acoustics
      PubDate: 2022-09-15
      DOI: 10.3390/acoustics4030048
      Issue No: Vol. 4, No. 3 (2022)
  • Acoustics, Vol. 4, Pages 297-312: UAV Noise Emission—A Combined
           Experimental and Numerical Assessment

    • Authors: Kai Cussen, Simone Garruccio, John Kennedy
      First page: 297
      Abstract: Noise emission will be a significant obstacle to the widespread uptake of unmanned aerial vehicles or UAVs. The assessment and mitigation of UAV noise will require validated modelling approaches. The European Union has recently mandated an UAV sound power measurement procedure based on a procedure for measuring machinery or equipment. It is not clear if this legally mandated noise assessment will provide useful data for environmental noise modelling of UAVs. This research aimed to determine the sound power level of a UAV according to the legally mandated ISO 3744 and to investigate the suitability of commercial implementations of ISO 9613 for modelling noise emission from UAVs. A class C1 UAV was used for the investigation which also included controlled flyover tests. Several different operating conditions were measured and modelled and the results compared. The small scale UAV used had a sound power of 86.8 dB (A) and modelled flyover tests agreed with experimental values within ±2.1 decibels at distances up to 30 m and within angles of 45–90° of the receiver. The validated model was then used for a case study of UAV noise emission in an urban setting. The model demonstrated the potential for UAV noise emission to significantly exceed urban background noise levels by up to 10 dB. It was found that flight altitude relative to building height had a significant impact on the number of allowable UAV operations within WHO LDEN guidelines.
      Citation: Acoustics
      PubDate: 2022-03-23
      DOI: 10.3390/acoustics4020018
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 313-328: Dual-Axis MEMS Resonant Scanner Using
           128∘Y Lithium Niobate Thin-Film

    • Authors: Yaoqing Lu, Kangfu Liu, Tao Wu
      First page: 313
      Abstract: The micro-electro-mechanical systems (MEMS) resonant scanners are in great demand for numerous light scanning applications. Recently, the development of LiDAR in micro-robotics and mobile devices has led to the requirement of ultra-small systems with low driving voltage, low power, compact size and high performance. We have first proposed the dual-axis MEMS scanner using the lithium niobate (LN) thin-film platform, which is expected to fulfill the requirement. This paper describes the actuation principle and scanner structure, meanwhile develops the analytical model for the scanner. The analytical model is later validated by the finite element analysis. The performance of the proposed scanner is improved with the optimization of the orientation of LN and layer thickness. The proposed scanner achieves the θopt·D·f up to 937.8∘·mm·kHz in simulation. The simulated optical angle in the x-axis and y-axis are 50∘ and 42∘ at 1 V, corresponding to resonant frequencies of 79.9 kHz and 558.2 kHz, respectively. With the superior performance of large deflection, high scanning frequency, high figure of merit and low voltage, the proposed MEMS scanner is a promising candidate for fast scanner applications (e.g., wavelength-selective switches and submicron biomedical system), especially the application of LiDAR in mobile devices or micro-robotics.
      Citation: Acoustics
      PubDate: 2022-04-01
      DOI: 10.3390/acoustics4020019
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 329-344: Efficient Modelling of Acoustic
           Metamaterials for the Performance Enhancement of an Automotive Silencer

    • Authors: Daniel Deery, Lara Flanagan, Gordon O’Brien, Henry J. Rice, John Kennedy
      First page: 329
      Abstract: Significant potential for acoustic metamaterials to provide a breakthrough in sound attenuation has been unlocked in recent times due to advancements in additive manufacturing techniques. These materials allow the targeting of specific frequencies for sound attenuation. To date, acoustic metamaterials have not been demonstrated in a commercial automotive silencer for performance enhancement. A significant obstacle to the practical use of acoustic metamaterials is the need for low cost and efficient modelling strategies in the design phase. This study investigates the effect of acoustic metamaterials within a representative automotive silencer. The acoustic metamaterial design is achieved using a combination of analytical and finite element models, validated by experiment. The acoustic metamaterial is then compared with commonly used techniques in the silencer industry to gauge the effectiveness of the acoustic metamaterials. COMSOL simulations were used to validate the developed test rig and were compared to experimental results which were obtained using the two-load transmission loss test method. Through this testing method, the implementation of a labyrinthine metamaterial cylinder proved to be a significant improvement in transmission loss within the silencer, with an increase in transmission loss of 40 dB at 1500 Hz. The research has successfully shown that acoustic metamaterials can be used in practical settings, such as an automotive silencer, to improve the overall sound attenuating performance. The described analytical model demonstrates the potential for industrially relevant low cost design tools.
      Citation: Acoustics
      PubDate: 2022-04-01
      DOI: 10.3390/acoustics4020020
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 345-361: Simulation-Based Study on Round Window
           Atresia by Using a Straight Cochlea Model with Compressible Perilymph

    • Authors: Wenjia Hong, Yasushi Horii
      First page: 345
      Abstract: The sound stimulus received by the pinna is transmitted to the oval window of the inner ear via the outer ear and middle ear. Assuming that the perilymph in the scala vestibuli and scala tympani is compressible, we report that the sound wave generated in the cochlea due to the vibration of the oval window can be expressed by the combination of even and odd symmetric sound wave modes. Based on this new approach, this paper studies the cause of hearing deterioration in the lower frequency region seen in round window atresia from the viewpoint of cochlear acoustics. Round window atresia is an auditory disease in which the round window is ossified and its movement is restricted. Using the finite element method, a round window atresia model was designed and the acoustic behavior of the round window was discussed corresponding to the level of disease. From this, we report that the healthy round window works as a free-end reflector to the incident sound waves, but it also works as a fixed-end reflector in the case of round window atresia. Next, we incorporated the round window atresia model into a cochlear model and performed a simulation in order to determine the acoustic aspects of the cochlea as a whole. The simulation results indicate that hearing deterioration occurs in a lower frequency range, which is also coincident with the clinical reports (hearing deterioration of approximately 10 to 20 dB below 4000 Hz). Finally, we explain that the cause of hearing deterioration due to round window atresia is considered to be the even sound wave mode enlarging due to the fixed-end reflection at the ossified round window, and, as a result, the odd sound wave mode that generates the Békésy’s traveling wave on a basilar membrane is significantly weakened.
      Citation: Acoustics
      PubDate: 2022-04-06
      DOI: 10.3390/acoustics4020021
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 362-381: Investigation of Alberich Coating to
           Optimise Acoustic Stealth of Submarines

    • Authors: Callum Daniels, Noel Perera
      First page: 362
      Abstract: Due to the nature of their deployment, very few people know the location and course of a submarine during its time at sea, including only a handful of the ship’s crew. The possibility of immediate retaliation by the UK and her allies is aided by the submarine’s ability to remain undetected by SONAR at all times. To investigate one method for improving acoustic stealth, a finite element model (FEM) was created on ANSYS to model a unit-cell of an Alberich coating and impeding sound wave representative of SONAR. A simplification of a widely used acoustic impedance equation was adopted into MATLAB code to attain values of impedance that were applied to the model in place of a water loading boundary. Using the results given by five sets of simulations, an optimised Alberich coating was modelled, containing a 26 mm spherical cavity, 40 mm anechoic layer and 30 mm long steel backplate. This optimised model improved the acoustic stealth of submarines by displaying greater acoustic absorption at both ends of the frequency range, compared with other models used, showing that Alberich-style coatings can be used to improve acoustic stealth, to combat new low-frequency SONAR.
      Citation: Acoustics
      PubDate: 2022-04-11
      DOI: 10.3390/acoustics4020022
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 382-393: On the Influence of Certain Geometric
           Characteristics of the Resonator on the Impedance Determined by the
           Dean’s Method

    • Authors: Vadim Palchikovskiy, Igor Khramtsov, Oleg Kustov
      First page: 382
      Abstract: This article considers the influence of the orifice arrangement in a cover of a cylindrical resonator on the impedance determined by the Dean’s method. A resonator with a small height and a low perforation degree is studied. This geometry provides different non-uniformity of the sound field at the resonator backing depending on the orifice arrangement in the resonator cover, while the number of orifices does not change. It is shown that, with different orifice arrangements, the impedance values determined by Dean’s method at high frequencies (3000 Hz and more) differ greatly. The authors propose the modification of Dean’s formula by using the amplitude coefficient of the zeroth order mode instead of the acoustic pressure at the resonator backing. The computations performed demonstrate that, in this case, the impedance does not depend on the orifice arrangement in the resonator cover. The computations consist of three stages: numerical simulation of the plane wave incidence onto the resonator (simulating a full-scale experiment); carrying out a modal analysis of the sound field at the resonator backing to extract the zeroth order mode; and determination of the resonator impedance according to the modified Dean’s formula.
      Citation: Acoustics
      PubDate: 2022-04-11
      DOI: 10.3390/acoustics4020023
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 394-405: A Method for Modeling Acoustic Waves in
           Moving Subdomains

    • Authors: Milan Brankovic, Mark E. Everett
      First page: 394
      Abstract: Forward modeling plays a key role in both the creation of predictive models and the study of the surrounding environment through inversion methods. Due to their competitive computational cost and modest algorithmic complexity, finite difference methods (FDM) are commonly used to model the acoustic wave equation. An algorithm has been developed to decrease the computational cost of acoustic-wave forward modeling that can be applied to most finite difference methods. An important feature of the algorithm is the calculation, at each time step, of the pressure in only a moving subdomain which contains the grid points across which waves are passing. The computation is skipped at grid points at which the waves are negligibly small or non-existent. The novelty in this work comes from flexibility of the subdomain and its ability to closely follow the developing wavefield. To demonstrate the efficacy of the algorithm, it is applied to a standard finite difference scheme and validated against 2-D modeling results. The algorithm herein can play an important role in the reduction in computation time of seismic data analysis as the volumes of seismic data increase due to developments in data acquisition technology.
      Citation: Acoustics
      PubDate: 2022-04-13
      DOI: 10.3390/acoustics4020024
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 406-418: Measurement of Ultrasound Parameters of
           Bovine Cancellous Bone as a Function of Frequency for a Range of
           Porosities via through-Transmission Ultrasonic Spectroscopy

    • Authors: Alina Karki, Junru Wu
      First page: 406
      Abstract: The relationship between ultrasonic parameters (attenuation coefficients and velocity) and bone porosity in bovine cancellous bone is explored to understand the possibility of fracture risk diagnosis associated with osteoporosis by applying ultrasound. In vitro measurements of ultrasonic parameters on twenty-one bovine cancellous bone samples from tibia were conducted, using ultrasonic spectroscopy in the through-transmission mode. Transducers of three different center frequencies were used to cover a wide diagnostic frequency range between 1.0–7.8 MHz. The nonlinear relationship of porosity and normalized attenuation coefficient (nATTN) and normalized broadband attenuation coefficient (nBUA) were well described by a third-order polynomial fit, whereas porosity and the phase velocity (UV) were found to be negatively correlated with the linear correlation coefficients of −0.93, −0.89 and −0.83 at 2.25, 5.00 and 7.50 MHz, respectively. The results imply that the ultrasound parameters attain maximum values for the bone sample with the lowest porosity, and then decrease for samples with greater porosity for the range of porosities in our samples for all frequencies. Spatial variation in the ultrasound parameters was found to be caused by non-uniform pore size distribution, which was examined at five different locations within the same bone specimen. However, it did not affect the relationship of ultrasound parameters and porosity at these frequencies.
      Citation: Acoustics
      PubDate: 2022-05-03
      DOI: 10.3390/acoustics4020025
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 419-440: Investigation of a Tuff Stone Church in
           Cappadocia via Acoustical Reconstruction

    • Authors: Ali Haider Adeeb, Zühre Sü Gül
      First page: 419
      Abstract: This study investigates the indoor acoustical characteristics of a Middle Byzantine masonry church in Cappadocia. The Bell Church is in partial ruins; therefore, archival data and the church’s remains are used for its acoustical reconstruction. The study aims to formulate a methodology for a realistic simulation of the church by testing the applicability of different approaches, including field and laboratory tests. By conducting qualitative and quantitative material tests, different tuff stone samples are examined from the region. Impedance tube tests are performed on the samples from Göreme and Ürgüp to document their sound absorption performances. Previous field tests on two sites in Cappadocia are also used to compare the sound absorption performance of tuff stones, supported by acoustical simulations. The texture, physical and chemical characteristics of the stones together with the measured sound absorption coefficient values are comparatively evaluated for selecting the most suitable material to be applied in the Bell Church simulations. The church was constructed in phases and underwent architectural modifications and additions over time. The indoor acoustical environment of the church is analyzed over objective acoustical parameters of EDT, T30, C50, C80, D50, and STI for its different phases with different architectural features and functional patterns.
      Citation: Acoustics
      PubDate: 2022-05-16
      DOI: 10.3390/acoustics4020026
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 441-459: Speech Enhancement Framework with Noise
           Suppression Using Block Principal Component Analysis

    • Authors: Abdullah Zaini Alsheibi, Kimon P. Valavanis, Asif Iqbal, Muhammad Naveed Aman
      First page: 441
      Abstract: With the advancement in voice-communication-based human–machine interface technology in smart home devices, the ability to decompose the received speech signal into a signal of interest and an interference component has emerged as a key requirement for their successful operation. These devices perform their tasks in real time based on the received commands, and their effectiveness is limited when there is a lot of ambient noise in the area in which they operate. Most real-time speech enhancement algorithms do not perform adequately well in the presence of high amounts of noise (i.e., low input-signal-to-noise ratio). In this manuscript, we propose a speech enhancement framework to help these algorithms in situations when the noise level in the received signal is high. The proposed framework performs noise suppression in the frequency domain by generating an approximation of the noisy signals’ short-time Fourier transform, which is then used by the speech enhancement algorithms to recover the underlying clean signal. This approximation is performed by using the proposed block principal component analysis (Block-PCA) algorithm. To illustrate efficacy of the proposed framework, we present a detailed performance evaluation under different noise levels and noise types, highlighting the effectiveness of the proposed framework. Moreover, the proposed method can be used in conjunction with any speech enhancement algorithm to improve its performance under moderate to high noise scenarios.
      Citation: Acoustics
      PubDate: 2022-05-20
      DOI: 10.3390/acoustics4020027
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 460-468: A Preliminary Investigation on Frequency
           Dependant Cues for Human Emotions

    • Authors: Manish Kumar, Thushara D. Abhayapala, Prasanga Samarasinghe
      First page: 460
      Abstract: The recent advances in Human-Computer Interaction and Artificial Intelligence have significantly increased the importance of identifying human emotions from different sensory cues. Hence, understanding the underlying relationships between emotions and sensory cues have become a subject of study in many fields including Acoustics, Psychology, Psychiatry, Neuroscience and Biochemistry. This work is a preliminary step towards investigating cues for human emotion on a fundamental level by aiming to establish relationships between tonal frequencies of sound and emotions. For that, an online perception test is conducted, in which participants are asked to rate the perceived emotions corresponding to each tone. The results show that a crossover point for four primary emotions lies in the frequency range of 417–440 Hz, thus consolidating the hypothesis that the frequency range of 432–440 Hz is neutral from human emotion perspective. It is also observed that the frequency dependant relationships between emotion pairs Happy—Sad, and Anger—Calm are approximately mirrored symmetric in nature.
      Citation: Acoustics
      PubDate: 2022-05-22
      DOI: 10.3390/acoustics4020028
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 469-478: The Dipole Resonator and Dipole
           Waveguide Insulator in Dense Liquid Medium

    • Authors: Mikhail Mironov
      First page: 469
      Abstract: In this paper, the propagation of sound in an acoustically narrow waveguide, the wall of which is lined with identical dipole resonators and masses on springs, is theoretically considered. It is shown that, in the frequency range above the resonant frequency of the resonators, sound waves exponentially attenuate, and the waveguide is locked. The width of this range depends on two parameters—the ratio of the cross-sectional areas of the resonators and the waveguide and the ratio of the mass of the resonator to the mass of the medium displaced by it. As the resonator mass decreases, the locking band width expands and may become infinite.
      Citation: Acoustics
      PubDate: 2022-05-22
      DOI: 10.3390/acoustics4020029
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 479-491: Environmental Noise Evolution during
           COVID-19 State of Emergency: Evidence of Peru’s Need for Action

    • Authors: Rubén Rodríguez, María Machimbarrena, Ana I. Tarrero
      First page: 479
      Abstract: In Peru, as in many countries worldwide, varying degrees of restrictions have been established on the movement of the population after the World Health Organization (WHO) declared the condition of pandemic by COVID-19. In Lima, there have been different degrees of compulsory social immobilization (CSI), and the resumption of activities was planned in three consecutive phases. To analyse and evaluate the influence of such restrictions on the evolution of environmental noise, an investigation was carried out in one of the main avenues in the city of Lima during various successive mobility restriction conditions. The sound pressure level was measured, and the traffic flow was also registered. Considering that in Peru there is no environmental noise monitoring system whatsoever, in situ data are extremely valuable and allow the environmental noise problem to be depicted, even if in a limited area of the big city. The results show that in spite of the strongly restrictive social immobilization conditions, the measured noise levels have remained above the WHO recommendations and often above the Peruvian environmental noise quality standards. The results highlight the need to properly assess the environmental noise and noise sources in the city of Lima as well as the number of people exposed in order to adequately implement effective and cost-efficient noise mitigation action plans.
      Citation: Acoustics
      PubDate: 2022-06-02
      DOI: 10.3390/acoustics4020030
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 492-516: Soundscape Approach in the Seaport of
           Ancona: A Case Study

    • Authors: Samantha Di Loreto, Fabio Serpilli, Valter Lori
      First page: 492
      Abstract: Today, the art of knowing how to listen is more urgent than ever. The perceptive sound system of the human being is stimulated daily by countless artificial sounds that dominate natural ones. When it comes to the idea of the soundscape, the terminology was initially referred to by composer and environmentalist Raymond Murray Shafer, who defined “soundscape” as a relationship between the ear, humans, built environments, and society. This paper aims to apply the sound landscape approach in the seaport area of Ancona (Italy); a large area, frequented daily by many people, which is divided into passenger and ferry terminals, container terminals, plants for solid bulk, and commercial and recreational activities. The purpose of the study was to evaluate the perception that a human has of the urban layout of the port area by correlating the parameters of traditional acoustics with psychoacoustics. To evaluate the subjective parameters, a questionnaire was developed and applied, enabling the analysis of demographic and behavioral factors such as age, visit frequency, and length of stay of the participants in the clusters of the seaport. This way, it was possible to give an indication of the sound quality of the different clusters of the port area, from an acoustic and emotional point of view, and this information could be particularly helpful in the planning phase of new attractions for the Ancona seaport.
      Citation: Acoustics
      PubDate: 2022-06-14
      DOI: 10.3390/acoustics4020031
      Issue No: Vol. 4, No. 2 (2022)
  • Acoustics, Vol. 4, Pages 14-25: Acoustical Environment Studies in the
           Modern Urban University Campuses

    • Authors: Hsiao Mun Lee, Heow Pueh Lee, Zhiyang Liu
      First page: 14
      Abstract: The quality of the acoustic environments at Xi’an Jiatong-Liverpool University (XJTLU) and Soochow University (Dushuhu Campus, SUDC) in Suzhou City were investigated in the present work through real-time noise level measurements and questionnaire surveys. Before commencing the measurements and surveys, these two campuses’ sound sources were summarized and classified into four categories through on-site observation: human-made, machinery, living creatures, and natural physical sounds. For the zones near the main traffic road, with a high volume of crowds and surrounded by a park, sound from road vehicles, humans talking, and birds/insects were selected by the interviewees as the major sound sources, respectively. Only zone 3 (near to a park) at XJTLU could be classified as A zone (noise level < 55 dBA) with an excellent quality acoustical environment. All other zones had either good or average quality acoustical environments, except zone 1 (near to main traffic road) at XJTLU, with a fair-quality acoustical environment.
      Citation: Acoustics
      PubDate: 2022-01-07
      DOI: 10.3390/acoustics4010002
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 26-52: On the Incipient Indicial Lift of Thin
           Wings in Subsonic Flow: Acoustic Wave Theory with Unsteady
           Three-Dimensional Effects

    • Authors: Marco Berci
      First page: 26
      Abstract: Enhanced approximate expressions for the incipient indicial lift of thin wings in subsonic potential flow are presented in this study, featuring explicit analytical corrections for the unsteady downwash. Lifting-line and acoustic-wave theories form the basis of the method, within an effective synthesis of the governing physics, which grants a consistent generalised framework and unifies previous works. The unsteady flow perturbation consists of a step-change in angle of attack or a vertical sharp-edged gust. The proposed model is successfully evaluated against numerical results in the literature for the initial airload development of elliptical and rectangular wings with a symmetric aerofoil, considering several aspect ratios and Mach numbers. While nonlinear downwash and compressibility terms demonstrate marginal (especially for the case of a travelling gust), both linear and nonlinear geometrical effects from a significant taper ratio, sweep angle or curved leading-edge are found to be more important than linear downwash corrections (which are crucial for the circulation growth at later times instead, along with linear compressibility corrections). The present formulae may then be used as a rigorous reduced-order model for validating higher-fidelity tools and complex simulations in industrial practice, as well as for estimating parametric sensitivities of unsteady aerodynamic loads within the preliminary design of aircraft wings in the subsonic regime.
      Citation: Acoustics
      PubDate: 2022-01-18
      DOI: 10.3390/acoustics4010003
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 53-73: On the Robustness and Efficiency of the
           Plane-Wave-Enriched FEM with Variable q-Approach on the 2D Room Acoustics

    • Authors: Shunichi Mukae, Takeshi Okuzono, Kimihiro Sakagami
      First page: 53
      Abstract: Partition of unity finite element method with plane wave enrichment (PW-FEM) uses a shape function with a set of plane waves propagating in various directions. For room acoustic simulations in a frequency domain, PW-FEM can be an efficient wave-based prediction method, but its practical applications and especially its robustness must be studied further. This study elucidates PW-FEM robustness via 2D real-scale office room problems including rib-type acoustic diffusers. We also demonstrate PW-FEM performance using a sparse direct solver and a high-order Gauss–Legendre rule with a recently developed rule for ascertaining the number of integration points against the classical linear and quadratic FEMs. Numerical experiments investigating mesh size and room geometrical complexity effects on the robustness of PW-FEM demonstrated that PW-FEM becomes more robust at wide bands when using a mesh in which the maximum element size maintains a comparable value to the wavelength of the upper-limit frequency. Moreover, PW-FEM becomes unstable with lower spatial resolution mesh, especially for rooms with complex shape. Comparisons of accuracies and computational costs of linear and quadratic FEM revealed that PW-FEM requires twice the computational time of the quadratic FEM with a mesh having spatial resolution of six elements per wavelength, but it is highly accurate at wide bands with lower memory and with markedly fewer degrees of freedom. As an additional benefit of PW-FEM, the impulse response waveform of quadratic FEM in a time domain was found to deteriorate over time, but the PW-FEM waveform can maintain accurate waveforms over a long time.
      Citation: Acoustics
      PubDate: 2022-01-20
      DOI: 10.3390/acoustics4010004
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 74-86: Sideband Peak Count in a Vibro-Acoustic
           Modulation Method for Crack Detection

    • Authors: Abdullah Alnutayfat, Sophia Hassiotis, Dong Liu, Alexander Sutin
      First page: 74
      Abstract: This paper presents a new method of signal processing for vibro-acoustic modulation (VAM) methods in order to detect damage accumulation in steel samples. Damage in the tested samples was produced by cycle loading, which, with a small amplitude, was used as a pump wave to modulate an ultrasonic probe wave. Multiple sideband peaks were observed, which were used to characterize the modulation effect. We propose the effectiveness sideband peak number (SPN) method as an indicator of any damage accumulation when the load cycle is applied. Moreover, after comparing the SPN with the previously used modulation index (MI), we concluded that, for some of the samples, the SPN provided better damage indication than the MI. The presented results can be explained by a simple model of bilinear crack nonlinearity. This model demonstrates that the amplitude dependences of the sideband components on the pump and the probe wave amplitudes are very different from the quadratic crack model that is usually used for MI test explanation.
      Citation: Acoustics
      PubDate: 2022-01-24
      DOI: 10.3390/acoustics4010005
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 87-88: Acknowledgment to Reviewers of Acoustics
           in 2021

    • Authors: Acoustics Editorial Office Acoustics Editorial Office
      First page: 87
      Abstract: Rigorous peer-reviews are the basis of high-quality academic publishing [...]
      Citation: Acoustics
      PubDate: 2022-01-26
      DOI: 10.3390/acoustics4010006
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 89-110: Analysis of Sensitivity of Distance
           between Embedded Ultrasonic Sensors and Signal Processing on Damage
           Detectability in Concrete Structures

    • Authors: Joyraj Chakraborty, Xin Wang, Marek Stolinski
      First page: 89
      Abstract: Damage detection of reinforced concrete (RC) structures is becoming a more attractive domain due to the safety issues arising in the last few decades. The damage in concrete can be caused by excessive exploitation of the structure or environmental effects. The cracks in concrete can be detected by different nondestructive testing methods. However, the available methods used for this purpose have numerous limitations. The technologies available in the market nowadays have difficulties detecting slowly progressive, locally limited damage. In addition, some of these methods cannot be applied, especially in hard-to-reach areas in the superstructures. In order to avoid these deficiencies, an embedded ultrasonic methodology can be used to detect cracks in RC structures. In this study, the methodology of crack detection supported with the advanced signal processing algorithm was proposed and verified on RC structures of various types, and cracks occurring between embedded sensors can be detected. Moreover, different pairs of ultrasonic sensors located in the considered structures are used for the analysis of the sensitivity of distance between them. It is shown that the ultrasonic sensors placed in the range of 1.5–2 m can detect cracks, even when the other methods failed to detect changes in the structure. The obtained results confirmed that diffuse ultrasonic sensor methodology is able to monitor real structures more effectively than traditional techniques.
      Citation: Acoustics
      PubDate: 2022-02-01
      DOI: 10.3390/acoustics4010007
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 111-122: Design of Digital Constrained Linear
           Least-Squares Multiple-Resonator-Based Harmonic Filtering

    • Authors: Miodrag D. Kušljević, Vladimir V. Vujičić
      First page: 111
      Abstract: Although voiced speech signals are physical signals which are approximately harmonic and electric power signals are true harmonic, the algorithms used for harmonic analysis in electric power systems can be successfully used in speech processing, including in speech enhancement, noise reduction, speaker recognition, and hearing aids. The discrete Fourier transform (DFT), which has been widely used as a phasor estimator due to its simplicity, has led to the development of new DFT-based algorithms because of its poor performance under dynamic conditions. The multiple-resonator (MR) filter structure proposed in previous papers has proven to be a suitable approach to dynamic harmonic analysis. In this article, optimized postprocessing compensation filters are applied to obtain frequency responses of the transfer functions convenient for fast measurements in dynamic conditions. An optimization design method based on the constrained linear least-squares (CLLS) is applied. This way, both the flatness in the passband and the equiripple attenuation in the stopband are satisfied simultaneously, and the latency is reduced.
      Citation: Acoustics
      PubDate: 2022-02-01
      DOI: 10.3390/acoustics4010008
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 123-138: Acoustic Attenuation of COVID-19 Face
           Masks: Correlation to Fibrous Material Porosity, Mask Breathability and
           Bacterial Filtration Efficiency

    • Authors: Milena Martarelli, Luigi Montalto, Paolo Chiariotti, Serena Simoni, Paolo Castellini, Gianmarco Battista, Nicola Paone
      First page: 123
      Abstract: This paper presents an experimental study on acoustic attenuation of different types of face masks in use by the general population during the COVID-19 pandemic. In particular, measurements are performed on ten samples of masks, of which four are medical masks, three are respirators, and three are community masks. Breathability and Bacterial Filtration Efficiency (BFE) tests, in compliance to the standard characterization process of medical masks, are also carried out. The porosity on each layer composing the masks is measured by processing their scanning electron microscopy (SEM) images. The analysis of the results aims to establish if acoustic attenuation is correlated to any of these parameters. It emerges that porosity and breathability are strongly correlated to acoustic attenuation, while bacterial filtration efficiency is not.
      Citation: Acoustics
      PubDate: 2022-02-16
      DOI: 10.3390/acoustics4010009
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 139-167: Simulation of Ultrasonic Backscattering
           in Polycrystalline Microstructures

    • Authors: Dascha Dobrovolskij, Katja Schladitz
      First page: 139
      Abstract: Ultrasonic testing of polycrystalline media relies heavily on simulation of the expected signals in order to detect and correctly interpret deviations due to defects. Many effects disturb ultrasonic waves propagating in polycrystalline media. One of them is scattering due to the granular microstructure of the polycrystal. The thus arising so-called microstructural noise changes with grain size distribution and testing frequency. Here, a method for simulating this noise is introduced. We geometrically model the granular microstructure to determine its influence on the backscattered ultrasonic signal. To this end, we utilize Laguerre tessellations generated by random sphere packings dividing space into convex polytopes—the cells. The cells represent grains in a real polycrystal. Cells are characterized by their volume and act as single scatterers. We compute scattering coefficients cellwise by the Born approximation. We then combine the Generalized Point Source Superposition technique with the backscattered contributions resulting from the cell structure to compute the backscattered ultrasonic signal. Applying this new methodology, we compute the backscattered signals in a pulse-echo experiment for a coarse grain cubic crystallized Inconel-617 and a fine grain hexagonal crystallized titanium. Fitting random Laguerre tessellations to the observed grain structure allows for simulating within multiple realizations of the proposed model and thus to study the variation of the backscattered signal due to microstructural variation.
      Citation: Acoustics
      PubDate: 2022-02-18
      DOI: 10.3390/acoustics4010010
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 168-182: Contribution of Even/Odd Sound Wave
           Modes in Human Cochlear Model on Excitation of Traveling Waves and
           Determination of Cochlear Input Impedance

    • Authors: Wenjia Hong, Yasushi Horii
      First page: 168
      Abstract: Based on the Navier–Stokes equation for compressible media, this work studies the acoustic properties of a human cochlear model, in which the scala vestibuli and scala tympani are filled with compressible perilymph. Since the sound waves propagate as a compression wave in perilymph, this model can precisely handle the wave–based phenomena. Time domain analysis showed that a sound wave (fast wave) first propagates in the scala vestibuli and scala tympani, and then, a traveling wave (slow wave) is generated by the sound wave with some delay. Detailed studies based on even and odd mode analysis indicate that an odd mode sound wave, that is, the difference in the sound pressures between the scala vestibuli and scala tympani, excites the Békésy’s traveling wave, while an even mode sound determines the input impedance of the cochlea.
      Citation: Acoustics
      PubDate: 2022-02-21
      DOI: 10.3390/acoustics4010011
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 183-202: A Review of Finite Element Studies in
           String Musical Instruments

    • Authors: Evaggelos Kaselouris, Makis Bakarezos, Michael Tatarakis, Nektarios A. Papadogiannis, Vasilis Dimitriou
      First page: 183
      Abstract: String instruments are complex mechanical vibrating systems, in terms of both structure and fluid–structure interaction. Here, a review study of the modeling and simulation of stringed musical instruments via the finite element method (FEM) is presented. The paper is focused on the methods capable of simulating (I) the soundboard behavior in bowed, plucked and hammered string musical instruments; (II) the assembled musical instrument box behavior in bowed and plucked instruments; (III) the fluid–structure interaction of assembled musical instruments; and (IV) the interaction of a musical instrument’s resonance box with the surrounding air. Due to the complexity and the high computational demands, a numerical model including all the parts and the full geometry of the instrument resonance box, the fluid–structure interaction and the interaction with the surrounding air has not yet been simulated.
      Citation: Acoustics
      PubDate: 2022-02-23
      DOI: 10.3390/acoustics4010012
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 203-226: Prediction of Sound Insulation Using
           Artificial Neural Networks—Part I: Lightweight Wooden Floor

    • Authors: Mohamad Bader Eddin, Sylvain Ménard, Delphine Bard Hagberg, Jean-Luc Kouyoumji, Nikolaos-Georgios Vardaxis
      First page: 203
      Abstract: The artificial neural networks approach is applied to estimate the acoustic performance for airborne and impact sound insulation curves of different lightweight wooden floors. The prediction model is developed based on 252 standardized laboratory measurement curves in one-third octave bands (50–5000 Hz). Physical and geometric characteristics of each floor structure (materials, thickness, density, dimensions, mass and more) are utilized as network parameters. The predictive capability is satisfactory, and the model can estimate airborne sound better than impact sound cases especially in the middle-frequency range (250–1000 Hz), while higher frequency bands often show high errors. The forecast of the weighted airborne sound reduction index Rw was calculated with a maximum error of 2 dB. However, the error increased up to 5 dB in the worse case prediction of the weighted normalized impact sound pressure level Ln,w. The model showed high variations near the fundamental and critical frequency areas which affect the accuracy. A feature attribution analysis explored the essential parameters on estimation of sound insulation. The thickness of the insulation materials, the density of cross-laminated timber slab and the concrete floating floors and the total density of floor structures seem to affect predictions the most. A comparison between wet and dry floor solution systems indicated the importance of the upper part of floors to estimate airborne and impact sound in low frequencies.
      Citation: Acoustics
      PubDate: 2022-03-02
      DOI: 10.3390/acoustics4010013
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 227-247: Sound Reflections in Indian Stepwells:
           Modelling Acoustically Retroreflective Architecture

    • Authors: Densil Cabrera, Shuai Lu, Jonothan Holmes, Manuj Yadav
      First page: 227
      Abstract: Retroreflection is rarely used as a surface treatment in architectural acoustics but is found incidentally with building surfaces that have many simultaneously visible concave right-angle trihedral corners. Such surfaces concentrate reflected sound onto the sound source, mostly at high frequencies. This study investigated the potential for some Indian stepwells (stepped ponds, known as a kund or baori/baoli in Hindi) to provide exceptionally acoustically retroreflective semi-enclosed environments because of the unusually large number of corners formed by the steps. Two cases—Panna Meena ka Kund and Lahan Vav—were investigated using finite-difference time-domain (FDTD) acoustic simulation. The results are consistent with retroreflection, showing reflected energy concentrating on the source position mostly in the high-frequency bands (4 kHz and 2 kHz octave bands). However, the larger stepped pond has substantially less retroreflection, even though it has many more corners, because of the greater diffraction loss over the longer distances. Retroreflection is still evident (but reduced) with non-right-angle trihedral corners (80–100°). The overall results are sufficiently strong to indicate that acoustic retroreflection should be audible to an attuned visitor in benign environmental conditions, at least at moderately sized stepped ponds that are in good geometric condition.
      Citation: Acoustics
      PubDate: 2022-03-02
      DOI: 10.3390/acoustics4010014
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 248-267: The Effects of a Morphed Trailing-Edge

    • Authors: Joseph Watkins, Abdessalem Bouferrouk
      First page: 248
      Abstract: This paper presents initial results on the aeroacoustic and aerodynamic effects of morphing the trailing-edge flap of the 30P30N aerofoil, over five flap deflections (5–25°), at an 8° angle of attack and a Reynolds number of Re=9.2×105. The Ffowcs-Williams–Hawkings acoustic analogy estimates the far-field noise, whilst the flow field is solved using URANS with the four-equation Transition SST model. Aerodynamic and aeroacoustic simulation data for the 30P30N’s full configuration compare well with experimental results. A Courant number (C) ≤ 1 should be used for resolving tonal noise, whilst a C of up to 4 is sufficient for broadband noise. Sound pressure level results show an average 11% reduction in broadband noise across all flap deflections and frequencies for the morphed configuration compared with the conventional, single-slotted flap. The morphed flap eliminates the multiple tonal peaks observed in the conventional design. Beyond 15° flap deflection, the morphing flap achieves higher stall angles, but with increased drag, leading to a maximum reduction of 17% in Cl/Cd ratio compared with the conventional flap. The methodology reported here for the 30P30N is a quick tool for initial estimates of the far-field noise and aerodynamic performance of a morphing flap at the design stage.
      Citation: Acoustics
      PubDate: 2022-03-03
      DOI: 10.3390/acoustics4010015
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 268-275: Molecular Dynamics Simulations of
           Shockwave Affected STMV Virus to Measure the Frequencies of the
           Oscillatory Response

    • Authors: Jeffrey Burkhartsmeyer, Kam Sing Wong
      First page: 268
      Abstract: Acoustic shockwaves are of interest as a possible means of the selective inactivation of viruses. It has been proposed that such inactivation may be enhanced by driving the virus particles at frequencies matching the characteristic frequency corresponding to acoustic modes of the viral structures, setting up a resonant response. Characteristic frequencies of viruses have been previously studied through opto-mechanical techniques. In contrast to optical excitation, shockwaves may be able to probe acoustic modes without the limitation of optical selection rules. This work explores molecular dynamics simulations of shockwaves interacting with a single STMV virus structure, in full atomistic detail, in order to measure the frequency of the response of the overall structure. Shockwaves of varying energy were set up in a water box containing the STMV structure by assigning water molecules at the edge of the box with an elevated velocity inward—in the direction of the virus. It was found that the structure compressed and stretched in a periodic oscillation of frequency 65 ± 6.5 GHz. This measured frequency did not show strong dependency on the energy of the shockwave perturbing the structure, suggesting the frequency is a characteristic of the structure. The measured frequency is also consistent with values predicted from elastic theory. Additionally, it was found that subjecting the virus to repeated shockwaves led to further deformation of the structure and the magnitude of the overall deformation could be altered by varying the time delay between repeated shockwave pulses.
      Citation: Acoustics
      PubDate: 2022-03-18
      DOI: 10.3390/acoustics4010016
      Issue No: Vol. 4, No. 1 (2022)
  • Acoustics, Vol. 4, Pages 276-296: Acoustical Treatments on Ventilation
           Ducts through Walls: Experimental Results and Novel Models

    • Authors: Erik Nilsson, Sylvain Ménard, Delphine Bard Hagberg, Nikolaos-Georgios Vardaxis
      First page: 276
      Abstract: Sound reduction is complex to estimate for acoustical treatments on ventilation ducts through walls. Various acoustical treatments are available for ventilation ducts, including internal lining (absorption along the inner perimeter), external lagging (external sound insulation), silencer, and suspended ceilings. Previous studies have examined how silencers and the internal lining affect the sound transmission of ventilation ducts. However, there are few theories to predict the effect of external lagging in combination with ventilation ducts and how the total sound reduction is affected. This article aims to investigate different acoustical treatments and develop theoretical models when external lagging with stone wool is used to reduce flanking sound transmission via the surface area of ventilation ducts. Theoretical models are developed for external lagging and compared with measurement data. Measurements and theory are generally in good agreement over the third-octave band range of 100–5000 Hz. The developed models clarify that the distance closest to the wall has the main impact on sound reduction for a combined system with a wall and a ventilation duct. Suspended ceilings and silencers are found to be enough as acoustical treatments for certain combinations of ventilation ducts and walls. However, external lagging seems to be the only effective solution in offices and schools when a large ventilation duct passes through a wall with high sound reduction.
      Citation: Acoustics
      PubDate: 2022-03-18
      DOI: 10.3390/acoustics4010017
      Issue No: Vol. 4, No. 1 (2022)
School of Mathematical and Computer Sciences
Heriot-Watt University
Edinburgh, EH14 4AS, UK
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