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Publisher: Springer-Verlag (Total: 2353 journals)

 Acoustics Australia   [0 followers]  Follow         Hybrid journal (It can contain Open Access articles)    ISSN (Print) 0814-6039 - ISSN (Online) 1839-2571    Published by Springer-Verlag  [2353 journals]
• Sound Quality Experiments in a Student Hostel with Newly Designed Sonic
Crystal Window
• Authors: Hsiao Mun Lee; Long Bin Tan; Kian Meng Lim; Heow Pueh Lee
Abstract: Abstract A new design of sonic crystal window was designed to replace the existing glass louver window in a student hostel in NUS in order to achieve good balancing of natural ventilation, daylighting and noise mitigation. Numerical studies were performed on the SC window to confirm the window design. The noise level inside the room was measured using sound quality head and torso simulator for simulated white noise, pink noise and construction noise on the ground floor as well as the actual environmental noise. Ten human subjects were asked to evaluate the construction noise and environmental noise inside the room. Psychoacoustics analyses were also performed on these two types of noises. The SC window was designed such that it can attenuate the noise at frequency range of traffic noise. The SC window was able to attenuate extra 4.59 and 9.40 dBA of white noise at full frequency range and frequencies ranging from 700 to 1400 Hz, respectively. The overall amount of pink noise attenuated by the SC window was similar to that of white noise. It can be concluded that gender affected the human subjective perception toward construction noise. All human subjects felt that the degree of annoyance for environmental noise passing through the glass louver window was higher than the SC window. The SC window would successfully reduce the loudness of the construction and environmental noises compared to the glass louver window.
PubDate: 2017-09-13
DOI: 10.1007/s40857-017-0111-x

• Developing an Underwater Sound Recorder: The Long and Short (Time) of
It...
• Authors: Robert D. McCauley; Frank Thomas; Miles J. G. Parsons; Christine Erbe; Douglas H. Cato; Alec J. Duncan; Alexander N. Gavrilov; Iain M. Parnum; Chandra P. Salgado-Kent
Abstract: Abstract Passive acoustic recording of marine noise has advanced considerably over recent years. For a long time, a lack of widely available technology limited the acquisition of long-term acoustic data sets to a small number of large, cabled installations mostly restricted to military use. For other users, recordings were limited by the available technology to short snapshots of minutes to possibly days of data at a time. As technology has improved, passive acoustic monitoring has shown marine soundscapes are filled with biotic and abiotic sounds that occur on a range of often unpredictable timescales. Thus, snapshot recordings can lead to biased data. In 1999, the Centre for Marine Science and Technology, together with Australia’s Defence Science and Technology Organisation, began developing remote underwater sound recorders to increase the duration and quality of recordings. As time passed, the sound recorders were developed significantly, have been deployed over 600 times at a variety of Australian and international locations and have identified a plethora of biological, geophysical and anthropogenic sound sources. This paper presents a brief history of the recorders’ development and characteristics, some examples of the information they have provided and future direction for their next generation.
PubDate: 2017-09-13
DOI: 10.1007/s40857-017-0113-8

• A Study of the Effects on Transmission Loss of Modelled Water Column
Variations within an Area off the East Australian Coast
• Authors: Adrian D. Jones; Alex Zinoviev; Michael V. Greening
Abstract: Abstract The present accuracy of ocean and atmospheric models permits the description of water column features, and sea surface wind stress, at a resolution which enables employment in underwater acoustic transmission applications. In an investigation of aspects of linking modelled ocean data with range-dependent acoustic transmission models, a Parabolic Equation (PE) transmission code was used with data generated by the BLUElink suite of ocean and atmospheric models for a deep-water region off the east Australian coast for a particular summer period. A typical presence of warm and cold core eddies was observed to accompany a highly variable acoustic environment. Variations in expected range to particular levels of Transmission Loss were found to be mainly related to changes in the depth of the mixed surface layer, but also due to changes in the sound speed gradient in the thermocline. The study also made a brief consideration of the likely impact of wind speed variation over the region, and the effects of modelled ocean currents on acoustic transmission.
PubDate: 2017-09-01
DOI: 10.1007/s40857-017-0110-y

• Sound Production by Mulloway ( Argyrosomus japonicus ) and Variation
Within Individual Calls
• Authors: Miles J. G. Parsons; Robert D. McCauley
Abstract: Abstract Several soniferous (sound-producing) fish species can generate a number of different call types, providing significant information for intended recipients and observers. Understanding the level of variation they are capable of and whether it is voluntary or not gives an indication of how individually specific their calls might be. Similar to other Sciaenidae, mulloway (Argyrosomus japonicus) produce calls associated with spawning behaviour by vibrating their swimbladder. Dissection revealed mature mulloway have bi-lateral, highly vascularised ‘sonic’ muscles, with dorsoventrally orientated muscle fibres along the posterior two-thirds of the swimbladder, similar to French meagre (A. regius). Repetitive contraction of these muscles likely impinges on the sides of a loosely supported swimbladder, to generate motion. In the Swan River, Western Australia, mulloway produce a category of ‘long’ calls comprising 11–32 contractions at pulse repetition intervals and resulting carrier frequencies of approximately 16.6 ms and 60 Hz, respectively. However, throughout the $$\approx$$ 0.3 s calls this repetition rate may stay constant, rise, fall or a combination. In 13% of analysed calls, a pre-call pulse of lower amplitude than subsequent pulses was observed. A category of short calls (1–5 pulses) employed carrier frequencies of up to 114 Hz initially, but this decreased with each pulse, suggesting that these calls are at the limit of contraction rates of the sonic muscles. The study shows that even within previously defined call categories mulloway have the ability to produce several variations. Whether these variations are generated voluntarily or not and whether they can be perceived by the intended recipient are unknown and suggested as a topic of further work.
PubDate: 2017-09-01
DOI: 10.1007/s40857-017-0112-9

• A Case Study of the Influence of Urban Morphology on Aircraft Noise
• Authors: R. Flores; P. Gagliardi; C. Asensio; G. Licitra
Abstract: Abstract Aircraft noise is a very important environmental problem that has been addressed in many ways over the years. Many strategies have been developed to mitigate aircraft noise exposure. To help identify the problem, computer simulations with mathematical models for aircraft noise have been developed. However, those models do not consider urban morphology effects on aircraft noise propagation. Urban morphology contains a set of features that modify noise, and it is necessary to be aware of its effects as it can be a factor that can potentially increase sound pressure levels to which the general population is exposed. This paper evaluates different aspects of urban morphology and determines the impact of street topologies, line of sight angles of buildings, façade positions, façade heights, and the combination of street topologies and LOS angles on aircraft noise. Measurements in front of the façade and in free field conditions were performed around buildings that make up educational facilities near Madrid Adolfo Suárez Barajas and Pisa Galileo Galilei airports. With the experimental work, it was demonstrated that front façades, U topologies, and greater LOS angles result in higher levels on façade as all these factors contribute to the transmission of noise in an urban environment. Correction factors for measurements made in façades with and without direct transmission with similar surroundings to the ones measured in this study and within a 95% confidence level were proposed for extrapolating the levels of aircraft noise events in free field conditions.
PubDate: 2017-08-28
DOI: 10.1007/s40857-017-0102-y

• Reducing the Ambulance Siren Noise for Distant Auscultation of the Lung
Sound
• Authors: Bing-Yuh Lu; Meng-Lun Hsueh; Huey-Dong Wu
Abstract: Abstract Ambulance sirens sound very loud for transportation safety. However, loud sounds interfere with the auscultation of lung sounds. This study proposed an auscultation system that includes (1) an ACER Aspire 17 notebook as a server; (2) a smart mobile as a wireless hotspot (HwaWei Amazing A6); and (3) an ACER Aspire 5 notebook as a client. National Instruments data socket software gives read and write privileges to the IP addresses of the server and client. This real-world distant auscultation system works. The real-time adaptive filter reduced siren noise of 60 dB in power intensity. Surprisingly, a previous simulation of the adaptive filter had performed a noise reduction of 60 dB. Therefore, this real-time remote auscultation system is a reliable device for the ambulance service.
PubDate: 2017-08-17
DOI: 10.1007/s40857-017-0109-4

• The Tympanal Recess of the Cetacean Cochlea: Function and Evolution
• Authors: Travis Park; Erich M. G. Fitzgerald; Alistair R. Evans
Abstract: Abstract Cetaceans (whales and dolphins) primarily use sound to communicate and hunt for prey. Their auditory anatomy is highly specialised, but much about its function remains unknown. In particular, a feature of the cochlea known as the tympanal recess present in some mysticetes (baleen whales) and odontocetes (toothed whales) has defied functional explanation. Here, we present and discuss several hypotheses that may clarify the function and evolution of the tympanal recess. One potential function in particular, the vibroacoustic duct mechanism, seems most plausible although further work is needed to test the hypothesis, which hints at the possibility of sperm whales and beaked whales being able to detect both high and low frequencies.
PubDate: 2017-08-17
DOI: 10.1007/s40857-017-0104-9

• Potential Use of Broadband Acoustic Methods for Micronekton Classification
• Authors: Arti Verma; Rudy J. Kloser; Alec J. Duncan
Abstract: Abstract Broadband acoustic methods are an emerging technology with potential use in identification and classification of marine organisms. The application of broadband methods to scientific surveys of mesopelagic micronektons (animals of 2–20 cm length found at depths of 200–1000 m) is described. The principles of the broadband system are briefly outlined with particular emphasis on its use for micronekton detection and identification employing the TS-frequency curve of single targets. The use of acoustic scattering models to determine characteristics of the marine organism such as size and material properties is also discussed. As an example of the application of this technique, broadband echosounders mounted on a depth-profiling platform were used to collect high-frequency (55–160 kHz) acoustic data from mesopelagic depths (up to 600–1000 m) of the Great Australian Bight region. Some example results from narrowband and broadband echosounders are compared. The resulting frequency-dependent target strength curves of selected targets enabled classification into different acoustic groups, demonstrating the significant advantage provided by the broadband system. There is still a large gap between the achievable acoustic classification and the ultimate aim of species level classification, and to this end some limitations of broadband echosounder systems in identifying targets are discussed along with the use of video and still cameras to assist in the interpretation of acoustic data.
PubDate: 2017-08-17
DOI: 10.1007/s40857-017-0105-8

• An Unsupervised Acoustic Description of Fish Schools and the Seabed in
Three Fishing Regions Within the Northern Demersal Scalefish Fishery
(NDSF, Western Australia)
• Authors: Sven Gastauer; Ben Scoulding; Miles Parsons
Abstract: Abstract Fisheries acoustics is now a standard tool for monitoring marine organisms. Another use of active-acoustics techniques is the potential to qualitatively describe fish school and seafloor characteristics or the distribution of fish density hotspots. Here, we use a geostatistical approach to describe the distribution of acoustic density hotspots within three fishing regions of the Northern Demersal Scalefish Fishery in Western Australia. This revealed a patchy distribution of hotspots within the three regions, covering almost half of the total areas. Energetic, geometric and bathymetric descriptors of acoustically identified fish schools were clustered using robust sparse k-means clustering with a Clest algorithm to determine the ideal number of clusters. Identified clusters were mainly defined by the energetic component of the school. Seabed descriptors considered were depth, roughness, first bottom length, maximum $$S_{v}$$ , kurtosis, skewness and bottom rise time. The ideal number of bottom clusters (maximisation rule with D-Index, Hubert Score and Weighted Sum of Squares), following the majority rule, was three. Cluster 1 (mainly driven by depth) was the sole type present in Region 1, Cluster 2 (mainly driven by roughness and maximum $$S_{v})$$ dominated Region 3, while Region 2 was split up almost equally between Cluster 2 and 3. Detection of indicator species for the three seabed clusters revealed that the selected clusters could be related to biological information. Goldband snapper and miscellaneous fish were indicators for Cluster 1; Cods, Lethrinids, Red Emperor and other Lutjanids were linked with Cluster 2, while Rankin Cod and Triggerfish were indicators for Cluster 3.
PubDate: 2017-08-17
DOI: 10.1007/s40857-017-0100-0

• A Tale of Two Soundscapes: Comparing the Acoustic Characteristics of Urban
Versus Pristine Coastal Dolphin Habitats in Western Australia
• Authors: S. A. Marley; C. P. Salgado Kent; C. Erbe; D. Thiele
Abstract: Abstract Underwater noise environments are increasingly being considered in marine spatial planning and habitat quality assessments. Although the overall aim of regulation is to quieten anthropogenically noise-rich habitats whilst maintaining pristine habitats free of man-made noise, effective management plans require knowledge upon which to base decisions. This is particularly true for managers of acoustically specialised species. This study aimed to compare the acoustic environment of coastal dolphins in two locations within Western Australia by comparing a ‘pristine’ habitat (Roebuck Bay) with an ‘urban’ habitat (Fremantle Inner Harbour). Autonomous underwater acoustic recorders collected approximately 940 and 1080 h of data from these two sites, respectively. Additionally, in Roebuck Bay opportunistic in situ recordings with concurrent visual observations were collected in the presence of two dolphin species. Acoustic data were assessed via weekly spectrograms, power spectrum density percentile plots and probability densities, octave band levels, broadband noise levels, and generalised estimating equations. Results indicated that the two sites had highly contrasting acoustic environments. In Roebuck Bay, the local soundscape was dominated by biotic sounds, with only sporadic vessel noise. However, in Fremantle Inner Harbour, anthropogenic noise was prevalent. On average, Roebuck Bay was 20 dB quieter than the Fremantle Inner Harbour over the frequency band 10 Hz–11 kHz. Dolphin communications had a greater potential to be masked in Fremantle Inner Harbour than in Roebuck Bay based on elevated anthropogenic noise levels. If noise levels were to increase in Roebuck Bay, coastal dolphins may show behavioural and/or acoustical responses as observed at other locations.
PubDate: 2017-08-11
DOI: 10.1007/s40857-017-0106-7

• Underwater particle motion (acceleration, velocity and displacement) from
recreational swimmers, divers, surfers and kayakers
• Authors: Christine Erbe; Miles Parsons; Alec J. Duncan; Klaus Lucke; Alexander Gavrilov; Kim Allen
Abstract: Abstract When humans take to the water, they generate sound. This is helpful for the detection, classification, localisation and tracking of certain activities for purposes of border security, health and safety of offshore industrial development, environmental management, etc. The most commonly measured acoustic quantity is pressure. Vector quantities related to particle motion, such as particle velocity and acceleration, can equally identify the activity and they carry directional information. Acoustic pressure and particle motion were measured from 10 water sports activities within an Olympic-sized pool: swimming backstroke, breaststroke, butterfly and freestyle; snorkelling with fins; kicking a boogie board with fins; paddling with alternating or simultaneous arms while lying on a surfboard; scuba-diving; kayaking and jumping into the pool. Activities that occurred at the surface and that involved repeatedly piercing the surface were the strongest sound generators. Surface activities that produced fewer bubbles and scuba-diving at depth generated less broadband power. The vector fields around water sports activities can be expected somewhat different in the open ocean from within a pool, and more research is needed to understand how marine fauna might perceive these vector quantities.
PubDate: 2017-08-10
DOI: 10.1007/s40857-017-0107-6

• High-Frequency Modulated Signals Recorded Off the Antarctic Peninsula
Area: Are Killer Whales Emitting Them'
• Authors: M. V. Reyes Reyes; S. Baumann-Pickering; A. Simonis; M. L. Melcón; J. Trickey; J. Hildebrand; M. Iñíguez
Abstract: Abstract High-frequency modulated signals with a stereotyped down-swept contour were recorded in the northwestern Antarctic Peninsula using an autonomous recorder and a towed hydrophone array. Signals have a mean start frequency at 21.6 kHz, end frequency at 15.7 kHz, −10 dB bandwidth of 5.9 kHz, and duration of 65.2 ms. Bouts of signals were generally recorded with a median inter-signal interval of 2.1 s. HFM signals partially modulated in the non-ultrasonic range similar to the ones described in this paper have already been reported for killer whales in the North Pacific, Western South Atlantic and Western Australian coast. The HFM signals were recorded in the presence of other odontocete sounds such as whistles, echolocation clicks and burst-pulsed sounds. The similarities of these sounds with vocalizations described for killer whales in the Western Australian coast lead us to strongly believe that the described HFM signals were produced by Antarctic killer whales. This paper described for the first time HFM signals in Antarctica and discussed evidence suggesting that Antarctic type A killer whales are the most probable candidates to produce such signals. However, a visual confirmation is still needed and the function of the HFM signals remains unknown.
PubDate: 2017-08-01
DOI: 10.1007/s40857-017-0103-x

• A Review of Wind Turbine-Generated Infrasound: Source, Measurement and
Effect on Health
• Authors: Renzo Tonin
Abstract: Abstract Some people who reside in proximity to wind turbines complain of a range of adverse health impacts. These include tinnitus, raised blood pressure, heart palpitations, tachycardia, stress, anxiety, vertigo, dizziness, nausea, blurred vision, fatigue, cognitive dysfunction, headaches, ear pressure, exacerbated migraine disorders, motion sensitivity, inner ear damage and sleep deprivation. This article begins with a historical review of prognoses such as Vibroacoustic Disease and Wind Turbine Syndrome which were proposed to explain the reported health symptoms and the hypothesised link to the emission of infrasound from wind turbines. A review of noise measurements at wind turbine sites conducted by various investigators shows that the level of infrasound is below the threshold of hearing. Notwithstanding, others postulate that stimulation by infrasound of the otolith organs causes nauseogenic symptoms or that stimulation of the outer hair cells, which are said to be particularly sensitive to infrasound frequencies, explains the symptoms. A review of social surveys is undertaken of self-reported health effects attributable to wind turbine noise, including the effects of sleep disturbance. A description is finally provided of physical exploration studies which subject participants to infrasound and measure their response.
PubDate: 2017-07-07
DOI: 10.1007/s40857-017-0098-3

• Flow Noise Calculation and Experimental Study for Hydrophones in
Fluid-Filled Towed Arrays
• Authors: Kunde Yang; Qiulong Yang; Peng Xiao; Xuegang Li; Rui Duan; Yuanliang Ma
Abstract: Abstract Understanding the physical features of the flow noise for hydrophones in a fluid-filled towed array is important for designing a towed line array sonar. The flow noise of hydrophones in fluid-filled towed arrays generated by the turbulent pressure is derived by the frequency–wave number decomposition method. The results show that the flow noise increases rapidly with the towed speed and decreases with the length of the hydrophone. Meanwhile, the flow noise is closely related to the material parameters of the elastomer tube. It decreases with the attenuation factor, outside radius, and thickness of the elastomer tube. Furthermore, a spatial filter designed by the constant sector inverse-beamforming method is used for suppressing the tow-ship-radiated noise and the ambient noise from the sensor data. The analysis results of the experimental data are consistent well with the theoretical values, which indicate that the tow-ship-radiated noise and the ambient noise are suppressed effectively by the spatial filter. In addition, the correlation features of the flow noise received by the acoustic array are analyzed, which is important for the sonar system design.
PubDate: 2017-07-07
DOI: 10.1007/s40857-017-0086-7

• A Review of the Factors that Influence Sound Absorption and the Available
Empirical Models for Fibrous Materials
• Authors: R Dunne; D Desai; R Sadiku
Abstract: Abstract There is a drastic need in industries, such as the automotive and construction industry, for easy-to-use empirical models that can effectively and efficiently predict the sound absorption coefficient of fibrous absorbers. Hence, this paper presents a review of the factors that influence sound absorption, such as bulk density, composite thickness, porosity, fibre diameter, airflow resistivity, tortuosity and surface impedance. Also, the available empirical models for the prediction of the sound absorptions coefficient of porous fibrous materials and their working range are presented. These models have been tested using experimental data, based on natural fibres such as coir, kenaf, hemp and sheep’s wool, in order to test their accuracy. An analysis of the data is presented. It is seen that the present empirical models available are not adequate for the prediction of the sound absorption coefficient for the natural fibres presented, and hence, new models that can accurately predict the sound absorption coefficient need to be developed. The current models available are also seen to be extremely sensitive to composite thickness and bulk density changes. However, they are able to give the designer a good starting point. Therefore, this review is intended to be a comprehensive and valuable reference source for designers of sound absorbing materials in order to save time and costs during the design phase. Therefore, this contribution will enable the designers to make quick informed decisions on the type of absorber to use for a particular application as well as allow for quick selection of an appropriate empirical model for accurate prediction of the sound absorption coefficient of the selected fibrous porous material.
PubDate: 2017-07-07
DOI: 10.1007/s40857-017-0097-4

• Differences in Vocalisation Patterns of Dugongs Between Fine-Scale
Habitats Around Talibong Island, Thailand
• Authors: Kotaro Tanaka; Kotaro Ichikawa; Hideaki Nishizawa; Kongkiat Kittiwattanawong; Nobuaki Arai; Hiromichi Mitamura
Abstract: Abstract Examining characteristics of a species’ fine-scale habitat use contributes to effective and practical spatially explicit conservation. Dugongs (Dugong dugon) are endangered herbivorous mammals that use vocalisation for communication. In a small, specific area of Thai waters, classified here as a “vocal hotspot,” vocalisation rates are elevated, implying that in this area acoustic communication plays an important role. We recorded dugong calls in the vocal hotspot and a nearby feeding area. We then compared temporal patterns of vocalisation between the two sites to investigate the degree of variability in vocalisation between fine-scale habitats, which is important for understanding dugong habitat use by passive acoustic monitoring. From the 489 total hours of recording, 6607 and 2032 calls were observed in the vocal hotspot and feeding area, with mean vocalisation rates (calls per hour) 13.5 and 4.2, respectively. Vocalisation rate had distinctive 24-h periodicity in only the vocal hotspot. Environmental factors that correlated with changes in detected vocalisation rate also differed between the two locations. Water level correlated with vocalisation rate in the feeding area; in contrast, current direction correlated with vocalisation rate in the vocal hotspot. In conclusion, the vocalisation pattern for dugongs differed between the two sites, and we suggest that their habitat use varies at fine spatial scales.
PubDate: 2017-06-21
DOI: 10.1007/s40857-017-0094-7

• Accuracy of the Far-Field Approximation for the Underwater Sound Radiated
When Immersed Steel and Lead Piles (with Non-reflective Toes) are Driven
by a Harmonic Axisymmetric Force
• Authors: Marshall V. Hall
Abstract: Abstract Steel and lead piles immersed in seawater and their toes made non-reflective (for clarity of the results) are driven by an axisymmetric harmonic force. Axial and radial vibrations travel from head to toe. Radial vibration, which radiates sound into the surrounding medium, is computed using Membrane thin-shell vibration theory. At 1 kHz, a typical construction steel pile (radius 38 cm, wall thickness 2.5 cm) has a phase velocity of 4943 m/s and in cold seawater (sound speed 1485 m/s), the Mach wave radiates at $$a\hbox {cos}(1485 /4943) = 73^{\circ }$$ from the pile axis. According to ray theory, a Mach wave is received at any position providing a $$73^{\circ }$$ line from that position intersects the pile (at what was the emitting point). The vibration energy at this emitting point has travelled there from the pile head. For a given slant range (R) to a receiver, ray theory predicts that a Mach wave is not received below a minimum colatitude (COMIN). For a typical steel pile, it is found that as R increases beyond the pile length (L), COMIN increases rapidly from $$0^{\circ }$$ , passes through $$68^{\circ }$$ at $$10 \times L$$ , and asymptotes to $$73^{\circ }$$ as R increases further. For the same pile made of lead, the phase velocity at 1 kHz is 1332 m/s, and no Mach wave is radiated. For both steel and lead piles, radiated SPLs were calculated using both exact and far-field approximate radiation theories as functions of colatitude, at slant ranges from 10 to 1000 m. For the steel piles, the far-field approximate model (which omits the Mach wave) underestimates SPL by up to 20 dB if the receiver’s colatitude exceeds COMIN. For the lead piles however, the far-field approximate model is accurate to within 1 dB.
PubDate: 2017-06-21
DOI: 10.1007/s40857-017-0096-5

• Automated Insect Detection Using Acoustic Features Based on Sound
Generated from Insect Activities
• Authors: Quoc Viet Phung; Iftekhar Ahmad; Daryoush Habibi; Steven Hinckley
Abstract: Abstract This paper presents an automated insect detection technique using acoustic features and machine learning techniques based on sound signals generated from insect activities. The input sound signal was first pre-processed and segmented into windows frames from which the low-level set of signal properties and Mel-Frequency Cepstrum Coefficients were extracted. The detection accuracy of the features was tested on 11 insects of 6 species using a number of classifiers. The results have shown that a suitable acoustic feature set can be used to detect insects with high accuracy. Furthermore, the ensemble classifiers such as Bagged Tree provided the best accuracy in detecting both species classification (over 97.1%) and insect classification (over 92.3%). On the other hand, fine k-nearest neighbour classifier offered a balance between the quick training time (around 1 s) and the detection accuracy (over 88.5%).
PubDate: 2017-06-10
DOI: 10.1007/s40857-017-0095-6

• Shape Dependence of Acoustic Performances of Buildings with a Hyperbolic
Paraboloid Cable Net Membrane Roof
• Authors: Fabio Rizzo; Paolo Zazzini
Abstract: Abstract The paper investigates the shape dependence of the acoustic performances of space with different plans covered by a hyperbolic paraboloid cables net and membrane roof. In addition, the paper study the differences of acoustic performances between four different configurations: sport arena and empty, partially occupied and full concert hall. The aim is to compare the shape dependence of the acoustic response for each configuration. The study is focused on different geometries: four different plan shapes (i.e., square, circular, rectangular and elliptical) and two different curvatures. The differences of acoustic efficiency are compared using some representative parameters like the reverberation time, ( $$T_{30}$$ ), the clarity ( $$C_{80}$$ ), the definition ( $$D_{50}$$ ) and the initial time delay gap. In addition, the paper compares the acoustic response for all concert hall configurations and all geometries with permanent and temporary improvements.
PubDate: 2017-05-29
DOI: 10.1007/s40857-017-0092-9

• Acoustic Emissions of Semi-Permeable Trailing Edge Serrations
• Authors: Carlos Arce León; Roberto Merino-Martínez; Stefan Pröbsting; Daniele Ragni; Francesco Avallone
Abstract: Abstract The trailing edge of a NACA 0018 airfoil is modified through the attachment of serrations with different degrees of permeability. Acoustic beamforming is used to inspect the turbulent boundary layer-trailing edge noise emissions from the unmodified and serrated trailing edges. Different freestream velocities and angles of attack are investigated. The serration permeability is prescribed by having slits cut into the solid surface of the serrations in two different configurations. The results indicate that a certain benefit in noise reduction is obtained from a mixed solid/slitted configuration, while a fully slitted configuration loses most of the noise reduction performance.
PubDate: 2017-05-22
DOI: 10.1007/s40857-017-0093-8

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