Showing papers in "Journal of the Acoustical Society of America in 2019"

Machine learning in acoustics: Theory and applications

Abstract: Acoustic data provide scientific and engineering insights in fields ranging from biology and communications to ocean and Earth science. We survey the recent advances and transformative potential of machine learning (ML), including deep learning, in the field of acoustics. ML is a broad family of techniques, which are often based in statistics, for automatically detecting and utilizing patterns in data. Relative to conventional acoustics and signal processing, ML is data-driven. Given sufficient training data, ML can discover complex relationships between features and desired labels or actions, or between features themselves. With large volumes of training data, ML can discover models describing complex acoustic phenomena such as human speech and reverberation. ML in acoustics is rapidly developing with compelling results and significant future promise. We first introduce ML, then highlight ML developments in four acoustics research areas: source localization in speech processing, source localization in ocean acoustics, bioacoustics, and environmental sounds in everyday scenes.

Acoustic perfect absorbers via Helmholtz resonators with embedded apertures.

Abstract: Acoustic perfect absorption via a structure with deep subwavelength thickness is of great and continuing interest in research and engineering. This study analytically and experimentally investigates acoustic systems based on Helmholtz resonators which have embedded-apertures. The strategy of embedding apertures greatly improves the ability to manipulate the impedance of the systems. Based on the inverted configuration, perfect absorption has been realized (reaching 0.999 in experiments) via a design whose thickness is only ∼1/50th of the operating wavelength. Moreover, a tunable resonant frequency (137–300 Hz) and tunable absorption frequency bandwidth (22%–46%) can be achieved while preserving the perfect absorption performance and constant external shape. In tuning the perfect absorbers having a constant thickness, a conservation factor is revealed experimentally and then verified analytically, which could guide absorbers' design and facilitate the tuning. In addition, the distinct features of the proposed design were evaluated and validated and were compared with those of a related structure, a metasurface with a coiled backing cavity. The results have the potential to help with the design of highly efficient, thin, and tunable acoustic absorbers.

Design and experimental investigation of V-folded beams with acoustic black hole indentations.

Abstract: This paper proposes a strategy to broaden complete bandgap attenuating flexural and longitudinal modes, and to shift them to lower frequencies by spatially folding designs. Numerical simulations show that the V-folded acoustic black hole beam exhibits an ultra-wide complete bandgap below 1 kHz due to longitudinal-flexural waveform transformation, and experimental results verify this finding. The proposed folded beams are easy-to-fabricate, of compact dimensions, and exhibit excellent wave attenuation functionality that makes them promising for low-frequency vibration reduction and wave attenuation applications.

Occupational noise exposure: a review of its effects, epidemiology, and impact with recommendations for reducing its burden

Abstract: Exposure to hazardous noise is one of the most common occupational risks, both in the U.S. and worldwide. Repeated overexposure to noise at or above 85 dBA can cause permanent hearing loss, tinnitus, and difficulty understanding speech in noise. It is also associated with cardiovascular disease, depression, balance problems, and lower income. About 22 million U.S. workers are currently exposed to hazardous occupational noise. Approximately 33% of working-age adults with a history of occupational noise exposure have audiometric evidence of noise-induced hearing damage, and 16% of noise-exposed workers have material hearing impairment. While the Mining, Construction, and Manufacturing sectors typically have the highest prevalence of noise exposure and hearing loss, there are noise-exposed workers in every sector and every sector has workers with hearing loss. Noise-induced hearing loss is preventable. Increased understanding of the biological processes underlying noise damage may lead to protective pharmacologic or genetic therapies. For now, an integrated public health approach that (1) emphasizes noise control over reliance on hearing protection, (2) illustrates the full impact of hearing loss on quality of life, and (3) challenges the cultural acceptance of loud noise can substantially reduce the impact of noise on worker health.

A round robin on room acoustical simulation and auralization

Abstract: A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, “real-world” spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large extent can be traced back to the simplified use of random incidence absorption and scattering coefficients and shortcomings in the simulation of early reflections due to the missing or insufficient modeling of diffraction.A round robin was conducted to evaluate the state of the art of room acoustic modeling software both in the physical and perceptual realms. The test was based on six acoustic scenes highlighting specific acoustic phenomena and for three complex, “real-world” spatial environments. The results demonstrate that most present simulation algorithms generate obvious model errors once the assumptions of geometrical acoustics are no longer met. As a consequence, they are neither able to provide a reliable pattern of early reflections nor do they provide a reliable prediction of room acoustic parameters outside a medium frequency range. In the perceptual domain, the algorithms under test could generate mostly plausible but not authentic auralizations, i.e., the difference between simulated and measured impulse responses of the same scene was always clearly audible. Most relevant for this perceptual difference are deviations in tone color and source position between measurement and simulation, which to a large exten...

Sex differences in hearing: Probing the role of estrogen signaling

Abstract: Hearing loss is the most common form of sensory impairment in humans, with an anticipated rise in incidence as the result of recreational noise exposures. Hearing loss is also the second most common health issue afflicting military veterans. Currently, there are no approved therapeutics to treat sensorineural hearing loss in humans. While hearing loss affects both men and women, sexual dimorphism is documented with respect to peripheral and central auditory physiology, as well as susceptibility to age-related and noise-induced hearing loss. Physiological differences between the sexes are often hormone-driven, and an increasing body of literature demonstrates that the hormone estrogen and its related signaling pathways may in part, modulate the aforementioned differences in hearing. From a mechanistic perspective, understanding the underpinnings of the hormonal modulation of hearing may lead to the development of therapeutics for age related and noise induced hearing loss. Here the authors review a number of studies that range from human populations to animal models, which have begun to provide a framework for understanding the functional role of estrogen signaling in hearing, particularly in normal and aberrant peripheral auditory physiology.

Inflammation associated with noise-induced hearing loss

Abstract: Inflammation is a complex biological response to harmful stimuli including infection, tissue damage, and toxins. Thus, it is not surprising that cochlear damage by noise includes an inflammatory component. One mechanism by which inflammation is generated by tissue damage is the activation of damage-associated molecular patterns (DAMPs). Many of the cellular receptors for DAMPS, including Toll-like receptors, NOD-like receptors, and DNA receptors, are also receptors for pathogens, and function in the innate immune system. DAMP receptors are known to be expressed by cochlear cells, and binding of molecules released by damaged cells to these receptors result in the activation of cell stress pathways. This leads to the generation of pro-inflammatory cytokines and chemokines that recruit pro-inflammatory leukocytes. Extensive evidence indicates pro-inflammatory cytokines including TNF alpha and interleukin 1 beta, and chemokines including CCL2, are induced in the cochlea after noise exposure. The recruitment of macrophages into the cochlea has also been demonstrated. These provide substrates for noise damage to be enhanced by inflammation. Evidence is provided by the effectiveness of anti-inflammatory drugs in ameliorating noise-induced hearing loss. Involvement of inflammation provides a wide variety of additional anti-inflammatory and pro-resolution agents as potential pharmacological interventions in noise-induced hearing loss.

Sound radiation and transonic boundaries of a plate with an acoustic black hole.

Abstract: The acoustic black hole (ABH) phenomenon has shown promise for noise and vibration control applications. In this paper, a two-dimensional (2-D) Daubechies wavelet (DW) model is established for the sound radiation prediction of plates embedded with a circular ABH indentation. ABH plates are shown to exhibit a reduced sound radiation efficiency as compared with their flat counterpart. Below the critical frequency, this is caused by the weakening of the structural stiffness due to the ABH indentation. Above the critical frequency, a subsonic region inside the ABH cell may appear, containing acoustically slow structural waves. This region, confined within a transonic boundary, is due to the ABH-specific phase velocity reduction of the bending waves. Drawing energy away from the supersonic region of the plate, this subsonic region warrants a reduced sound radiation to the far field. Numerical results on the investigated configuration show an increase in the sound radiation efficiency due to the added stiffness effect of damping layers. Sound radiation efficiency alongside the transonic boundary changes is scrutinized and quantified. Visualization of the supersonic acoustic intensity and radiation allows identifying the effective sound radiation regions of ABH plates and their relationship with the transonic boundaries at different frequencies.

Acoustical boundary hologram for macroscopic rigid-body levitation.

Abstract: In previous studies, acoustical levitation in the far-field was limited to particles. Here, this paper proposes the “boundary hologram method,” a numerical design technique to generate a static and stable levitation field for macroscopic non-spherical rigid bodies larger than the sound wavelength λ. This paper employs boundary element formulation to approximate the acoustic radiation force and torque applied to a rigid body by discretizing the body surface, which is an explicit function of the transducer's phase and amplitude. Then, the drive of the phased array is numerically optimized to yield an appropriate field that stabilizes the body's position and rotation. In experiments, this paper demonstrates the levitation in air of an expanded polystyrene sphere with a diameter of 3.5 λ and a regular octahedron with diagonal length of 5.9 λ, both located 24 λ from the acoustic elements, by a 40 kHz (λ = 8.5 mm) ultrasonic phased array. This method expands the variety of objects that can be levitated in the far-field of an ultrasonic phased array.

Slowing deep-sea commercial vessels reduces underwater radiated noise.

Abstract: During 2017, the Vancouver Fraser Port Authority's Enhancing Cetacean Habitat and Observation program carried out a two-month voluntary vessel slowdown trial to determine whether slowing to 11 knots was an effective method for reducing underwater radiated vessel noise. The trial was carried out in Haro Strait, British Columbia, in critical habitat of endangered southern resident killer whales. During the trial, vessel noise measurements were collected next to shipping lanes on two hydrophones inside the Haro Strait slowdown zone, while a third hydrophone in Strait of Georgia measured vessels noise outside the slowdown zone. Vessel movements were tracked using the automated identification system (AIS), and vessel pilots logged slowdown participation information for each transit. An automated data processing system analyzed acoustical and AIS data from the three hydrophone stations to calculate radiated noise levels and monopole source levels (SLs) of passing vessels. Comparing measurements of vessels participating in the trial with measurements from control periods before and after the trial showed that slowing down was an effective method for reducing mean broadband SLs for five categories of piloted commercial vessels: containerships (11.5 dB), cruise vessels (10.5 dB), vehicle carriers (9.3 dB), tankers (6.1 dB), and bulkers (5.9 dB).

Using recurrent neural networks to improve the perception of speech in non-stationary noise by people with cochlear implants.

Abstract: Speech-in-noise perception is a major problem for users of cochlear implants (CIs), especially with non-stationary background noise. Noise-reduction algorithms have produced benefits but relied on a priori information about the target speaker and/or background noise. A recurrent neural network (RNN) algorithm was developed for enhancing speech in non-stationary noise and its benefits were evaluated for speech perception, using both objective measures and experiments with CI simulations and CI users. The RNN was trained using speech from many talkers mixed with multi-talker or traffic noise recordings. Its performance was evaluated using speech from an unseen talker mixed with different noise recordings of the same class, either babble or traffic noise. Objective measures indicated benefits of using a recurrent over a feed-forward architecture, and predicted better speech intelligibility with than without the processing. The experimental results showed significantly improved intelligibility of speech in babble noise but not in traffic noise. CI subjects rated the processed stimuli as significantly better in terms of speech distortions, noise intrusiveness, and overall quality than unprocessed stimuli for both babble and traffic noise. These results extend previous findings for CI users to mostly unseen acoustic conditions with non-stationary noise.

Developing a large scale population screening tool for the assessment of Parkinson's disease using telephone-quality voice

Abstract: Recent studies have demonstrated that analysis of laboratory-quality voice recordings can be used to accurately differentiate people diagnosed with Parkinson's disease (PD) from healthy controls (HCs). These findings could help facilitate the development of remote screening and monitoring tools for PD. In this study, 2759 telephone-quality voice recordings from 1483 PD and 15 321 recordings from 8300 HC participants were analyzed. To account for variations in phonetic backgrounds, data were acquired from seven countries. A statistical framework for analyzing voice was developed, whereby 307 dysphonia measures that quantify different properties of voice impairment, such as breathiness, roughness, monopitch, hoarse voice quality, and exaggerated vocal tremor, were computed. Feature selection algorithms were used to identify robust parsimonious feature subsets, which were used in combination with a random forests (RFs) classifier to accurately distinguish PD from HC. The best tenfold cross-validation performance was obtained using Gram-Schmidt orthogonalization and RF, leading to mean sensitivity of 64.90% (standard deviation, SD, 2.90%) and mean specificity of 67.96% (SD 2.90%). This large scale study is a step forward toward assessing the development of a reliable, cost-effective, and practical clinical decision support tool for screening the population at large for PD using telephone-quality voice.

Asymmetric scattering of flexural waves in a parity-time symmetric metamaterial beam.

Abstract: Non-Hermitian parity-time ( PT) symmetric systems that possess real eigenvalues have been intensively investigated in quantum mechanics and rapidly extended to optics and acoustics demonstrating a lot of unconventional wave phenomena. Here, a PT symmetric metamaterial beam is designed based on shunted piezoelectric patches and asymmetric wave scattering in the form of flexural waves is demonstrated through analytical and numerical approaches. The gain and loss components in the PT symmetric beam are realized by the introduction of negative and positive resistances into the external shunting circuits, respectively. Effective medium theory and transfer matrix method are employed to determine the effective material parameters and scattering properties of the PT symmetric metamaterial beam. Unidirectional reflectionlessness has been demonstrated analytically and numerically, together with illustrations of the PT phase transition and exceptional points. The tunability of exceptional points is studied by changing the spacing between piezoelectric patches and shunting circuit parameters. The design explores complex material parameters of the beam structure, and could open unique ways to asymmetric wave control, enhanced sensing, amplification, and localization of flexural waves.

Deep-learning source localization using multi-frequency magnitude-only data

Abstract: A deep learning approach based on big data is proposed to locate broadband acoustic sources using a single hydrophone in ocean waveguides with uncertain bottom parameters. Several 50-layer residual neural networks, trained on a huge number of sound field replicas generated by an acoustic propagation model, are used to handle the bottom uncertainty in source localization. A two-step training strategy is presented to improve the training of the deep models. First, the range is discretized in a coarse (5 km) grid. Subsequently, the source range within the selected interval and source depth are discretized on a finer (0.1 km and 2 m) grid. The deep learning methods were demonstrated for simulated magnitude-only multi-frequency data in uncertain environments. Experimental data from the China Yellow Sea also validated the approach.

Cognitive factors contribute to speech perception in cochlear-implant users and age-matched normal-hearing listeners under vocoded conditions.

Abstract: This study examined the contribution of perceptual and cognitive factors to speech-perception abilities in cochlear-implant (CI) users. Thirty CI users were tested on word intelligibility in sentences with and without semantic context, presented in quiet and in noise. Performance was compared with measures of spectral-ripple detection and discrimination, thought to reflect peripheral processing, as well as with cognitive measures of working memory and non-verbal intelligence. Thirty age-matched and thirty younger normal-hearing (NH) adults also participated, listening via tone-excited vocoders, adjusted to produce mean performance for speech in noise comparable to that of the CI group. Results suggest that CI users may rely more heavily on semantic context than younger or older NH listeners, and that non-auditory working memory explains significant variance in the CI and age-matched NH groups. Between-subject variability in spectral-ripple detection thresholds was similar across groups, despite the spectral resolution for all NH listeners being limited by the same vocoder, whereas speech perception scores were more variable between CI users than between NH listeners. The results highlight the potential importance of central factors in explaining individual differences in CI users and question the extent to which standard measures of spectral resolution in CIs reflect purely peripheral processing.

Deep convolutional network for animal sound classification and source attribution using dual audio recordings.

Abstract: This paper introduces an end-to-end feedforward convolutional neural network that is able to reliably classify the source and type of animal calls in a noisy environment using two streams of audio data after being trained on a dataset of modest size and imperfect labels. The data consists of audio recordings from captive marmoset monkeys housed in pairs, with several other cages nearby. The network in this paper can classify both the call type and which animal made it with a single pass through a single network using raw spectrogram images as input. The network vastly increases data analysis capacity for researchers interested in studying marmoset vocalizations, and allows data collection in the home cage, in group housed animals.

Current models of speech motor control: A control-theoretic overview of architectures and properties

Abstract: This paper reviews the current state of several formal models of speech motor control, with particular focus on the low-level control of the speech articulators. Further development of speech motor control models may be aided by a comparison of model attributes. The review builds an understanding of existing models from first principles, before moving into a discussion of several models, showing how each is constructed out of the same basic domain-general ideas and components-e.g., generalized feedforward, feedback, and model predictive components. This approach allows for direct comparisons to be made in terms of where the models differ, and their points of agreement. Substantial differences among models can be observed in their use of feedforward control, process of estimating system state, and method of incorporating feedback signals into control. However, many commonalities exist among the models in terms of their reliance on higher-level motor planning, use of feedback signals, lack of time-variant adaptation, and focus on kinematic aspects of control and biomechanics. Ongoing research bridging hybrid feedforward/feedback pathways with forward dynamic control, as well as feedback/internal model-based state estimation, is discussed.

High-speed video microscopy and numerical modeling of bubble dynamics near a surface of urinary stone.

Abstract: Ultra-high-speed video microscopy and numerical modeling were used to assess the dynamics of microbubbles at the surface of urinary stones. Lipid-shell microbubbles designed to accumulate on stone surfaces were driven by bursts of ultrasound in the sub-MHz range with pressure amplitudes on the order of 1 MPa. Microbubbles were observed to undergo repeated cycles of expansion and violent collapse. At maximum expansion, the microbubbles' cross-section resembled an ellipse truncated by the stone. Approximating the bubble shape as an oblate spheroid, this study modeled the collapse by solving the multicomponent Euler equations with a two-dimensional-axisymmetric code with adaptive mesh refinement for fine resolution of the gas-liquid interface. Modeled bubble collapse and high-speed video microscopy showed a distinctive circumferential pinching during the collapse. In the numerical model, this pinching was associated with bidirectional microjetting normal to the rigid surface and toroidal collapse of the bubble. Modeled pressure spikes had amplitudes two-to-three orders of magnitude greater than that of the driving wave. Micro-computed tomography was used to study surface erosion and formation of microcracks from the action of microbubbles. This study suggests that engineered microbubbles enable stone-treatment modalities with driving pressures significantly lower than those required without the microbubbles.

Examining the hearing abilities of fishes.

Abstract: Forum is intended for communications that raise acoustical concerns, express acoustical viewpoints, or stimulate acoustical research and applications without necessarily including new findings. Publication will occur on a selective basis when such communications have particular relevance, importance, or interest to the acoustical community or the Society. Submit such items to an appropriate associate editor or to the Editor-in-Chief, labeled FORUM. Condensation or other editorial changes may be requested of the author.

Effects of flow recirculation on unmanned aircraft system (UAS) acoustic measurements in closed anechoic chambers.

Abstract: An experimental campaign was undertaken to identify the effects of flow recirculation on an isolated rotor's acoustic emissions in a closed anechoic chamber. It is shown that flow recirculation results in a significant increase in higher harmonic noise, with an increase of more than 15 dB in some harmonics. This increase in noise is due to the nature of testing in a closed facility and does not represent the acoustic emissions of a similar rotor in hovering flight outdoors. Future measurements of rotors and full unmanned aerial vehicles in closed anechoic chambers must acknowledge recirculation effects and attempt to mitigate the effect on reported measurements.

Representing arbitrary acoustic source and sensor distributions in Fourier collocation methods

Abstract: Accurately representing acoustic source distributions is an important part of ultrasound simulation. This is challenging for grid-based collocation methods when such distributions do not coincide with the grid points, for instance when the source is a curved, two-dimensional surface embedded in a three-dimensional domain. Typically, grid points close to the source surface are defined as source points, but this can result in "staircasing" and substantial errors in the resulting acoustic fields. This paper describes a technique for accurately representing arbitrary source distributions within Fourier collocation methods. The method works by applying a discrete, band-limiting convolution operator to the continuous source distribution, after which source grid weights can be generated. This allows arbitrarily shaped sources, for example, focused bowls and circular pistons, to be defined on the grid without staircasing errors. The technique is examined through simulations of a range of ultrasound sources, and comparisons with analytical solutions show excellent accuracy and convergence rates. Extensions of the technique are also discussed, including application to initial value problems, distributed sensors, and moving sources.

Effects of droplet size and perfluorocarbon boiling point on the frequency dependence of acoustic vaporization threshold.

Abstract: Phase shift liquid perfluorocarbon (PFC) droplets vaporizable by ultrasound into echogenic microbubble above a threshold pressure, termed acoustic droplet vaporization (ADV), are used for therapeutic and diagnostic applications. This study systematically investigated the effect of excitation frequency (2.25, 10, and 15 MHz) on the ADV and inertial cavitation (IC) thresholds of lipid-coated PFC droplets of three different liquid cores—perfluoropentane (PFP), perfluorohexane (PFH), and perfluorooctyl bromide (PFOB)—and of two different sizes—average diameters smaller than 3 μm and larger than 10 μm—in a tubeless setup. This study found that the ADV threshold increases with frequency for the lowest boiling point liquid, PFP, for both large and small size droplets. For higher boiling point liquids, PFH and PFOB, this study did not detect vaporization for small size droplets at the excitation levels (maximum 4 MPa peak negative) studied here. The large PFOB droplets experienced ADV only at the highest excitation frequency 15 MHz. For large PFH droplets, ADV threshold decreases with frequency that could possibly be due to the superharmonic focusing being a significant effect at larger sizes and the higher excitation pressures. ADV thresholds at all the frequencies studied here occurred at lower rarefactional pressures than IC thresholds indicating that phase transition precedes inertial cavitation.

Speech recognition as a function of the number of channels in perimodiolar electrode recipients

Abstract: This study investigated the number of channels needed for maximum speech understanding and sound quality in 30 adult cochlear implant (CI) recipients with perimodiolar electrode arrays verified via imaging to be completely within scala tympani (ST). Performance was assessed using a continuous interleaved sampling (CIS) strategy with 4, 8, 10, and 16 channels and n-of-m with 16 maxima. Listeners were administered auditory tasks of speech understanding [monosyllables, sentences (quiet and +5 dB signal-to-noise ratio, SNR), vowels, consonants], spectral modulation detection, as well as subjective estimates of sound quality. Results were as follows: (1) significant performance gains were observed for speech in quiet (monosyllables and sentences) with 16- as compared to 8-channel CIS, (2) 16 channels in a 16-of-m strategy yielded significantly higher outcomes than 16-channel CIS for sentences in noise (percent correct and subjective sound quality) and spectral modulation detection, (3) 16 channels in a 16-of-m strategy yielded significantly higher outcomes as compared to 8- and 10-channel CIS for monosyllables, sentences (quiet and noise), consonants, spectral modulation detection, and subjective sound quality, (4) 16 versus 8 maxima yielded significantly higher speech recognition for monosyllables and sentences in noise using an n-of-m strategy, and (5) the degree of benefit afforded by 16 versus 8 maxima was inversely correlated with mean electrode-to-modiolus distance. These data demonstrate greater channel independence with perimodiolar electrode arrays as compared to previous studies with straight electrodes and warrant further investigation of the minimum number of maxima and number of channels needed for maximum auditory outcomes.

Non-reciprocal wave propagation in mechanically-modulated continuous elastic metamaterials.

Abstract: Acoustic and elastic metamaterials with time- and space-dependent effective material properties have recently received significant attention as a means to induce non-reciprocal wave propagation. Recent analytical models of spring-mass chains have shown that external application of a nonlinear mechanical deformation, when applied on time scales that are slow compared to the characteristic times of propagating linear elastic waves, may induce non-reciprocity via changes in the apparent elastic modulus for perturbations around that deformation. Unfortunately, it is rarely possible to derive analogous analytical models for continuous elastic metamaterials due to complex unit cell geometry. The present work derives and implements a finite element approach to simulate elastic wave propagation in a mechanically-modulated metamaterial. This approach is implemented on a metamaterial supercell to account for the modulation wavelength. The small-on-large approximation is utilized to separate the nonlinear mechanical deformation (the "large" wave) from superimposed linear elastic waves (the "small" waves), which are then analyzed via Bloch wave analysis with a Fourier expansion in the harmonics of the modulation frequency. Results on non-reciprocal wave propagation in a negative stiffness chain, a structure exhibiting large stiffness modulations due to the presence of mechanical instabilities, are then shown as a case example.

Time domain room acoustic simulations using the spectral element method.

Abstract: This paper presents a wave-based numerical scheme based on a spectral element method, coupled with an implicit-explicit Runge-Kutta time stepping method, for simulating room acoustics in the time domain. The scheme has certain features which make it highly attractive for room acoustic simulations, namely (a) its low dispersion and dissipation properties due to a high-order spatio-temporal discretization; (b) a high degree of geometric flexibility, where adaptive, unstructured meshes with curvilinear mesh elements are supported; and (c) its suitability for parallel implementation on modern many-core computer hardware. A method for modelling locally reacting, frequency dependent impedance boundary conditions within the scheme is developed, in which the boundary impedance is mapped to a multipole rational function and formulated in differential form. Various numerical experiments are presented, which reveal the accuracy and cost-efficiency of the proposed numerical scheme.

The chinchilla animal model for hearing science and noise-induced hearing loss

Abstract: The chinchilla animal model for noise-induced hearing loss has an extensive history spanning more than 50 years. Many behavioral, anatomical, and physiological characteristics of the chinchilla make it a valuable animal model for hearing science. These include similarities with human hearing frequency and intensity sensitivity, the ability to be trained behaviorally with acoustic stimuli relevant to human hearing, a docile nature that allows many physiological measures to be made in an awake state, physiological robustness that allows for data to be collected from all levels of the auditory system, and the ability to model various types of conductive and sensorineural hearing losses that mimic pathologies observed in humans. Given these attributes, chinchillas have been used repeatedly to study anatomical, physiological, and behavioral effects of continuous and impulse noise exposures that produce either temporary or permanent threshold shifts. Based on the mechanistic insights from noise-exposure studies, chinchillas have also been used in pre-clinical drug studies for the prevention and rescue of noise-induced hearing loss. This review paper highlights the role of the chinchilla model in hearing science, its important contributions, and its advantages and limitations.

The effects of classroom noise on the reading comprehension of adolescents

Abstract: An investigation has been carried out to examine the impact of different levels of classroom noise on adolescents' performance on reading and vocabulary-learning tasks. A total of 976 English high school pupils (564 aged 11 to 13 years and 412 aged 14 to 16 years) completed reading tasks on laptop computers while exposed to different levels of classroom noise played through headphones. The tasks consisted of reading science texts, which were followed by multiple-choice questions probing comprehension and word learning. Number of questions attempted, times taken to read the texts and to answer questions were recorded, as well as correct answers to different types of question. The study consisted of two similar experiments, the first comparing performance in classroom noise at levels of 50 and 70 dB LAeq; and the second at levels of 50 and 64 dB LAeq. The results showed that the performance of all pupils was significantly negatively affected in the 70 dB LAeq condition, for the number of questions attempted and the accuracy of answers to factual and word learning questions. It was harder to discern effects at 64 dB LAeq, this level of noise having a detrimental effect upon the older pupils only.

Acoustic voice variation within and between speakers.

Abstract: Little is known about the nature or extent of everyday variability in voice quality. This paper describes a series of principal component analyses to explore within- and between-talker acoustic variation and the extent to which they conform to expectations derived from current models of voice perception. Based on studies of faces and cognitive models of speaker recognition, the authors hypothesized that a few measures would be important across speakers, but that much of within-speaker variability would be idiosyncratic. Analyses used multiple sentence productions from 50 female and 50 male speakers of English, recorded over three days. Twenty-six acoustic variables from a psychoacoustic model of voice quality were measured every 5 ms on vowels and approximants. Across speakers the balance between higher harmonic amplitudes and inharmonic energy in the voice accounted for the most variance (females = 20%, males = 22%). Formant frequencies and their variability accounted for an additional 12% of variance across speakers. Remaining variance appeared largely idiosyncratic, suggesting that the speaker-specific voice space is different for different people. Results further showed that voice spaces for individuals and for the population of talkers have very similar acoustic structures. Implications for prototype models of voice perception and recognition are discussed.

The rat animal model for noise-induced hearing loss.

Abstract: Rats make excellent models for the study of medical, biological, genetic, and behavioral phenomena given their adaptability, robustness, survivability, and intelligence. The rat's general anatomy and physiology of the auditory system is similar to that observed in humans, and this has led to their use for investigating the effect of noise overexposure on the mammalian auditory system. The current paper provides a review of the rat model for studying noise-induced hearing loss and highlights advancements that have been made using the rat, particularly as these pertain to noise dose and the hazardous effects of different experimental noise types. In addition to the traditional loss of auditory function following acoustic trauma, recent findings have indicated the rat as a useful model in observing alterations in neuronal processing within the central nervous system following noise injury. Furthermore, the rat provides a second animal model when investigating noise-induced cochlear synaptopathy, as studies examining this in the rat model resemble the general patterns observed in mice. Together, these findings demonstrate the relevance of this animal model for furthering the authors' understanding of the effects of noise on structural, anatomical, physiological, and perceptual aspects of hearing.

Risk of noise-induced hearing loss due to recreational sound: Review and recommendations.

Abstract: This review was conducted to address three questions related to recreational sound exposure: (1) what criteria are used to determine noise exposure limits, (2) are there differences in the risk of hearing loss from occupational noise versus recreational sound, and (3) what is an appropriate exposure limit for recreational sound? For the first question, most standards specify an 8-h occupational noise exposure limit (LEX) of 85 dBA. This limit assumes that some workers exposed at the limit will develop hearing loss. To eliminate the risk of hearing loss, a 24-h equivalent continuous level (LEQ24h) limit of 70 dBA is appropriate. For the second question, there is some evidence that the effects of occupational noise on hearing may be worse than energetically equivalent recreational sound. Limits developed for noise are nevertheless applicable to recreational sound, and use of existing statistical models to predict hearing loss from recreational sound is appropriate, with the caveat that these models are limited to durations ≤40 years. For the third question, a recreational sound limit of 80 dBA LEX, equivalent to a 75 dBA LEQ24h, will virtually eliminate the risk of recreationally induced hearing loss in adults. Lower limits may be warranted for vulnerable or susceptible individuals.