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During the COVID-19 outbreak, the auscultation of heart and lung sounds has played an important role in the comprehensive diagnosis and real-time monitoring of confirmed cases. With clinicians wearing protective clothing in isolation wards, a potato chip tube stethoscope, which is a secure and flexible substitute for a conventional stethoscope, has been used by Chinese medical workers in the first-line treatment of COVID-19. In this study, an optimal design for this simple cylindrical stethoscope is proposed based on the fundamental theory of acoustic waveguides. Analyses of the cutoff frequency, sound power transmission coefficient, and sound wave propagation in the uniform lossless tube provide theoretical guidance for selecting the geometric parameters for this simple cylindrical stethoscope. A basic investigation into the auscultatory performances of the original tube and the optimal tube with proposed dimensions was conducted both in a semi-anechoic chamber and in a quiet laboratory. Both experimental results and front-line doctors' clinical feedback endorse the proposed theoretical optimization.

The Reflections series takes a look back on historical articles from The Journal of the Acoustical Society of America that have had a significant impact on the science and practice of acoustics.

Capacitor microphones are widely used to transduce sound waves into electrical voltages. The converting capacitor can either be operated in baseband (audio-frequency) or passband (radio-frequency, RF). A baseband operation can use a straightforward circuit implementation while a passband operation becomes more complex. The advantage of operating the capacitor in passband is a drastically lowered sensor impedance leading to superior performance, especially at high humidity levels. In this work, a digitized RF microphone is presented. Measurements prove the microphone to exceed commercial state-of-the-art small-diaphragm capacitor microphones in signal-to-noise ratio. Additionally, as the signal is digitized before demodulation, the electrical low-frequency 1 / f-noise is circumvented. Furthermore, an all-digital gain ranging approach is presented, which is especially suited for the proposed system. The approach increases the system's dynamic range by digitally adjusting and correcting the microphone's sensitivity.

© 2019 Acoustical Society of America. This paper investigates the feasibility of increasing the noise reduction performance of active noise control (ANC) systems on ground by introducing two vertical reflecting surfaces with an included angle. By using the image source method, the theory of sound wave propagation in a wedge-shaped reflector and the integral equation method, the noise reduction of the ANC systems with two infinitely large or finite size reflecting surfaces with different included angles are studied. It is demonstrated that the noise reduction of the system can be increased significantly with two reflecting surfaces after optimizing their included angle and size. The simple empirical formulas for the optimal included angle of the surfaces and the noise reduction are presented. It is found that the noise reduction at 500 Hz increases by 13.6 dB when two vertical reflecting surfaces are arranged with an optimal angle of 125° and the source distance is 0.1 m. By optimizing the size of the reflecting surfaces to about 0.35 of the wavelength, the noise reduction can be further increased by approximately 2.8 dB. The mechanisms for the performance improvement are disclosed, and the experiments are conducted to validate the results.

Sound absorption or dissipation principally involves joint interactions between sound waves, material morphology and the air medium. How these elements work most efficiently for sound absorption remains elusive to date. In this paper, we suggest a fundamental relation concisely cross-linking the three elements, which reveals that optimal sound absorption efficiency occurs when the pore size of the material is twice the thickness of the viscous boundary layer of the acoustic air medium. The study is validated by microlattice materials comprising of well-controlled regular structures that absorb sound in a tunable manner. Optimized material morphology in terms of pore size and porosity is determined to provide a robust guidance for optimizing sound absorbing materials., 14 pages, 7 figures

This paper describes analytical and experimental studies conducted to investigate the acoustic properties of axially non-uniform multiple cavity resonance liner for absorbing higher-order duct modes. A three-dimensional analytical model is proposed based upon transfer element method. The model is assessed by making a comparison with results of a liner performance experiment concerning higher-order modes propagation, and the agreement is good. According to the present results, it is found that the performance of multiple cavity resonance liner is related to the incident sound waves. Moreover, an analysis of the corresponding response of liner perforated panel-cavity system is performed, in which the features of resonance frequency and dissipation of the system under grazing or oblique incidence condition are revealed. The conclusions can be extended to typical non-locally reacting liners with single large back-cavity, and it would be beneficial for future non-locally reacting liner design to some extent.

Over the past decade there has been a great amount of research effort devoted to the topic of acoustic metamaterials (AMMs). The recent development of AMMs has enlightened the way of manipulating sound waves. Several potential applications such as low-frequency noise reduction, cloaking, angular filtering, subwavelength imaging, and energy tunneling have been proposed and implemented by the so-called membrane- or plate-type AMMs. This paper aims to offer a thorough overview on the recent development of membrane- or plate-type AMMs. The underlying mechanism of these types of AMMs for tuning the effective density will be examined first. Four different groups of membrane- or plate-type AMMs (membranes with masses attached, plates with masses attached, membranes or plates without masses attached, and active AMMs) will be reviewed. The opportunities, limitations, and challenges of membrane- or plate-type AMMs will be also discussed.

Based on one-dimensional lossy Bragg stacks, an asymmetric absorber is realized for low-frequency sound waves, that is, perfect absorption can be obtained when sound waves are normally incident from one side while a small absorption can be obtained from the opposite side. Moreover, the asymmetric absorption persists for a wide incident angle of sound waves in the range from 0° to 42° with the absorptive coefficient larger than 90% from one side while less than 20% from the other side. By changing the thickness of the top sublayer, a series of interesting absorption phenomena such as Fano-resonance type absorption are further investigated.

We investigate the possibility for acoustic waves to propagate with a constant amplitude in disordered media. We find that this remarkable property is possible if one adds a tailored distribution of gain and loss on top of the disorder, making the medium non-Hermitian. We present the theory of constant-amplitude acoustic waves in both cases of continuous and discrete media, and provide an experimental demonstration in a metamaterial at audible frequencies.

The broad absorption of low-frequency noise typically requires the utilization of large thicknesses of sound absorbing materials. As this creates space issues, there is a demand for thin broad low-frequency absorbers. This research aims to develop an acoustic transparent panel for low-frequency broad sound absorption. Destructive sound resonance tubes were created for this scope using modern tools for generating complex geometries in systems of a few centimeters of thickness. The capability of digital fabrication to enable design freedom and to support the production of complex geometries is explored in this paper. Destructive interference means that two interfering sound waves that are in counter-phase, cancel each other. Digital fabrication is shown to play an important role in developing customized sound absorbing components to absorber below 500 Hz, and especially well below 200 Hz. A parametric script using Grasshopper through Rhinoceros to generate automatically the geometric parameters of the 3d resonators is described. Different materials for 3d printing the resonators are compared. Finally, the challenges of additive manufacturing techniques are finally reported.

The authors present an acoustic system, designed by DGA Naval Systems, dedicated to the study of sound propagation in challenging environments. The system is called ALMA for Acoustic Laboratory for Marine Applications. Shallow and coastal waters, where oceanographic phenomena (such as linear internal waves, tides and 3-D effects) interact with acoustic propagation, represent the main area of deployments. Since 2014, 5 at-sea campaign have been successfully conducted in the Mediterranean Sea and in the Atlantic Ocean. They mainly consisted in propagating sound waves in the 1–15 kHz frequency band using fixed or towed sources towards a modular passive acoustic array. The latter is composed of 8 rigid arms carrying 16 hydrophones each. These arms can be, and actually were, arranged in various shapes, depending on the goal of the experiment. Environmental sensing using thermistor strings and CTD cast complete the experimental equipment. The analysis of the 2016 campaign demonstrates the ability of the system ...

The acoustic characteristics of bladderless fishes were examined by measuring the target strength (TS) of three species, pointhead flounder (flat-shaped), Arabesque greenling (spindle-shaped) and sandeel (cylinder-shaped). TS measurements were collected in a seawater tank (10 × 6 × 5 m) using the EK80 echo sounder (Simrad, Norway) and ES70-7C transducer (Simrad) over a frequency range of 45–90 kHz with a tether method. After TS measurement of the whole fish, we separated the flesh from the body (for pointhead flounder and arabesque greenling) and measured the TS of the head and bones. Pitch angle characteristics were measured from a head-down orientation (−30 deg) to a head-up orientation (30 deg), and TS was processed using Echoview 9 software (Echoview, Australia). TS patterns were examined with respect to orientation using the distorted-wave Born approximation model. The standard length, width, and height of fish were inputted into the model. The three bladderless fishes tested have different body shapes, meaning different areas are exposed to sound waves at the same body length. Therefore, the relationship between TS and the cross-section of the dorsal aspect of bladderless fish is discussed. [Work supported by the Sasakawa Scientific Research Grant from The Japan Science Society.]

Electret microphones with stiff plates instead of flexible diaphragms are described. The stiff plate and a backplate, separated by a soft cellular polymer spacer ring, yield a capacitance that is varied by the incoming sound wave; thus a voltage change in the plates is induced. Various such plate microphones were built and characterized. Sensitivities of more than 10 mV/Pa and equivalent noise levels of 23 dB(A) are obtained. An analytical model for the sensitivity of plate microphones was developed. Advantages of the plate microphones are high mechanical robustness, low harmonic distortion, and no risk of membrane collapse.

A transmission-line acoustic metamaterial is an engineered, periodic arrangement of relatively small unit-cells, the acoustic properties of which can be manipulated to achieve anomalous physical behaviours. These exotic properties open the door to practical applications, such as an acoustic leaky-wave antenna, through the implementation of radiating channels along the metamaterial. In the transmitting mode, such a leaky-wave antenna is capable of steering sound waves in frequency-dependent directions. Used in reverse, the antenna presents a well defined direction-frequency behaviour. In this paper, an acoustic leaky-wave structure is presented in the receiving mode. It is shown that it behaves as a sound source direction-finding device using only one sensor. After a general introduction of the acoustic leaky-wave antenna concept, its radiation pattern and radiation efficiency are expressed in closed form. Then, numerical simulations and experimental assessments of the proposed transmission-line based structure, implementing only one sensor at one termination, are presented. It is shown that such a structure is capable of finding the direction of an incoming sound wave, from backward to forward, based on received sound power spectra. This introduces the concept of sound source localization without resorting to beam-steering techniques based on multiple sensors.

The active noise control in free space for a global attenuation is always very challenging, especially for extended and complex radiators. This work focuses on a finite simple line source possessing strong directivity of multi-lobe radiation pattern as the primary source, which is frequently encountered in traffic noise control problems modelling a busy road or the train noise. Conventional secondary sources of compact size radiate the sound wave omnidirectionally, resulting in tangible pressure level increase in off-axis areas. This paper introduces a novel constructed control source, which has reasonably directional sound radiation capability even with a very compact size in low-frequency. Comparing to common directive sources, such as axially oscillating baffled pistons, the novel sources can significantly improve the active control result in a global way.

In order to obtain high presence, it is necessary to reproduce the sound environment of remote places. Conventionally, sound environments at remote places are reproduced by recreating a sound signal at that place. In this study, an acoustic technique that reproduces sound environments of remote places by recreating the dynamics of the environment at that place is proposed. In the proposed acoustic technique, the desired sound environment is attained by making listeners on the spot feel as if there were a wall that reflects and absorbs the sound waves. By controlling the acoustic impedance at the position where the wall is constructed, the wall is virtually built. In addition, the acoustic impedance including the virtual viscosity and elasticity that can be arbitrarily determined at the position where the wall constructed is set. As a result, by deciding the acoustic output from the secondary sound source so as to attain the desired acoustic impedance, the wall is virtually constructed to reproduce the desired sound environment. In order to obtain high presence, it is necessary to reproduce the sound environment of remote places. Conventionally, sound environments at remote places are reproduced by recreating a sound signal at that place. In this study, an acoustic technique that reproduces sound environments of remote places by recreating the dynamics of the environment at that place is proposed. In the proposed acoustic technique, the desired sound environment is attained by making listeners on the spot feel as if there were a wall that reflects and absorbs the sound waves. By controlling the acoustic impedance at the position where the wall is constructed, the wall is virtually built. In addition, the acoustic impedance including the virtual viscosity and elasticity that can be arbitrarily determined at the position where the wall constructed is set. As a result, by deciding the acoustic output from the secondary sound source so as to attain the desired acoustic impedance, the wall is virtually constructed to reproduce the des...

A series of measurements in the NRL shallow water laboratory were designed and conducted to measure the sound waves propagating in an un-consolidated fluid-saturated porous medium. The novel design used a pair of small receivers, one buried in the bottom and one mounted in the water column to a linear vertical positioner. The buried receiver was carefully inserted into the sandy bottom using a small water-jet, engineered to have no entrained air, to minimally disturb the bottom. The receiver pair were incrementally pulled up through the bottom or water column to map out the sound propagating from a source mounted in the water column. The position of the source was varied to measure above critical angle and below critical angle sound penetration into the bottom. Measurements of carefully smoothed and roughened interfaces were also conducted. This synthetic vertical array technique proved very successful in the laboratory and was transitioned to at-sea measurements in a variety of sandy bottom locations around Panama City, FL. The analysis and modeling of these laboratory and at-sea experiments will be discussed.A series of measurements in the NRL shallow water laboratory were designed and conducted to measure the sound waves propagating in an un-consolidated fluid-saturated porous medium. The novel design used a pair of small receivers, one buried in the bottom and one mounted in the water column to a linear vertical positioner. The buried receiver was carefully inserted into the sandy bottom using a small water-jet, engineered to have no entrained air, to minimally disturb the bottom. The receiver pair were incrementally pulled up through the bottom or water column to map out the sound propagating from a source mounted in the water column. The position of the source was varied to measure above critical angle and below critical angle sound penetration into the bottom. Measurements of carefully smoothed and roughened interfaces were also conducted. This synthetic vertical array technique proved very successful in the laboratory and was transitioned to at-sea measurements in a variety of sandy bottom locations aro...

Horseshoe bats (Rhinolophidae) have dynamic biosonar systems with interfaces for ultrasonic emission/reception that deform while diffracting the outgoing/incoming sound waves. This peripheral dynamics has been shown to enhance sensory information encoding. To investigate the properties and potential uses of these system features in the real world, a biomimetic sonar head is being developed with the goal of mimicking as much of the bats' peripheral dynamics as faithfully as possible. Further constraints on this development were suitability for integration with mobile platforms and support for interactive quantitative/in-depth experimentation. Flexible noseleaf and pinna shapes along with an actuation system have been designed to mimic the static geometry of the respective structures in bats as well as several of the animals' degrees of freedom in deforming them. The electrical subsystem has been designed to support high-quality ultrasound generation and recording. Generation of all source voltages and signal amplification have been consolidated into a single circuit board to reduce weight and complexity of the overall system. The frame has been altered to reduce weight and add modularity to the noseleaf and pinna elements. The software architecture is based on a back-end (Python, LabVIEW) combined with a flexible front-end (MATLAB) for experimental design and data analysis.Horseshoe bats (Rhinolophidae) have dynamic biosonar systems with interfaces for ultrasonic emission/reception that deform while diffracting the outgoing/incoming sound waves. This peripheral dynamics has been shown to enhance sensory information encoding. To investigate the properties and potential uses of these system features in the real world, a biomimetic sonar head is being developed with the goal of mimicking as much of the bats' peripheral dynamics as faithfully as possible. Further constraints on this development were suitability for integration with mobile platforms and support for interactive quantitative/in-depth experimentation. Flexible noseleaf and pinna shapes along with an actuation system have been designed to mimic the static geometry of the respective structures in bats as well as several of the animals' degrees of freedom in deforming them. The electrical subsystem has been designed to support high-quality ultrasound generation and recording. Generation of all source voltages and sign...

The Technical Committee on Physical Acoustics (TCPA) of the Acoustical Society of America (ASA) is home to scientists and engineers with an interest in the underlying physics of acoustical phenomena and/or use acoustic waves to study the physical properties of matter. It is one of the broader communities within the Acoustical Society, as the research areas and methods cover the entire frequency range from infrasound to ultrasound, while studying the interaction of these sound waves in all three states of matter: liquids, solids, and gasses. TCPA currently has about 575 members with a primary interest in physical acoustics with 75–125 typically attending open TCPA meetings.

Life is living in a different place. There are mammals and birds living in the air through oxygen. There is a life extension using oxygen present in the water. There are fish and mammals in the water that use oxygen in the water. The whales, belonging to the mammals in the sea, breathe out of the water at regular intervals and then back into the water. Fish do not hinder the extension of life without these actions. This study uses speakers as means for generating oxygen in water molecules. It is a study to decompose oxygen in water by using the dense wave of the speaker sound wave. It is a study that removes oxygen by affecting the bonding structure of water molecules through the vibration of sound waves. Unlike other chemical methods, this characteristic can generate oxygen without generating hydrogen.

Recent work in network audio transport transforms advanced networks into a new kind of acoustical medium in which sound waves propagate, as if traveling through air, water, or solids. Waves sent through the medium are reflected or altered as they bounce between hosts. Propagation delays are used to create echo chambers and build the resonances for ‘‘distributed musical instruments.’’ As a side‐effect, tones created by network resonances can be used to monitor the quality of the underlying network. The presentation presents three areas of research: (1) Auditory methods for monitoring QoS, especially for networks supporting real‐time, interactive, bidirectional flows; (2) remote musical collaboration using professional‐quality, low‐latency audio; (3) empirical study of human factors affected by some unique acoustical properties of the medium network latency; jitter and delay asymmetry affect the speed of sound and are never uniform. By creating distributed virtual sound objects like instruments and rooms, and by studying distributed ensembles, we can begin to understand this new sound world. Some effects have been measured empirically and the results contain some surprises.

Recent fundamental results concerning the ultimate performance of electromagnetic absorbers were adapted and extrapolated to the field of sound waves. It was possible to deduce some appropriate figures of merit indicating whether a particular structure was close to the best possible matching properties. These figures of merit had simple expressions and were easy to compute in practical cases. Numerical examples illustrated that conventional state-of-the-art matching structures had an overall efficiency of approximately 50% of the fundamental limit. However, if the bandwidth at -6 dB was retained as a benchmark, the achieved bandwidth would be, at most, 12% of the fundamental limit associated with the same mass for the matching structure. Consequently, both encouragement for future improvements and accurate estimates of the surface mass required to obtain certain desired broadband properties could be provided. The results presented here can be used to investigate the broadband sound absorption and to benchmark passive and active noise control systems.

This paper introduces a miniaturized microphone array using the Directionally Constrained Minimization of Power (DCMP) method, which utilizes the transfer functions of microphones located at the same place, namely aggregated microphones. The phased microphone array realizes a noise reduction and direction of arrival (DOA) estimation system according to differences in the arrival time, phase shift, and/or the level of the sound wave for each microphone. Hence it is difficult to miniaturize the microphone array. The objective of our research is to miniaturize the system size using aggregated microphones. In this paper, we first show that the phased microphone array system and the proposed aggregated microphone system can be described within the same framework. We then apply a microphone array under directional constraint to the aggregated microphones and compare the proposed method with the microphone array. We show the directional pattern of the aggregated microphones. We also show the experimental results regarding DOA estimation.

Thermoviscous dissipation plays an important role in sound propagation through acoustic metastructures for a variety of applications. The thermoviscous effects rely on the resonances in the structures of subwavelength features. Our analyses and numerical simulations reveal that thermoviscous dissipation can significantly reduce the transmission of sound waves through acoustic metastructures of hybrid resonances in certain scenarios even when the thickness of the viscous boundary layer is much smaller than the width of the slit in the structure [Jiang et al., J. Acous. Soc. Am. (2017)]. To further explore how the resonances affect the significance of the losses, we analyze and simulate sound propagation in acoustic metamaterials of various configurations, including a slit connected to one or multiple resonators at the side of the slit or at the end of the slit. We take into account both wall friction and thermoviscous diffusivity in both the slits and the resonators. The results are compared with that with...

Acoustic metamaterials can, in principle, overcome the fundamental limitations of passive structures and can enable novel applications that are hard or impossible with passive media. However, active acoustic metamaterials remain elusive, and the few implementations going beyond basic material parameter tunability lag significantly behind the true potential of active media. We will present a design method that results in active metamaterials whose acoustic response is electronically programmed to cover a very large range of non-linear acoustic responses. Specifically, metamaterials obtained with this approach can be configured to have almost any second and higher harmonic response, making them very effective and versatile non-linear acoustic media. We demonstrate experimentally this design methodology in an application in which an acoustically thin metamaterial funnel responds to incident sound waves by producing collimated second harmonics. Past demonstrations of this type of active metamaterials will als...

One of the visions for Acoustically enabled Autonomous Underwater Vehicles (AUVs) is a fleet of these vehicles to be held on a ship, deployed for a specific mission and then recovered by the ship. A component of this mission is finding the ship after deployment to be recovered, since both the ship and AUVs have probably drifted from their original locations and intended deployments. While many vehicles can surface, utilize radio and GPS to relocate the ship and navigate towards it, the method presented allows the ship to be found by deploying an acoustic beacon, while the AUVs utilize an observer system to navigate towards the ship. The spatial decay of spreading sound waves provides a spatially dependent variable for the AUV to measure. Then, utilizing a linear model of the dynamics, a linear observer is constructed. The absolute value of the sound pressure readings are fit to a spatial decay model, which is then linearized to form the observer equation. By tuning the observer gain, the AUV can directly ...

Preparation A discussion of Archaeological theory and archaeoacoustics in a post processual era. The author considers the goals and objectives of archaeoacoustic research in the light of current trends; the nature of the human perception of sound is discussed in the light of the philosophical discussions of “Intentionality.” The importance of a preliminary model displaying accurate reproduction of the resonant space, and use of light as indicator of sound wave propagation is emphasized (using examples from previously published Mousa broch and Minehowe papers). Execution Notes on practical considerations in the field. Equipment, sound makers, recording audio and image photos, tools, and markers. Mic and source recording locations. Wind noise and soundscapes. Notes on theoretical considerations in the field. Sound wave length and the word frequency, the myth of infrasound, and discrete echoes. Documentation Notes on types of documentation. Photo/video record, model record, audio record, and sound analysis. ...

The field of acoustic metamaterials borrowed ideas from electromagnetics and optics to create engineered structures that exhibit desired fluid or fluid-like properties for the propagation of sound. These metamaterials offer the possibility of manipulating and controlling sound waves in ways that are challenging or impossible with conventional materials. Metamaterials with zero, or negative, refractive index for sound offer new possibilities for acoustic imaging and for the control of sound at subwavelength scales. The combination of transformation acoustics theory and highly anisotropic acoustic metamaterials enables precise control over the deformation of sound fields, which can be used, for example, to hide or cloak objects from incident acoustic energy. And active acoustic metamaterials use external control and power to create effective material properties that are fundamentally not possible with passive structures. Challenges remain, including the development of efficient techniques for fabricating la...

Helical structured acoustic metamaterial has been proposed to provide non-dispersive sound wave slowdown, which is an interesting topic that not only matters about fundamental explorations of slow wave physics, but also will benefit a lot of applications. Although the effect of delay acoustic signal the sound wave phase modulation is obvious, the helical structured acoustic metamaterial only provides satisfying transmission performance over narrow frequency range. In this presentation, I will introduce an improved design developed based on the original helical structured acoustic metamaterial. Such improved design can slow down acoustic wave propagation through refractive index tuning and wave-front revolution, over a much wide spectra.

Large halls, such as shopping malls, atria or big entrance halls often suffer from various acoustic discomfort issues, which are not necessarily caused by extremely high noise levels. Due to the large size of halls and consequently the long trajectories that sound waves travel between the source, interior surfaces and the receiver, sound reflections arriving from surrounding surfaces are not as strong as they would be in smaller rooms. Reports in literature and comments by users of large halls concerning acoustic discomfort in large halls, refer mainly to continuous reverberation related noise. Therefore, quantification of the acoustic comfort by the reverberation time, which is related to the average absorption of interior surfaces and by the equivalent sound pressure level, which in a large space is dominated by direct sound, is not adequate to describe the global acoustic comfort or soundscape. Based on statistical noise analysis on auralized soudscapes, this article proposes a set of measurable monaur...

Numerical results of sound wave propagation in a realistic three-dimensional (3-D) oceanic environment are reported. The region of interest is the west coast of Brittany, near the harbor of Brest, France. The numerical simulations were performed running a fully 3-D parabolic equation based code considering omnidirectional point sources emitting at low frequencies (e.g. 50—100 Hz) and located in the water column near the entrance of the strait linking the roadstead of Brest to the Atlantic Ocean (also known as 'Goulet de Brest'). Numerical simulations clearly show that, depending on position of the acoustic sources, sound waves can be strongly affected by out-of-plane propagation effects resulting from complicated multiple reflections off the sloping bottom and channeling effects due to the three-dimensionally varying bathymetry in this particular region, and hence can predict interesting modal arrivals at specific receivers (with typical source-receiver distances of 30 km), not predicted by two-dimensiona...

A number of methods exist for determining far‐field sound radiation from structures. Among such prediction techniques are purely analytical models and use of discrete sensors placed directly on the structure or in the surrounding fluid media. Analytical methods suffer from a lack of ability to model the structure completely and adapt to unforeseen system changes. Discrete sensors on the beam may require a large number of transducers to obtain an accurate estimate of the radiation and may also suffer from aliasing problems. Far‐field sensors are often not suitable due to environmental constraints. An alternative method is the use of shaped distributed sensors on the structure, which act as low‐pass filters in the wave‐number domain. The use of this type of sensor helps to isolate the radiating portion of the wave‐number spectrum and is also beneficial in reducing the number of sensors required to avoid aliasing. This work presents numerical results of using shaped polyvinylidene fluoride (PVDF) film to predict the far‐field radiated sound. These results are compared to the theoretical results and to the results obtained when discrete sensors mounted to the structure are used.

This article on acoustic cavitation is a revision of a tutorial lecture presented at the Acoustical Society of America meeting in Austin, Texas, on 28 November 1994. The general approach adopted here differs from a review article in stressing the overarching themes that come under the category of acoustic cavitation, rather than being an encyclopedic reference on the topic. When possible, specific order-of-magnitude estimates have been given so that the reader can better understand the particular phenomena being described. The basic physics is discussed, and applications are reviewed with the goal of putting them in a useful context.

A passive sonic detection and ranging (SODAR) technology is developed to locate sound sources that emit arbitrarily time-dependent signals in a typical environment encountered in practice in real time. This passive SODAR is built on a comprehensive approach including the pre-processing of input data to enhance the signal-to-noise ratio, acoustic modeling of sound radiation from a point source, iterative triangulations, and post-processing of output data to ensure the accuracy in source localization. Moreover, it employs an optimization process to extend the source detection range and improve the source localization accuracy in a highly non-ideal environment that involves a large number of unspecified reflected and diffracted sound waves. This is accomplished through computations based on the source locations predicted by the individual units of four microphones that are not lying on the same plane. Experimental results confirm that passive SODAR works for arbitrarily time-dependent signals that include continuous, transient, impulsive, random, narrow-, and broadband sounds with frequencies above 20 Hz. The minimum number of microphones that are required in passive SODAR is six. These microphones can be mounted anywhere as long as they are not on the same plane and the lines of sight from sound sources remain unblocked.

One of the reasons for using foam wedges or cones in hemi-anechoic rooms is a gradual change of the acoustical impedance in order to reduce the reflection of incident sound waves from the sound absorbing walls. By analogy, popular papers on science (in particular, in acoustics and vibration) facilitate a smooth introduction to new theories because of their small cognitive "impedance" to understanding the written information. Such papers are relevant mostly for extramural reading but they help engineers and students to promptly perceive important effects and applications via interesting case stories and simplified physics and mathematics. Generally speaking, this approach is not new: in particular, it was successfully applied by Y. Perelman in his book "Physics for Entertainment". But in author's opinion, for better effectiveness such texts should be limited in size and include 3-4 related short case stories from actual engineering or consulting practice, history, news, or literature. To illustrate this method, several one-page papers published in the "Sound and Vibration" magazine will be briefly discussed: "Haunted Buildings and Other Acoustical Challenges", "Vibroacoustic Measurements without Transducers", and "Only the Best Will Do".

The perception of pitch forms the basis of musical melody and harmony. It is also among the most precise of all our human senses, and with imagination, this precision can be used experimentally to investigate the functioning of the auditory system. This tutorial presents auditory demonstrations from the zoo of pitch effects: pitch shifts, noise pitch, virtual pitch, dichotic pitch, and the pitches of things that are not there at all. It introduces models of auditory processing, derived from contemporary psychoacoustics and auditory physiology, and tests these models against the experimental effects. It concludes by describing the critical role played by pitch in the important human ability to disentangle overlapping sources of sound.

The paper ‘‘Overcoming ray chaos’’ [J. Acoust. Soc. Am. 95, 3167–3170 (1994)] by Collins and Kuperman incorrectly suggests that ray chaos can be overcome by a suitable choice of numerical techniques. Chaos, when present, is a property of the ray equations, and not the numerical techniques used to solve these equations.

The sound transmission performance of finite multilayer systems containing poroelastic materials is of utmost importance for noise control in automobiles, aircrafts, buildings, and several other engineering applications. Currently, the need for tools predicting the acoustical and structural behaviors of such structures is considerably increasing. In this paper, such a tool is presented. It is applied to the sound transmission loss through multilayer structures made from a combination of elastic, air, and poroelastic materials. The presented approach is based on a three‐dimensional finite element model. It uses classical elastic and fluid elements to model the elastic and fluid media. For the poroelastic material, it uses a two‐field displacement formulation derived from the Biot theory. Furthermore, it couples with a boundary element approach to account, when important, for fluid–structure coupling and to calculate the transmission loss through the multilayer structure. Numerical predictions of the transm...

The three types of algorithms that have been developed for solving parabolic wave equations are compared. Until recently, it was necessary to choose between the finite‐difference and split‐step Fourier algorithms and make a trade‐off between efficiency and capability. Test problems are presented to illustrate the efficiency of the split‐step Pade algorithm, which provides the capability of the finite‐difference algorithm. For deep water problems, the split‐step Pade algorithm provides efficiency comparable to the split‐step Fourier algorithm. For the shallow water problems that are currently of interest, the split‐step Pade algorithm can be more than an order of magnitude faster than the split‐step Fourier algorithm.

Three experiments compared the ability of pairs of modulated narrow‐band sounds with identical power spectra to mask signals above, below, and at their center frequency. In the first experiment, forward‐masked psychophysical tuning curves (PTCs) were measured using a 1600‐Hz 10‐ms signal and 400‐ms ‘‘damped’’ and ‘‘ramped’’ sinusoidal maskers. The damped maskers were produced by repeating a 25‐ms sinusoid which had been shaped by an exponentially decaying function with a half‐life of 4 ms. The ramped maskers were simply time reversals of the damped maskers. When the masker frequency was below that of the signal, ramped maskers were more effective than damped maskers, whereas the reverse was true for maskers above the signal. Experiment 2 measured thresholds for a 400‐ms 1000‐Hz damped or ramped sinusoidal signal, in the presence of a simultaneous masker with the same envelope shape, as a function of the masker frequency. Again, ramped maskers were more effective below the signal frequency, and damped maskers more effective above it. Experiment 3 was similar to experiment 2 except that the masker was a damped or ramped narrow‐band noise, and the signal was an unmodulated sinusoid. The pattern of results was generally similar to that obtained in experiments 1 and 2. The results of all three experiments are inconsistent with the ‘‘traditional’’ method of calculating excitation patterns, which is based on the power spectrum of the stimulus, and also differ from the predictions of a recent model of auditory processing [R. D. Patterson, J. Acoust. Soc. Am. 96, 1409–1418 (1994)]. It is suggested that changes to the peripheral filtering stage of Patterson’s model may provide a useful first step toward accounting for the data.

Membranes used for building materials have a certain degree of acoustic permeability, which has been disregarded in general membrane‐vibration theory, and may cause serious effects especially on the acoustic properties. In this study, a theory for sound absorption of, and sound transmission through, a single permeable membrane is developed. Subsequently, sound absorption of structures composed of air layers, absorptive layers, and the facings of permeable membranes is investigated theoretically, and discussed in comparison with the experimental data measured by using the reverberation‐room method. The results are in fairly good agreement; thus the present theory should give an effective tool for prediction of the acoustic properties of this type of membrane structure.

It is found that when beads are inserted into the interior of a pipelike structure, the damping of this beaded structure may substantially exceed that of the unbeaded structure. The beads are modeled by a ‘‘beaded fluid’’ characterized by a low density, a low sound speed, and a high loss factor. Statistical energy analysis (SEA) is developed to account for the presence of the beaded fluid within the structure. It is shown that in certain frequency regimes and certain choices of the parameters that characterize the beaded fluid, relative to those that characterize the structure, the loss factor of the beaded structure can be designed to significantly exceed that of the unbeaded structure. The mechanism for the increase lies in that the stored energy in the beaded fluid may, in the ‘‘steady state,’’ be made to substantially exceed that in the structure. The bulk of the stored energy is then decimated by the high damping capability that the beaded fluid enjoys. A selected number of computer experiments are c...

An adaptive control algorithm with on‐line system identification capability has been developed. One of the great advantages of this scheme is that an additional system identification mechanism such as an additional uncorrelated random signal generator as the source of system identification [Eriksson and Allie, J. Acoust. Soc. Am. 85, 797–802 (1989)] is not required. A time‐varying plate‐cavity system is used to demonstrate the control performance of this algorithm. The time‐varying system consists of a stainless‐steel plate which is simply supported on a rigid cavity where the cavity temperature can depend on time. For a given externally located harmonic sound excitation, the system identification and the control are simultaneously executed to minimize the transmitted sound in the cavity. The control performance of the algorithm is examined for two cases. Keeping the cavity temperature constant for the first case, the external disturbance frequency is swept with 2 Hz/s from below to above a resonance freq...

Using an acoustic pointer, three listeners matched the intracranial position of dichotic pitches presented with interaural intensitive differences (IIDs). Unlike data previously reported [Raatgever, ‘‘Binaural time processing and time‐intensity trading,’’ in Psychophysics, Physiology, and Behavioural Studies in Hearing, edited by G. van den Brink and F. A. Bilsen (Delft U.P., Delft, The Netherlands, 1980), pp. 425–453], the intracranial position of the dichotic pitch image was moved substantially by IIDs. When the dichotic stimuli were presented continuously and turned off only when the listeners used the acoustic pointer, one listener produced data like those previously reported by Raatgever. Consequently, in terms of lateralization, it does not appear necessary to maintain a theoretical cleavage between images produced by dichotic pitches (previously thought to be influenced only by ITDs) and images produced by other binaural stimuli.

Theoretical and computational analyses of wind-instrument sound production in the time domain have emerged as useful tools for understanding musical instrument acoustics, yet there exist few experimental measurements of the air-column response directly in the time domain. A new experimental, time-domain technique is proposed to measure the reflection function response of woodwind and brass-instrument air columns. This response is defined at the location of sound regeneration in the mouthpiece or double reed. A probe assembly comprised of an acoustic source and microphone is inserted directly into the air column entryway using a foam plug to ensure a leak-free fit. An initial calibration phase involves measurements on a single cylindrical tube of known dimensions. Measurements are presented on an alto saxophone and euphonium. The technique has promise for testing any musical instrument air columns using a single probe assembly and foam plugs over a range of diameters typical of air-column entryways.

Two experiments were conducted in order to assess listeners’ ability to utilize interaural disparities within interaurally ‘‘mistuned’’ envelopes of two‐tone complexes centered at 3500 Hz. In the first experiment, listeners were required to distinguish between rightward or leftward directions of intracranial movement produced by the beat. The stimuli and experimental paradigm were designed so that such judgments would be made on the basis of the dynamically varying, envelope‐based interaural temporal disparities (ITDs). In the second experiment, listeners were required only to distinguish between the presence or absence of an envelope‐based binaural beat in a paradigm similar to that employed by McFadden and Pasanen [Science 190, 394–396 (1975)]. For both experiments, monaural envelope (beat) rates of between 10 and 640 Hz were employed with interaural beat rates of 0.25, 0.5, and 1.0 Hz. The data indicate that listeners are indeed capable of discriminating the direction of intracranial movement based on time‐varying ITDs conveyed by the envelopes of high‐frequency two‐tone complexes. Changes in sensitivity produced by altering the rate of change of the ITD and/or its extent appear to be accounted for by assuming that there is a relatively simple trade‐off between these two parameters. When the task is changed to one that is similar to that employed by McFadden and Pasanen [Science 190, 394–396 (1975)] such that listeners are merely required to discriminate between the presence and absence of an envelope‐based interaural beat, the data appear to be accounted for quite parsimoniously by assuming that listeners base their decisions upon the presence or absence of dynamically varying interaural intensitive disparities.

The recent article by Burdisso and Fuller [‘‘Design of active structural acoustic control systems by eigenproperty assignment,’’ J. Acoust. Soc. Am. 96, 1582–1591 (1994)] does not fully illuminate the contributions of a number of prior authors for a crucial part of the work, that is, the development of weak radiator modes. This comment places the subject development of Burdisso and Fuller in context with the prior art. Further, it demonstrates the similarities of the subject development to prior work published by K. A. Cunefare [‘‘The minimum multimodal radiation efficiency of baffled finite beams,’’ J. Acoust. Soc. Am. 90, 2521–2529 (1991)]. The authors recognize and acknowledge that Burdisso and Fuller’s implementation of the concept, through eigenproperty assignment, is unique and valuable.

Measurements of the sound absorption coefficients of blocks of occupied theatre chairs varied approximately linearly with the ratio of sample perimeter-to-area ratio. Extrapolations of such measurements were used to predict the absorption coefficients of occupied chairs in auditoria. Analyses of these and other published data show that the absorption coefficients of occupied chairs also vary with the absorbing properties of the chairs. A more general method for predicting the sound absorption of occupied chairs as a function of sample perimeter-to-area ratio is proposed based on classifying chairs as having low, average, or high absorption characteristics. The new method is simple to apply and is thought to be more accurate than currently accepted methods.

In 1987 the United States Air Force (USAF) collected the lateral distribution of sonic booms produced by 43 supersonic flights of military aircraft near Edwards Air Force Base (EAFB). These flights were accomplished using eight different aircraft at several Mach number and altitude combinations. The flights were planned for steady and level operation, but unsteadiness and maneuvering in some of the flight profiles caused variability and focusing of the propagated booms along the lateral measurement array. The full sonic boom waveforms collected during this study are included in a digital database, BoomFile, which is accessible to researchers. The database also includes the aircraft tracking and local weather profiles. A comparison of the measured to predicted peak overpressures along the lateral spread of the boom carpet demonstrates the results from this study agree as expected with previous sonic boom studies. The measurements are compared with predictions calculated by Carlson’s simplified sonic boom m...