bluuebunny/crossref_metadata_2025 huggingface dataset:
SGP analysis of excised larynges in anechoic chamber
Authors: Castellanos Paul F. , Hung Sang , Skinner Craig , Elder Samuel A.
Published: July 2002

Single glottic pulse analysis will be presented of experimental data obtained on excised larynges in an anechoic chamber. Attention is directed to understanding the nature of the acoustic source, and comparison will be made with data taken from live subjects. In vivo measurements include those taken in the chamber as well as those recorded by Sondhi tube.
Modeling and synthesis of the lateral consonant /l/
Authors: Prahler Adrienne M.
Published: July 2002

The lateral consonant in English is generally produced with a backed tongue body, a midline closure of the tongue blade at the alveolar ridge, and a path around one or both of the lateral edges of the tongue blade. In prevocalic lateral consonants, the release of the closure causes a discontinuity in the spectral characteristics of the sound. Past attempts to synthesize syllable-initial lateral consonants using formant changes alone to represent the discontinuity have not been entirely satisfactory. Data from prior research has shown rapid changes in not only the formant frequencies but also in the glottal source amplitude and spectrum and in the amplitudes of the formant peaks at the consonant release. Further measurements have been made on additional utterances, guided by models of lateral production. Based on these data, new synthesis attempts have incorporated changes in source amplitudes, formant bandwidths, and the location of a pole-zero pair. Including these additional parameters improves the naturalness of the synthesized lateral-vowel syllables in initial perception tests. Results of listening tests indicating the relative importance of the various factors to the naturalness of the synthesized syllables will be reported. [Work supported in part by a LeBel Fellowship and by NIH Grant No. DC00075.]
The use of a subgrid-scale quasi-stationary approximation in finite-difference time-domain simulations to calculate the absorption by Helmholtz resonators
Authors: De Poorter John , Botteldooren Dick
Published: July 2002

To calculate Helmholtz resonators using a finite-difference time-domain (FDTD) simulation technique, one has to deal with two important difficulties. First, the determining structures of a Helmholtz resonator are typically subwavelength geometries with dimensions that are smaller than the FDTD cell size normally used for the wavelengths of interest. Therefore, the FDTD cell size should be reduced, resulting in a very high computational cost. On the other hand, the viscous absorption in the resonator neck influences the resonator behavior a lot and has to be included in the calculation. The first problem was solved by using a coarse FDTD grid but applying detailed simulated quasistationary pressure distribution to modify the FDTD equations in the neighborhood of the resonator neck. For the second problem the analytical solution for viscous boundary layer absorption was introduced into the FDTD equations. However, this solution is only correct for the viscous absorption near an infinite plate. Therefore, the calculated quasi-stationary solutions were applied to correct for the nonuniform velocity distribution in the resonator neck. The results are compared with both analytical solutions and with experimental results.
Cooperative behavior in the Fitzhugh–Nagumo neuron: Consequences for acoustic perception
Authors: Tapson Jonathan
Published: July 2002

Recent studies have shown that a type of stochastic resonance, known as cooperative behavior, can occur in biological neurons. This behavior is characterized by phase locking between the pulse position modulation of the neuron’s activation and weak sinusoidal input signals. The behavior is strongly influenced by the level of background noise in the system. Significantly, it is common for the phase of the neuron activation to lock on a subharmonic of any sinusoidal input stimulation or on subharmonics of a combination of tones. If the Fitzhugh–Nagumo neuron is simulated as an integrate-and-fire (Wiener) process, it can be shown that a single neuron demonstrates cooperative behavior modes which correspond to the known phenomena of acoustic perception (if the neural input is assumed to be a sonic stimulus). Most significantly, the perception of virtual pitch is apparent, as is the pitch shift effect. When presented with an amplitude modulated waveform, the neuron locks on peak features of the time representation of the waveform, thereby recreating the effects discovered by Schouten [Philips Tech. Rev. 5, 286–301 (1940)]. It seems likely that this simple model explains some of the physiological bases for the nature of pitch perception.
Actice control of traffic noise around barriers
Authors: Duhamel Denis
Published: July 2002

Active control was previously found efficient to reduce noise behind barriers for compact and immobile sources [Omoto and Fujiwara, J. Acoust. Soc. Am. 94, 2173–2180 (1993)]. For real road traffic there are usually many sources at quite different positions, so the sound pressure is very complex. It is simulated by an incoherent line source in which different point sources placed along a straight line radiate independently. The structure of the sound pressure, mainly the coherence properties, are calculated around the noise barrier. This is done by a boundary element method to get precise results for low frequencies and near the barrier. A good coherence is necessary to obtain an efficient active control. Simulations of active control systems are done for different placements and numbers of secondary sources. A sufficient number of sources is determined according to the frequency to get a significant attenuation. Simulations of feedback control near the top of the barrier are investigated and compared to feedforward control. For a feedforward control a reference signal is necessary which is difficult to provide because of the low coherence of the sound pressure. A sufficient number of sensor microphones and their positions are also determined in that case.
Traffic noise barrier overlap gap analysis
Authors: Herman Lloyd A. , Clum Craig M.
Published: July 2002

Sound propagation through the gap produced by two parallel vertical barriers with overlapped ends was formulated for traffic noise sources. The method accounts for sound propagated from vehicle source positions for a maximum of ten roadway lanes. Six receiver regions were considered based on potential receiver locations with respect to a gap. The analysis identified both source and receiver regions according to the mechanisms that influence noise propagation in the vicinity of an overlap gap, which can result in: direct rays, diffracted rays from the top edge of one barrier, diffracted rays from the top edge of both barriers, rays reflected between the barriers, and rays that are both reflected and diffracted. The derived method could be implemented using various equations for sound propagation. The results of using equations approved by the United States Federal Highway Administration (FHWA) for traffic noise propagation are given. Field measurements for up to 30 receiver positions from four overlap gaps were compared with uncalibrated predictions. The equivalent continuous levels, A weighted, were overpredicted by 2–3 dB. When the analysis was based on an octave band characterization of the source, the mean overprediction was reduced to less than 1 dB.
Propagation of sonic booms through the atmosphere
Authors: Raspet Richard , Bass Henry E.
Published: July 2002

During the past 20 years the authors have been involved in developing physically based prediction calculations for sonic booms and other nonlinear atmospheric waves. Early work developed a calculation method for the effects of atmospheric absorption and dispersion on sonic booms in a quiescent atmosphere. The validity of this method has been confirmed by recent collaborative work with the University of Texas [J. Acoust. Soc. Am. 100, 3017–3027 (1996)]. More recently, the authors have been working on a method of predicting the effect of turbulence on sonic boom waveforms in the planetary boundary layer. A Monte Carlo approach has been employed so that histograms of measured variables which are needed for environmental assessment can be developed, rather than a single average value [J. Acoust. Soc. Am. 99, 147–152 (1996)]. This prediction method can be combined with the earlier sonic boom propagation algorithm to predict the ensemble of received waveforms at the ground, given the waveform in the vicinity of the aircraft, based solely on physical considerations.
A Hong Kong approach to control noise from outdoor entertainment activities
Authors: Ng P. S. , Wong Sam W. H. , Kam Y. K. , Chan K. S.
Published: July 2002

With 6.5 million people living on some 1000 square kilometers of land, about 70% of which are hilly terrains, one could imagine how difficult it would be in planning compatible land use. High-rise residential blocks surrounding sports ground are not uncommon in Hong Kong. They should co-exist harmoniously if the latter is intended solely for recreational sports. Hong Kong, being a cosmopolitan city, hosts many kinds of outdoor entertainment activities of cultures and many are held frequently in these sports grounds owing to the absence of purpose-built outdoor venues for these activities. With increasing environmental expectations, complaints against noise from these activities are on the rise. Special considerations will have to be struck between efficient use of land and adequate noise protection of the nearby noise-sensitive receivers. This paper describes the various outdoor entertainment activities being held in Hong Kong, their noise generation characteristics, and the approaches taken to control the noise.
Acoustic modeling and simulation of an urban substation
Authors: Medeiros Eduardo Bauzer , Kroeff Gia
Published: July 2002

Demographic growth has often resulted in a disorganized occupation of large urban areas. Regions which were previously empty started to be populated, frequently resulting in an increasingly more common proximity between residential construction and industrial installations. As a consequence, very serious environmental problems have occurred, including those caused by acoustic emission from industrial installations. A common problem these days is the disturbance caused by electric substations closely positioned to residential buildings. The disregard for acoustic effects during the design stage can still be observed in some of the older substation designs, particularly in areas previously far from city centers. In some countries, such as Brazil, a systematic acoustic evaluation of substations only started in the 1980s, with the main bulk of the work still under development. This paper describes some of the joint work being carried out on noise control by the researchers of Universidade Federal de Minas Gerais and CEMIG (the state power administration). The initial definition of a series of acoustic elements, followed by the discussion of the governing equations, is considered. The computational implementation of the resulting model is presented, aimed at the definition of the most convenient noise control strategy. Finally, a few results obtained at a real substation are considered, including some experimental results obtained during actual operation.
Linear resonant duct thermoacoustic refrigerator having two regenerator stacks
Authors: Kim Yong Tae , Suh Sang Joon , Kim Min Gon
Published: July 2002

The measurements of acoustically generated temperature difference between the two ends of a TAC (thermoacoustic couple) in a resonant tube are made using the similar method suggested by Atchley et al. [J. Acoust. Soc. Am. 88, 251–263 (1990)] with a ceramic TAC cylinder. The linear duct was made of PVC pipe with an inner diameter of 30 mm and 680 mm long. Measurements are made for a frequency range of 150–350 Hz in atmospheric air along the TAC length from 2.5 to 10 cm with a 1-cm step. The unknown information of ceramic can be obtained from nonlinear fitting of experimental data with the equation reported by Atchley et al. From the result of this experiment and prediction by theory it is found that the direction of acoustic heat transport is altered at the point of a quarter of a wavelength. From the hint of the above experiment, a newly designed thermoacoustic refrigerator having two regererator stacks is tested.
Role of pinna cavities in median plane localization
Authors: Iida Kazuhiro , Yairi Motoki , Morimoto Masayuki
Published: July 2002

This paper investigates the role of pinna cavities in median plane localization. First, sound image localization tests were carried out under the conditions of progressively occluding three pinna cavities: scapha, fossa, and concha. Second, HRTFs were measured under the same conditions as those of the localization tests. Finally, the results of the localization tests and those of HRTFs measurements were compared. The results of the localization tests and the HRTFs measurements show: (1) Concha plays a great role in median plane localization regardless of the source elevation. (2) The amplitude spectrum of HRTFs shows a significant change in cases of concha occlusion. The comparisons of these results suggest that (3) the spectral cue in median plane localization is mainly formed by concha. (4) However, the degree of localization error which was caused by the occlusion of the pinna cavities depends on the subjects.
A model of auditory localization in noise using neural networks
Authors: Isabelle Scott K. , Janko James A. , Gilkey Robert H.
Published: July 2002

Janko et al. [Binaural and Spatial Hearing in Real and Virtual Environments, edited by Gilkey and Anderson (Erlbaum, Hillsdale, NJ, 1996), pp. 557–570] used neural networks to describe auditory localization and found that data in quiet were insufficient to discriminate among models. To further constrain the models, localization in the presence of a spatially fixed masker is considered here. The wideband targets and maskers were filtered by head-related transfer functions, then by a gammatone filter bank. A model for binaural interaction similar to that of Lindemann [J. Acoust. Soc. Am. 80, 1608–1622 (1986)] was used to process the filter-bank outputs. The inhibited cross-correlation output of the binaural processor was sampled and used as input to a neural network (e.g., 24 correlation lags at each of 13 frequency channels for 312 input nodes). The network was trained using back propagation to estimate the target location in quiet, then tested on targets in noise at several values of signal-to-noise ratio (SNR). The network was also trained across several values of SNR. Results are compared to localization in noise by humans [Good and Gilkey, J. Acoust. Soc. Am. 99, 1108–1117 (1996)]. [Work supported by AFOSR F49620-95-1-0106 and the Ohio Board of Regents.]
Vibration characteristics of high frequency and complex vibration systems of 160 kHz to 1 MHz for ultrasonic wire bonding
Authors: Tsujino Jiromaru , Yoshihara Hiroyuki
Published: July 2002

Vibration characteristics of high frequency and complex vibration systems of 160 kHz to 1 MHz for ultrasonic wire ball bonding are studied. High-frequency and complex vibrations have been shown to be very effective for ultrasonic wire bonding of IC, LSI, or various electronic devices. Required vibration displacement amplitude for successful bonding of a 600-kHz system is about 1/30 that of a conventional 60-kHz system. For installing a conventional ceramic capillary 1.8575 mm in diameter required for ball bonding, longitudinal to complex transverse vibration systems 5.5–7.0 mm in diameter are proposed. Vibration velocity distributions along longitudinal, transverse vibration systems and ceramic capillaries and vibration loci are measured by laser Doppler vibrometers. The ceramic capillaries are measured vibrating in transverse vibration modes with one, two, or three vibration nodes along them at 160 kHz to 1 MHz, and the conventional capillaries are revealed applicable in such high-frequency systems. The free edge of the capillary vibrates in elliptical or circular locus with the two longitudinal vibration systems driven simultaneously. Maximum vibration velocity at a capillary tip is over 0.5 m/s (peak-to-zero value) which is enough for bonding of thin wires successfully at high frequencies.
A method of target characterization based on the analysis of Scholte–Stoneley and Lamb-type waves scattered by submerged fluid-filled thin-walled shells
Authors: Tesei Alessandra , Fox Warren L. J. , Maguer Alain , Lo/vik Arne
Published: July 2002

The scattering inverse problem is addressed as a powerful aid to target classification. Broadband sonar signals are used to insonify submerged elastic objects, and signal processing techniques are applied to the backscattered response. Cylindrical fluid-filled thin-walled shells are considered. The ka range is (2,50). One characteristic of target echoes playing a major role at low-intermediate frequencies is the resonance contribution, which depends on the target’s elastic properties. Here resonance information is extracted by algorithms based on autoregressive (AR) spectral estimation techniques. Assuming a target as a linear acoustic system, AR modeling is used for estimating its poles and, among them, resonance modes which are identified on the basis of resonance scattering theory. Previous investigations on scattering by thin plates and shells demonstrated the existence of fluid-born Scholte–Stoneley waves and shell-born Lamb-type waves. Here, from the study of these waves and internal reflections, a set of equations are formulated which correlate resonance characteristics with geometrical and geophysical target parameters. The algorithms are shown to succeed in estimating parameters such as the shell outer radius, material, and wall thickness. Simulated and real data backscattered by cylinders at broadside are considered. Analyzing simple-shaped objects is seen as preliminary for characterizing more complicated targets.
Angular distribution of incident sound energy for estimating the sound transmission loss of multilayered panels
Authors: Kang Hyun-Ju , Kim Hyun-Sil , Kim Jae-Seung , Kim Sang-Ryul , Ih Jeong-Guon
Published: July 2002

The sound transmission coefficient in the diffuse field depends on the angular distribution of the incident sound energy. Although the field incidence formula has suggested that instead of the random incidence formula, the determination of the limit angle near the grazing incidence is very empirical and various limit angles have been defined by many researchers until now. This angle is especially important when dealing with the sound transmission loss of multilayered panel systems. In order to find the angular energy distribution of the incident sound in the actual test situation, a numerical simulation by using ray tracing is performed for the bounding surfaces of a sphere and a reverberation chamber. The results show that the sound energy distribution of the incidence angle on a bounding surface may be approximated to the Gaussian distribution. Sound transmission losses are predicted by utilizing the concept of the Gaussian distribution of the incidence energy for various single and multilayered panels and they agree very well with experimental results.
Near field acoustic source identification based on numerical models and operational pressure data
Authors: Sas Paul , Mas Peter
Published: July 2002

When pressure measurements are taken in the near field of possible sources, a global inversion of an input–output model of the acoustic medium can be accomplished to calculate the source velocities, and thus to identify the main noise radiating parts. The acoustic medium can be represented by a frequency response function (FRF) matrix which can either be derived analytically based on a point source assumption, or experimentally under laboratory conditions, as well as numerically using a finite or a boundary element model. The operational source velocities can be calculated by multiplying the inverted FRF matrix with the vector of operational pressure measurements. The inversion process, however, is usually an ill-conditioned problem. Regularization techniques based on a singular value decomposition can be used to solve for the ill-conditioned nature of the inverse acoustic problem. In this paper, the applicability of numerically derived FRF models using the boundary element modeling technique, is shown for the calculation of the velocities at the boundary of a source model, based on operational pressure measurements. The results are compared with near field acoustic holography calculations, and the usefulness of an L-curve criterion for the selection of the optimal regularization parameter is indicated based on simulations as well as experiments.
Recent activities in spoken language processing at LIMSI
Authors: Gauvain Jean-Luc S.
Published: July 2002

This paper summarizes recent activities at LIMSI in speech recognition and its applications. The LIMSI recognizer, which has state-of-the-art performance, uses phone-based continuous density HMM for acoustic modeling, and word and class backoff n-grams for language modeling. Acoustic model adaptation techniques (PMC, MAP, MLLR) are used to reduce the mismatch between test and training conditions, in particular through unsupervised adaptation. While the main goal of speech recognition is to provide a transcription of the speech signal as a sequence of words, the same basic technology can be applied to other areas. This recent work is oriented towards automatic systems for information access and for automatic indexation of audiovisual data. In the former case, the speaker-independent, continuous speech recognizer is embedded in a spoken language dialog system for travel information on an information kiosk (ESPRIT MASK) or by telephone (LE ARISE). User trials highlight the importance of appropriate dialog strategies for satisfactory performance. The latter case is a challenging application for LVCSR as the data contain segments of various acoustic and linguistic natures (prepared/spontaneous speech, studio/telephone quality, background noise/music). Word error rates on this data (about 30%) appear to be sufficient for indexation and retrieval purposes.
Acoustics of outdoor surfaces
Authors: Attenborough Keith
Published: July 2002

While the development of absorbing materials for barrier surfaces is attracting considerable research interest, relatively little effort is being devoted to modifying ground surfaces for optimum ground effect. Indeed current schemes for predicting outdoor noise levels due to transportation and industry distinguish only between two types of ground; acoustically hard and acoustically soft. Ground effect phenomena are described with reference to relevant laboratory and outdoor data which indicate the influences of surface characteristics including porosity, small-scale roughness, elasticity, vegetation, extended reaction, and topography. Theories for the propagation of curved wavefronts near to porous ground and above rough ground predict the existence of surface waves. The relationship between these waves is discussed. The robustness of ground effects to meteorological influences is considered. Optimum characteristics for porous pavement with regard to propagation effects are described. Other possibilities for passive noise control reviewed include deployment of rough pavements and poroelastic materials, modifications to railway ballast, roadside cultivation, and landscaping. [Work supported by EPSRC and BBSRC (UK).]
The restoration of La Fenice in Venice: The consultant’s viewpoint
Authors: Commins Daniel E.
Published: July 2002

Following the destruction by a fire of La Fenice in Venice, an extremely complex process was set in motion to attempt to rebuild the opera house as soon as possible. In this instance, acoustics is of utmost importance but it tends to be overshadowed by many other technical economical, and political requirements. Other major problems have surfaced, among which are the following: Very few opera houses, including La Fenice, are correctly documented from the point of view of acoustics; the leaders of such projects are not always aware of the impact of acoustics; the science of opera house acoustics is incomplete, to say the least. In the case of La Fenice, the decision was made to reconstruct it ‘‘as was’’ through a series of discussions with experts and users, and a well organized and efficient competition was set up. The present paper will attempt to analyze the strengths and weaknesses of this process, from the point of view of the ‘‘acoustics’’ referee.
Role of cavitation during high intensity focused ultrasound treatment of prostate tissue
Authors: Sanghvi Narendra T.
Published: July 2002

The use of high intensity focused ultrasound (HIFU) has been well established to produce deep seated tissue necrosis using a short time ultrasound exposure. The scavenging system of the body replaces the necrosed tissue over time from the treated organ. However, in the case of benign prostatic hyperplasia (BPH) treatment, it is essential to remove treated tissue immediately after the treatment to offer improved urine flow rate and relief from the symptoms. Therefore, it was necessary to develop an ultrasound treatment system that not only provides thermal lesions that are deep in the tissue but also mechanical disintegration of urethra and surrounding tissue. Once the urethra is mechanically disintegrated, the necrosed tissue is sloughed with urine and provides an improved flow rate. The mechanical defect in tissue is produced using the cavitation process. The acoustic cavitation is produced by inserting a silastic catheter in the urethra. The catheter blocks the HIFU energy and produces standing waves which produce cavitation, and converts HIFU in a thermal dose larger than that produced by only absorption of acoustic energy by tissue. This method of treatment yields far greater results. The system is now being used in human BPH treatment.
Acoustical imaging in air by a low-cost system working in the audio band
Authors: Trucco Andrea
Published: July 2002

In order to generate a two-dimensional acoustic image of an aerial scene, a system working in the audio band and composed of low-cost conventional electroacoustic and computation devices has been developed and tested. Such a system uses a loudspeaker for the emission of acoustic pulses, eight microphones for the reception of backscattered waves, a generation/acquisition digital board, and a personal computer. As in medical echography, the adopted algorithm for the image formation is a wideband coherent beamforming followed by a scan conversion in order to display the image in a Cartesian format (as a top view of the imaged scene). Robotic vision and remote measurement are potential applications of the system developed. Two major problems that were faced are the calibration of the microphones and the study of the best configuration in terms of pulse waveform and microphone placement. A simple calibration algorithm was achieved by comparing the obtained point spread function with the theoretical expectations, whereas the best configuration was obtained by taking into account the constraints imposed by the instrumentation and the application addressed. The obtained images are of good quality, also considering the low-cost instrumentation and the highly reverberant environment in which the experiments were performed.
Nonlinear properties of microbubbles and applications to medical ultrasound imaging
Authors: Uhlendorf Volkmar , Fritzsch Thomas , Reinhardt Michael , Scholle Frank-Detlef
Published: July 2002

Gas bubbles smaller than 10 μm dissolve within milliseconds even in gas-saturated liquids, but coatings, etc. can prevent dissolution. These stabilized microbubbles serve as transpulmonary contrast agents. When only their linear properties are employed, physical laws limit the diagnostic potential to detection in large diameter vessels. Nonlinear acoustic properties of contrast agents permit very important additional applications. Nonlinearity arises from bubble pulsations, shell properties, finite amplitude waves, and electronic hardware. The first two sources can dominate, allowing new diagnostic imaging modes sufficiently sensitive to detect isolated microbubbles in vivo. Harmonic imaging modes detect 2nd harmonics of the transmit frequency, mainly from microbubbles. Acoustic Emission modes destroy bubble shells by one pulse of moderate amplitude. Consequently, the free bubbles respond strongly to this and other pulses before dissolving. Observed lifetimes of 1–20 ms are enough for harmonic or conventional Doppler detection. Typically, bubbles are replenished too slowly to get similar signal intensity for more than one frame at normal rates. Optimal pulse timing should allow new microbubbles to move close to the beam axis before the next pulse arrives. Applications may be counting methods, flow tagging, and quantification of tissue perfusion, possibly combined with single-shot three-dimensional acquisition and HI modes.
Benchmarking two three-dimensional parabolic equation methods
Authors: Sturm Frederic B. , Fawcett John A. , Jensen Finn B.
Published: July 2002

Results of acoustic propagation modeling using two different three-dimensional parabolic equation methods are presented. One model [J. Fawcett, J. Acoust. Soc. Am. 93, 2627–2632 (1993)] uses standard splitting and operator approximations while the other method [F. Sturm, M. Pélissier, and D. Fattaccioli, Proc. of the Third European Conference on Underwater Acoustics, 243–248 (1996)] does not split the azimuthal operator and maps the bathymetry into an equivalent flat bottom problem. Examples of propagation over wedge and corrugated bathymetries are considered for different frequencies. Both point-source and modal initial fields are used. The three-dimensional solutions exhibit interesting three-dimensional refractive effects. The convergence of the solutions with respect to azimuthal discretization is also discussed.
Three-dimensional acoustic effects due to ocean currents
Authors: Godin Oleg A.
Published: July 2002

In the presence of currents, vertically stratified fluids become acoustically anisotropic in the horizontal plane and the group and phase velocities of the acoustic normal mode are generally not parallel. In this paper, the resulting 3-D effects and their implications for acoustic monitoring of ocean currents are discussed in terms of the normal modes. The sensitivity of various acoustic quantities to the vertical and in-plane and out-of-plane horizontal components of the flow velocity is estimated. Despite anisotropy, there is no azimuth coupling at long-range sound propagation in a stratified moving medium. When a waveguide varies in the horizontal plane, the 3-D effects due to current-induced anisotropy and horizontal refraction are superimposed. The relative importance of these two phenomena in shallow- and deep-water scenarios is analyzed by considering horizontal (modal) rays in the presence of currents. For the purposes of numerical simulations, a parabolic approximation is considered for sound in a moving fluid. A new parabolic equation is proposed for efficient numerical modeling of the 3-D acoustic effects in the ocean with currents. [Work supported by NSERC.]
Psychoacoustics of cochlear hearing impairment and the design of hearing aids
Authors: Moore Brian C. J.
Published: July 2002

Cochlear hearing impairment is usually associated with damage to the hair cells within the cochlea. When the damage is restricted to the outer hair cells (OHCs), the main consequence is disruption of the ‘‘active’’ mechanism which normally enhances the response of the basilar membrane to weak sounds and which sharpens the tuning (frequency selectivity) of the basilar membrane. Psychoacoustically, damage to OHCs results in loss of sensitivity (elevated absolute thresholds), loudness recruitment, and reduced frequency selectivity. Damage to the inner hair cells (IHCs) causes basilar membrane vibrations to be transduced less effectively, so absolute thresholds are elevated, but does not result in altered frequency selectivity or loudness recruitment. Sometimes, IHCs and/or neurons may be completely inoperative at certain places within the cochlea, giving rise to ‘‘dead regions.’’ Such regions can strongly influence the perception of pitch and loudness. Current hearing aids can partially compensate for the effects of loudness recruitment by using compression amplification, but there is much controversy about the ‘‘best’’ form of compression. The deleterious effects of reduced frequency selectivity on speech intelligibility in noise can be alleviated by various methods for improving the speech-to-noise ratio, although so far only directional microphones have given clear benefits.
Early sound distribution in auditorium
Authors: Wang Jiqing , Jiang Guorong
Published: July 2002

It is known that the strength of the audience area of a hall is largely dependent on the early sound, i.e., the direct sound and the first reflections. They are varied not only with reverberation time, but also with the geometry of the room, the absorption arrangement of the room, and the location of the source and(or) the receiver. Results from digital simulation and field measurements in halls show that the attenuation rate of early sound with the distance between the source and the receiver is much larger than ordinary predictions. It is more rational in complying with the subjective judgment. Therefore it should not be ignored in the acoustical design of a hall.
A neural network analysis of concert hall acoustics
Authors: Fricke Fergus R. , Han Young G.
Published: July 2002

A neural network analysis using data from 51 concert halls was undertaken. The analysis related the acoustic quality of halls, as judged by musicians, to ten hall parameters: volume, surface area, number of seats, length, width, height, mean rake angle of seats, a surface diffusion index, stage height, and extent of stage shell/enclosure. The surface diffusion index and the extent of the stage shell were determined by a group of architects who made judgments on the basis of photographs and drawings of the halls. The results of the analysis are tentative and difficult to generalize, as there are so many inputs and so many possible combinations of parameters, and the effect of a particular factor is, in some cases, neither linear nor monotonic. The results are applied to a particular hall, the concert hall of the Sydney Opera House, where changes are being contemplated. There are some unexpected results which, at this stage, give food for thought rather than the basis for action, as there are obvious limitations to this work, such as extraneous factors influencing judgments of acoustic quality, surface diffusion estimation, and extent of the stage shell and the limited number inputs used to describe the halls.
Directional dependence of the change of auditory source width by very short time-delay reflections
Authors: Morimoto Masayuki , Watanabe Mariko
Published: July 2002

Barron [J. Sound Vib. 15, 475–494 (1971)] showed that spatial impression (SI) corresponding to auditory source width (ASW) decreases when the time delay of reflections relative to the direct sound is shorter than 10 ms. This paper investigates the effect of the direction of lateral reflections on the decrease of ASW. The music motif used in this investigation was a 6.5-s section of the 4th movement of Mozart’s Jupiter Symphony (No. 41), which was the same motif as Barron used. The sound fields used as stimuli consisted of a direct sound and two discrete reflections with a 1-ms interval between them. The time-delay of the first reflection relative to the direct sound was 2, 4, or 8 ms. The directions of the reflections were ±18°, ±45°, or ±72°. The experimental results demonstrate that the decrease of ASW depends on the direction of the reflections. As the reflections arrive from a more frontal direction, ASW decreases more sharply relative to the delay time.
Acoustical design of the Queensland Conservatorium of Music
Authors: Oguchi Keiji , Toyota Yasuhisa , Nagata Minoru
Published: July 2002

The auditorium of the Queensland Conservatorium of Music was planned for both classical music concerts and lyric performances in the newly constructed conservatorium in the Southbank of Brisbane, Australia. The retractable orchestra shell is moved forward to the proscenium on the stage, and forms a shoebox style concert space with 643 seats. Small doors are installed on the orchestra shell for acoustical fine tuning in the stage space. Absorptive materials appear when the doors are opened. In lyric performances, the orchestra shell is retracted backward. The frontal area of the stage floor is sunk as an orchestra pit. The reverberation time becomes short, from 2.0 to 1.6 s, with retracting the orchestra shell, and varies by 0.3 s with acoustic curtains on the audience side walls for both concert and lyric use. The acoustical design and characteristics of the auditorium and players’ preference on the acoustical tuning elements are reported in this paper.
Acoustic behavior of a tense-structure
Authors: Cocchi Alessandro , Tronchin Lamberto
Published: July 2002

During the design of a concert hall, the acoustical behavior of the sound field is often investigated by using numerical models. In the case of a restoration of the hall, or during the design of the orchestra chamber, acoustic measurements of impulse responses in the hall give precious information on the sound fields, e.g., RT, clarity, and so on. By using numerical simulation, it is then possible to verify the efficiency of the acoustic solution. Much commercial software is available, all of them following the geometric assumptions, as the Eikonal equation, while the diffraction and diffusion of sound are not usually taken into account, and all of them require the absorption coefficient of the walls. The tense-structure, on the other hand, is not so easy to model, owing to the peculiar characteristics, i.e., modal behavior and impossibility to measure the absorption of the membrane. In this paper, the design of an acoustic intervention in a tense-structure is shown. A procedure to find out the ‘‘equivalent absorption‘‘ of the membrane is shown. The results of such a model are compared with the experimental measures.
Modeling of acoustic parameters and speech intelligibility in long enclosures
Authors: Yang Lening , Shield Bridget M.
Published: July 2002

Ray tracing computer models have been developed for the prediction of the sound field and speech intelligibility in long enclosures of any cross-sectional shape. The models for enclosures of circular and rectangular cross section are particularly suitable for the prediction of speech intelligibility in underground railway stations. The model for use in long enclosures of rectangular cross section has been validated using data measured in a real underground station in Hong Kong. Measurements of acoustics parameters including sound propagation, early decay time, clarity index C50, and center time D50 were made along the length of the platform, with a single source towards one end of the platform. The model correctly predicts the acoustic parameters, the predictions being particularly accurate at midfrequencies. In addition the speech transmission index is accurately predicted at all frequencies, especially in the far field of the source.
Measurements of snapping shrimp colonies using a wideband mobile passive sonar
Authors: Olivieri Marc , Glegg Stewart A. L. , Coulson Robert K.
Published: July 2002

A wideband passive sonar has been developed to study ambient noise levels in coastal regions. During the past two years a large number of measurements have been made with this system in shallow water off Boca Raton, Florida. The results have demonstrated that the noise from snapping shrimp dominates in this area during low sea states. Localization of the colonies has been possible by moving the sonar to different locations over the period of a few hours. Typically the shrimp are clustered close to man-made structures at or near the shore line, with additional smaller colonies on nearby coral reefs. To speed up the data collection the system has been mounted to an autonomous underwater vehicle and on-board intelligence is being developed to optimize the survey locations in real time. Results from a demonstration experiment will be presented. [Work supported by ONR.]
Effects of pulse width, phase, and intensity on echoes from ultrasound contrast agents
Authors: Morgan Karen E. , Dayton Paul A. , Ferrara Katherine W. , Klibanov Alexander L. , Brandenburger Gary H.
Published: July 2002

Contrast-assisted imaging shows great promise for the imaging of microvascular perfusion, although current techniques cannot differentiate the echoes from tissue and ultrasound contrast agents. Harmonic schemes for imaging with these agents have limited spatial resolution due to the transmission of a narrow-band pulse. The potential for wideband contrast-assisted imaging through a systematic evaluation of the effects of imaging parameters on the received echoes is evaluated. Our results indicate that the echo intensity received from contrast agents following wideband transmission is at least as large as or larger than that for narrow-band transmission, with both exhibiting nonlinear increases with increasing transmitted signal intensity. While the echo intensity at harmonic multiples of the bubble resonant frequency can be larger for narrow-band insonation, echoes received after wideband insonation demonstrate a broadband spectrum with significant amplitude over a very wide range of frequencies. The authors also demonstrate that the transmission of wideband high intensity pulses produces consistent time domain echoes from microbubbles. These echoes are unchanged whether the microbubbles break or remain intact over several pulses. Additionally, if the phase (order of compressional and rarefactional half-cycles) of the transmitted pulse is changed, the polarity of the received signal changes accordingly for a stationary reflector but remains unchanged for a microbubble.
Acoustic detection of microbubble destruction in gaseous contrast agents
Authors: Shi William T. , Forsberg Flemming
Published: July 2002

The destruction of microbubbles from ultrasound contrast agents has recently received much attention because the disintegration can be used to create new imaging modalities and may produce adverse bioeffects as well. Both passive and active acoustic detection techniques were employed in our experiments to investigate the collective and individual behaviors of contrast microbubbles at different insonification levels. With the passive technique, the oscillation and destruction of microbubbles were studied by characterizing the waveforms of scattered acoustic signals and analyzing the harmonic and noise contents in the spectra of the signals. It was observed that discrete subharmonics and superharmonics (up to the 20th order) were generated at low acoustic pressures. When the bubble destruction occurred at high acoustic pressures, the noise level in the spectra was raised and the discrete harmonic structure in the higher frequency domain reduced to broadband noise. The noise spectrum in the higher frequency range was found to broaden as the acoustic pressure increased. A modified ACD (acoustic cavitation detector) with improved spatial resolution was utilized to study the disintegration process of an individual microbubble. The comparison of results from passive and active detections will be presented.
Theoretical analysis of reactive silencers with two propagating modes
Authors: Kergomard J. , Pachebat M.
Published: July 2002

A general modeling of sound ducts with reactive (or dissipative) treatments considers one main guide and a secondary one (the treatment), with another propagation constant, including discontinuities, coupled to the main one by perforations, i.e., a shunt impedance and a series impedance [see Kergomard et al., Acta Acustica 2, 1–16 (1994)]. For a periodical system the calculation can be made analytically for a succession of N cells by diagonalization: the impedance matrix of the portion of the duct with treatment can be deduced. At low frequencies only one mode propagates in each duct and the matrices are of fourth order. From the boundary conditions for the treatment the insertion loss (IL) for the main duct is deduced. Examples are an array of coupled resonators, a lining with perforated facing, and a perforated tube muffler with partitions. A conclusion is the proof of the interest of the interferences between two propagating modes of the periodical system: resonances occur and IL is proportional to log N. It is more efficient than a single propagating mode (e.g., in expansion chambers). Compared to the evanescent case (IL proportional to N), it is less efficient but the frequency band is wider. Many facts of practical interest can be deduced.
Applications of sonic soot cleaning techniques
Authors: Tian Jing
Published: July 2002

Sonic soot cleaning is a method that is applied to clean the ash or fossil deposit on surfaces of heat exchangers in boilers. The technique includes a set of hardware and software for the designing, production, installation, debugging, and operation of sound wave generators and the controller. Although it has been applied in boilers in power plants, petrochemical works, and general industries worldwide, still most of the correlated basic problems, such as the relationships between sound field and the mass delivery, the heat conduction as well as the combustion process in boilers, have not been well solved. It is almost a purely empirical method that its application is far in the lead of fundamental research. Now in China more than ten institutions and companies are engaged in the research, development, and marketing of sonic soot cleaning techniques. These techniques cover sound generators ranging a frequency domain from infrasound up to ultrasound, under the protection of more than 20 patents. In this paper, several applications are analyzed as examples to demonstrate the effectiveness. Some basic phenomena and unsolved problems are revealed. The course of sonic soot cleaning development is discussed. [Project supported by the Natural Science Fund of China.]
Modeling the effect of a hearing protector on the waveform of intense impulses
Authors: Price G. Richard , Kalb Joel T.
Published: July 2002

Implicit in microphone-in-real-ear (MIRE) or real-ear-attenuation-at-threshold (REAT) tests with a hearing protector is the potentiality that such tests would establish its ability to ameliorate hazard. However, because the sound field under the protector is very different from the free field for which traditional DRCs customarily predict hazard, it is not clear how such measures should be used. The theoretically based mathematical model of auditory hazard we proposed by us as the basis for such assessments calculates motions of structures in the ear [Price and Kalb, J. Acoust. Soc. Am. 100, 2674 (1996)]. Thus phase relationships in waveforms matter and the model must accurately couple them to the ear. Where only REAT data and free-field pressure measures are available, single path conduction through the protector is assumed and minimum-phase processing to calculate waveforms under protectors is used. Empirical tests with free-field impulses and an artificial head test fixture indicate that such an approximation is surprisingly good. With such calculated waveforms or MIRE measures, a Thevinin-equivalent source to drive the ear which allows the full calculation of auditory hazard with the model is created.