bluuebunny/crossref_metadata_2025 huggingface dataset:
Psychophysical suppression measured with bandlimited noise extended below and/or above the signal: Effects of age and hearing loss
Authors: Dubno Judy R. , Ahlstrom Jayne B.
Published: July 2002

The objectives of this study were to measure suppression with bandlimited noise extended below and above the signal, at lower and higher signal frequencies, between younger and older subjects, and between subjects with normal hearing and cochlear hearing loss. Psychophysical suppression was assessed by measuring forward-masked thresholds at 0.8 and 2.0 kHz in bandlimited maskers as a function of masker bandwidth. Bandpass-masker bandwidth was increased by introducing noise components below and above the signal frequency while keeping the noise centered on the signal frequency, and also by adding noise below the signal only, and above the signal only. Subjects were younger and older adults with normal hearing and older adults with cochlear hearing loss. For all subjects, suppression was larger when noise was added below the signal than when noise was added above the signal, consistent with some physiological evidence of stronger suppression below a fiber’s characteristic frequency than above. For subjects with normal hearing, suppression was greater at higher than at lower frequencies. For older subjects with hearing loss, suppression was reduced to a greater extent above the signal than below and where thresholds were elevated. Suppression for older subjects with normal hearing was poorer than would be predicted from their absolute thresholds, suggesting that age may have contributed to reduced suppression or that suppression was sensitive to changes in cochlear function that did not result in significant threshold elevation.
Comment on “Reducing seat dip attenuation” [J. Acoust. Soc. Am. 108, 2211–2218 (2000)]
Authors: Klepper David Lloyd
Published: July 2002

A recent article has proposed a novel approach to reducing the “seat dip attenuation” commonly observed in major auditoria. The proposed solution might have significant impact on other attributes of auditorium acoustics. An approach to evaluate such effects is proposed.
Comment on “Ultrasound-induced lung hemorrhage is not caused by inertial cavitation” [J. Acoust. Soc. Am. 108, 1290–1297 (2000)]
Authors: Apfel Robert E.
Published: July 2002

This contribution summarizes the reasons for disagreeing with a conclusion by O’Brien et al. [J. Acoust. Soc. Am. 108, 1290–1297 (2000)] that ultrasound-induced lung hemorrhage is not caused by inertial cavitation. An argument is provided that illustrates how cavitation inception conditions in the lungs of animals are not altered significantly if the hydrostatic pressure is increased by increasing the pressure of air that is being breathed by the animal.
Evaluation of a fundamental integral in rough-surface scattering theory
Authors: Drumheller David M. , Gragg Robert F.
Published: July 2002

An algorithm is presented for the numerical evaluation of a fundamental but intractable integral that occurs in the physical theory of scattering from random rough surfaces. It is based on a rational-function approximation to an integrand factor, augmented with techniques for excluding poles and zeros from the path of integration. Examples, complete with error analysis, are provided for cases relevant to acoustic sea-floor and sea-surface scattering.
Acoustic and dynamic mechanical properties of a polyurethane rubber
Authors: Mott Peter H. , Roland C. Michael , Corsaro Robert D.
Published: July 2002

Acoustical and dynamic mechanical measurements were carried out on a commercial polyurethane rubber, DeSoto PR1547. The sound speed and attenuation were measured over the range from 12.5 to 75 kHz and 3.9 to 33.6 °C. Shear modulus was measured from 10−4 to 2 Hz and −36 to 34 °C. The peak heights of the shear loss tangent varied with temperature, demonstrating thermorheological complexity. At higher temperatures, time–temperature superpositioning could be applied, with the shift factors following the Williams–Landel–Ferry equation. From the combined acoustical and mechanical measurements, values for the dynamic bulk modulus were determined. Moreover, superposition of the bulk modulus data was achieved using the shift factors determined from the dynamic mechanical shear measurements. Finally, this work illustrates the capability and the working rules of acoustical measurements in a small tank.
Masking of a brief probe by sinusoidal frequency modulation
Authors: Edwards Brent W. , Viemeister Neal F.
Published: July 2002

Contrary to level detection models, the thresholds for a brief-duration probe masked by a sinusoidal frequency modulation (FM) masker increases as the modulation index (β) of FM increases [Zwicker, Acustica 31, 243–256 (1974)]. In this paper the reason for this phenomenon is investigated. In experiment 1, a 10-ms, 1-kHz probe was detected in the presence of an FM masker centered at 1 kHz and sinusoidally modulated at 16 Hz. Thresholds increased by over 15 dB with increasing β, consistent with Zwicker’s findings. In experiment 2, the instantaneous frequency changes of the masker used in experiment 1 were clipped and the resulting thresholds indicated that detection was determined primarily by the masker’s total frequency excursion rather than by its instantaneous sweep rate. In experiment 3, the FM maskers from the first two experiments were passed through a roex filter centered at 1 kHz and the resulting envelope was used to amplitude modulate a 1-kHz tone, producing approximately the same effective envelope at 1 kHz as the FM maskers. Threshold functions for the amplitude modulated (AM) maskers were similar to those for their corresponding FM maskers. Thresholds increased by over 15 dB while the total energy of the AM masker decreased by over 10 dB, again contrary to standard level-detection models. The results from these experiments can be explained, at least qualitatively, by a model based on envelope shape discrimination: similarities between the envelopes of the masker alone and masker-plus-probe at the output of an auditory filter centered on the frequency of the probe are primarily responsible for the observed masking, particularly at large β’s.
Extension of the tip excitation technique to the rotational compliance measurement of curved structures
Authors: Cheng L. , Qu Y. C.
Published: July 2002

The present paper presents an extension of the so-called tip excitation technique for measuring the rotational compliance of curved structures. On the basis of the original form of the technique, developed for attached plane structures, the technique is improved to take into account the presence of the in-plane vibration and the rigid motion. Two derivatives of the technique are developed: the first one using two accelerometers allows a more accurate indication of rotational response, thus providing a good accuracy in middle frequency range; the second one using double excitation effectively eliminates the in-plane force excitation, thus providing an excellent measurement accuracy at both low and middle frequencies. Numerical simulations using finite element modeling are performed to analyze different parameters affecting the performance of the technique. Experimental validations are then reported. It is shown that the technique is successfully extended to curved structures while retaining the advantages of the original version of the method in terms of its simplicity and its capacity for mass loading compensations.
Optimal binaural processing based on point process models of preprocessed cues
Authors: Yue Lin , Johnson Don H.
Published: July 2002

Toward localizing high-frequency tonal signals in the horizontal plane, the lateral superior olive (LSO) encodes the interaural level differences, the crucial cue for azimuthal angle extraction by more central nuclei in the binaural pathway. This paper derives optimal processors for localization using inputs from the LSO and anteroventral cochlear nucleus. Both Poisson and non-Poisson point processes are developed to model cellular responses. The LSO projection is shown to be the only input needed in maximum likelihood angle estimation, and it is processed similarly under different LSO response models. However, localization performance depends strongly on the model’s regularity, with increasing regularity improving localization accuracy and precision.
On the Mie potential and the acoustic nonlinear parameter B/A
Authors: Frank B. , Cheeke J. D. N.
Published: July 2002

The set of two coupled equations of Hartmann connecting the acoustical nonlinear parameter B/A with the reciprocal sound velocity 1/c, for liquids, through the parameters of the Mie potential, is replaced by a simple empirical equation linear and near quadratic in linear combinations of B/A and 1/c. The latter equation contains an exponent μ which is a function of the Mie exponents m and n. It is shown that this empirical relation closely approximates the pair solution over a significantly wider range of variables than the purely linear equation posited by Hartmann to explain the empirical Ballou’s rule.
Narrow-band source localization in the presence of internal waves for 1000-km range and 25-Hz acoustic frequency
Authors: Book Paul J. , Nolte L. W.
Published: July 2002

The effects of internal waves on low-frequency (25 Hz) narrow-band source localization performance are investigated at a very long range (1000 km). Sound-speed perturbations induced by internal waves obeying the Garrett–Munk spectral model are incorporated into the normal mode solution to the wave equation using the adiabatic approximation. Sensitivity of source localization on the internal wave modal content is examined. For the entire range of signal-to-noise ratios (SNR) and degrees of internal-wave field structure, the optimal uncertain field processor (OUFP) provides both the signal processing algorithm as well as the limitations on source localization performance. For high SNR, the localization errors are local and the performance level of the OUFP is predicted by the hybrid Cramer–Rao lower bound (CRLB). In fairly structured internal-wave environments, significant performance gains are made optimally localizing the source. Under very random internal-wave environments, the environmental variability limits the performance of all signal processing algorithms.
Masking by modulated and unmodulated noise: Effects of bandwidth, modulation rate, signal frequency, and masker level
Authors: Bacon Sid P. , Lee Jungmee , Peterson Daniel N. , Rainey Dawne
Published: July 2002

The threshold for a sinusoidal signal masked by a band of noise is often times lower when the masking noise is modulated than when it is unmodulated. The difference in masked thresholds is referred to as the modulated–unmodulated difference, or MUD. These present experiments examined the effects of masker bandwidth, masker rate, and masker level on the MUD at several different signal frequencies. The MUD generally increased with increasing masker bandwidth; for masker bandwidths wider than a critical band (or an equivalent rectangular bandwidth—ERB), the results may be influenced by across-channel processes underlying comodulation masking release. The MUD for an ERB masker (MUDERB) was influenced less by masker rate than was the MUD for a broadband (BB) masker (MUDBB). The MUDERB and especially the MUDBB increased significantly with increasing masker level when the modulated masker was modulated at a depth (m) of 1.0, but not when it was modulated at a depth of 0.75. These results have significant implications for extending the MUD paradigm to hearing-impaired subjects. Finally, the MUDERB and the MUDBB increased with increasing signal frequency. This effect for the ERB masker is largely (if not completely) due to the wider absolute bandwidths at higher frequencies. The effect with the BB masker may be influenced by differences in the magnitude of suppression across frequency.
Grazing incidence propagation over a soft rough surface
Authors: Chambers James P. , Sabatier James M. , Raspet Richard
Published: July 2002

Attenborough has recently proposed [J. Acoust. Soc. Am. 98, 1717–1722 (1995)] that the effects of surface roughness on an otherwise flat surface of finite acoustic admittance can be modeled as a smooth flat surface with an effective acoustic admittance β*. This effective admittance is determined by the normalized admittance βs and wave number ks of the original smooth surface, as well as a surface roughness parameter σν. Attenborough tested his theory by conducting excess attenuation measurements over plywood and Styrofoam surfaces with two-dimensional roughness elements. Specifically, he investigated the interference pattern between the direct and reflected signals over both smooth and rough surfaces. Experiments are conducted here with three-dimensional roughness elements at grazing incidence. Such a configuration is typical for outdoor sound propagation problems. The results presented here generally confirm Attenborough’s model and open up the analogy to a broader class of problems. It was also found that placing the effective admittance plane at the top of the roughness elements rather than at the bottom yielded slightly better results for the higher acoustic frequencies investigated.
Vorticity and entropy boundary conditions for acoustical finite-difference time-domain simulations
Authors: Botteldooren D.
Published: July 2002

In this paper a time-domain numerical model for describing the presence of vorticity and entropy boundary layers is introduced. The boundary model can be inserted in acoustic time-domain models such as the finite-difference time-domain (FDTD) model for studying the acoustic behavior of high-quality resonator structures. The main focus in deriving the model is on numerical efficiency. Boundary layer theory is reviewed to obtain a three-dimensional formulation of its influence on FDTD equations that must be applied in boundary discretization cells. The ω dependence that is encountered is approximated in time domain in such a way that no numerical convolution is required. Although this approximation is rather inaccurate, it is sufficient for most applications and introduces almost no extra computational effort. Several numerical examples illustrate the applicability of the model.
The effects of randomizing values of interaural disparities on binaural detection and on discrimination of interaural correlation
Authors: Bernstein Leslie R. , Trahiotis Constantine
Published: July 2002

The purpose of this study was to assess whether randomizing (roving) baseline interaural parameters of binaural stimuli would adversely affect performance in masking-level difference and in interaural correlation-discrimination paradigms. Listeners’ detection thresholds were measured in NoSo and NoSπ configurations for both broadband (100–3000 Hz) and narrow-band (450–550 Hz) maskers centered at 500 Hz. In addition, thresholds of interaural decorrelation (from a reference correlation of 1.0) were measured for 100-Hz-wide bands of noise centered at 500 Hz. Data were obtained under conditions in which either values of ITD or values of IID were roved both within and across trials. Data were also collected in the absence of a rove. The range of the rove was ±500 μs for ITDs and was ±6 dB for IIDs. The duration of the stimuli was varied between 17 and 310 ms. Overall, the results indicate that, independent of duration, roving the interaural cues produced small degradations of performance as compared to data obtained in the absence of a rove. The data are inconsistent with the notion that binaural detection depends upon reliable changes in laterality produced by adding Sπ signals to diotic maskers. On the other hand, the data are consistent with modern models of binaural processing.
Effects of reflective ground on the actively created quiet zones
Authors: Guo Jingnan , Pan Jie
Published: July 2002

Previous studies on the local active control of noise in free space show that the size of the quiet zone and the total sound power output of the control system are mainly determined by the spatial arrangement of primary sources, secondary sources, and error sensors. When a nearby reflective surface is introduced, the size of the quiet zone and the total power output of the system will be affected. The research presented in this paper examines the influence of the presence of a nearby reflective plane on the control system with different alignments to the reflective surface. It is found that the reflective surface significantly affects the size of the quiet zone and the sound power output of the system, as compared with the same control system in free space. The effect is related to two important parameters of the control system: the heights of the sources and the error sensor above the surface and the distances between the primary and secondary sources and between the secondary source and the error sensor. While the quiet zones created by most arrangements of the control system in half-space are smaller than those for free space, the quiet zones created by the arrangements of the control system perpendicular to the reflective surface may be larger than those for free space.
Scattering of ultrasonic compression waves by particulate filler in a cured epoxy continuum
Authors: Challis Richard E. , Holmes Andrew K. , Tebbutt John S. , Cocker Richard P.
Published: July 2002

Absorption of ultrasound in adhesive materials is significant in forming ultrasonic signals obtained in nondestructive evaluation (NDE) procedures, and may also have diagnostic value in the evaluation of adhesive materials themselves. This paper investigates the effects of filler particles in adhesive polymers on ultrasonic compression wave absorption and phase velocity dispersion as functions of frequency. Wave propagation is affected by relaxations in the continuous polymer phase as well as by scattering at filler particles. The complex compression wave number for the composite material is derived on the basis of conventional theories of scattering in randomly distributed fields of particles, together with a formulation of the particle diffraction problem based on a combination of the cases for solid particles in solid continua and solid particles in liquid continua first proposed by Ying and Truell, and Allegra and Hawley, respectively. Experiments are described which demonstrate the effects of relaxations and scattering on absorption and phase velocity as functions of frequency in an epoxy material containing a mineral filler. Good agreement is obtained between theory and experiment.
Doppler spread in an undersea acoustic transmission channel
Authors: Rice Joseph , Baxley Paul , Bucker Homer , Shockley Richard , Green Dale , Proakis John , Newton John
Published: July 2002

This paper examines spectral dispersion of narrowband sound energy transmitted between two stationary, horizontally displaced, undersea, electroacoustic transducers. Any frequency smearing arises kinetically and is imparted by the aggregate motions of scatterers influencing the forward-propagated, physical channel. From this time-variant cause, hypotheses are drawn about the statistics of the spectrally dispersive effect. The hypotheses are tested by analyzing representative acoustic data in the 8–12-kHz band obtained from ocean experiments. To further study the phenomena, a numerical ray model is constructed with 3-D Gaussian beams, evolving sea–surface boundary, and dynamic volume inhomogeneities. The model represents the sea surface as a nonstationary mosaic of polygonal tiles, each reflecting energy with an appropriate Doppler shift. Evolution of the faceted sea surface is governed by assumed oceanographic processes. Spectral density is computed by accumulating the energy contributions at a specified receiver location. In conclusion, the implications of spectral dispersion on undersea acoustic signaling are summarized. [Work supported by the SSC San Diego Independent Research Program, sponsored by the Office of Naval Research.]
Aperture synthesis of time-limited X waves and analysis of their propagation characteristics
Authors: Chatzipetros Argyrios A. , Shaarawi Amr M. , Besieris Ioannis M. , Abdel-Rahman Mohamed A.
Published: July 2002

The feasibility of exciting a localized X-wave pulse from a finite aperture is addressed. Also, the possibility of using a finite-time excitation of a dynamic aperture to generate a finite-energy approximation to an X-wave pulse is explored. The analysis is carried out by using a Gaussian time window to time limit the infinite X-wave initial excitation. Huygens’ construction is used to calculate the amplitude of the radiated wave field away from the finite-time source. The decay rate of the peak of the X wave is compared to that of a quasi-monochromatic signal. It is shown that the finite-time X-wave propagates to much farther distances without significant decay. Furthermore, the decay pattern of the radiated X-wave pulse is derived for a source consisting of an array of concentric annular sections. The decay behavior of the radiated pulse is similar to that of an X-wave launched from a finite-time aperture. This confirms the fact that time windowing the infinite energy X-wave excitation is a viable scheme for constructing finite apertures. A discussion of the diffraction limit of the X-wave pulse is also provided.
Various loss factors of a master harmonic oscillator coupled to a number of satellite harmonic oscillators
Authors: Maidanik G. , Becker K. J.
Published: July 2002

Three loss factors are defined for a master harmonic oscillator (HO); the I-loss factor, the U-loss factor, and the effective loss factor. A conductance (β) is conventionally defined as the ratio of the power imparted to a dynamic system by an external drive to the stored energy that this input power generates. The conductance (β) is related to the loss factor (η) by the frequency (ω); β=(ωη). In light of this definition, it is shown that all three loss factors are identical for an isolated master HO at resonance. Differences arise among these loss factors when the master HO is coupled to satellite harmonic oscillators (HO’s). The first two loss factors retain their definitive format in the sense that the stored energy is reckoned only in the master HO; the energy stored in the coupled satellite HO’s and in the couplings is discounted. The effective loss factor, on the other hand, is defined by accounting for the total stored energy that the external drive applied to the master HO generates in the complex. The complex here is composed of the master HO, the satellite HO’s, and the in situ couplings. In those situations in which the portion of the total energy stored in the satellite HO’s and in the couplings substantially exceeds the stored energy in the master HO, the I-loss factor and the U-loss factor may substantially exaggerate the true loss factor of the coupled master HO. Situations of this type are illustrated by data obtained in computational experiments, and it is argued that the true loss factor of the master HO in the complex as a whole is the effective loss factor.
Release from masking due to spatial separation of sources in the identification of nonspeech auditory patterns
Authors: Kidd Gerald , Mason Christine R. , Rohtla Tanya L. , Deliwala Phalguni S.
Published: July 2002

A nonspeech pattern identification task was used to study the role of spatial separation of sources on auditory masking in multisource listening environments. The six frequency patterns forming the signal set were comprised of sequences of eight 60-ms tone bursts. Bursts of masking sounds were played synchronously with the signals. The main variables in the study were (1) the difference in spatial separation in the horizontal plane between signals and maskers and (2) the nature of the masking produced by the maskers. Spatial separation of signal and masker ranged from 0–180 degrees. The maskers were of two types: (1) a sequence of eight 60-ms bursts of Gaussian noise intended to produce predominantly peripherally based “energetic masking” and (2) a sequence of eight 60-ms bursts of eight-tone complexes intended to produce primarily centrally based “informational masking.” The results indicated that identification performance improved with increasing separation of signal and masker. The amount of improvement depended upon the type of masker and the center frequency of the signal patterns. Much larger improvements were found for spatial separation of the signal and informational masker than for the signal and energetic masker. This was particularly apparent when the acoustical advantage of the signal-to-noise ratio in the more favorable of the two ears (the ear nearest the signal) was taken into account. The results were interpreted as evidence for an important role of binaural hearing in reducing sound source or message uncertainty and may contribute toward solving the “cocktail party problem.”
Modulation detection interference in cochlear implant subjects
Authors: Richardson Louise M. , Busby Peter A. , Clark Graeme M.
Published: July 2002

The aim of this study was to determine whether detection thresholds for amplitude modulated signals on a single electrode were influenced by a masking modulation on a second electrode in cochlear implant users. Data were collected from four post-linguistically deafened subjects using the Cochlear Limited prosthesis. Investigated were the effects of the spatial separation between test and masker electrodes, 0 to 5 electrodes (0 to 3.75 mm), and the amount of masking modulation: 24%, 48%, 72%, and 96% above detection thresholds. Initially, modulation detection thresholds for stimulation on a single electrode without masking modulation were obtained for a set of six electrodes in the middle of the array. Modulation detection thresholds on a fixed test electrode were then obtained with unmodulated and modulated masking on a second electrode, which was one of the six electrodes in the initial study. In both studies, thresholds were measured for modulated pulse duration at the modulation frequencies of 10–200 Hz. In the first study, the shape of the detection thresholds as a function of modulation frequency, the temporal modulation transfer function, generally resembled a low-pass filter for two subjects. For the other two subjects, the functions were relatively flat across modulation frequencies. In the second study, unmodulated masking resulted in a small elevation in detection thresholds across electrodes. Modulation detection interference (MDI), the difference between thresholds for the modulated maskers and the unmodulated masker, was greater for larger amounts of masking modulation than for smaller amounts of masking modulation. For three of the four subjects, MDI was higher for smaller spatial separations between the two electrodes than for larger spatial separations suggesting that a portion of MDI may be due to overlap of neural excitation distributions produced by stimulation on two electrodes in close proximity on the array.
Temporal dynamics of pitch strength in regular interval noises
Authors: Wiegrebe L. , Patterson R. D. , Demany L. , Carlyon R. P.
Published: July 2002

The pitch strength of rippled noise and iterated rippled noise has recently been fitted by an exponential function of the height of the first peak in the normalized autocorrelation function [, J. Acoust. Soc. Am. 100, 3329–3335 (1996)]. The current study compares the pitch strengths and autocorrelation functions of rippled noise (RN) and another regular-interval noise, “AABB.” RN is generated by delaying a copy of a noise sample and adding it to the undelayed version. AABB with the same pitch is generated by taking a sample of noise (A) with the same duration as the RN delay and repeating it to produce AA, and then concatenating many of these once-repeated sequences to produce AABBCCDD⋯ . The height of the first peak (h1) in the normalized autocorrelation function of AABB is 0.5, identical to that of RN. The current experiments show the following: (1) AABB and RN can be discriminated when the pitch is less than about 250 Hz. (2) For these low pitches, the pitch strength of AABB is greater than that for RN whereas it is about the same for pitches above 250 Hz. (3) When RN is replaced by iterated rippled noise (IRN) adjusted to match the pitch strength of AABB, the two are no longer discriminable. The pitch-strength difference between AABB and RN below 250 Hz is explained in terms of a three-stage, running-autocorrelation model. It is suggested that temporal integration of pitch information is achieved in two stages separated by a nonlinearity. The first integration stage is implemented as running autocorrelation with a time constant of 1.5 ms. The second model stage is a nonlinear transformation. In the third model stage, the output of the nonlinear transformation is long-term averaged (second integration stage) to provide a measure of pitch strength. The model provides an excellent fit to the pitch-strength matching data over a wide range of pitches.
Temporal processing in the aging auditory system
Authors: Strouse Anne , Ashmead Daniel H. , Ohde Ralph N. , Grantham D. Wesley
Published: July 2002

Measures of monaural temporal processing and binaural sensitivity were obtained from 12 young (mean age=26.1 years) and 12 elderly (mean age=70.9 years) adults with clinically normal hearing (pure-tone thresholds ⩽20 dB HL from 250 to 6000 Hz). Monaural temporal processing was measured by gap detection thresholds. Binaural sensitivity was measured by interaural time difference (ITD) thresholds. Gap and ITD thresholds were obtained at three sound levels (4, 8, or 16 dB above individual threshold). Subjects were also tested on two measures of speech perception, a masking level difference (MLD) task, and a syllable identification/discrimination task that included phonemes varying in voice onset time (VOT). Elderly listeners displayed poorer monaural temporal analysis (higher gap detection thresholds) and poorer binaural processing (higher ITD thresholds) at all sound levels. There were significant interactions between age and sound level, indicating that the age difference was larger at lower stimulus levels. Gap detection performance was found to correlate significantly with performance on the ITD task for young, but not elderly adult listeners. Elderly listeners also performed more poorly than younger listeners on both speech measures; however, there was no significant correlation between psychoacoustic and speech measures of temporal processing. Findings suggest that age-related factors other than peripheral hearing loss contribute to temporal processing deficits of elderly listeners.
Does hearing aid benefit increase over time?
Authors: Turner Christopher W. , Bentler Ruth A.
Published: July 2002

In a recent tutorial for the journal, Palmer et al. [J. Acoust. Soc. Am. 103, 1705–1721 (1998)] reviewed the literature on the potential for increases in hearing aid benefit over time (acclimatization). Their review might leave some readers with the impression that acclimatization has implications for the fitting and selection of hearing aids today. We (Turner and Bentler), along with two other researchers in the field (Humes and Cox), conducted a similar review of the literature a few years earlier [Turner et al., Ear and Hearing 17, 14S–28S (1996)] and found little evidence of a robust effect. The bulk of the existing evidence, including the most recent studies on this topic, support earlier conclusions, i.e., that there is no evidence for the existence of a strong acclimatization effect in current hearing aid use.
Improved vertical array performance in shallow water with a directional noise field
Authors: Yoo Kwang , Yang T. C.
Published: July 2002

The detection and localization performance of a vertical array against a submerged target in shallow water can be significantly improved if the noise field is directional and the signal arrives in the null (notch) of the noise field. This often happens in a summer environment with a downward refractive sound speed profile in which the surface generated noise field exhibits a notch in the noise vertical directionality distribution at mid (e.g., 500 Hz) frequencies. Using conventional beamforming, by steering the beams to the shallow arrival angle of the target signal, the (undesired) noise which arrives at steep angles can be suppressed. However, conventional beamforming often suffers from significant signal gain degradation due to multipaths in the shallow water environment. Matched-field processing yields a theoretical signal gain by coherently processing the signal, but its ability to reject the directional noise is limited. Matched-beam processing, which is matched-field processing in the beam domain, incorporates the advantages of matched-field processing for coherent signal integration, and conventional beamforming for noise rejection. For the summer environment studied, matched-beam processing yields the highest array gain, almost a twice longer detection range, and a superior capability in detecting a deep target compared with the other two processors. This is demonstrated using simulated signal and noise fields with a full water column vertical array.
Fluctuations in acoustic propagation seen in the SWARM 95 experiment
Authors: Pasewark Bruce H. , Wolf Stephen N. , Orr Marshall H. , Lynch James F.
Published: July 2002

Fluctuations in acoustic propagation as seen in data collected during the SWARM 95 experiment are analyzed and related to the oceanographic environment. Acoustic data were collected on a 32 element vertical receiver array which spanned the 88 m water column from depths of 23 to 85 m. The receiver array was located 42 km seaward from two fixed acoustic projectors which transmitted a 224 Hz PRN signal (16 Hz bandwidth) and a 400 Hz PRN signal (100 Hz bandwidth). Intensity statistics, such as scintillation index (SI) and the probability distribution function (PDF), are discussed as a function of depth and time for narrow-band and broadband (replica correlation) processing. Broadband SI is shown to be less than the narrow-band SI which has a typical value of 2. The PDF is shown to be neither a Rayleigh nor a log-normal distribution and evidence is presented that unsaturated scattering processes are involved. [Work supported by the Office of Naval Research.]
Coherence of acoustic modes propagating through shallow water internal waves
Authors: Rouseff Daniel , Turgut Altan
Published: July 2002

The 1995 Shallow Water Acoustics in a Random Medium (SWARM) experiment was conducted off of the New Jersey coast [Apel et al., IEEE J. Ocean. Eng. (1997)]. The experiment featured two well-populated vertical receiving arrays allowing the measured acoustic field to be decomposed into its normal modes. The decomposition was repeated for successive transmissions allowing the amplitude of each mode to be tracked. The modal amplitudes were observed to decorrelate with time-scales of the order 100 s. In the present work, a theoretical model is proposed explaining the observed decorrelation. Internal solitary wave packets are modeled as mode coupling structures advecting along the acoustic propagation path. Motion of the packets cause the acoustic interference pattern to change. The model is first tested in simple continuous-wave simulations using canonical forms for the internal waves. More detailed time-domain simulations are presented mimicking the situation in SWARM. [Work supported by ONR.]
Airbag noise hazard: From theory to validation
Authors: Price G. Richard
Published: July 2002

Airbag noise is problematic. Peak pressures rise above 170 dB and noise standards declare it hazardous; yet airbags continue to be designed into our automobiles. Scientists agree, however, that the standards may be overconservative and indeed, no epidemic of hearing loss is reported from the highways. A general mathematical model of auditory hazard has been developed [Price and Kalb, J. Acoust. Soc. Am. 100, 2674 (1996)] which addresses such exposures. It predicts and a study shows that the average cat receives a 37 dB PTS from an airbag impulse [Price et al., J. Acoust. Soc. Am. 99, 2464 (1996)]. However, the model suggests the human ear is more robust and predicts the ‘‘at risk ear’’ is one which is not warned, is in a vented compartment (windows open), is facing the noise source and is one which is naturally more fragile [Price, J. Acoust. Soc. Am. 102, 3201 (1997)]. An epidemiological study of airbag noise testing these contentions is just beginning. It will use the Department of Defense hearing conservation database to provide pre- and postexposure audiograms following exposures in automobile accidents. Preliminary data should be available at the time of the meeting.
An experimental evaluation of individual partition segment configurations for the active control of sound transmission
Authors: Leishman Timothy W. , Tichy Jiri
Published: July 2002

Lightweight partitions segmented into discretely actuated subsections with mutual interstices and compliant suspensions have been proposed for active sound transmission control (ASTC). In this work, experimental efforts are undertaken to explore important active and passive characteristics of two partition segment models under normal-incidence excitation. The control objective for the configurations is to actively minimize the normal vibration of their transmitting surfaces—instead of an acoustic field quantity in the receiving space. For this functional strategy to be effective, experiments affirm the importance of efficiently and simultaneously controlling vibrations of transmitting subpanels, suspensions, and interstices to achieve high transmission loss. Distinct segment configurations and control schemes allow varying degrees of global transmitting surface vibration control. However, one configuration tested has been theoretically shown to produce efficient control of its various transmitting surfaces using simple control schemes. Measurements confirm that it also provides exceptionally high transmission loss over a broad frequency range—including very low frequencies. a)Currently at Crown International, 1718 W. Mishawaka Rd., Elkhart, IN 46515-1000.
Energy-time relations in a room with an electroacoustic system
Authors: Svensson U. Peter
Published: July 2002

This paper presents an extended diffuse field model for estimating the energy-time relationships in a room with an electroacoustic system. Discrete-time room impulse responses are used with a direct sound pulse and an exponentially weighted white-noise sequence modeling the reverberation tail. Transducer directivities and electronic finite impulse response (FIR) filters are included as model parameters. It is shown that the convolution of two exponentially weighted noise sequences is expressed as t exp(−δt). Early and total energy levels can easily be estimated and it is demonstrated that when direct sound components are omitted, this impulse response model results in the classical value of total energy supplied to a room by an electroacoustic system with feedback. Comparisons of such estimates with measurements in an auditorium with a single electroacoustic channel are presented. Four configurations were examined, including close and far microphone positions, combined with a single electronic delay or an FIR filter pattern. In the 500-Hz and 1-kHz octave bands, the early energy contribution from the electroacoustic channel spanned a 15-dB range. Predictions were reasonable, coming within 2 dB of the measured values for all four configurations.
The effect of spatial separation of signal and noise on masking in the free field as a function of signal frequency and age in the mouse
Authors: Ison James R. , Agrawal Punit
Published: July 2002

Masking of low- (4 kHz) and high-frequency (25 kHz) signals by one-octave bandpass maskers either spatially coincident with the signal or contralateral to it was examined in mice, 4–6 and 20–22 months of age, in the free field. Signals were presented 120 ms prior to a startle stimulus and differences in their inhibition of the startle reflex, relative to startle stimulus alone trials, were used to measure the severity of masking. Inhibition was reduced or eliminated by spatially coincident noise for weak but not for relatively intense signals, providing the type of “loudness recruitment” effect characteristic of human listeners in similar stimulus conditions. The spatial separation of the signal and its masker relieved this maskinglike effect for the high-frequency pair in both young and old mice. In contrast there was no beneficial effect of the shift in spatial location for the low-frequency pair at either age. This finding of masking release for high- but not low-frequency stimuli supports the hypothesis that the sound shadow provided by the head and pinna would yield a favorable signal-to-noise level difference for a contralateral masker and an ipsilateral signal only at very high frequencies in the mouse. The presence of masking release in these old mice, a first generation hybrid strain with near-normal high-frequency hearing in ABR measures, agrees with reports that the masking release resulting from a similar manipulation in aged human listeners with minimal high-frequency hearing loss is the equal of that obtained in the young listener.
Sound localization in noise in hearing-impaired listeners
Authors: Lorenzi Christian , Gatehouse Stuart , Lever Catherine
Published: July 2002

The present study assesses the ability of four listeners with high-frequency, bilateral symmetrical sensorineural hearing loss to localize and detect a broadband click train in the frontal-horizontal plane, in quiet and in the presence of a white noise. The speaker array and stimuli are identical to those described by Lorenzi et al. (in press). The results show that: (1) localization performance is only slightly poorer in hearing-impaired listeners than in normal-hearing listeners when noise is at 0 deg azimuth, (2) localization performance begins to decrease at higher signal-to-noise ratios for hearing-impaired listeners than for normal-hearing listeners when noise is at ±90 deg azimuth, and (3) the performance of hearing-impaired listeners is less consistent when noise is at ±90 deg azimuth than at 0 deg azimuth. The effects of a high-frequency hearing loss were also studied by measuring the ability of normal-hearing listeners to localize the low-pass filtered version of the clicks. The data reproduce the effects of noise on three out of the four hearing-impaired listeners when noise is at 0 deg azimuth. They reproduce the effects of noise on only two out of the four hearing-impaired listeners when noise is at ±90 deg azimuth. The additional effects of a low-frequency hearing loss were investigated by attenuating the low-pass filtered clicks and the noise by 20 dB. The results show that attenuation does not strongly affect localization accuracy for normal-hearing listeners. Measurements of the clicks' detectability indicate that the hearing-impaired listeners who show the poorest localization accuracy also show the poorest ability to detect the clicks. The inaudibility of high frequencies, “distortions,” and reduced detectability of the signal are assumed to have caused the poorer-than-normal localization accuracy for hearing-impaired listeners.
The contribution of spectral cues to human sound localization
Authors: Langendijk Erno H. , Bronkhorst Adelbert W.
Published: July 2002

The contribution of spectral cues to human sound localization was investigated by removing cues in 1/2-, 1-, or 2-octave bands in the frequency range above 4 kHz. Localization responses were given by placing an acoustic pointer at the same apparent position as a virtual target. The pointer was generated by filtering a 100-ms harmonic complex with equalized head-related transfer functions (HRTFs). Listeners controlled the pointer by a hand-held stick that rotated about a fixed point. In the baseline condition the target, a 200-ms noise burst, was filtered with the same HRTFs as the pointer. In other conditions the spectral information within a certain frequency band was removed by replacing the directional transfer function within this band with the average transfer of this band. Analysis of the data showed that the effect of bandwidth is larger than that of center frequency. There appears to be an interaction between center frequency and target position. Effects related to center frequency varied substantially among listeners. This indicates that listeners use different cues when localizing sounds from a certain direction.
A cocktail party effect in the median plane?
Authors: Bolia Robert S. , Ericson Mark A. , Nelson W. Todd , McKinley Richard L. , Simpson Brian D.
Published: July 2002

Recent research has been conducted on the effects of spatialized audio on a listener’s ability to detect and identify a target speech signal when presented among nontarget speech signals in the horizontal plane [W. T. Nelson et al., Proceedings of the 1998 IMAGE Conference (1998), pp. 159–166]. However, the existence of a ‘‘cocktail party effect’’ in the median plane has not been addressed. The purpose of the present investigation was to determine whether or not the spatial separation of multiple simultaneous speech sources in the median plane leads to improved detection and intelligibility. Independent variables include the number and angular separation of the speech signals, the sex of the target talker, and the presence or absence of head motion cues. All speech signals—phrases from a modified Coordinate Response Measure [T. J. Moore, AGARD Conference Proceedings 311: Aural Communication in Aviation (1981), pp. 2.1–2.6]—were digitally filtered via nonindividualized HRTFs and presented over headphones. Results will be compared with those obtained in the horizontal plane. Inplications for the design of auditory displays will be discussed.
Meridional ray contributions to scattering by tilted cylindrical shells above the coincidence frequency: ray theory and computations
Authors: Morse Scot F. , Marston Philip L.
Published: July 2002

High-frequency scattering enhancements from a submerged infinite cylindrical shell are studied by means of partial wave series (PWS) calculations and a ray approximation. For certain oblique angles of incidence it is possible to launch a generalized leaky Lamb wave which propagates strictly in the axial direction on the shell. This meridional leaky wave radiates with a locally flat wavefront curvature and produces large far-field amplitudes over a range of tilt angles. When combined with a reflection from a discontinuity in the shell, this process can give rise to large backscattering enhancements at large tilt angles for thick finite cylindrical shells [S. F. Morse et al., J. Acoust. Soc. Am. 103, 785–794 (1998)] and is present in sonar images. A convolution formulation ray theory for the far-field meridional ray amplitude is compared with the exact PWS solution in the region where enhancements are observed for both the a0 and s0 Lamb waves. The ray theory correctly predicts both the peak enhancement amplitude and the general shape of the enhancement curve.
Shear interfacial waves in piezoelectrics
Authors: Darinskii A. N. , Lyubimov V. N.
Published: July 2002

An analysis was made of the SH-interfacial wave propagation on an interface between semi-infinite piezoelectric media. In particular, a sufficient condition for the existence of the SH-wave on the metallized rigid contact was derived. It has been shown that on the metallized rigid contact between two completely identical piezocrystals the SH-localized wave always exists, with the exception of at most two orientations of the interface. An investigation was performed of specific features of the sound reflection—transmission at incident angles corresponding to the resonant excitation of the leaky wave originating from the “supersonic” interfacial wave due to misorientation of crystals that constitute the bicrystal. Also, it has been established that in 6 mm crystals an interfacial “supersonic” wave may remain purely localized even when the direction of propagation is not perpendicular to the axis 6 or when the interface is not parallel to this axis.