bluuebunny/crossref_metadata_2025 huggingface dataset:
Maximum-likelihood estimation of source parameters from time-sampled outputs of a linear array
Authors: El-Behery Ibrahim N. , MacPhie Robert H.
Published: October 2005

This paper considers the joint estimation of the bearing and strength parameters of a noise source, by a uniformly spaced array of sensors in the presence of self-noise, assumed to be independent between any pair of sensors. Contrary to the analogue systems of processing (i.e., correlation and beamforming), the present scheme, which is based on the maximum-likelihood (ML) principle, operates on a set of time samples representing the bandlimited output of the array’s elements. The system, as a result, does not require the assumption of long observation time normally used in other schemes and is easily implemented on a digital computer. The resulting ML estimator is not in theory a sufficient one. Nevertheless, when the estimator’s variance is compared with the Cramer–Rao lower bound, the estimator virtually attains its asymptotic sufficiency as the number of array elements exceeds a ’’threshold’’ which is a decreasing function of the signal-to-noise ratio (SNR) and the length of the observation time. Except when the SNR is very poor and the observation time is quite short, the ’’threshold’’ is found to be surprisingly small. It is also demonstrated, at least when the error in the bearing estimate is small, that the ML estimator is unbiased.
Acoustic pressure field alongside a manikin’s head with a view towards i
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u hearing-aid tests
Authors: Kuhn George F. , Burnett Edwin D.
Published: October 2005

The frequency responses of hearing aids measured in a free field differ from those measured on the head of a person or a manikin due to the scattering of the sound by the head and the torso. In order to compare and interpret the response of hearing aids located on the head at various frequencies it is necessary to know precisely the spatial pressure distribution. The amplitude and phase of the acoustic pressure were measured alongside a manikin’s head in increments ranging from 2 to 5 mm with frontal sound incidence . The acoustic driver was located in front of the manikin at distances of 1.0 and 3.5 m from the ear-canal axis. The test frequencies were the octave band center frequencies from 0.5 to 4.0 kHz and the third-octave band center frequencies from 4.0 to 8.0 kHz. The sound pressure level varies smoothly, as a function of position, alongside the head for frequencies equal to or less than 2.0 kHz. At frequencies equal to or greater than 4.0 kHz the pressure level changes rapidly with position. Particulary severe pressure minima were found to exist around the pinna at 6.3 and 8.0 kHz. The smoothing effect of test signals using pink noise of 6% and 29% bandwidth on the acoustic pressure variation alongside the head and behind the pinna is also shown.
Frequency coherence and time coherence in random multipath channels
Authors: Adams S. L. , Doubek J. W.
Published: October 2005

The underwater acoustic propagation channel is dispersive in time, frequency, and space. This paper investigates frequency coherence and time coherence for simple multipath channel models with an emphasis on situations where there are a few paths. The propagation channel is postulated to consist of a finite set of paths with random amplitudes and lengths. The fluctuation characteristics of the frequency selective fading in a random time spread channel are investigated in terms of the statistics of the channel transfer function. The effects of the fluctuations in path length are clearly separated from the effects of nominal multipath structure in the channel statistics. The conditions under which coherence bandwidth and coherence time provide reasonable characterizations for the multipath channel are examined. All of the results obtained for the random time spread channel can be applied to the mathematically dual problem of a random frequency spread channel.
Variational solution for the reflection and transmission of waves at a material interface between waveguides
Authors: Bedford A. , Sorensen A. L.
Published: October 2005

A variational procedure is presented for the modal superposition solution of the reflection and transmission of steady-state waves at a material interface between two elastic waveguides. As an example, the solution is applied to the reflection and transmission of waves at an interface between two elastic plates using the Rayleigh–Lamb modes.
Speech-quality testing of some variable-frame-rate (VFR) linear-predictive (LPC) vocoders
Authors: Huggins A. W. F. , Viswanathan R. , Makhoul J.
Published: October 2005

VFR transmission of LPC vocoder coefficients is a technique developed to reduce the average transmission rate without appreciable loss of quality. The technique transmits parameters at a variable rate in accordance with the changing characteristics of the speech signal. In order to assess the effectiveness of VFR transmission, we performed an experiment to compare it with two other methods for reducing the bit rate: (a) reducing the number of poles, and (b) increasing the quantization step size of the LPC coefficients (log–area ratios). Thirty-two stimulus sentences were prepared by passing four utterances (2 sentences × 2 speakers) through eight vocoder systems in a 2×2×2 factorial design; two values were assigned to each of the three parameters: average frame rate, number of poles, and quantization step size. Eight listeners made seven-point category ratings of quality degradation. The results of the experiment show that, of the three methods studied, the VFR technique produced the highest quality at any given transmission rate (or, equivalently, yielded the lowest bit rate for a fixed level of speech quality).
Stimulus variability and auditory filter shape
Authors: Patterson Roy D. , Henning G. Bruce
Published: October 2005

We have investigated the way in which stimulus variability will affects the attenuation characteristic or auditory filter shape inferred from masking experiments. Stimulus variability was found to have a pronounced effect on filter shapes derived from bandlimiting experiments in which the signal is a tone, the masker is a band of noise centered on the tone, and the independent variable is the width of the noise band. But stimulus variability had virtually no effect on filters obtained from notched noise masking experiments. In an attempt to extend the utility of the filter-shape concept we have replicated an earlier experiment in which the masker is two tones rather than noise. The tones, each 57 dB SPL, were used to mask a narrow band of noise centered midway between them and threshold for the noise signal was measured as a function of the frequency separation of the tonal maskers. The form of the data is in good agreement with the auditory filter shape derived using a notched-noise masker and a tonal signal. In order to predict the absolute levels obtained in the noise-masking experiments, it was necessary to assume that internal noise adds to the variability of the stimuli. The resulting model, which incorporates the filter shape from the notched noise experiment and the energy detection model, predicts not only the form but also the absolute levels obtained in the bandlimiting and notched noise experiments. In addition, it predicts the shape of the data from the two-tone masking experiment but it does not predict the overall level.
Two-tone auditory spectral resolution
Authors: Feth Lawrence L. , O’Malley Honor
Published: October 2005

Two component complex tones were synthesized so that each member of a complementary pair exhibited identical amplitude modulations; frequency modulations, however, were in opposite directions. Previous work has shown that the discriminability of the members of a complementary pair is related to the envelope-weighted differences in their instantaneous frequency functions. Listeners report that they base their discriminations upon differences in pitch between complementary two component signals. We assumed that the high discriminability found for moderate separations between the two component frequencies would not obtain if the components were resolved into separate critical bands. Thus we could define the just discriminable (75%) frequency separation as a direct estimate of spectral resolving power without recourse to assumptions about masking effectiveness, loudness summation, or other subjective changes thought to depend upon auditory spectral resolving power. Our findings indicate that resolution bandwidths resulting from the discriminability of complex tone pairs approximate the width of the traveling-wave envelope observed by von Békèsy. In light of our results, the implications for other critical bandwidth estimates are discussed.
Coaxial circular spherical array for ultrasonic imaging
Authors: Shibata Shuji , Koda Toshio , Matsumoto Shuntetsu , Yamaga Joji
Published: October 2005

A new type of receiving array has been designed and constructed for the purpose of visualizing an object by using the ultrasonic wave at low frequency. The array consists of 24 receiving elements around three coaxial circles on a spherical surface. The multiplication of three additive outputs, each of which is the sum of the eight element outputs on a circle, is performed for the signal processing of the array. After theoretical and experimental studies, it has been proven that the array proposed is appropriate for the high-directional receiver in the ultrasonic visualization system. A preliminary experiment on imaging the object in the air has been carried out.
Procedure for evaluating a reflection-reduction coating
Authors: Neubauer Werner G.
Published: October 2005

A new method for utilizing recent new results of the classical solution to the problem of reflection by a two-layer cylindrical shell has been devised for the determination of the material properties of a reflection-reduction coating. In that solution, both layers or either layer may have inherent wave attenuations. A measurement of the incident and reflected free-field pressure amplitudes must be made and elastic constants must be known that define all materials involved except the layer of material whose reflection-reduction properties are sought. A method of least-squares fitting of the exact theory to the measured data will allow determination of the lognitudinal- and shear-wave speeds and their attenuations. Measurements at a given frequency range and cylinder size can be confidently extrapolated to other frequencies or cylindrical curvatures. Defined quantities such as impedance can be determined once the longitudinal- and shear-wave speeds are known.
Diffusion loss in refractive sound channels: Bottom-loss effects
Authors: Mellen R. H. , Schneider H. G.
Published: October 2005

The excess diffusion loss in refractive sound channels is a function of the stochastic variability of the medium and the bottom loss. Attenuation coefficients obtained by approximate solution of the ray-diffusion equation are in reasonable agreement with those obtained previously by means of a random-walk ray-tracing program.
Reciprocal acoustic transmission in a midocean environment
Authors: Worcester Peter F.
Published: October 2005

The simultaneous transmissions of acoustic pulses in opposite directions between two point in midocean has been used to separate current effects on acoustic propagation from the effects of sound-speed structure. Two 2250-Hz sources were suspended at about 1-km depth from ships 25 km apart. Differences in travel times of the oppositely traveling pulses are interpreted in terms of ray-averaged currents. The measured values contain an unknown contribution from ship drift, but differences between upper and lower ray paths present in this experiment are insensitive to drift. Further, the nonreciprocity in pulse shape and amplitude of opposing transmissions is found to be of the same order as the fluctuations in time of one-way transmissions. This demonstrates that currents contribute to acoustic scattering.
Band-limited power flow into enclosures
Authors: Pope L. D. , Wilby J. F.
Published: October 2005

Acoustic power flow into enclosures is an area of continued research activity. Recent work [Pope and Wilby, BBN Report No. 3286 (1976)] resulted in band-limited power-flow formulations which account for coupling of structure and volume modes in the low-frequency regime and allow for a general description of the exciting external random pressure fields.
Reply to ’’Comments on ’Environmental effects on microphones of various constructions’ ’’ [J. Acoust. Soc. Am. 61, 1647 (1977)]
Authors: Hruska Gale R. , Magrab Edward B. , Penzes William B.
Published: October 2005

To answer the question as to whether or not the microphones were given sufficient time to ’’recover’’ from a particular humidity we elaborate further on the experimental procedure.
Effect of a random ocean current on acoustic transmission in an isospeed channel
Authors: Newhall B. K. , Jacobson M. J. , Siegmann W. L.
Published: October 2005

The effects of a random current on the fluctuations of underwater cw sound transmissions are considered for a horizontal isospeed channel. A statistical ensemble of currents is employed, whose members are depth dependent only, and current influence on ray geometry is investigated. Approximations to the total acoustic field at a receiving point are obtained, and it is shown that a current ensemble member has a significant effect on phase. A mean current is taken, on which are superimposed small depth-dependent current changes in speed and direction. These changes are members of statistical ensembles, which lead to an ensemble of phase functions. Expressions for the mean and standard deviation of the phase, in terms of statistics of the depth-averaged current fluctuations, are determined and analyzed. The inverse problem of determining second-order moments of the random current, given the standard deviation of phase, is examined also. If the mean current is known, phase information at three receivers is sufficient to specify the second moments of the current fluctuations.
Ambient-sea-noise directionality: Measurement and processing
Authors: Yen N.
Published: October 2005

The fundamental relationships between acoustic array parameters and the noise field are reviewed to establish the connection among the various processing techniques for estimation of the ambient-sea-noise directionality. The analyses, based on the concept of multidimensional space, conclude that basic information about the ambient-sea-noise directionality can be obtained directly from the cross-spectral matrix of the array’s hydrophone outputs. The angular resolution of the processed noise field depends on the array structure, the stationarity of the noise field, and the precision in numerical computation. The cross-spectral data also can be used to indicate the dominant coherent noise sources in a certain multidimensional representation. Examples of a simulated noise field and actual sea data are illustrated for the directional AUTOBUOY.
Internal friction of metal spheres showing the effect of the anisotropy of the component metals
Authors: Mason W. P. , Marfurt K. J. , Beshers D. N. , Kuo J. T.
Published: October 2005

By using the resonant vibrations of metal spheres it is possible to separate the contributions involving different amounts of shear, hydrostatic, and longitudinal strain merely by choosing the appropriate resonant frequencies. Birch [J. Geophys. Res. 80, 756–764 (1975)] has applied this method to the radical, spheriodal, and torsional modes of metals, glasses, and rocks. He has shown that if there is no loss connected with the hydrostatic component of vibration, the ratio of the Q of the radial mode to the Q of the torsional modes should be 9 to 1 whereas his measurements of steel indicated a ratio of about 3 to 1. We have measured several cubic metals (Al, Fe, Ta, Nb, W, V, and α-brass) and have found that this ratio of Q’s varies systematically with elastic anisotrophy. It is shown that the difference in the elastic constants of adjacent grains introduces a shearing stress in the body of the material which adds a component of the internal friction proportional to the anisotropic factor minus one which accounts for the drop in Q for a longitudinal vibration. For the radical mode the much larger effect has not been explained and the value of K found is experimental.
Moderate frequency compression for the moderately hearing impaired
Authors: Mazor M. , Simon H. , Scheinberg J. , Levitt H.
Published: October 2005

The intelligibility of frequency-compressed speech was measured for four normal and eight hearing-impaired subjects with sensory-neural high-frequency loss. Hearing levels were roughly 40 dB. Four conditions of frequency compression, 0%, 20%, 33%, and 55% were obtained using a Varispeech compressor. The test materials were PB-50 word lists recorded by one male and one female speaker. The effect of frequency compression was to reduce intelligibility in all cases except one, that of the female speaker at 20% frequency compression. For this case, the hearing-impaired listeners showed a small average improvement. Although the effect was small, it represents one of the few instances when an experimental evaluation of a frequency-compression system has yielded positive results with the hearing impaired. i
Application of cross-spectral density to a measurement of vibration power flow between connected plates
Authors: Fahy Frank J. , Pierri Remo
Published: October 2005

It is shown that the flow of vibration power through a rigid ’’point’’ connection between flexible plate structures may be evaluated by measuring the imaginary part of the cross-spectral density between the coupling force and the acceleration at the connection point.
Decay of reverberant sound in a spherical enclosure
Authors: Carroll M. M. , Chien C. F.
Published: October 2005

The assumption of diffuse reflection (Lambert’s Law) leads to integral equations for the wall intensity in a reverberant sound field in the steady state and during decay. The latter equation, in the special case of a spherical enclosure with uniformly absorbent walls and uniform wall intensity, allows exponential decay with a decay time which agrees closely with the Norris–Eyring prediction. The sound-intensity and sound-energy density in the medium, during decay, are also calculated.
High k
a scattering of elastic cylinders and spheres
Authors: Flax Lawrence
Published: October 2005

Reflection characteristics of elastic cylinders and spheres for large values of ka are determined by explicit evaluation of the wave harmonic series for a nonabsorptive medium.
Plane wave diffraction by a wedge with finite impedance
Authors: Pierce Allan D. , Hadden W. James
Published: October 2005

A theory is presented for the diffraction of acoustic waves by barriers with finite acoustical impedance, the shape of the barriers being such that, insofar as diffraction into the shadow zone is concerned, they may be idealized as semi-infinite wedges. The analytical development is based on the known exact solution for plane wave diffraction by a finite impedance wedge, versions of which have been previously given in the literature by Williams [Proc. R. Soc. London Ser. A: 252, 376–393 (1959)], by Senior [Commun. Pure Appl. Math. 12, 337–372 (1959); Proc. R. Soc. London Ser. A: 213, 436–458 (1952)], and by Maliuzhinets [Sov. Phys. Acoust. 1, 152–174; 240–248 (1955)]. This solution is described in detail and the asymptotic limit is derived in a form which demonstrates the satisfaction of the reciprocity principle. Practical implementation is discussed, both through numerical examples and through the presentation of graphs of quantities which will be helpful in barrier design.
Auditory-nerve response from cats raised in a low-noise chamber
Authors: Liberman M. Charles
Published: October 2005

A litter of four cats, born and raised in a soundproofed chamber, was studied in an attempt to determine which, if any, features of the auditory-nerve response from routinely available cats might be due to the chronic effects of noise exposure. Two features of routine-normal response were especially suspect in this regard: (1) a ’’notch’’ in the distribution of single-unit thresholds centered at characteristic frequencies (CF’s) near 3 kHz and (2) a compression of the distribution of rates of spontaneous discharge for units with CF above 10 kHz. A third feature of response in routine animals was the presence of a small number (roughly 10%) of units with virtually no spontaneous discharge and very high thresholds, sometimes 80 dB less sensitive than high-spontaneous units of similar CF. In the data from chamber-raised animals, the high-spontaneous units showed exceptionally low thresholds at all CF regions, however, there were signs of the midfrequency notch in the threshold distribution of at least two of these animals. The compression of the spontaneous rate distribution was not seen in any of the three most sensitive animals. The data suggest that there is a significant amount of ’’normal pathology’’ in the high-CF units from routine animals. Low-spontaneous, high-threshold units were present in all four chamber-raised ears with the same characteristics as in routine animals (exceptionally narrow tuning curves and exceptionally low maximum discharge rates) and at roughly the same percentage of the unit sample. A class of units with medium spontaneous rates and intermediate thresholds could also be identified. The possible significance of a classification of auditory-nerve units according to spontaneous rate is discussed.
Compatibility between psychophysical and physiological measurements of aural combination tones
Authors: Goldstein Julius L. , Buchsbaum Gershon , Furst Miriam
Published: October 2005

Neural studies of combination-tone (CT) responses in the eighth nerve and antroventral cochlear nucleus of anesthetized cats give evidence of stimuluslike intracochlear CT’s with a similar amplitude spectrum as inferred from human psychophysics. An unsolved problem raised in these studies is the gross discrepency between the phase of CT’s measured psychophysically and neurally. It is unknown whether incompatibility lies in the cochleae or the criteria for measuring CT’s in the different experiments. New psychophysical experiments were developed to clarify this issue. Secondary CT’s (SCT) were generated by the interaction between a primary cubic CT (CTT) and a third tone in the stimulus. The SCT measured by cancellation exhibits similar properties to those of a CT generated by the comparable two-tone stimulus. The SCT is eliminated when the CCT is cancelled. These findings support the view that CT’S exist in the cochlea as spatially distinct, stimuluslike excitations, and that CT excitations are eliminated by psychophysical cancellation. The SCT phase provides a measure of the CCT phase without requiring direct cancellation of the CCT. Phase measurements by the new indirect and older direct methods imply that the CT phase may be constant with changing sound level of the primary stimulus as found in the neural studies; these measurements also reveal nonlinear phase effects not found in neural studies. The new data suggest that the CT phase discrepancy may be caused by a real difference between the nonlinear mechanisms in the alert humans and anesthetized cats, and provide new constraints for clarifying this issue through further study.
Conformal array beam patterns and directivity indices
Authors: Frank T. H. , Kesner J. W. , Gruen H. M.
Published: October 2005

Simulated beam patterns and the directivity indices of a particular 97-element conformal array configured on less than half the surface of a quasiright circular cone have been studied. A comparison of two methods to calculate directivity index was made as a function of frequency and steering angle. At broadside, a directivity index of 19.54 dB was obtained for this conformal array. This value exceeds that of a conventional planar array which could be enclosed in the same-sized circular aperture by more than 3 dB. The technique to calculate directivity index which sums the correlation coefficients among discrete array element pairs avoids both the computer evalution expense and the sensitivity to approximation errors inherent in numerical integration procedures required to evaluate the volume under the directed array response. For this array, it was found that the directivity index did not fall off as rapidly as predicted for a planar array, of the same area as the conformal array, as the beam is steered from broadside to endfire. The expression 10 log10N was found to be useful in readily evaluating the directivity index, where N is the number of elements.
Iterative technique for ambient-noise horizontal-directionality estimation from towed line-array data
Authors: Wagstaff R. A.
Published: October 2005

A new method of estimating noise-field horizontal directionality from towed line-array data is presented. The method utilizes iterative techniques to estimate the time-averaged noise-field horizontal directionality by convolving the estimate with the calculated beam pattern and comparing the results with the measured beam output data. The estimate is appropriately changed until the pooled standard deviation for the differences between the calculated and the measured beam outputs is less than some arbitrarily chosen small value. The results are given for both stationary and nonstationary noise fields.
Steered planar nearfield calibration array
Authors: Van Buren A. L.
Published: October 2005

The Trott planar nearfield calibration array (NFCA) is a two-dimensional array of small, reciprocal hydrophones whose responses are shaded to produce a nearly uniform plane wave throughout a volume in the nearfield of the array. When a transducer to be calibrated is placed in the plane-wave volume, the signal received by the NFCA is proportional to the farfield pressure radiatied by the transducer in the direction opposite to the plane wave. Previous NFCA’s were shaded so that the plane-wave direction was normal to the array. It was necessary to rotate the transducer in order to obtain the farfield pressure distribution. In the present study we obtain shading coefficients that allow the nearfield plane wave to be steered to angles up to 70° from the normal to the array. These coefficients allow the determination of a 140° sector of the azimuthal farfield pattern without rotating the transducer. We experimentally verified the shading coefficients by successfully calibrating a large piston transducer. Here we synthesized the steered planar NFCA by combining responses of a single line of shaded hydrophones to form a virtual NFCA. The synthetic aperture technique allows the calibration of large sound sources without having to build the entire NFCA.
Time-harmonic solution of the elastic head wave problem incorporating the influence of Rayleigh poles
Authors: Tsang Leung
Published: October 2005

The classical Lamb problem of a time-harmonic line load applied to the surface of an elastic solid is considered in this paper. In the past, ordinary asymptotic methods have been applied to the branch-cut evaluation of the time-harmonic compressional and shear head waves. It is shown here that the application of these methods generally leads to erroneous results. The problem of the shear branch cut is associated with the Rayleigh pole, and the problem of the compressional branch cut is associated with the other two roots of the Rayleigh equation, which lie in the neighborhood of the compressional branch point. These two roots affect the compressional branch-cut integration and can contribute a residue to the total solution. To evaluate the time-harmonic fields, we utilize the following methods of integration—the modified saddle-point method, the method of numerical integration along the branch cut, and the method of numerical integration along the Sommerfeld contour. With the inclusion of the effects of all three roots of the Rayleigh equation, the results from the three methods are in excellent agreement.
Acoustic radiation pressure on an absorbing sphere
Authors: Hasegawa Takahi , Watanabe Yumiko
Published: October 2005

The theory of the acoustic radiation pressure on an elastic sphere, placed freely in an inviscid fluid in a field of plane progressive sound waves, is modified to include the effect of a hysteresis type of absorption of shear and compressional waves in the solid material of the sphere. This type of absorption is typical of some types of polymer materials. Calculated results are presented for polymethylmethacrylate lucite and polyethylene spheres in water for ka values between 0 and 24. The results are of interest in view of the use of radiation pressure measurements to determine sound intensity.
Acoustically dependent latency shifts of BSER (wave V) in man
Authors: Klein Alan J. , Teas Donald C.
Published: October 2005

The latencies of wave V in Brain Stem Evoked Responses (BSER) elicited by a set of acoustic transients were measured. The stimuli were produced by delivering pulses to two filters, arranged in series. The filters were set so that the maximum acoustic energy in the transients, i.e., filtered clicks, occurred at 0.5, 1, 2, 4, or 8 kHz. The filtered clicks were presented via earphones at a rate of 30/s at 20, 40, or 60 dB HL to ten subjects with normal hearing. The latencies of wave V varied systematically with center frequency of the filtered clicks when they were each at the same HL. Stimuli presented at 40 dB HL produced the greatest opportunity for relating stimulus frequency to latency. The latencies for a smaller set of responses to stimuli presented at 10/s were the same as those for the principal data taken at 30/s. The changes in latency of wave V due to frequency are similar to those observed by other investigators in whole-nerve responses recorded in man.
Presumed noise-induced permanent threshold shift resulting from exposure to an A-weighted Leq of 89 dB
Authors: Berger E. H. , Royster L. H. , Thomas W. G.
Published: October 2005

The noise-induced permanent threshold shift (NIPTS) resulting form up to ten years of exposure to an average A-weighted sound level Leq of 89 dB was investigated. Prior occupational noise exposure was controlled for by eliminating subjects with previous high-noise-level jobs or uncertain exposure histories. The final population consisted of 42 males and 58 females working in steady-state broadband noise environments. No attempt was made to screen subjects for any auditory pathology. A 222-subject control group from the same geographic area as the exposed subjects was selected such that none of its constituents had any effective industrial noise exposure. Presumed NIPTS was calculated by correcting each individual audiogram of the exposed subjects according to the aging curves developed from the control popultion hearing levels. The results indicated a considerable male–female difference in NIPTS, even though both groups were exposed to the same Leq. Averaging the results for all 100 subjects, in order to make comparisons to other available data, yielded results in close agreement to predictions based upon the work of Burns and Robinson, Baughn, NIOSH, and Passchier–Vermeer, indicating that 10 years of exposure to a daily Leq of 89 dB causes measurable hearing loss at 4 kHz.
Effects of atmospheric turbulence on the interference of sound waves near a hard boundary
Authors: Daigle G. A. , Piercy J. E. , Embleton T. F. W.
Published: October 2005

The mean sound levels resulting from the interference between direct waves and those reflected from the ground are strongly influenced, especially at frequencies near interference minima, by fluctuations in phase and amplitude of the sound waves induced by propagation through atmospheric turbulence. Since it was found experimentally that the correlation length (∠1.1 m) of the meteorological fluctuations is comparable to the separation between the interfering sound paths, previous theoretical work by Ingard and Maling [J. Acoust. Soc. Am. 35, 1056–1058 (1963)] has been extended to allow for partial covariance between the two waves. The theory has been further extended to use the calculations of fluctuations in phase and amplitude of spherical waves, and to include the explicit calculation of the fluctuating acoustical index of refraction from the fluctuating values of temperature and wind velocity. Measurements (1–6 kHz) have been made of the interference spectrum at 15, 30, and 45 m from a point source 1.2 m above a large asphalt surface. Simultaneously, the fluctuating values of temperature and horizontal wind velocity (atmospheric turbulence) were measured at two related points close to the sound path. There is satisfactory quantitative agreement between the sound levels calculated from the measured fluctuating meteorological variables (with one adjustable parameter) and those measured experimentally.
Threshold shifts in chinchillas exposed to octave bands of noise centered at 63 and 1000 Hz for three days
Authors: Burdick Charles K. , Patterson James H. , Mozo Ben T. , Camp Robert T.
Published: October 2005

Audiograms were obtained on eight binaural chinchillas trained on a shuttlebox avoidance procedure. Four of the animals were exposed to three successive levels of an octave band of noise centered at 63 Hz: 100 dB SPL (74 dBA), 110 dB SPL (84 dBA), and 120 dB SPL (94 dBA). The other four animals were also exposed to three successive levels of an octave band of noise centered at 1000 Hz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposure durations were 72 h. Little threshold shift (TS) resulted from the lower two exposure levels of the 63-Hz noise band. At the 120-dB exposure level, maximum TS of 43 dB occurred at 2000 Hz. Permanent threshold shifts (PTSs) of 16 dB at 2000 Hz and 11 dB at 1400 Hz were found. Exposure to the three levels of the 1000-Hz noise band produced TSs of 20, 45, and 61 dB at 1400 Hz. The 95-dB exposure level resulted in PTSs of 6 dB at 1400 Hz and 9 dB at 2000 Hz. The major results were (1) high-frequency hearing loss to a low-frequency noise and (2) that noise bands matched within 1 dBA were not equally hazardous as dictated by damage-risk criteria. The 63-Hz noise band produced nearly twice as much PTS as the 1000-Hz noise band.
Squirrel monkey temporary threshold shift from 48-h exposures to low-frequency noise
Authors: Nielsen Donald W. , Burnham Jane , Talley Carol
Published: October 2005

Five squirrel monkeys were exposed for 1, 2, 4, 8, 16, 24, and 48 h to a 375–750-Hz band noise at an overall SPL of 95 dB. The TTS4.5 growth pattern for the 750-Hz test frequency was biphasic and did not reach an asymptote after 48 h of exposure. For all exposures, the mean thresholds of the five monkeys returned to within 5 dB of the preexposure mean 20 h after exposure. Recovery curves from all exposures at the 750-Hz test frequency appeared biphasic. Increasing SPL from 95 to 105 dB increased TTS4.5 by 4 dB at 750 Hz for a 1-h exposure. Recovery from the 105-dB exposure followed the same pattern as recovery from the 95-dB exposure. When compared with data collected from human subjects under similar conditions, these experiments indicate that the growth and recovery of TTS in squirrel monkeys are sufficiently similar to growth and recovery in man to justify further comparative investigation.
Finite-element equivalent circuits for acoustic field
Authors: Kagawa Yukio , Yamabuchi Tatsuo
Published: October 2005

An equivalent electrical circuit results from the process of representing a general three-dimensional system approximately by the corresponding nondimensional discrete network. The equivalent electrical circuits for acoustic field problems are presented based on the finite-element approach. Basic equivalent circuits are first developed for a triangular or tetrahedral acoustic element in which the pressure is assumed to change linearly within the element. The circuit of an arbitrary sound field can be obtained simply by connecting these basic elements. The lossy field and the boundary wall with an acoustic impedance are then considered.
Superharmonic vibrations of order 3 in stretched strings
Authors: Raghunandan C. R. , Anand G. V.
Published: October 2005

Superharmonic vibrations of order 3 in stretched strings driven by a single-mode planar simple-harmonic force are investigated. It is shown that planar as well as nonplanar superharmonic resonances can occur. After giving a few analytical results, the problem is thoroughly investigated numerically. The stability analysis shows that the region of stable nonplanar oscillations is much smaller than that of stable planar oscillation. It is observed in the case of nonplanar oscillations that the amplitude of the superharmonic in the plane normal to the plane of excitation is larger than that in the plane of excitation.
Paraxial and nonparaxial ray speeds in strongly range-dependent SOFAR channels
Authors: Shockley R. C.
Published: October 2005

The adiabatic invariance of the phase integral c−1 sinϑ dz≡J leads to new analytic results for the average horizontal ray speed in constricting parabolic, Hirsch, and bilinear sound velocity profiles (SVPs). Theoretical predictions agree well with exact numerical raytracing solutions even for nonslowly varying SVPs, and show that the average ray speed may either increase or decrease in a contricting channel, depending on the SVP type. The adiabatic invariant approximation (AIA) appears to provide physical insight, an accuracy check for present range-dependent codes, and an alternative in some cases to long-range raytracing, for conditons typical of SOFAR propagation. We illustrate the latter point with an application of the AIA to a set of SVPs representative of the eastern North Pacific.
Acoustic input impedance of excised dog lungs
Authors: Jackson Andrew C. , Butler James P. , Pyle Robert W.
Published: October 2005

Input impedances of six excised dog lungs were computed from Fourier analysis of their response to a transient pulse pressure excitation. Impedances, between 156 Hz and 10 000 Hz, were measured at transpulmonary pressures of 30, 20, 10, and 5 cm H2O. There was a substantial amount of interindividual variability in the impedance. There were, however, generally three well defined impedance peaks and the frequencies of these peaks seemed to be dependent upon body size and lung volume. If the airways are modeled simply as a constant diameter tube one is led to the paradoxical conclusion that substantial airway closure occurs at relatively large lung volumes. However, conditions of open airways are consistent with our results if the airways are modeled as having a more complex geometrical shape. We conclude that the input impedance at these high frequencies is variable among individuals, and between lung volumes in any given individual, and that estimates of pathlength or the alveolar boundary condition cannot be easily obtained by interpretation based on simple geometrical models.
Analysis of a composite compliant baffle
Authors: Gonzalez M. A.
Published: October 2005

The response of a composite baffle, consisting of a compliant layer and a signal conditioning plate, to mechanical and acoustical excitations is calculated. Fluid loading is included in the calculation, and the coupling of the structure to the acoustic field is treated exactly. Comparison is made between the response of the compliant layer to a mechanical excitation, and another commonly used metric for baffle performance, viz., acoustic insertion loss. Calculations are carried out for a representative example.
A correction to the parabolic approximation
Authors: DeSanto J. A. , Perkins J. S. , Baer R. N.
Published: October 2005

In a previous paper [J. A. DeSanto, J. Acoust. Soc. Am. 62, 295 (1977)] we showed that the solutions of the Helmholtz and parabolic equations were related by an integral transform. The stationary phase approximation of the transform led to corrections of the parabolic approximation (PA). Based on this analysis, we define in this paper a corrected parabolic approximation (CPA) involving the second range derivative of the parabolic field, numerically compare the results to a normal mode example, and show how the CPA reduces the error of the PA. The error reduction is most marked in the phase.
Experimental speakerphone system for teleconferencinga)
Authors: West J. E. , MacLean D. J. , Nelson J. R. , Flanagan J. L.
Published: October 2005

Travel to distant conferences consumes time, energy, and human resources. An alternative, should it prove an adequate replacement for face-to-face communication, is ’’teleconferencing.’’ While the necessary and desirable elements of conferencing by telephone are yet to be quantified, we describe a rudimentary experimental system which provides a communication versatility that belies its simplicity. We establish a dedicated 4-wire connection between distant conference rooms. We modify conventional speakerphones (Model 4A) by disconnecting the electronic hybrid to give separate transmit (microphone) and receive (loudspeaker) leads. We give each conferee an individual instrument. In a given conference room, we sum the signals from individual transmit leads and connect the results to the transmit path of the 4-wire circuit. Similarly, we distribute the receive path of the 4-wire connection to the individual receive leads. The voice operated attenuator (variolosser) and the noise-operated gain-adjusting device (NOGAD) in each individual speakerphone are left completely intact. Complementary connections are made in the other conference room. As a result of these features, the teleconferencing system is able to provide effective, interactive conferencing among large groups of users. Because of the distributed configuration of transmitters and receivers, it copes well with room reverberation and background noise.
Cross-spectral method of measuring acoustic intensity without error caused by instrument phase mismatch
Authors: Chung J. Y.
Published: October 2005

The theory of a new method of measuring acoustic intensity is presented. The method uses measurements of the cross spectrum of the pressures at two closely spaced microphones. To eliminate the measurement error due to instrument phase mismatch, a circuit switching procedure is used. The method is applicable to any acoustic field subject to the condition that the product of the wave number and the microphone spacing remains small. The method has been verified by laboratory experiment.
Experimental evaluation of the aeroacoustic characteristics of a source of pulsating gas flow
Authors: Kathuriya M. L. , Munjal M. L.
Published: October 2005

Among various methods, the transmission line or the impedance tube method has been most popular for the experimental evaluation of the acoustical impedance of a termination. The existing methods, including the ones reported earlier, by the authors require location of the sound pressure minima and/or maxima, or else make use of some iterative procedures. The present paper deals with a method of analysis of standing waves which does not depend on any of these involved procedures. It is applicable to the case of stationary as well as moving media. It enables on to evaluate the impedance of any passive black box, as well as the aeroacoustic characteristics of a source of pulsating gas flow, with the least experimental work and computation time and with the extra advantage of using a given impedance tube for wavelengths as large as four times its length. A method of external measurements, not involving use of any impedance tube, for evaluating the aeroacoustic characteristics of a source of pulsating gas flow is also dealt with, based on the definition of attenuation or insertion loss of a muffler.
Light column display of sound pressure levels
Authors: Dunlop J. I.
Published: October 2005

The design of a system for enabling large public display of sound pressure levels is described. The design uses a sound level meter as the detector and a rising light column, divided into ten 5 dB intervals, as the display.
High resolution cross-sensor beamforming for a billboard array
Authors: Bucker Homer P.
Published: October 2005

The cross-sensor field of an array consists of all products of the narrow-band quadrature signal measured at one sensor multiplied by the complex conjugate of the quadrature signal measured at a second sensor. Three algorithms which use the cross-sensor field to determine the level and direction of a set of acoustic waves incident on a billboard array are compared. These are correlation (conventional) beamforming, maximum likelihood estimation, and iterative decomposition.
Approximate methods to describe the reflections from cylinders and spheres with complex impedance
Authors: George Jacob , Überall H.
Published: October 2005

We have studied the scattering of plane waves from cylinders and spheres with complex impedance boundary conditions using the Kirchhoff method and the Luneburg–Kline method. A stationary phase approximation is made in the Kirchhoff derivation to eliminate spurious contributions from the boundary of the insonified region. Terms of order up to (ka)−2 are retained. Dependence of the cross section on the complex impedance, the incident wave frequency, as well as on the azimuthal angle is illustrated. The curves are found to obey several near symmetries. Further, the Luneburg–Kline method is found to lead to predictions which are often qualitatively different from those of the Kirchhoff method, and the former is observed to be more reliable. Convergence of the Luneburg–Kline terms is studied and is found to be quite satisfactory.
On errors in some papers on array processing
Authors: Hinich Melvin J.
Published: October 2005

Some errors in the literature are noted concerning the calculation of the maximum-likelihood estimator.
Forced torsional vibration of an elastic circular rod on an elastic half space and on an elastic stratum
Authors: Paul H. S. , Sridharan K.
Published: October 2005

The forced torsional vibration of an elastic circular rod, whose lower end is attached to the free surface of an elastic half space or stratum, while the upper end is subjected to a periodic torque is investigated. Expression for the driving point impedance is obtained for low-frequency oscillations using specific boundary conditions at the interface. Resonance curves are plotted which exhibit the damping of the vibrations of the rod due to dissipation of waves to infinity. It is found that damping increases as the length-to-radius ratio of the rod decreases. Damping also increases as the ratio of shear modulus of the support to the shear modulus of the rod decreases. If a stratum supports the rod, the damping is lesser when the lower face of the stratum is rigidly fixed than when it is free.
Automatic speech recognition using psychoacoustic models
Authors: Zwicker E. , Terhardt E. , Paulus E.
Published: October 2005

An approach to automatic speech recognition is described, which, in a straightforward way, follows the concept of (1) preprocessing in terms of auditory parameters and (2) subsequent classification and recognition. The preprocessing system has been realized in analog hardware, while recognition is carried out on a digital computer. In the preprocessing system, the essential psychoacoustic principles of the perception of loudness, pitch, roughness, and subjective duration are implemented with some approximation. The system essentially consists of 24 bandpass filters, nonlinear transformation of each filter output into specific loudness and specific roughness, and final transformation of these parameters into total loudness, total roughness, and three spectral momenta. As a means to further reduce the information flow, continuous selection of dominant parameters is also considered on the basis of psychoacoustic data. The subsequent recognition process is mainly characterized by (1) discrimination between speech and silent periods, (2) detection of syllable peaks and classification of syllable nuclei, and (3) assumption of syllable boundaries and classification of consonant clusters. Though the entire system as yet is far from being complete and perfect, the present results indicate that the concept provides a systematic and promising way towards automatic recognition of continuous speech.