bluuebunny/crossref_metadata_2025 huggingface dataset:
Observations of the effects of atmospheric turbulence on low- frequency sound propagation
Authors: Chessell C. I.
Published: October 2005

The propagation of low-frequency acoustic waves in the lower atmosphere is studied using observations of explosive sound sources at ranges of 4.3 and 9.3 km. By observing groups of 30 firings spaced closely in time, the effects of atmospheric turbulence on the propagation are determined; the differences in arrival time between microphone pairs in an approximately 1-km array being the experimental parameter measured. The time difference distributions are found to be Gaussian with standard deviations which show a strong diurnal variation, the increased effect of atmospheric turbulence being evident in mid-day observations. Propagation over nearby paths is shown to be spatially correlated out to separations of several hundred meters and this correlation is shown to be in agreement with the theoretical predictions of Chernov [Wave Propagation in a Random Medium, L. A. Chernov (McGraw–Hill, New York, 1960)]. Using these theoretical relations, atmospheric scale sizes in the range from 200 to 500 m (mean 320 m) are obtained together with acoustic velocity fluctuations with standard deviations in the range from 0.5 to 1.2 m/sec (mean 0.8 m/sec).

Subject Classification: [43]28.40, [43]28.60.
Study of wave motions in fluid-saturated porous rocks
Authors: Yew C. H. , Jogi P. N.
Published: October 2005

In this investigation, Biot’s theory was employed in the study of wave motions in fluid-saturated porous rocks. Consistent with the described experimental arrangement, Biot’s equations were solved using a Laplace transformation. The theory predicts two dilatational waves: a slightly dispersed fast wave propagating ahead of a heavily dispersed and attenuated slow wave. By comparing these results with experimental results, it becomes evident that the measured waves are in fact the fast waves.

Subject Classification: [43]20.15, [43]20.40.
Measurement from the optical nearfield of an ultrasonically produced phase grating
Authors: Cook Bill D.
Published: October 2005

A simplified expression is derived for the optical irradiance in the nearfield of a sinusoidal phase grating. Application of this expression to an ultrasonically produced optical phase grating permits the interpretation of experimental data for the magnitude of retardation and relative position of the grating. From these parameters, it is possible to evaluate the acoustic pressure distribution, total acoustic power, and sound velocity of a progressive ultrasonic beam.

Subject Classification: [43]35.65.
Relationship between acoustic reflection and vibrational modes of elastic spheres
Authors: Vogt Richard H. , Neubauer Werner G.
Published: October 2005

The behavior of the solution to acoustic backscattering by elastic spheres in water expressed as a form function vs ka, relative to the normal modes of vibration of solid homogeneous elastic spheres is examined. Specific free modes of vibration are identified with significant changes in form function. The solution for spheres of tungsten carbide, aluminum, and brass are considered for values of ka as high as 28. Minima in the form function usually occur at or near frequencies at which sphere resonances occur. Form functions are examined which are computed from mixing rigid and elastic terms in the waveharmonic series. In this way it is possible to see the effect of an isolated mode of vibration on the form function that describes the backscattering. Calculated resonance widths as well as observed pulse decay times allow determination of analytical and experimental Q’s of isolated resonances.

Subject Classification: [43]20.30, [43]20.60, [43]20.50; [43]40.20.
Production of cochlear potentials by inner and outer hair cells
Authors: Dallos Peter , Cheatham Mary Ann
Published: October 2005

Cochlear microphonic and summating potential recordings were obtained from preparations where only either inner hair cells (first-turn recording) or outer hair cells (fourth-turn recording) could have contributed to the potentials. A comparison suggests that outer hair cells do produce the preponderance of receptor potentials.

Subject Classification: [43]65.40, [43]65.42.
Gap detection: Two-channel detection of the missing event
Authors: Gilliom J. D. , Mills W. M.
Published: October 2005

The ability to detect gaps in continuous sinusoids was studied in both single- and two-channel tasks. From single-channel tasks, psychometric functions were obtained. Pulse and gap functions were found to be essentially parallel, with gap detection being 3–4 dB poorer than pulse detection. In two-channel tasks, two-channel detection of gap signal events produced a lower level of performance than two-channel detection of pulse signal events. However, in an unusual condition where a gap stimulus produced what sounded like a pulse to the observer, performance in two-channel gap detection and two-channel pulse detection was quite similar. This latter result suggests (1) gap stimuli enter the system as efficiently as pulse stimuli, and (2) it is the system’s inferior ability to process perceptual gaps which leads to the lower performance normally observed in two-channel gap detection. In a fourth two-channel task which required the observer to detect gap stimuli in one channel and pulse stimuli in the other, no detrimental effect on performance could be detected—a result illustrating the flexibility of the two-channel processing mechanism. Implications of the results for the INR model of two-channel processing are discussed.

Subject Classification: [43]65.75, [43]65.58, [43]65.68.
Masking period patterns of harmonic complex tones
Authors: Zwicker E.
Published: October 2005

Masking period patterns, i.e., the SPL of just audible triggered sequences of short high-frequency test tone bursts as a function of their temporal spacing throughout the period of a masker, were measured using the following maskers: low-frequency two-tone and three-tone complexes, Gaussian-shaped impluses and differentiated Gaussian impulses with both condensation and rarefaction peaks. The similarity between masking period patterns and neurophysiologically measured period histograms was confirmed with respect to the temporal structure. However, distinct differences appear in the amplitude structure of both patterns, indicating a strong nonlinearity involved in the transformation of the masker’s time function into the masking period pattern. Starting a few decibels above threshold in quiet, the peaks of the patterns are elevated by 10 dB for each 5-dB increment of masker level. This fact points towards a square law for high-frequency test signals and low-frequency maskers. The steepness of slope of the masking period pattern seems to reach a maximal value of 10 dB/msec. Relations between neurophysiological period histograms and corresponding masking period patterns as well as differences between the patterns produced by condensation and rarefaction peak maskers, respectively, are discussed.

Subject Classification: [43]65.58, [43]65.35, [43]65.68.
Acoustic propagation in shallow water overlying a consolidated bottom
Authors: Ingenito Frank , Wolf Stephen N.
Published: October 2005

An experiment designed to measure normal mode amplitude functions and attenuation coefficients was conducted in shallow water on Campeche Bank off the Yucatan Peninsula. Measurements were made at two locations on the bank in water of about 30 m in depth over a bottom consisting of consolidated limestone having a measured and sound velocity of 1900 m/sec. Pulsed cw signals with frequencies of 400, 750, and 1500 Hz were used. Theoretical calculations of the mode amplitude functions using a fluid model of the bottom were found to agree well with the measurements. In order to reconcile the measured mode attenuation coefficients with theory, it was necessary to assume that the shear velocity of the bottom was 1000 m/sec. The latter is lower than the minimum sound velocity in the water column so that the generation of propagating shear waves in the bottom was the dominant attenuation mechanism. Significant differences in the measured mode attenuation coefficients at the two stations were explained by the deepening of the low velocity channel at the bottom of the water column.

Subject Classification: [43]30.20, [43]30.50.
Acoustic spectral analysis of three tornadoes
Authors: Arnold Roy T. , Bass Henry E. , Bolen Lee N.
Published: October 2005

Three sound recordings of tornadoes have been spectrally analyzed over the frequency interval between 100 and 2000 Hz. The low-frequency analysis was limited by the response of the microphones used for the recordings; the upper frequency limit was imposed both the microphone response and the low-signal level. One recording was made by James Cramer of a tornado which passed through Clay Center, Kansas on 25 September 1973. A second recording was made by Richard Allen Lindley of a tornado that passed through Guin, Alabama on 3 April 1974, and a third recording was made by Tom Bittman of a tornado which damaged his home in Tulsa, Oklahoma on 8 June 1974. All of the recordings are of low quality and the audio information required major spectral corrections, but the data analysis does indicate that the audio emissions from the tornadoes decrease in intensity as a function of increasing frequency. An attempt has been made to correlate the data with real (and conjectured) physical characteristics of the tornadoes and attendent atmospheric phenomena. It is clear to us from an objective analysis (and the more difficult subjective evaluation of the recordings) that identification of tornadoes based on acoustic emissions is possible . A study of tornadic sounds can not only provide a new tool for gaining insight into electrical and mechanical disturbances within a tornadic storm, but will also allow acoustic detection of a tornadic storm. A study of the change in intensity of the sounds emitted by the approaching Guin storm at both high and low frequencies suggests that noises generated by the high-speed winds of the principal tornado vortex as its base scoured the ground might be discerned from noises generated by the winds of one or more smaller vortices moving around the tornado, and/or electrical discharges aloft.

Subject Classification: [43]28.45, [43]28.65.
Light-scattering heterodyne interferometer for vibration measurements in auditory organs
Authors: Dragsten P. R. , Webb W. W. , Paton J. A. , Capranica R. R.
Published: October 2005

An interferometric optical heterodyne technique has been developed especially for vibrational amplitude and phase measurements on auditory organs of live animals. Laser light diffusely scattered from the vibrating structure is used for the measurement. Continuous calibration and feedback compensation systems were developed to cope with the problems of drift in interferometer alignment and small background movements. Vibrational amplitudes from below 0.1 Å to above 400 Å have been detected on the posterior tympanic membranes of live crickets.

Subject Classification: [43]65.20; [43]40.60; [43]35.65.
Binaural time discrimination
Authors: Nordmark Jan O.
Published: October 2005

The least discriminable change in the position of a sound image was measured for pure tone with and without initial interaural delay, as well as for complex tones. The signals were either perfectly regular or jittered. The introduction of jitter allowed the subjects to lateralize equal-amplitude tones beyond 1500 Hz, which has been assumed to represent the limit for binaural phase discrimination. No frequency limit for jittered tones either in a fixed relationship or as binaural beats could be found. The smallest deviation from regularity employed was 0.2 μsec, and under certain conditions it was effective in producing lateralization. With no jitter in one ear, jitter in the other ear was ineffective. For a given high-frequency jittered tone, discrimination improves up to a limit with level and jitter magnitude. Complex tones, jittered and unjittered, show smaller just-noticeable differences for low and medium frequencies. Some other implications of these findings are discussed. A striking similarity between the curves for binaural time discrimination and those for pitch discrimination was found.

Subject Classification: [43]65.68, [43]65.62, [43]65.60.
Rayleigh wave velocity for a stress-induced slightly anisotropic solid
Authors: Gerhart G. R.
Published: October 2005

The Rayleigh wave velocity on an otherwise isotropic-free surface is changed by the application of a static stress. A technique is described for calculating these changes as a function of the third-order elastic constants and the static stress configuration. Conversely, these velocity changes can be used to measure the third-order elastic constants. These corrections in the velocity appear as additional terms to the isotropic Rayleigh equation. Three independent Rayleigh velocity measurements are sufficient to determine the third-order elastic tensor for an isotropic solid. Experimental data is provided to validate the calculated results.

Subject Classification: [43]35.26; [43]20.35; [43]35.54.
Ultrasonic propagation properties of mammalian testes
Authors: Brady J. K. , Goss S. A. , Johnston R. L. , O’Brien W. D. , Dunn F.
Published: October 2005

The ultrasonic absorption and reflection properties of sexually mature, freshly excised mouse, rabbit, cat, and dog testes have been investigated at 37°C in the frequency range 0.5–7MHz by the transient thermoelectric absorption, the pulse–reflection, and the pulse–transmission methods. The absorption coefficient is found to exhibit values considerably less than those of other parenchymal tissues and to possess a frequency dependence mimicking a simple relaxation process of characteristic frequency approximately 0.9 MHz.

Subject Classification: [43]80.20.
Reevaluation of Wilson’s sound-speed measurements for pure water
Authors: Chen Chen-Tung , Millero Frank J.
Published: October 2005

The pure-water high-pressure sound-speed data of Wilson have been analyzed, and it is concluded that all Wilson’s values should be shifted by the apparent error of his 1-atm values. A new equation has been determined to represent the shifted pressure data of Wilson, as well as the best 1-atm data of Del Grosso and Mader.

Subject Classification: [43]30.25.
Abnormal attenuation in Chesapeake Bay waters
Authors: Turner William R.
Published: October 2005

During a 1957 field study at the Chesapeake Bay, abnormal attenuation was detected in 18% of the 1.0-MHz data, 22% of the 2.0-MHz data, and 45% of the 3.0- and 5.0-MHz data. This ranged from 0.4 to 7.4 dB/m above the attenuation of fresh water. The interpretation of the data was facilitated by stable water conditions and the strong location orientation of results which permitted a separation of variables. The added attenuation appears to arise wholly from the presence of microbubbles which enter principally from atmospheric aerosols. The absence of abnormal attenuation in regions that receive significant drainage from residential and industrial areas is attributed to trace chemicals that modify of manner the microbubble stabilization. In regions of heavy ship traffic, on the other hand, wake bubbles may transport these trace chemicals to the surface, leaving a residue of smaller microbubbles that produce a high level of excess attenuation.

Subject Classification: [43]30.20.
Note on a general relation between diffraction and radiation problems in acoustics
Authors: Mei C. C.
Published: October 2005

A general relation between the farfield amplitudes of the diffraction and the radiation problems by a rigid body is deduced.
Investigation of procedures for estimation of sound power in the free field above a reflecting plane
Authors: Holmer Curtis I.
Published: October 2005

This paper presents results from an experimental investigation of the accuracy and precision of various measurement procedures for determing sound-power output of ’’large’’ machines in the free field over a reflecting plane out of doors. The purpose of the investigation was to place error bounds on several proposed nearfield measurement procedures, chiefly through the comparison of such properties with sound power levels determined from farfield measurements. The sources used in the study included 17 portable air compressors of various types and sizes powered by internal combustion engines. The data analysis centers on the comparison of sound power levels estimated from measured sound pressure levels on two measurement surfaces, one at 7-m radius (farfield) and a second at 1 m from the surface of the machine (nearfield). Empirical estimates of precision and accuracy are derived for each of several proposed ISO procedures for determination of sound power level. The nearfield measurements were found to produce an overestimate of the farfield power level with the magnitude of the overestimate depending on the measurement surface shape. A measurement surface shape which ’’conformed’’ to the shape of the source was found to have the smallest associated overestimate. Microphone directivity was found to lead an underestimate of sound power level.
Reproduction of familiar melodies and the perception of tonal sequences
Authors: Davies J. B. , Jennings J.
Published: October 2005

Experimental studies of memory for tonal sequences have been extended to include well-known melodies and long-term memory. W. J. Dowling and D. S. Fujitani [J. Acoust. Soc. Am. 49, 524–531 (1971)] used real melodies in an investigation of interval (magnitude of pitch changes) and contour (direction of pitch changes). The study used the recognition paradigm, one of its advantages being that it enables subjects who have no skill in music production to carry out the tasks. However, it may be that the recognition paradigm is more useful for investigating stimulus variables rather than subject variables. The present study used a sample of professional classical musicians and a selected nonmusicians group. Both groups used an original production method to represent melodies and tonal sequences. The performance of the two groups was compared under conditions of dictation and production, using a contour task and a magnitude-estimation task. Although the musicians were generally superior, there was little difference between musicians and nonmusicians in terms of perception of melodic contour. However, both groups performed at a much lower level when estimating interval magnitudes, suggesting that the size of pitch intervals is not normally coded in terms of magnitude. This finding is discussed in the light of Dowling and Fujitani’s interpretation; and an alternative ’’matching’’ model is proposed.
Perception of one-third octave-band filtered speech
Authors: Chari N. C. A. , Herman George , Danhauer Jeffrey L.
Published: October 2005

Intelligibility, redundancy (frequency domain), and phoneme confusions of speech were investigated through narrow-band filtering. Filtered syllables (CV) and words (CVC) were presented to twelve paid, normally hearing subjects. Stimuli consisted of 17 English consonants paired with three vowels /i, u, a/, and filtered through five conventional one-third octave bands centered at 0.5, 1, 2, 3.15, and 4 kHz, and one ’’critical’’ band (500 Hz wide) centered at 3.15 kHz. Results revealed (1) no significant differences between syllable and word intelligibility; (2) word or syllable intelligibility was maximum (50%) for the band centered at 2 kHz, and was greater for the bands above 2 kHz compared to those situated below this frequency; (3) speech intelligibility was reduced for the critical band compared to the one-third octave band centered at 3.15 kHz; (4) about half of the syllables or words were perceived correctly in more than one band reflecting redundant perceptual cues along the frequency domain; and (5) consonantal-confusion data revealed that manner and voicing features were least affected, and the place feature was most affected by filtering.
Cylindrically symmetric coherence formulation for the ocean
Authors: McCoy J. J. , Beran M. J.
Published: October 2005

In a number of papers, equations have been derived which govern acoustic propagation in the ocean from an initial plane surface. In this paper we present the governing equation in cylindrical coordinates and then give the simplification introduced by cylindrical symmetry. The loss of coherence along a horizontal direction is then treated in three special cases.
Model for parametric acoustic sources
Authors: Moffett Mark B. , Mellen Robert H.
Published: October 2005

A theoretical model for the difference-frequency radiation from a parametric acoustic array is developed. The (two-frequency) primary wave is assumed to be radiated by a piston source and may be effectively limited in either the nearfield or the farfield of the piston. Either small-signal absorption or saturation of the primary beam may serve as the limiting mechanism. The parametric gain is defined as a complex number whose (i) magnitude is the ratio of secondary and primary source pressures and (ii) phase is an indication of how much generation occurs within the nearfield and how much within the farfield of the primary beam. The parametric gain is evaluated as a function of the primary-to-secondary frequency (downshift) ratio, the amount of small-signal primary absorption within the nearfield, and a ’’scaled’’ primary source level. Then, the parametric gain may be used to determine the beam pattern characteristics via a simple closed-form expression. The theoretical results are found to be in good agreement with other theoretical treatments (within their realms of applicability) and in fair agreement with experimental results from various types of parametric sources. The discrepancies that do exist appear to stem from the approximation that the primary nearfield can be treated as a plane wave.
Optimal design and evaluation criteria for acoustic emission pulse signature analysis
Authors: Houghton J. R. , Townsend M. A. , Packman P. F.
Published: October 2005

Design of pulse-recording systems and evaluation criteria (method of analyzing the pulse signature) are investigated with the objective of defining optimal approaches to pulse signal analysis. A representative situation which this paper addresses is the modeling of acoustic emission (AE) pulse analysis as a nondestructive means of failure detection in which pulse density counting is presently the most common evaluative criterion. The instrumentation is modeled and selected analytical pulses are passed through the system. Two alternatives are considered here: frequency spectrum analysis, and time domain reconstruction of the pulse or pulse train (deconvolution). The pulse recording/analysis problem is modeled, and the various analysis techniques are considered. Within practical constraint optimal system designs are defined. It is shown that deconvolution of a pulse is a superior approach for transient pulse analysis. Reshaping of a transducer output back of the original input pulse is possible and gives an accurate representation of the generating pulse in the time domain. Frequency spectrum analysis methods and AE measurement systems have potential for segregation of different pulse shapes. Using deconvolution, in principle any definable transducer and filter system can be used to reconstruct pulse characteristics, i.e., to generate time domain signature. A number of major conclusions about the selection of design variables are made for general usage. In addition there are families of optimal selections for transducer and filter system parameters which give superior deconvoluted output signals. These may be significant when working with actual hardware and unknown characteristics. The optimal design results are new and possibly different from the expectations of engineers accustomed to working in the field of signal conditioning. In obtaining these results modern rational design techniques on a rather complex design problem are demonstrated.
Nearfield beam patterns of end-fire line arrays with arbitrary shading
Authors: Mellen R. H.
Published: October 2005

The contour numerical integration method can be used to calculate nearfield beam patterns of continuous end-fire line arrays with arbitrary amplitude shading. Other applications include parametric virtual arrays and scattering.
Hearing distribution in a population that has suffered hearing loss
Authors: Thiessen G. J.
Published: October 2005

The assumption that a person’s hearing cannot be improved by aging, noise exposure, or any other otologically pathogenic agent, has the logical consequence that an initially normal distribution of hearing in a given population cannot remain so after the action of the pathogenic agent. The distribution must become skewed. Extrapolations that are often made assuming normal distribution may be practical approximations but they have no logical foundation.
Determination of monaural sensitivity changes due to the pinna by use of minimum-audible-field measurements in the lateral vertical plane
Authors: Bloom P. Jeffrey
Published: October 2005

Monaural minimum-audible-field (MAF) measurements were taken for five subjects at seven angles of source elevation, φ  (−60°?φ?+60°), in the lateral vertical plane containing the interaural axis. These measurements were made by automated ’’method of limits’’ threshold determinations, using narrow-band random noise (center frequencies from 4 to 16 kHz), emitted from a special ’’point’’ source. A method was devised for extracting from the MAF data, functions which display the elevation-dependent changes in sensitivity, primarily caused by the pinna. Most of these derived functions contain a narrow response dip, whose minimum increases in frequency from ∠6.5 kHz monotonically to ∠14 kHz, with increasing source elevation. For corresponding elevations there are many intersubject similarities in these derived response functions and also strong agreement with known data regarding the pinna’s acoustic response. The percept of source elevation is hypothesized to be based upon the detection of the relative absence of specific high-frequency spectral- energy content related to minima in the pinna’s response functions.
Digital processing of Doppler sonar signals
Authors: Wang H. S. C.
Published: October 2005

The signal processing gain by digital beamforming in Doppler sonar was investigated in terms of the enhancement of signal-to-reverberation ratio (SRR) at the postbeamforming Doppler-filter output with an objective to determine the minimum number of bits necessary for the quantization of beamformer channel input signals without appreciable degradation of sonar performance. The formulation of the problem follows closely the author’s earlier work which extends Davenport’s analysis of bandpass limiter to the more general multichannel multibit signal processors. Owing to the Doppler shift of target signal frequency and the relatively narrow bandwidth of Doppler filters, we express the frequency selective effect in the nonlinear interacting power series in terms of a new set of coefficients cmk, which bear crucial significance in sonar performance. Extensive numerical calculations of ’’Doppler processing gain’’ were carried out to demonstrate that four-bit quantization of array transducer signals is theoretically sufficient to yield a performance essentially identical to that of a linear beamformer, but severe loss of gain could result if fewer than four bits are taken at the quantizer output. It is further demonstrated numerically and substantiated analytically that, for small input SRR, the processing gain of a digital beamformer with Doppler filters cannot exceed that of a linear (or optimized four-bit digital) beamformer even it its channel signals are quantized into more than four bits.
Comments on ’’Wave propagation in a viscoelastic rod with temperature-dependent properties’’ [E. C. Ting, J. Acoust. Soc. Am. 58, 1018–1022 (1975)]
Authors: Rao Y. Vasudeva , Rao K. Bhaskara
Published: October 2005

Ting’s solution for the problem of ways propagation in a viscoelastic rod with temperature-dependent properties is shown to be obtainable due to a more straightforward method due to Keller and Keller.
Measurement of surface acoustic impedances at oblique angles of incidence and ultrasonic frequencies
Authors: Jones H. W. , Stredulinsky D. C.
Published: October 2005

This letter describes an apparatus for measuring the acoustic impedance of materials at grazing angles over a frequency range of 10–160 kHz.
Torsional vibrations of a sapphire rod: A numerical description
Authors: Wilson Lynn O. , Gatto Mary Ann
Published: October 2005

A numerical description of the lowest-order torsional mode of vibration of a c-axis sapphire rod is obtained from two approximate theories. One theory involves an infinite series perturbation expansion about an expression which describes modes along a thransversly isottropic rod. The other theory involves a low-frequency asymptotic expansion for the lowest-order torsional mode of spphire. At frequencies for despersive; its phase and group velocities are obtained. The mode can be visualized as consisting of towq waves which travel down the rod π/2 rad out of phase. In one wave, each cross section rotates rigidly ints cross section undergoes a transverse distortion. Both the warping and the transverse distortion have a threefold symmetry about the rod axis.
Correlations of duration for nonadjacent segments in speech: Aspects of grammatical coding
Authors: Cooper William E. , Sorensen John M. , Paccia Jeanne M.
Published: October 2005

Two speakers read versions of the following sentence: Dick will take the jeep x Clark will take the truck, in which x was one of the conjunctions and, but, since, or if. Each sentence was read 40 times. Product-moment correlations were computed for segment durations in all word pairs involving Dick, take1, jeep, Clark, take2, and truck. Statistically significant correlations were obtained for both speakers, particularly for the sentence containing the coordinate conjunction and. The results showed positive correlations for words having the same grammatical relation (subjects, verbs, direct objects) lying on opposite sides of the major clause boundary. Positive correlations were also obtained for the two contrastively stressed words in the second clause (Clark, truck). Negative correlations were obtained primarily between noncontrastive words within each clause. The results suggest that a speaker’s grammatical code plays a role in regulating speech timing and that this influence is not restricted to the domain of a single clause.
Resilient mounting of machinery on platelike and modified platelike substructures
Authors: Snowdon J. C.
Published: October 2005

The problem of isolating machinery vibration from platelike substructures is analyzed. Simply supported, internally damped, square, rectangular, and circular plates are considered, as are rectangular plates with rigid cross members that divide the plates into separate quadrants. The machinery is supported either by eight or by four antivibration mounts located symmetrically about the plate centers. The attachment of dynamic vibration absorbers or lumped masses to the plates at each mount location is shown to be effective in reducing the force transmitted to the plate boundaries. The dynamic absorbers are tuned to suppress transmissibility at the fundamental resonance of the plate of concern, whereas the lumped masses become effective at frequencies above this resonance where their impedance predominates that of the plate. Utilization of the circular and quadrant plates greatly reduces the number of plate resonances that contribute to the force transmitted to the plate boundaries. Further, when machinery is supported by four antivibration mounts on square and rectangular plates, the number of resonances that are excited can also be reduced significantly if the mount locations are chosen judiciously. However, the use of other mount locations can yield a large number of pronounced resonances in excess of those excited when the machinery is supported by various arrangements of eight antivibration mounts—for which transmissibility does not appear to change greatly with the choice of mount location.
Experimental determination of acoustic properties using a two-microphone random-excitation technique
Authors: Seybert A. F. , Ross D. F.
Published: October 2005

An experimental technique is presented for the determination of normal acoustic properties in a tube, including the effect of mean flow. An acoustic source is driven by Gaussian white noise to produce a randomly fluctuating sound field in a tube terminated by the system under investigation. Two stationary, wall-mounted microphones measure the sound pressure at arbitrary but known positions in the tube. Theory is developed, including the effect of mean flow, showing that the incident- and reflected-wave spectra, and the phase angle between the incident and reflected waves, can be determined from measurement of the auto- and cross-spectra of the two microphone signals. Expressions for the normal specific acoustic impedance and the reflection coefficient of the tube termination are developed for a random sound field in the tube. Three no-flow test cases are evaluated using the two-microphone random-excitation technique: a closed tube of specified length, an open, unbaffled tube of specified length, and a prototype automotive muffler. Comparison is made between results using the present method and approximate theory and results from the traditional standing-wave method. In all cases agreement between the two-microphone random-excitation method and comparison data is excellent. The two-microphone random-excitation technique can be used to evaluate acoustic properties very rapidly since no traversing is necessary and since random excitation is used (in each of three test cases only 7 sec of continuous data was needed). In addition, the bandwidth may be made arbitrarily small, within limits, so that the computed properties will have a high degree of frequency resolution.
Additional characteristics of synthetic-aperture sonar systems and a further comparison with nonsynthetic-aperture sonar systems
Authors: Cutrona Louis J.
Published: October 2005

In a previous paper some performance characteristics achievable using sythetic-aperture sonars were compared with those achievable using more conventional techniques. In this paper additional characteristics of both types of sonars are derived and compared especially with respect to average power, number of beams required, and area-coverage rate achievable as the resolution and sonar speed are varied. As in the previous paper identical specifications and geometries are imposed upon the two system types in making the comparison. The only system parameters which may need to be different are frequency and horizontal aperture length. These then lead to different values for average power required to achieve the desired signal-to-noise ratio.
Optimization of acoustic receiver noise performance
Authors: Young J. W.
Published: October 2005

The reduction of signal-to-noise ratio due to hydrophone and preamplifier noise is a critical problem in the design of acoustic receiving systems. A signal-to-noise degradation factor is defined which depends upon figure of merit of the hydrophone, the amplifier noise figure, and the ambient noise spectrum. For piezoelectric hydrophones, the figure of merit is determined by fundamental material parameters and the volume of active material. Both voltage and charge amplifier configurations are considered. The charge amplifier is found to be inherently noisier.
Estimation of time delay in the presence of source or receiver motion
Authors: Knapp Charles H. , Carter G. Clifford
Published: October 2005

Signals, received at two (or more) locations, and originating from a remote acoustic point source, exhibit time delay(s) that are useful for estimating source location or receiver geometries. Consequently, numerous procedures have been proposed for passive time-delay estimation in such cases. Past investigations apply, however, only when source and receiver motion is negligible. This paper extends previous results for maximum-likelihood (ML) estimation of time delay to the situation where the source, or the receivers, or both are in motion. It is shown that in the simplest case with two receivers, one of the signals must be appropriately time scaled prior to computing a generalized cross correlation of the received signals.
Identification of speech sounds displayed on a vibrotactile vocoder
Authors: Yeni-Komshian Grace H. , Goldstein Moise H.
Published: October 2005

A vocoder-type speech analyzer interfaced to the tactile display of an Optacon was used to investigate how subjects learned, over a six-week period, to identify the vibrotactile patterns of different speech signals. Closed sets of four vowel durations, three different vowels, and four spondee words constituted the test material. Learning to identify vibrotactile patterns required many hours of training. Subjects in this study showed significant improvement in the identification of all three types of speech signals, especially the vowel durations and spondee words. Tests for transfer at the end of training showed that shifting the locus of stimulation did not result in decrement in performance.
Postnatal development in the acoustic system of the house mouse in the light of developing masked thresholds
Authors: Ehret G̈unter
Published: October 2005

Postnatal development of masked auditory thresholds in the house mouse Mus musculus were behaviorally measured from the 10th to the 24th day. An unconditioned stop reflex and an unconditioned pinna reflex to tones were used for threshold determinations. Masked threshold levels first decrease from day 10 to day 12, then increase or remain constant until day 14, and finally decrease until day 16–18, where the adult levels are reached. The results are in agreement with anatomical and electrophysiological data in the literature. It was concluded that in the developing acoustical system of the mouse two effects superimpose: peripheral completion and central maturation. The data can be interpreted such that the peripheral development which lasts until day 14 dominates between the 12th and 14th postnatal day, whereas development in the central nervous system influences thresholds between day 10 and day 16–18. The widths of critical masking bands are assumed to be constant during development and determined by peripheral mechanisms.
Acoustic diffraction of a plane wave by a semicircular infinite soft strip
Authors: Lal Bansi , Jain D. L.
Published: October 2005

The subject of this paper is the problem of diffraction of a time-harmonic obliquely incident plane acoustic wave by a semicircular infinite soft strip. An integral-equation technique is presented to solve this two-dimensional boundary-value problem by the standard perturbation method when the wavelength of the incident wave is much larger than the radius of the semicircular strip. Approximate expressions are obtained for the farfield amplitude and scattering cross section.
Reply to ’’Comments on ’Influence of range-dependent environments on low-frequency volume attentuation measurements in the sea’ ’’ [J. Acoust. Soc. Am. 60, 772–778 (1977)]
Authors: Hanna J. S. , Rost P. V.
Published: October 2005

The authors’ reply to comments by D. G. Browning et al. [J. Acoust. Soc. Am. 60, 369–374 (1977)].
Acoustical scale model study of the attenuation of sound by wide barriers
Authors: Ivey Elizabeth S. , Russell G. A.
Published: October 2005

Acoustical scale model experiments carried out with building-size barriers are described. The results of experiments conducted with the barrier in a free field and on a reflecting surface are presented. The free-field measurements are compared to several theoretical models and discrepancies between the theoretical and experimental results are discussed. Also presented is a simple expression which relates the excess attentuation obtained with the barrier situated on the ground to that of the same barrier in the free field. This expression predicts excess attenuations which agree quite closely with those actually measured in the scale model experiments.
Acoustic reflection from cylinders—nonabsorbing and absorbing
Authors: Schuetz Luise S. , Neubauer Werner G.
Published: October 2005

The reflection of an acoustic plane wave by an elastic cylinder of infinite length, which may absorb energy, is calculated and measured. Computations of reflection by an infinitely long elastic cylinder as a function of frequency and angle, are compared with experimental data taken using finite cylinders immersed in water. Good agreement is obtained.
Concerning the influence of echo carrier frequencies and antenna dimensions on the performance of echosonde (acoustic-radar) antennas
Authors: Adekola S. Adeniyi
Published: October 2005

A study of the influence of echo carrier frequencies and antenna dimensions on the performance of acoustic-radar antennas is reported with features of practical interest. For a steady-state plane-wave propagation, appropriate expressions are given for the acoustic impedance, the homogeneous boundary conditions analogous to the electromagnetic type of problems, and the time-averaged acoustic energy. Diffraction pattern integral equations for echosonde antennas are evaluated in closed forms using the Zernike polynomials and the generalized-hypergeometric functions, and physical interpretations are given where appropriate. Accurate computer simulations can contribute toward: (1) Better understanding of acoustic remote sensing of atomspheric structure/properties and (2) time-saving/avoidance of hidden problems in field work. Antenna-pattern simulations are examined using modifications of antenna design which improve antenna-system performance. By proper choices of echo carrier frequencies and antenna dimensions, quasiuniform phase distributions pertinent to modest phase shifts of experimental measurements (in striking contrasts with rapidly changing phases of previous results), are obtained. Severe side lobes are major detriments in acoustic remote sensing. Results presented include computer simulations of an antenna employed in probing the marine atmosphere remotely from a moving ship during a cruise in the Pacific Ocean/Caribbean Sea, and simulations of an antenna employed over dry-land; ground-level side lobes versus echo carrier frequencies; and 3-dB beamwidth variations with echo carrier frequencies and with antenna dimensions. For 1–5-kHz carrier-frequency range, acceptable antenna dimensions are 1.22, 1.8, and 1.8 m for the illuminating- transmitting-aperture diameters, and height of the absorbing cuffs, respectively. Half-power beamwidths within 7°–13.5° are obtained in the 1–2-kHz frequency range; and selection of antenna flare angles between 15° and 18° tends to give optimum side-lobe attenuations. Comparisons between theory and measurements show overall good agreements. Maximum relative side-lobe rejections of about −56.5 dB (in good accordance with measurements) in the 20° region near the ground, are obtained at 2-kHz carrier frequency.
Ultrasonic attenuation of myocardial tissue: Dependence on time after excision and on temperature
Authors: O’Donnell M. , Mimbs J. W. , Sobel B. E. , Miller J. G.
Published: October 2005

The ultrasonic attenuation coefficient of myocardium over the frequency range 2–10 MHz has been measured in vitro as a function of time following excision and as a function of temperature. Results indicate that the attenuation coefficient was approximately independent of time for 4 h following excision at 19.5 °C, but increased by about 20% over a 4-h interval at 35 °C. The attenuation coefficient decreases approximately linearly with increasing temperature over the range 20.5 °–37 °C, with the value at 37 °C being about 20% lower than at 20.5 °C
Speed of sound in seawater at high pressures
Authors: Chen Chen-Tung , Millero Frank J.
Published: October 2005

The speed of sound in standard seawater (diluted with pure water and evaporated) have been measured relative to pure water with a Nusonics single-transducer sound velocimeter as a function of salinity (5–40°/00), temperature 0°–40°C, and applied pressure (0–1000 bars). The effect of pressure on the relative speeds of sound, (UP−UPH2O) -UO−UOH2O), have been fitted to an equation of the form (with a standard deviation of 0.19 msec−1) (UP−UPH2O) - (UO−UOH2O) =AS (°/oo)+BS (°/oo)3/2 +CS (°/oo)2, where U and UH20 are the speeds of sound in seawater and pure water, respectively; superscripts P and O are used to denote applied pressure P and O (1 atm); A, B, and C are temperature- and pressure-dependent parameters; S (o/oo) is the salinity in parts per thousand. This equation has been combined with the refitted high-pressure pure-water sound-speed equation of Wilson [Naval Ordnance Lab. Rep.(1959)], Chen and Millero [J. Acoust. Soc. Am. 60, 1270–1273 (1976)], and the 1-atm seawater sound-speed data of Millero and Kubinski [J. Acoust. Soc. Am. 57, 312–319 (1975)] to calculate the speeds of sound for seawater at various salinities, temperatures, and pressures. Our results agree with the work of Wilson on the average to 0.36 msec−1 over the range of 5 to 40o/oo salinity, 0° to 30°C, and 0 to 1000 bars. Over the oceanic range our results agree on the average with the work of Wilson to 0.3 msec−1 (maximum deviation 0.6 msec−1), and with the work of Del Grosso to 0.5 msec−1 (maximum deviation 0.9 msec−1). The better agreement of our results with those of Wilson may be fortuitous since our measurements were made relative to his pure-water data.
Processing of phonemes in speech: A spees–accuracy study
Authors: Remington Roger
Published: October 2005

The present study investigated the serial or parallel processing of phonemes within a syllable. Subjects were required to press a key, on cue, to indicate whether two successive, binaural CVC syllables were the same or different. The cue was a tone which occurred at varying times after the onset of the second CVC and often interrupted its presentation. Subjects’ accuracy as a function of time was compared for discriminations involving the first, second, and third phonemes. The results show that information about the phonemes within a CVC syllable is accruing simultaneously. The importance of these results for models of speech perception is discussed.
Linear feedback AGC with input-level-invariant response times
Authors: Moskowitz Jacob
Published: October 2005

An Automatic Gain Control system using linear feedback with loop dynamics independent of input level is described. It avoids the need for the logarithmic and exponential conversions of Ricker’s method by using two ’’complementary’’ feedback loops. Response of the system to input amplitude changes is calculated, and compared with that of conventional linear AGC. Experimental results are shown. This paper is in response to D. W. Ricker [’’Nonlinear feedback system for the normalization of active sonar returns,’’ J. Acoust. Soc. Am. 59, 389–396 (1976)] where he describes the utility of input-level-invariant time constants for AGC in sonar echo processing.
Signal-processing techniques in a computerized hearing aid test system
Authors: Feldman Stanley , Malecek Ray
Published: October 2005

General background is given to describe the factors leading up to the implementation of a computerized hearing aid test system in a production environment. The digital measurement methods for determination of the required acoustical components such as fundamental, rms, distortion, etc., in the presence of noise are discussed. The use of the concept of the average cycle for repetitive signals is described with its advantages in a Fourier type system. An algorithm for measuring rms for nonrepetitive signals that trades off resolution for memory size is described. Features and advantages of computerized testing of hearing aids are listed.