bluuebunny/crossref_metadata_2025 huggingface dataset:
Keyboards for pure music
Authors: Mycielski Jan
Published: October 2005

Let S45 be the set all rational numbers of the form m/n, where m and n are positive integers with mn?45. We define an instrument M with three keyboards I, II, and III. Keyboards I and II permit one to play all consonant chords for which there exists a value φ such that the ratio of φ to the frequency of each simple tone of the chord belongs to S45. Keyboard II is organized so that pressing the keys on some straight lines yields the consonant chords. Keyboard III controls the quality of tones. The purpose of M is not to perform the music of today, but, hopefully, to inspire a new kind of music.
Theory of resonant scattering from spherical cavities in elastic and viscoelastic media
Authors: Gaunaurd G. C. , Überall H.
Published: October 2005

Plane incident p-waves which propagate through continuous (possibly absorptive) media are scattered by a fluid-filled spherical cavity contained in it. Using an approach familiar in nuclear scattering theory but novel to acoustics and elastodynamics, it is possible to express the scattering amplitudes (or the partial waves contained in them) for the scattered p-and s-waves in a form which clearly exhibits their dependence on two interacting contributions, one being the broad background of an ideally soft cavity, and the other the superimposed narrow spikes due to resonances excited in the cavity fluid. The cavity appears as a perfectly soft obstacle to the incident waves at all frequencies except in the near vicinity of the cavity eigenfrequencies where there is wave penetration into the filler fluid. When this happens, the interference of this wave with the ’’potential scattering’’ of the background is seen to cause the fluctuating character of the amplitudes (or cross section). We have numerically computed these isolated contributions for a variety of material combinations. The isolated resonances are traced (as Regge pole trajectories) as they reappear at the higher frequencies in subsequent partial waves. Due to its application in the analysis of acoustic-coating performance we have further studied the case of air-filled cavities in lossy rubber. The following findings have emerged: (1) The resonances are comparatively narrow, (2) their locations are apparently independent of the amount of absorption present, (3) absorption only affects the background, (4) shear absorption F1 only affects the mode-converted amplitude fps, and (5) the dilatational absorption, controlled by the parameter F, only influences the nonmode converted amplitude fpp.
Numerical calculation of the intensity distribution in sound channels using coherence theory
Authors: Whitman Alan M. , Beran Mark J.
Published: October 2005

We have demonstrated that coherence theory can be applied to the practical computation problem of the propagation of a beam in an infinite half-space with stratified but arbitrarily varying speed of sound variations. The intensity distributions found in this manner are the same as those of an equivalent point source in regions removed from the caustics of the geometrical ray family, but the intensity formula is continuous everywhere in the field and may be used in the vicinity of caustics. The computer time and storage requirements are equivalent to those of a ray program.
Multitube turbojet noise-suppression studies using cross-correlation techniques
Authors: Regan Dennis R. , Meecham William C.
Published: October 2005

The noise-producing region of a suppressed turbojet exhaust is studied by cross-correlating static pressure fluctuations within the exhaust with farfield sound for Mach numbers up to Mj=0.99, using a 31-tube nozzle having an area ratio Ar=3.1. Measurements made with an unsuppressed turbojet exhaust having an equivalent exit area and operating under effectively equal thrust levels serve as the experimental control for this work. Static pressure-level measurements, made with a calibrated high-temperature acoustically damped probe tube, show that noise suppression by multitube nozzles results from reduced turbulence levels. The maximum fluctuating static-pressure level in the unsuppressed turbojet exhaust is typically 5–6 dB higher than static-pressure levels in the suppressed exhaust under conditions of effectively equal static thrust. This suggests that the turbulence intensity in the multitube suppressor flow is reduced in excess of 20% compared with the unsuppressed jet exhaust. Static pressure fluctuation spectrums in the suppressor flow are peaked at the eddy passage frequency and a double spectral peak is found in the region where the suppressor jets coalesce. Estimates of the eddy-scale-length to jet-diameter ratio made from measurements of local jet velocity and eddy passage frequency indicate that a reduction in eddy size occurs when neighboring suppressor tube flows are brought into close proximity to one another. Maximum normalized cross-correlation coefficients in the unsuppressed turbojet exhaust of approximately cPF?0.2 are found for Mj=0.99 at an angle of 30° from the jet axis. Normalized cross-correlation coefficients are significantly lower in the interior of the multitube suppressor flow. Measurements of the partially normalized cross-correlation function show that sound radiated from within the hot, high-speed suppressor flow is refracted by the flow from neighboring jets. This work demonstrates that the high-frequency sound radiated directly to the farfield by a multitube suppressor nozzle is primarily from the exterior tubes and that the overall suppression of noise can be attributed to a reduction in turbulence intensity.
Coherent ray tracing—measured and predicted shallow-water frequency spectrum
Authors: Wakeley J.
Published: October 2005

Experiments have been conducted by the Applied Research Laboratory, The Pennsylvania State University, to study the acoustic signals received from underwater explosive charges under various environmental conditions. This paper describes a computer simulation study incorporating a model of a pressure signature for an underwater explosive charge and ray-tracing techniques to predict the received energy spectrum in an environment where more than one acoustic path may exist between the source and the receiver. Measured and calculated one-third-octave received energy levels are compared for a standard Mk 83 SUS detonated at a depth of 18.3 m at a range of 18–128 km in water 35–79-m deep. The site of the experiment was approximately 64 km east–northeast of Daytona Beach, Florida. The model shows good agreement with the experimental data in the prediction of a low frequency rolloff and frequency window in the received signal energy spectrum that varies with range separation between source and receiver.
Signal-processing techniques for resolving individual pulses in a multipath signal
Authors: Ehrenberg J. E. , Ewart T. E. , Morris R. D.
Published: October 2005

A maximum-likelihood procedure for estimating the amplitudes and arrival times of individual pulses in a multipath signal is derived. Computer simulation results are presented that compare this procedure with the more traditional matched-filter and inverse-filter techniques. The maximum-likelihood technique is shown to be significantly more accurate than either the matched or inverse filter. A computer algorithm for implementing the maximum-likelihood estimation procedure is described.
Sparse array performance
Authors: Greene Charles R. , Wood Roger C.
Published: October 2005

In a linear array with equispaced elements, any elements not forming a unique pair spacing with at least one other element are redundant and may be eliminated to form a sparse array. The average power output of a sparse array can be made the same as for the full array by substituting self- and cross-power terms from the remaining elements. Such processing assures identical signal-to-noise gain and directivity (beam patterns) for the sparse and full arrays, but the output variability for any finite averaging time will generally be greater for the sparse array. Linear combinations of possible substitution terms for each missing term may be optimized for minimum output variance. This concept has been applied to both sparse and full arrays to develop an optimum processing technique that minimizes output variance. An analysis technique has been developed for evaluating the output variance of sparse arrays operating in sound fields with specified signal-to-noise ratio and noise fields with arbitrary portions of independent, isotropic, and directional interference. For example, in isotropic noise with a wave length 2.5 times the basic element spacing and a signal-to-noise ratio of 0.001, a five-element sparse array providing the same average output as a full, ten-element equispaced line array will have an output standard deviation 2.08 times the standard deviation of the full array. For a signal-to-noise ratio of 1.0, the factor is 1.09.
Effects of stimulus frequency on two-tone suppression: A comparison of physiological and psychophysical results
Authors: Abbas Paul J.
Published: October 2005

The effects of stimulus frequency on two-tone suppression were investigated in single auditory-nerve fibers of anesthetized cats and compared with human psychophysical data. In the physiological experiment, both average discharge rate and phase-locked activity were measured in response to one- and two-tone stimuli. The first component f1 produced an increase in rate above spontaneous activity when presented alone. The second tone f2 was always well below the fiber’s characteristic frequency and was held at a fixed sound pressure level appropriate to produce two-tone suppression. Responses were plotted as a function of stimulus level of the first tone both alone and in the presence of f2. For different values of f1 with f2 fixed, suppression was maximum with f1 near fiber CF. In the psychophysical experiment, similar stimulus parameters of f1 and f2 were used as the masker in a forward-masker paradigm. In this experiment the addition of the second masker tone at frequency f2 could produce less masking of the signal. When f1 was varied with f2 fixed, the relative decrease in masking, analogous to suppression, was greatest when f1was equal to the signal frequency.
Amplitude-modulated noise: The detection of modulation versus the detection of modulation rate
Authors: Patterson Roy D. , Johnson-Davies David , Milroy Robert
Published: October 2005

Modulation threshold, that is, the modulation depth required to discriminate a sample of amplitude-modulated (AM) noise from a sample of unmodulated noise, was measured as a function of modulation rate (16–320 Hz), modulator waveform (sine or square), and the bandwidth of the AM noise (0.5–8.0 kHz). Modulation threshold increases monotonically with modulation rate, sine-wave thresholds are greater than square-wave thresholds, and threshold rises as the bandwith of the AM stimulus decreases. These effects all support the use of some form of energy detection model to explain modulation threshold. The modulation thresholds were compared with pitch thresholds gathered under precisely the same conditions. Pitch threshold or, alternatively, rate threshold was taken to be the modulation depth required to decide which of two samples had the higher modulation rate; the rate difference was 20%—just over three semitones. In the region above about 70 Hz, rate threshold is essentially a constant multiple of modulation threshold, indicating that the primary constraint on rate threshold is the audibility of the modulation. Below 70 Hz, rate and modulation threshold diverge; it is argued that the limit on rate threshold in this region is probably the length of the correlation required to extract the periodicity.
Analysis of concentric-tube resonators having unpartitioned cavities
Authors: Sullivan Joseph W. , Crocker Malcolm J.
Published: October 2005

In muffler design, concentric-tube resonators are often used to provide high-frequency attentuation. These resonators are constructed by shaping a rigid shell around a length of perforated tube, forming an unpartitioned cavity. Often the entire length of tube is perforated. Because of the length of the assembly, it is not possible to use the simple Helmholtz resonator theory to predict the attentuation. Beginning with a one-dimensional control volume, a mathematical model was derived which accounted for mean flow in the tube and for the wave motion in the cavity and the coupling between cavity and tube via the impedance boundary of the perforate. For impedance in the linear regime, a closed-form solution for the resonator transmission loss was obtained. With this restriction and for the case of zero mean flow, excellent agreement was obtained with experimental results. Limited parametric studies suggest that the performance of this type resonator is quite sensitive to the porosity of the perforate, and that unusually large bandwidths of attenuation may be obtained for select geometries at zero or near-zero mean flow conditions. As mean flow is increased, however, the model suggest that such large bandwidths may not be attainable in practice.
Disturbance of sleep by noise
Authors: Thiessen G. J.
Published: October 2005

Young, middle-aged, and old subjects, 35 in all, were tested to determine the probability of disturbance of sleep, as judged by EEG records, by seven noises per night produced by a recording of a passing truck. There is roughly a linear relation with the A-weighted noise level. Young and old people have nearly the same response while middle-aged subjects are more sensitive by about 15 dB. This applies also to the probability of awaking. The probability of shifts in sleep to a shallower level does not appear to adapt in 24 successive nights with seven noises per night but the probability of waking drops to half value in about two weeks. Response increases with duration of the stimulus, at least over the limited range from fractions of a second to a minute.
Acoustic radiation due to a fluid loading discontinuity on an infinite membrane
Authors: Pierucci Mauro
Published: October 2005

Edge-mode radiation is determined for an infinite membrane with a discontinuous fluid loading condition. The upper half of the membrane is exposed to a heavy fluid which accounts for a fluid–structure interaction. The lower half of the membrane is exposed to very light fluid which imposes no fluid loading on the structure. A very soft compliant layer is attached to half of the membrane surface. The compliant layer lessens the local coupling between the fluid and the structure, thus creating the fluid loading discontinuity. The effect of this fluid loading discontinuity upon the radiated farfield is evaluated.
Effects of diffraction on stress pulse propagation
Authors: Layton M. R. , Carome E. F. , Hardy H. D. , Bucaro J. A.
Published: October 2005

Investigations have been made of the effect of diffraction on the propagation of acoustic impulses in water. Gaussian shape pressure pulses were obtained by applying 0.2-μs-wide voltage pulses to thick piezoelectric plates that act as piston sources. Acoustic probe techniques were used to examine in detail the resulting pressure profiles. These are strongly affected by diffraction phenomena, and because of the transient nature of the process, special care must be taken in interpreting the observed data. Comparisons between experimental and theoretical time and space pressure profiles are presented.
Intensity statistics for long-range acoustic propagation in the ocean
Authors: Frisk George V.
Published: October 2005

A statistical analysis of the intensity of acoustic signals received from three sources (9.8, 110, and 262 Hz) towed at long ranges (100–3000 km) in the ocean is presented. The experimental probability density functions for the linear intensity are tested against the following density functions using the Kolmogorov–Smironov test at the 5% significance level: exponential, Gamma, log-normal, and log-normal with a standard deviation of 5.57 dB. It is found that no single function adequately represents the experimental density functions at all three frequencies, and none of the functions is appropriate at 262 Hz. At 9.8 Hz, three distributions (Gamma, log-normal, and log-normal with a 5.57 dB sigma) give excellent results. At 110 Hz, only the log-normal (with 5.57 dB sigma) theory yields good results. The ability of all the functions to describe the experimental results decreases with increasing frequency.
Binaural summation of the loudness of pure tones
Authors: Marks Lawrence E.
Published: October 2005

Subjects made magnitude estimations of the loudness of pure tones (100, 400, and 1000 Hz), which were presented at equal and unequal sound pressure levels to the two ears. The results were consistent with a model of linear binaural loudness summation: The estimates of loudness approximated the linear sum of the loudness estimates of the individual left-ear and right-ear components. The relation between loudness and sound pressure, over moderate SPLs, can be described by a power function with an exponent of about 0.6 at 400 and 1000 Hz, 0.75 at 100 Hz.
Suppression and critical bands in band-limiting experiments
Authors: Weber Daniel L.
Published: October 2005

Band-limiting experiments were performed at three noise spectrum levels (N0=25, 40, and 55 dB SPL) for forward, simultaneous, and backward masking. Threshold for a 2-kHz sinusoid decreased for masker bandwidths greater than a ’’critical bandwidth’’ in nonsimultaneous masking. These results are evidence for a suppression effect not observed in simultaneous masking; however, a qualitative model of suppression can account for the results in all three types of masking. In addition, the data for simultaneous masking support Fletcher’s [Rev. Mod. Phys. 12, 47–61 (1940)] rectangular filter interpretation of the band-limiting experiment and are well described by a level-dependent critical band.
Nationwide urban noise survey
Authors: Fidell Sanford
Published: October 2005

Most current knowledge about community response to noise exposure is derived from studies of high-level transportation sources. A nationwide urban noise survey was undertaken to study effects associated with more moderate but far more common sorts of noise exposure. Over 2000 respondents at 24 sites in seven cities of varying noise exposure and population density were interviewed by telephone and in person about their reactions to everyday noises. A brief but comprehensive structured questionnaire was based on direct questioning about annoyance and related effects. Among the major findings of the survey were widespread annoyance and speech interference from exposure to urban noise and strong relationships between the extent of annoyance and exposure level, speech interference, and population density.
Betti’s identity and transition matrix for elastic waves
Authors: Pao Yih-Hsing
Published: October 2005

A transition matrix relating the coefficients of scattered waves to those of incident waves in elastic solids is derived by applying Betti’s third identity and orthogonality conditions for a set of basis functions. The transition matrix for a fluid inclusion, a cavity, a rigid inset, or a solid inclusion in a fluid can all be derived from the general result for an elastic inclusion of arbitrary shape by taking proper limiting values of the general result. This limiting process is illustrated for the case of a spherical inclusion.
Acoustic propagation in a rough-walled waveguide containing a medium whose index of refraction fluctuates randomly from point to point
Authors: Sutton G. R.
Published: October 2005

It is shown that this problem can be reduced to the same mathematical form as the equivalent smooth-walled problem. Consequently, the form of the general expressions obtained for the distribution of scattered acoustic intensity among the waveguide modes and for the azimuthal beam pattern in a specified waveguide mode obtained in an earlier paper [G. R. Sutton and J. J. McCoy, J. Acoust. Soc. Am. 60, 833–839 (1976)] are appropriate to this more general problem.
Stable microscopic bubbles in helium I and evaporation—condensation resonance
Authors: Marston Philip L. , Greene Douglas B.
Published: October 2005

Small bubbles in 4.2 K liquid helium were observed to be stable for several seconds in ultrasonic standing waves and to be acted on by acoustic radiation pressure. Applications are made to recent predictions of the evaporation–condensation resonance of small vapor bubbles.
Attenuation of surface-generated noise received deep in the ocean. II
Authors: Bradner Hugh , Howard R. S.
Published: October 2005

Attenuations versus frequency and depth in the ocean have been calculated from Fisher and Simmons [J. Acoust. Soc. Am 62, 1037 (1977)] relations for point source and distributed surface sources with isotropic, cosϑ, and cos2ϑ radiation distribution.
Multiple-reflection diffuse-scattering model for noise propagation in streets
Authors: Davies Huw G.
Published: October 2005

The sound field generated by an omnidirectional point source in an infinitely long, straight street is considered. The field is assumed to be the sum of a multiply-specularly reflected field and a diffuse field that is fed from scattering at the walls at each reflection of the specular field. It is shown that scattering is important close to the source. The sound level depends on the width of the street and the height of the walls and on the reflection and scattering coefficients of the walls.
Simple frequency modulation model for surface reflection of a cw tone
Authors: Preston John , Nisley Richard
Published: October 2005

Reflections of a cw tone from traveling waves and swells are shown to be the result of a frequency modulation process. The reflected spectrum can be predicted as a simple function of the cw frequency, angle of incidence, wave height, and relative wave or swell velocity. Comparison of the theory presented here with data published by other authors shows good agreement.
Strength of the pitches associated with ripple noise
Authors: Yost William A. , Hill Richard
Published: October 2005

A discrimination procedure was used to measure the pitch strength of the repetition pitches associated with comb-filtered or ripple noise. Pitch strength was measured as a function of overall ripple noise level, the repetition pitch of the noise, and as a function of the center frequency of 1/3-octave bandpass filtered noise. In addition, other experiments were conducted to help determine which parameters should be used in measuring pitch strength when the discrimination procedure is employed. Pitch strength was strongest for pitches of approximately 500 Hz. The stimuli had essentially no pitch strength for pitches below 50 and above 2000 Hz. The strongest pitches were obtained when 1/3-octave filters were placed in a frequency region cented at four times the repetition pitch. Filtering at other center frequencies resulted in a large decrease in pitch strength. These results are consistent with assumptions concerning the dominant region for pitch perception of complex stimuli. The results are also discussed in terms of processing information from reflected sound sources.
Design and implementation of a digital phase shift beamformer
Authors: Pitt S. Patrick , Adams W. Thomas , Vaughan J. Kenneth
Published: October 2005

This paper describes the design, implementation, and performance of a digital beamformer conceived in the late 1960’s to replace the mechanical video scanning switch found in many sonar systems of that time. The design goals included preserving the wide dynamic range typical of high powered sonars, increasing the scanning rate to be commensurate with system bandwidth, and providing sonar data in digital form for studies of post-beamforming processing. In Sec. I, a digital beamformer which uses geometric quantization of quadrature sampled stave data is described, and its properties are obtained via computer simulation for a circular array geometry. The combination of digital phase shift beamforming with circular array geometry leads naturally to a serial implementation, which amounts to a ’’finite impulse response (FIR)’’ filter, to obtain a scanned beam output. One version of this implementation was built and tested. Brief descriptions of the hardware and its measured properties are given in Sec. II.
Spectrum analyzer overlap requirements and detectability using discrete Fourier transform and composite digital filters
Authors: Williams Jack R. , Ricker George G.
Published: October 2005

In spectrum analysis, a primary measure of performance is the minimum detectable signal (MDS). Detectability dictates the compute speed necessary to meet both time and frequency overlap requirements. It is becoming increasingly popular to compute the discrete Fourier transform (DFT), and these elemental filters are complex weighted or otherwise combined to form more complex filters. Applications of this include the proportional bandwidth filter comb and all time-weighting functions such as Hanning, Hamming, and Taylor or their frequency equivalents. Overlap requirements are thereby changed and MDS must be defined so it can be extrapolated to these composite filters. The overlap requirement and MDS are so defined in this paper. Experimental performance is then given and compared to the predictions.
Free vibration analysis of rectangular plates with inelastic lateral support on the diagonals
Authors: Gorman D. J.
Published: October 2005

An analytical solution is obtained for the problem of the free vibration of a rectangular plate with simple support at the edges and inelastic lateral support along one diagonal. The solution, of the double sine series type introduced by Navier, can readily be extended to plates with similar support on both diagonals and different kinds of edge support.
Some statistical properties of lake surface reverberation
Authors: Frazer Marshall E.
Published: October 2005

This report describes the results of an experimental study of the properties of the outputs of a multielement sonar receiving array operating in a reverberant environment. The objective of the study is to obtain additional insight into the (statistical) properties of the receiver outputs through the application of statistical tests to the measured receiver outputs. The experimental data for the study are measurements of surface reverberation resulting from the scattering of 100-μs cw acoustic pulses by the wind driven surface of a freshwater lake. Simultaneous measurements were obtained of the outputs of six different elements of a horizontal, linear receiving array. The statistical validity of these experimental data was examined with statistical tests for independence and homogeneity. The statistical distribution of each receiver output was examined by testing for normality; each receiver output was tested at 900 different observation times. The results of these tests indicated that, when surface reverberation only was present, each output exhibited a Gaussian distribution. Tests of the mean receiver outputs were also conducted and resulted in the conclusion that the mean receiver outputs were negligibly small.
Marine biological choruses observed in tropical waters near Australia
Authors: Cato Douglas H.
Published: October 2005

Observations of biological choruses in the ambient noise of tropical waters of the east Indian Ocean, the west Pacific Ocean, and the Timor Sea near Australia are described. These choruses occurred for a few hours at a time and had most energy at frequencies between 400 Hz and 4 kHz, with spectral peaks mainly at 800 Hz, 1.6–2 kHz, and 3 kHz. During choruses, noise spectrum levels rose up to 30 dB above the usual background noise. Statistics of occurrence of the evening choruses indicate that they would occur on most, if not all evenings at the locations of measurement and are probably fairly widespread in and near shallow waters of the region. As well as these regular evening choruses, there were also transitory choruses which were observed at various times of day over periods of a few days but not before or after. Possible sources of the choruses are discussed. There are at least three sources of the regular evening choruses, possibly fish or sea urchins. Some of the transitory choruses, spectrally similar to the regular choruses, were composed of intense clicking sounds, apparently from sperm whales.
Three-field electroacoustic parametric interactions in piezoelectric crystals
Authors: Nelson D. F.
Published: October 2005

We derive the coupled mode equations governing the Thompson–Quate experiment, that is, the parametric interaction of two counterpropagating bulk acoustic waves and a spatially uniform electric field oscillating at the second harmonic of the acoustic frequency. The derivation applies to propagation of any acoustic mode type in any direction in any piezoelectric or pyroelectric crystal. A new result of the derivation is a general but explicit expression for the material interaction coefficient that governs the strength of the process. We also find that the equations differ from the generic equations assumed by Thompson and Quate by the replacement of a phase velocity with the component of the group velocity normal to the crystal surface. As an aid to this derivation we also derive the coupled mode equations governing the parametric interaction of three acoustic waves. This derivation applies to the propagation of any mode types in any directions (consistent with being close to or at phase matching) in any dielectric, piezoelectric, or pyroelectric crystal.
Acoustic diffraction of a plane wave by two staggered parallel soft or rigid strips
Authors: Goel G. C. , Jain D. L.
Published: October 2005

We discuss here the diffraction of a normally incident plane acoustic wave by two equal, staggered, parallel, perfectly soft or rigid infinite strips. In each case, expressions are obtained for the first few terms of the series for the farfield amplitude and the scattering cross section when the wave length is much larger than the distance between the outer edges of the strips and the distance between the strips is large. By taking appropriate limits, the corresponding results are derived for two equal, parallel, perfectly soft or rigid infinite strips lying exactly opposite to each other. Numerical calculations of the physical quantities of interest are presented graphically.
Acoustic signal processing extensions on ’’optimum detection of signals in non-Gaussian noise’’
Authors: Hecht Richard J. , Mole Louis A.
Published: October 2005

In a recent paper, Sheehy derived optimum processing structures for use in detection of signals in additive non-Gaussian noise. An analytical form was postulated for the distribution of the noise intensity level and found to be in good agreement with experimental data. Since this data was not presented in the article, it is the intent of this letter to clarify the nature of the experimental data previously reported.
New method to determine shear absorption using the viscoelastodynamic resonance-scattering formalism
Authors: Gaunaurd G. , Scharnhorst K. P. , Überall H.
Published: October 2005

We have recently developed a new resonance theory for the scattering of compressional waves by fluid-filled spherical cavities in viscoelastic materials, and have applied it to the study of the resonance frequencies and widths of peaks in the (monopole) fpp0 scattering amplitude. Using this theory, which is the viscoelastodynamical counterpart of the Breit–Wigner formalism of nuclear scattering theory, we find that (i) the relative half-width of the peaks depends linearly on the resonance frequency, (ii) the shear-absorption parameter of the viscoelastic material containing the cavity can be determined from the slope of a straight line fit to the data. This determination is possible precisely because our theory realistically accounts for absorption in the material, and thus its predictions compare favorably with experimentally measured data. Finally, the theory gives a self-consistent way to verify the weak absorption assumption inherent in the prediction.
Granule microphone using selenium–tellurium alloy
Authors: Ohga Juro , Shirai Seiiti , Ochi Osamu , Takagi Toru , Yoshikawa Akira , Nagai Haruo , Mizushima Yoshihiko
Published: October 2005

A new alternative material for the conventional granule-type microphone utilizing carbon, selenium, and tellurium alloy is proposed. The output voltage of the granule microphone using this alloy for the low dc feed current is higher than that of the carbon microphone. Moreover, the alloy granule microphone shows some interesting properties, for example, high impedance (200–1000 Ω), low dc feed current (10 mA is optimum for the conventional size granule chamber) and excellent low-harmonic distortion (less than −40 dB). It is concluded in this paper that the antimony–selenium–tellurium alloy granule shows very good properties that some properties of this alloy microphone are due to the mechanical characteristics of the granules. Finally, the durability of the characteristics is determined as satisfactory.
Broadband focusing through a lens: A linear systems approach
Authors: Norton Stephen J. , Macovski Albert
Published: October 2005

Using linear transform techniques, the transient focal plane pattern is derived for a plane wave impulse normally incident on a converging lens. The resultant function of space and time generated in the focal plane can be regarded as the temporal impulse response of a linear, time-invariant system consisting of the lens, its focal plane, and the intervening free space. The focal plane response to an incident plane wave disturbance with arbitrary time dependence is then obtained immediately by convolving the broadband waveform with the temporal impulse response of the lens. This impulse response is derived for two cases: a lens with a one-dimensional (slit) pupil function, and a lens with a circularly symmetric pupil function. It is shown that while the monochromatic focal plane pattern for a one-dimensional lens is proportional to the Fourier transform of the one-dimensional pupil function, the impulse response of the one-dimensional lens is proportional to the time derivative of the pupil function itself; also, while the monochromatic focal plane pattern for a circular lens is proportional to the Hankel transform of the pupil function, the impulse response of the circular lens is proportional to the time derivative of the Abel transform of the pupil function. These results also provide a valid description for the transient response of any broadband focusing system with linear, or circular, symmetry, including, for example, electronically focused linear, or circular, element arrays.
Experimental study of the aeroacoustic mechanism of rotor–vortex interactions
Authors: Leggat L. J. , Siddon T. E.
Published: October 2005

The interaction of a naturally occurring vortex and an axial flow fan is investigated using cross-correlation and real-time observation techniques. Results show that the vortex produces a countersign acoustic source strength distribution over the span of the fan blade at the blade passage frequency. Evidence of the influence of the vortex structure on the fluctuating blade pressure measurements is derived from real-time observations of on-blade pressure measurements. The experiments indicate that the rotor–vortex interaction can be a significant source mechanism producing discrete-tone fan noise.
Free vibration of circular plates of arbitrary thickness
Authors: Sundara Raja Iyengar K. T. , Raman P. V.
Published: October 2005

Free vibration of circular plates of arbitrary thickness is investigated using the method of initial functions. State-space approach is used to derive the governing equations of the above method. The formulation is such that theories of any desired order can be obtained by deleting higher terms in the infinite-order differential equations. Numerical results are obtained for flexural and extensional vibration of circular plates. Results are also computed using Mindlin’s theory and they are in agreement with the present analysis.
Ultrasonic imaging system which uses a rotating M-sequence phase disk and correlation analysis
Authors: Sato Takuso , Sunada Tadasu , Wadaka Shusou
Published: October 2005

A new ultrasonic imaging system is proposed which uses transformation of the two-dimensional spatial distribution of the wave field of a coherently illuminated object into a temporally coded scattered wave field, by rotating an M-sequence phase disk just behind the object. It is shown that a two-dimensional image of the object can be obtained by cross-correlation analysis of the signal detected by a stationary-point receiver in the farfield with the same M-sequence signal generated in a signal processor. Construction of such a system is described together with some experimental results. Typically, a 1-MHz ultrasonic wave is used and an image of the object in a 40×70-mm region is obtained in 15 s.
Mode coupling in a sound channel with range-dependent parabolic velocity profile
Authors: Chwieroth F. S. , Nagl A. , Überall H. , Graves R. D. , Zarur G. L.
Published: October 2005

Pierce and Milder have developed a normal-mode theory with adiabatic separability for sound propagation in a channel whose environmental parameters depend not only on depth, but in a gradual fashion also on range. If range dependence is less gradual, the range equations become coupled and energy transfer between modes takes place. We have investigated this coupling phenomenon for a parabolic profile model with linear range dependence, using a method of approximate diagonalization for uncoupling the range equations, and have shown the energy transfer between modes to become significant for sufficiently large range variations of the profile.
Scattering at a rough boundary to an inhomogeneous ocean
Authors: McCoy John J.
Published: October 2005

The development of randomly rough boundary interaction models formulated in terms of the (averaged) acoustic intensity angular spectral density is considered. The principal advantage of these models is that they are completely compatible with a previously presented propagation model, which in turn is applicable for a general inhomogeneous medium and is well suited for numerical computation. Thus, taken together, the boundary interaction models and the propagation model provide a general wave theoretic approach to experiments containing both a rough boundary and an inhomogeneous sound speed profile. Heretofore, such a general approach has been limited either to geometric theory analysis or to a perturbation analysis that is suitable for slightly rough boundaries. Two specific boundary interaction models are considered in some detail, one a phenomenological model that can be termed a linear filter model and the other a structural model based on Kirchhoff scattering theory. Any originality in these specific models is limited to the field measure in terms of which they are formulated, although the derivation of the Kirchhoff model is thought to provide further insight on the applicability of the theory as it applies to inhomogeneous media. The phenomenological model is shown to be a natural extension of the ray theory approach to scattering at a rough boundary, i.e., the use of reflection coefficients. The extension is required in order to incorporate some effects of diffraction. Finally, an idealized, but somewhat typical, experimental geometry is considered for which the combined application of the propagation and boundary interaction models is possible.
The nature of sound fluctuation in the upper ocean. I
Authors: Neubert Jerome A. , Lumley John L.
Published: October 2005

In this critique of sound propagation studies in turbulent fluids, the interpretations and limitations of some well-known scattering theories and experiments are brought into question. First, some earlier theories of sound propagation in turbulent ocean are reviewed. Second, some of the more recent developments in the analysis of sound propagation in turbulent fluids are presented. Finally, the earlier results and the contemporary accomplishments are compared in the single-scattering and one-dimensional cases. The more important revelations and confirmations, based on Part I, are reserved for Part II [J. Acoust. Soc. Am. 64, 1148–1158 (1978)], where it is shown, on the basis of turbulent scaling, that the scattering theories of Bergmann, of Mintzer, and of Potter and Murphy deserve closer scrutiny and that the Stone and Mintzer experiments were probably misinterpreted in regard to the actual scattering mechanism.
The nature of sound fluctuation in the upper ocean. II
Authors: Neubert Jerome A. , Lumley John L.
Published: October 2005

Having reviewed and critiqued the nature of sound fluctuation in turbulent media and the upper ocean in Part I [J. Acoust. Soc. Am. 64, 1132–1147 (1978)], it is now shown, on the basis of turbulent scaling, that the scattering theories of Bergmann, of Mintzer, and of Potter and Murphy are discrete-scattering, and not continuous-scattering theories when Gaussian refractive-fluctuation correlations are imposed. Furthermore, turbulent scaling and the experimentally observed turbulent microstructure strongly suggest that the scattering mechanism in the Stone and Mintzer experiments is not the turbulence, but is more likely discrete impurities (such as the ubiquitous, minute air bubbles which arise due to thermal degassing) which are shuffled about in a random manner by the turbulent fluid. It is strongly suggested that this is often the nature of sound fluctuation in the upper ocean. Finally, more effective methods of the analyzing sound fluctuation in the real ocean are presented.
Nonparametric estimation of the ocean bottom reflection coefficient
Authors: Schoenberg Michael
Published: October 2005

An inverse method for estimating the plane wave reflection coefficient of a stratified ocean bottom from the reflected field of a point source known at a finite number of receiver array points is described. Nothing need be assumed about the reflecting medium. Essentially, the individual phase shift and gain of each element of an arbitary listening array is found so as to ’’optimize’’ the estimation of the reflection coefficient at a specific angle of incidence, where optimization refers to improving resolution and maintaining accuracy. Computer simulations have been carried out and some results are shown.
Acoustic energy flux in nonhomogeneous ducts
Authors: Möhring W.
Published: October 2005

A study of the scattering matrix S of sound waves propagating in an inhomogeneous duct which consists of two semi-infinite ducts, connected somehow, is undertaken. The scattering matrix contains all reflection and transmission coefficients from the nth into the mth propagating mode for upstream and downstream propagation. A mean flow u0 is included. From energy conservation one finds, that S is unitary for potential flow, SS+=E, if the mode normalization is performed to unity energy flux. Invariance considerations with respect to time reversal reveal that S* (ω, −u0), the conjugate complex of the reverse flow scattering matrix, obeys the relation S* (ω, −u0) S (ω, u0) =E. From these two results, the reciprocity relation ST(ω, −u0) =s (ω, u0) is obtained, where ST denotes the transpose of S. Some implications of these results for sound waves propagating in potential flow are discussed. The modifications which occur in rotational flow are also described.
Basilar membrane motion in a spiral-shaped cochlea
Authors: Viergever Max A.
Published: October 2005

To examine the influence of the spiral coiling of the cochlear upon the motion of the basilar membrane, a mathematical model of the cochlea is constructed. The formulation of the problem leads to Laplace’s equation in three dimensions in a curvilinear coordinate system plus corresponding boundary conditons. By basing the choice of the coordinate system upon the form of the helix representing the centerline of the basilar membrane, a relatively simple formulation is obtained: The helix parameters appear only in the Laplacian, not in the boundary conditions. From experimental data the equations of the basilar membrane’s centerline are derived for a human cochlea, both in intrinsic form and in regular form. The relative simplicity of the formulation permits the tentative conclusion that, in spite of the large curvature near the apex, the spiral shape of the cochlea has only a small influence upon the motion of the basilar membrane.
Phase decorrelation effects on array beam scanning
Authors: Lim Tong L.
Published: October 2005

The beam scanning capability of a planar random array has been investigated for the case when the signal phase decorrelates across the array and conventional beam steering is used. The phases are assumed to have a joint Gaussian density, and the values of the correlation function used are assumed to decrease linearly with element separation. Analytical expressions are derived relating the array gain to the maximum angle of scan.
Pseudoresonances and virtual modes in underwater sound propagation
Authors: Williams A. O.
Published: October 2005

An underwater sound field can be expressed as a sum over a set of continuous normal modes (or a suitable branch line integral, BLI) plus a sum of discrete normal modes. It is known that the significant contributions of the continuous modes come from resonances in the integrand of the BLI—strong, sharp, symmetric peaks which can be located and approximated. Each strong resonance gives rise to a virtual mode, resembling a discrete mode except as to range dependence. We show that there may also be a pseudoresonance—strong, sharp, but asymmetric—which contributes a virtual mode of still different range dependence. A pseudoresonance occurs whenever the highest discrete mode is very near or at cutoff, or when physical parameters almost allow one more discrete mode. Sometimes a pseudoresonance may be the major or the only contributor from the BLI. Equations to fit a pseudoresonance are defined in a special case, and calculation of each consequent virtual mode is carried out. The special case, a homogeneous water layer overlying a bottom half space, was chosen to allow analytical calculations throughout, but pseudoresonances and consequent virtual modes are not peculiar to this case.
Doubly asymptotic approximations for transient motions of submerged structures
Authors: Geers Thomas L.
Published: October 2005

Doubly asymptotic approximations (DAA) are differential equations for simplified analysis of the transient interaction between a flexible structure and a surrounding infinite medium. These surface interaction approximations approach exactness in the limit of low- and high-frequency motions and effect a smooth transition in the intermediate frequency range. A finite-element DAA formulation for an acoustic medium is presented herein, with attention focused on the first and second members of the DAA hierarchy. The free-vibration and forced-response characteristics of the first and second approximations are examined through specialization to a spherical geometry.
Analysis of resonance standing-wave measurements
Authors: Mehl James B.
Published: October 2005

Linear and nonlinear numerical techniques for fitting measurements on resonant standing-wave systems to theoretical resonance formulas are described. The fits are correct for background and enable the normal-mode frequencies and widths to be precisely determined.