bluuebunny/crossref_metadata_2025 huggingface dataset:
Persisting questions in steady-state measurements of noise power and sound absorption
Authors: Schultz Theodore J.
Published: October 2005

Most steady-state methods for measuring the noise power of equipment and the sound absorption in a room depend on knowing the sound-power output of a standard source. But the output of any sound source depends in principle on the radiation impedance presented to it, and this impedance is likely to change with the location of the source, as well as with changes in the amount and distribution of absorptive material in the room. Moreover, no generally accepted method has been available for measuring the sound-power output directly. For these reasons, the validity of steady-state methods has been under suspicion for some time. This paper comments on recent progress in making steady-state methods respectable and calls attention to some remaining problems.
Calculation of the radiated field from the vibrational velocity of a wall in a reverberant field
Authors: Donato R. J.
Published: October 2005

The radiated energy from a vibrating wall is measured and compared to the value calculated from a knowledge of the correlation of the vibrational velocity over the wall surface. Detailed measurements were made on a single wall, but it is shown that the case of a double wall may be predicted with fair accuracy.
Transmission of radial shear forces to cochlear hair cells
Authors: Billone M. , Raynor S.
Published: October 2005

The radial shear forces transmitted to the cuticular plates of cochlear sensory cells are investigated by means of a mathematical model. The model is based on the fine anatomy of the hair cells and their supporting structures. It predicts that the inner hair cells are stimulated by a viscous force which is linearly proportional to, and in phase with, basilar membrane velocity. The outer hair cells are stimulated by a shear force which is linearly proportional to, and in phase with, basilar membrane displacement at low frequencies (e.g., less than 700 Hz for a midbasal turn cell). At higher frequencies, the shear force transmitted to the outer hair cells is a function of both displacement and velocity. This outer hair-cell shear force is at least an order of magnitude greater than the corresponding inner hair cell force for the frequencies and cochlear positions studied. These results compare favorably to recent cochlear microphonic data from normal and kanamycin-treated guinea pigs for frequencies less than 4000 Hz. Shear force amplitude envelopes are presented for 800- and 1600-Hz pure tones. The results suggest that the “velocity-sensitive” inner hair cells are candidates for “place-mechanism” receptors while the outer hail cells are candidates for “frequency-mechanism” receptors. The model predicts no mechanical fine tuning in the force transmission.
On the critical band in the acoustic stapedius reflex
Authors: Djupesland Gisle , Zwislocki J. J.
Published: October 2005

The critical band in the stapedius-muscle reflex was investigated by means of two-tone complexes of variable frequency separation. In confirmation of an earlier study, the results indicate that the reflex critical band is several times larger than the critical band known in psychophysics. More specifically, it was found to be numerically equal to the center frequency of the complexes. Outside the critical band, the reflex threshold for the complexes was 10 dB lower than for their components presented separately. The difference is equal to that found in loudness experiments.
Effect of interaural phase on frequency and amplitude discrimination
Authors: Henning G. Bruce
Published: October 2005

The resolution of frequency and amplitude is better at low signal-to-noise ratios with out-of-phase signals than with in-phase signals when the noise in which the signals are presented is the same at both ears. On the other hand, at high signal-to-noise ratios, the effects of the interaural phase of the signals are negligible. These findings are discussed in terms of the predictions of a modified version of Durlach's Equalization and Cancellation Model and the Webster-Jeffress Model of the binaural masking level difference.
Relation of noise measurements to temporary threshold shift in snowmobile users
Authors: Chaney R. B. , McClain S. C. , Harrison R.
Published: October 2005

To evaluate and quantify snowmobile noise, measurements were made as follows: (1) operator at-ear A-weighted sound levels and exposure patterns; (2) A-weighted levels at 50 ft to develop a test procedure for law enforcement purposes; (3) temporary threshold shift (TTS) in snowmobile users. Results indicate that (a) TTS of varying degrees was observed in 87% of snowmobile operators tested after operations periods as short as one-half hour; (b) for typical recreational riding, the Federal Occupational Safety and Health Act of 1970 noise limits are exceeded after approximately 2 1/2 hours of snowmobile operation; (c) the 50-ft noise-level measurement procedure which was developed can probably be used as a valid test procedure to measure the amount of noise produced by a snowmobile for law enforcement purposes. More correlation of data would be desirable.
Target strengths of humpback whales Megaptera novaeangliae
Authors: Love Richard H.
Published: October 2005

Measurements of the target strengths of humpback whales, Megaptera novaeangliae, have been made at short range. The use of a perfectly reflecting model has enabled the results obtained to be extrapolated to long ranges. The target strength at infinite range of adult humpbacks about 15 yd in length, insonified at 20 kHz, was found to be + dB, near the side aspect, and − 4 dB, near the head aspect. A juvenile humpback about 10 yd in length, insonified at 10 kHz, was found to have a target strength at infinite range of + 2 dB, near the side aspect.
Ray caustics and passive detection solutions for boundary reflections in a constant-gradient medium
Authors: Raphael David T.
Published: October 2005

For a bottomless medium characterized by a positive constant gradient, the multiple reflection problem is treated by analysis of the following: (1) The Simulation Problem: Given the relative coordinates x and y between source and receiver, determine the orientations of those rays which succeed in impinging upon the receiver by use of the acquiring-ray approach. The existence condition for real roots of the acquiring-ray cubic and quartic equations treated herein facilitate the determination of the caustic equations. When the condition is imposed that the discriminant of the cubic or quartic equation be zero valued, the caustic equation emerges as the boundary line among which repeated roots occur. For the single reflection case, a cubic equation must be solved and the associated caustic curve has the shape of a cusped semicubical parabola. For n reflections (n ⩾ 2), a quartic equation must be treated and the two caustics of the nth order are derived from the discriminants of the quadratic factors composing the quartic equation. Explicit closed-form solutions for the caustics are obtained by use of reciprocity and reduction-to-single-reflection-type arguments. The mathematical form and physical significance of the caustics is discussed. (2) The Passive Detection Problem: Given only the ray orientations at the receiver, determine the vertical and horizontal distances between source and receiver. For both problems, no restrictions are imposed on the source and receiver depths.
Finite-amplitude acoustic phenomena in aerosols from a single governing equation
Authors: Davidson George A. , Scott David S.
Published: October 2005

By extending a procedure originally developed in the study of finite-amplitude acoustics of clean gases, a single equation, describing plane finite-amplitude acoustic processes in aerosols is developed for monodisperse and polydisperse suspensions of nonvolatile spherical particulate matter. The results allow prediction of attenuation, dispersion, and harmonic growth up to the fourth harmonic, and include the effects of gas “self-dissipation.” Previous finite-amplitude theory in dusty gases was limited to the third harmonic and neglected gas “self-dissipation.” Physical mechanisms are suggested to account for the typical attenuation and dispersion behavior for the cases ωτ → 0, 1, ∞, where ω is the characteristic acoustic frequency and τ the particle momentum relaxation time. In addition, the power of the single governing equation approach to the study of finite-amplitude disturbances propagating through aerosols is well illustrated. The present theoretical results reduce to those of existing theories for the limiting cases of (i) infinitesimal and finite-amplitude acoustics of dissipationless gases, (ii) infinitesimal and finite-amplitude acoustics of clean, viscous, thermally conducting gases, (iii) infinitesimal amplitude acoustics of dusty gases including both gas and particulate dissipation mechanisms, and (iv) finite-amplitude acoustics of dusty gases neglecting gas dissipation terms.
Influence of input quantizer step sizes on the processing gain of digital beamformers
Authors: Wang H. S. C.
Published: October 2005

Utilizing a formulation of output power of a digital beamformer with input quantizers of unequal input and output step sizes given previously, the optimum quantizer step sizes which yield maximum processing gain for a typical array were searched by the method of “steepest ascent” with a digital computer. For the case of two-bit /channel quantization with small input SNR (⩽ − 10 dB), the array gain surface as a function of two independent step variables exhibits a maximum which is only slightly greater than the maximum array gain achievable with uniform input quantizers. For larger input SNR, the array gain surface tends to be concave upward, and the performance of uniform quantizers can at the best be a suboptimum. The high theoretical processing gain in the limiting case of very large step sizes is attributed to a threshold effect of the input quantizers. Except for these latter conditions, the optimum uniform quantizing condition previously reported by the author represents essentially valid optimum design.
Erratum: “Noise propagation in corridors” [H. G. Davies, J. Acoust. Soc. Am. 53, 1253–1262 (1973)]
Authors: Davies Huw G.
Published: October 2005

Omitted references are supplied.
Ranking the impact sound transmission of wood-framed floor-ceiling assemblies
Authors: Belmondo Victor E. , Heebink Thomas B. , Brittain Frank H.
Published: October 2005

A masking procedure has been developed to rank apartment floor-ceiling systems in order of their resistance to the transmitted sound of footfalls. Results obtained subjectively show that the current international standard for rating impact noise transmission using a tapping machine incorrectly ranks some wood-framed floor-ceiling systems. When the described procedure is used to mask tapping machine noise, the floors are also incorrectly ranked. This inadequacy continued even though low frequencies, below the 89-Hz cutoff of the 100-Hz 1/3 octave, were included in the masking procedure. Because the masking procedure described is subjective, the problems associated with the development of an objective test are also discussed. A simple objective test method is suggested for future development.
An optimum processor theory for the central formation of the pitch of complex tones
Authors: Goldstein Julius L.
Published: October 2005

A comprehensive theory is formulated for the central formation of the pitch of complex tones, i.e., periodicity pitch [Schouten, Ritsma, and Cardozo, J. Acoust. Soc. Amer. 34, 1418–1424 (1962)]. This theory is a logical deduction from statistical estimation theory of the optimal estimate for fundamental frequency, when this estimate is constrained in ways inferred from empirical phenomena. The basic constraints are (i) the estimator receives noisy information on the frequencies, but not amplitudes and phases, of aurally resolvable simple tones from the stimulus and its aural combination tones, and (ii) the estimator presumes all stimuli are periodic with spectra comprising successive harmonics. The stochastic signals representing the frequencies of resolved tones are characterized by independent Gaussian distributions with mean equal to the frequency represented and a variance that serves as free parameter. The theory is applicable whether frequency is coded by place or time. Optimum estimates of fundamental frequency and harmonic numbers are calculated upon each stimulus presentation. Multimodal probability distributions for the estimated fundamental are predicted in consequence of variability in the estimated harmonic numbers. Quantification of the variance parameter from musical intelligibility data in Houtsma and Goldstein [J. Acoust. Soc. Amer. 51, 520–529 (1972)] shows it to be dependent upon the frequency represented and not upon other stimulus frequencies. The quantified optimum processor theory consolidates known data on pitch of complex tones.
A system of nonlinear differential equations modeling basilar-membrane motion
Authors: Kim Duck On , Molnar Charles E. , Pfeiffer Russell R.
Published: October 2005

A phenomenological model for displacement of a point on the basilar membrane is developed by formulating a system of nonlinear differential equations: ẍi(t) + 2Di[1 + ηẋi2(t)]ẋi(t) + ω0i2xi(t) = Cxi−1(t), for i = 1, 2, …, 10, where x0(t) is the input (stapes displacement) and x10(t) is the output. This model, which behaves effectively linearly at low levels and nonlinearly at high levels, shows that a single nonlinear system is adequate to account for the following frequency-dependent nonlinear phenomena of the peripheral auditory system: (1) limiting of the output level; (2) decrease of Q with increasing input level; (3) decrease of the most effective frequency with increasing input level; (4) changes in phase angle of the output with input level; (5) changes in shape of the click response waveform with input level; (6) two-tone suppression with f1 = CF and f2 > CF; (7) generation of the combination tone 2f1 − f2 in response to two tones f1 < f2); (8) “amplitude” nonlinearity in response to click pairs; and (9) “temporal” nonlinearity in response to click pairs. The success of the model in reproducing phenomena observed in basilar-membrane motion (1–3), as well as in responses of single cochlear nerve fibers (1–9), suggested that all of these phenomena may occur in basilar-membrane motion. As predicted by the model, direct observations of the presence of phenomena 4, 5, and 6 in basilar-membrane motion have been recently reported.
Unified analysis of fan stator noise
Authors: Hanson Donald B.
Published: October 2005

A theory is developed which predicts the acoustic radiation of an axial-flow fan stator due to interaction with rotor viscous wakes. Calculations are compared in detail with experimental data. Both the harmonic and broadband noise-spectrum components are calculated from a unified model using methodology from the theories of random pulse amplitude modulation, PAM, and pulse position modulation, PPM. The stator is modeled as a circular array of pulsed dipoles. The amplitude and arrival time of each pulse are random variables whose means correspond to the values calculated from harmonic rotor-stator interaction theory. The standard deviations of these random variables are measures of the turbulence levels in the blade wakes. For the model proposed the solution is exact: when PAM is imposed on a periodic stator source, new broadband energy is generated whose spectrum shape is similar to the envelope of harmonics at high frequencies and the harmonic radiation is unchanged; however, when PPM occurs, new broadband energy is radiated but at the expense of harmonic energy. At frequencies significantly above duct cutoff it is shown for a fixed stator solidity that the spectrum is essentially independent of the number of stator vanes.
Ultrasound Axicon: a device for focusing over a large depth
Authors: Burckhardt C. B. , Hoffmann H. , Grandchamp P.-A.
Published: October 2005

The B-scan technique, which is used in ultrasonic medical diagnosis and in materials testing, suffers from a low lateral resolution because of the large diameter of the ultrasound beam. The present paper describes a beamforming device which focuses the beam over a large depth, i.e., the well-known depth of focus problem is circumvented. An experimental device is described which gives a lateral resolution of 2 to 3 mm at a frequency of 2 MHz (λ = 0.75 mm in water).
Determination of the signs of the ratios of strain-optical constants measured ultrasonically
Authors: Pettersen Howard E. , Narasimhamurty T. S.
Published: October 2005

It is shown that a single light intensity measurement does not allow the determination of the sign of the ratio of strain-optical constants determined ultrasonically. However, if an experiment is performed in which the ratios are overdetermined, it is possible to determine the signs by applying the criterion that the results of the various measurements must be consistent. The equations which must be satisfied for the criterion of consistency are obtained for nine of the 32 crystal classes. The application of the technique is presented with numerical values for the case of NaCl.
Shallow-water sound attenuation in a standard area
Authors: Wille P. , Thiele R. , Schunk E.
Published: October 2005

Shallow-water attenuation loss was studied under varying oceanographic conditions within a standard area. By using combined ship-aircraft measurement methods, sound-propagation characteristics were ascertained in conjunction with relevant environmental parameters. The selected sea area had only very slight lateral variation for all environmental characteristics permitting good control of measurements. Evaluations to date indicate typical frequency-response differences for attenuation, with or without sea-surface participation in sound propagation. With bottom participation only, the magnitude and frequency response of the attenuation have a first approximation consisting of a model with the bottom represented only as a quasiliquid smooth stratification of the complex sound velocity and density.
Effect of the acoustic boundary layer on the wave propagation in ducts
Authors: Nayfeh Ali Hasan
Published: October 2005

An analysis is presented for the wave propagation in two-dimensional and circular lined ducts taking into account the effects of viscosity in both the mean and the acoustic problems. The method of composite expansions is used to express each acoustic flow quantity as the sum of an inviscid part and a boundary layer part insignificant outside a thin layer next to the wall. The problem is reduced to solving a second-order ordinary differential equation for the pressure perturbation as in the inviscid acoustic case but with a modified specific wall admittance. An analytic expression is presented for the variation of the modified admittance with the wall and flow parameters, such as the acoustic boundary layer thickness, the mean velocity and temperature gradients at the wall, the frequency of oscillation, and the wavelength.
Reverberation in a city street
Authors: Aylor Donald , Parlange Jean-Yves , Chapman Courtland
Published: October 2005

The decay of 1/3-octave pink noise in a street was compared before and after the ivy on one building leafed out in the spring. The effect of the ivy on reverberation in the street was negligible except around 4000 Hz, where the decay of sound was increased by about 30 dB/sec. Since absorption of sound by the ivy is slight, the reduction of reverberation must be mainly by scattering of sound by the foliage.
Acoustic Properties of Rho-C Rubber and ABS in the Frequency Range 100-kHz-2 MHz
Authors: Adair L. C. , Cook R. L.
Published: October 2005

The acoustic properties of a Rho-C rubber and an ABS (Acrylonitrile-Butadiene-Styrene Type GSE-1000) material in the frequency range of 100 kHz to 2 MHz were measured experimentally. Three essential properties—transmission loss at normal incidence versus frequency, reflectivity at normal incidence versus frequency, and transmissions loss versus angle of incidence—were determined. Both materials were found to have excellent acoustic properties in the frequency range of interest.
Acoustic scattering from a stochastic sea surface
Authors: Scharf Louis L. , Swarts Robert L.
Published: October 2005

In this paper the spectral and covariance properties of surface-scattered acoustic fields are determined for slightly rough and very rough sea surfaces that are irradiated with plane wave single-frequency sources. The results obtained are general in the sense that they depend only on the frequency-wavenumber spectrum of the stochastic sea surface and not on any particular surface spectrum. Exact results are obtained for sinusoidal seas and these results are compared with various approximate solutions. The approximations clearly indicate the connection between sinusoidal seas and arbitrary seas.
Ultrasonic pumping of He II through a pinhole
Authors: Andrews E. C. , Pigott M. T.
Published: October 2005

Reported instances of stable nonflow in He II Josephson effect experiments have in most cases been achieved by a flow of liquid helium from one reservoir to another, a flow driven by ultrasonic pumping. We have examined some of the characteristics of this pumping. We confirm that a threshold transducer power is necessary to initiate pumping and find that the threshold power has a temperature dependence of ρsTα, 0 < α < 1, in the range 1.5 K < T < 2.1 K. A capacitor has always been used by others to measure the meniscus level. We find that the geometry of the core of this capacitor is important: when the core bottom is conical, with vertex pointing down, we achieve no pumping. We find that the orientation of an asymmetric pinhole plays no role. Finally, the pumping speed is a monotonic function of transducer power for powers exceeding threshold and for powers less than an upper limit, above which there is no further increase in pumping speed.
Frequency spectra of resonant vibration in disk plates of PbTiO3 piezoelectric ceramics
Authors: Ikegami Seiji , Ueda Ichiro , Kobayashi Shigeru
Published: October 2005

The frequency spectra of resonant vibration in disk plates of PbTiO3 piezoelectric ceramics were observed for diameter to thickness ratio (r) of 5 to 30 near the fundamental thickness extensional mode. The observed spectra could be classified into three groups of thickness mode and two groups of radial mode. For comparison, theoretical spectra for isotropic disk plate were also calculated for various Poisson's ratios (σ) of disk material on the basis of Gazis and Mindlin's theory. The calculations showed that the theoretical radial mode spectra can be divided into a strongly σ-dependent group and a slightly dependent one, and also showed that the upper ends of terrace-type spectra appear as a straight line at the cutoff frequency in a large-r region and may be corresponded to the thickness extensional mode. In fact, the fitting of the upper-end spectra to the experimental thickness extensional mode by adjusting σ, gives not only qualitative agreement of all experimental spectra with the theoretical ones, but also the best quantitative agreement with the strongly σ-dependent theoretical spectra. Thus, all observed spectra can be predicted nearly completely from the theory of isotropic disk plate by selecting a suitable equivalent σ which is 0.18 for the present anisotropic disk.
Time-spectral energy density—some of its properties
Authors: Kouskoulas V. , Barnard R.
Published: October 2005

The physical meaningfulness of the time-spectral energy concept [V. Kouskoulas, J. Appl. Phys. 42, No. 10 (1971)] and a relation to the corresponding output of a linear system are established. As it defines energy and it is always positive, it is physically meaningful and measurable.
Influence of consonant environment on duration of vowels in the speech of three-, six-, and nine-year-old children
Authors: DiSimoni Frank G.
Published: October 2005

The effect of consonant environment on vowel duration previously noted for adults is not present in the speech of three-year-old children.
Role of multiple reflections and reverberation in urban noise propagation
Authors: Lyon Richard H.
Published: October 2005

Various studies of sound transmission in urban areas that involve multipath propagation or multiple reflections are reviewed. Studies of propagation in a single street or corridors display important descrepancies between theoretical analyses and field experiments. Model studies suggest that scattering may play an important, but as yet unexplained role. Sources above the street show good correspondence between field and laboratory data and theory. Intrusion of aircraft noise into an urban area shows that sound may be slightly amplified above an open-terrain condition due to channeling effects. The general urban background noise appears to be accounted for by surface transportation sources distributed over the city, aside from a shielding factor of 10–15 dB of as yet undetermined origin.
Noise reduction by barriers
Authors: Kurze Ulrich J.
Published: October 2005

A literature review has been prepared to summarize the present state of knowledge concerning the attenuation by barriers. Frequently used prediction methods for the performance of screen-type barriers are analyzed with respect to errors resulting from particular source and receiver positions, from ground reflections, from absorptive properties of the barrier and the ground, and from the influence of wind. Recently developed formulas describing the diffraction by wedge-shaped and wide barriers are reduced to simplified methods for the prediction of the shielding achievable in comparison to screen-type barriers. Unsolved problems apparent from discrepancies of the field performance of barriers and the results of theoretical and model studies are summarized to outline areas requiring further research.
Axial shear waves in a medium with randomly distributed cylinders
Authors: Bose S. K. , Mal A. K.
Published: October 2005

The propagation of coherent elastic shear waves in a medium containing a dilute and uniform distribution of cylindrical inclusions is discussed. The waves are assumed to be polarized parallel to the axes of the cylinders while the cylinders are assumed to be thin compared to the wavelength. The complex wavenumber is calculated to a second order of approximation, the real part of which gives the propagation speed and the imaginary part gives the damping due to scattering. Numerical results are obtained for the case of identical inclusions with the properties of the inclusions varying between hollow (void) and rigid.
Basilar membrane tuning curves in the guinea pig
Authors: Johnstone Brian M. , Yates Graeme K.
Published: October 2005

Recent measurements on basilar membrane mechanical tuning reveal very fast high-frequency cut-offs, approaching those of neural tuning curves. The guinea pig's first turn does not seem to exhibit much nonlinearity in contrast to that found in the squirrel monkey, and the phase data are also different. This may be a place or a species variation. A simple model of a nonlinear resonant system was constructed, and it exhibits many of the properties ascribed to the basilar membrane.
Evidence from Mössbauer experiments for nonlinear vibration in the cochlea
Authors: Rhode William S. , Robles Luis
Published: October 2005

The Mössbauer technique has been applied to the measurement of vibration of the basilar membrane in the squirrel monkey cochlea. Both steady-state and transient responses have been recorded in the 7–8-kHz locus of the cochlea. The steady-state response indicates that the basilar membrane vibrates nonlinearly for frequencies of stimulation near or greater than the characteristic frequency. The nonlinearity can be observed at the lowest levels of stimulation, 70–80 dB SPL, for which measurements could be made. The nonlinearity extends to lower frequencies and the basilar membrane transfer function tends to broaden as SPL is increased. Rapid postmortem changes occur in the cochlea: (1) the amplitude of the transfer ratio (basilar membrane/malleus) decreases 10–15 dB over a period of several hours with a downward shift of 1.5–3 kHz in the characteristic frequency of the basilar membrane at a given location; (2) the low-frequency slope of the transfer ratio settles to 6 dB/octave by 6 h after death; (3) the slope of the phase of the transfer function increases the characteristic frequency decreases; (4) the basilar membrane vibrates linearly after death. The transient response was studied using acoustic clicks of approximately 150-μ duration, presented in sequences of 100 000 to 400 000. The transient response has an early component which has a fast decay and a second component which has an extremely slow rate of decay and which displays nonlinear behavior. Preliminary results for the vibration of Reissner's membrane in the 13-kHz region of the cochlea are also reported.
Tails of tuning curves of auditory-nerve fibers
Authors: Kiang N. Y. S. , Moxon E. C.
Published: October 2005

Békésy's interest in improving telephone communication led him eventually to make observations on the mechanical properties of the basilar membrane. For apical parts of the membrane he obtained resonance curves with steep high-frequency slopes and gradual low-frequency slopes. Tuning curves for auditory-nerve fibers in anesthetized cats also show significant low-frequency tails. Even fibers with high characteristic frequencies (CF) respond to tones throughout a wide range of low and middle frequencies. For low-frequency tones at moderate and high stimulus levels the responses of high-CF fibers tend to be time-locked either to the same phase of the stimulus or to a phase that differs by a half cycle. For complex stimuli such as speech, which contains many low-frequency components, these fibers behave as broadly tuned elements, discharging with time patterns that are principally determined by the temporal characteristics of the acoustic waveform. Results of experiments using low- and high-frequency masking stimuli reinforce the view that responses of high-CF fibers to low-frequency stimuli should not be ignored in theories that seek to describe the role of the auditory nerve in speech communication.
Simple form of the auditory running-average hypothesis: application to the temporal summation of loudness and to the delayed perception of the offset of brief stimuli
Authors: Robinson Charles E.
Published: October 2005

A simple form of the auditory running-average hypothesis is presented, and is applied to two phenomena: the temporal summation of loudness and the delayed perception of the offset of brief stimuli. For both phenomena, the predictions of the hypothesis describe the data well.
Transient fluid reaction on a baffled plane piston of arbitrary shape
Authors: Lindemann Oscar A.
Published: October 2005

The inverse Laplace transform of the frequency-dependent radiation impedance of a baffled piston, i.e., its impulse response, is a function which is more directly related to the geometry of the piston than the impedance itself. It is here shown how this function can be described in terms of a finite pulse called the characteristic pulse, whose shape depends on that of the piston, and that its evaluation depends on a relatively simple integration around the piston's contour. A number of examples show that the characteristic pulse can be evaluated exactly for certain piston shapes. Geometrical features of the piston's shape, such as corners, have a predictable effect on the characteristic pulse, and hence on the radiation impedance; some of these fundamental relationships are derived in the form of simple theorems.
An exact expression for the Lommel-diffraction correction integral
Authors: Rogers Peter H. , Van Buren A. L.
Published: October 2005

A number of authors have obtained diffraction corrections for a circular piston source by numerical or graphical integration of an approximate expression for the piston field attributable to E. Lommel [Abh. Bayer. Akad. Wiss. Math.-Naturwiss. Kl. 15, 233 (1886)]. Lommel's expression gives the piston field in terms of trigonometric functions and Lommel functions of two variables. It is shown here that the required integral of Lommel's expression can be evaluated analytically to obtain a simple closed-form expression for the diffraction correction. The extrema of this expression are obtained as roots of simple transcendental equations, and approximation formulas for these roots are given. It is also shown that the same expression can be obtained by taking the limit as ka → ∞ (k is the wavenumber and a is the piston radius) of Williams's exact integral expression [J. Acoust. Soc. Am. 23, 1–6 (1951)] for the diffraction correction. Finally, it is shown both analytically and by comparison with numerical values for Williams's exact expression that this simple closed-form expression is a good approximation for the diffraction correction at all distances from the source provided that (ka)1/2 ≫ 1.
Ray-acoustic intensity in a moving medium. II. A stratified medium
Authors: Thompson Robert J.
Published: October 2005

Techniques are developed for computing ray-acoustic intensity in a horizontally stratified moving medium. Under the assumptions that the speed of sound and the components of the wind vector are piecewise linear functions, it is shown that an exact expression for the intensity can be obtained by patching together functions with the aid of a table of integrals. For the general horizontally stratified moving medium, the ray paths and the intensity can often be approximated by numerically solving a system of ordinary differential equations.
Frequency smearing of sound forward-scattered from the ocean surface
Authors: Brown M. Vertner , Frisk George V.
Published: October 2005

The results of an open sea experiment are presented in which CW acoustic signals generated by an omnidirectional source and forward-scattered by the ocean surface were measured. The statistics of the surface waves were simultaneously measured by a surface sensing buoy. It is found that for acoustic frequencies in the range of 100–500 Hz and for conditions of small surface roughness, the acoustic spectrum contains the discrete carrier frequency component with sidebands symmetrically positioned about the carrier, as predicted theoretically. The sidebands are directly related to the surface wave spectrum through a response function, which in general depends on both the acoustic carrier and surface wave frequencies. The experimental response function is compared with response functions predicted theoretically by Roderick and Cron, Parkins, and Williams. In addition, for conditions of moderate roughness, marked asymmetry in the acoustic spectra and strong spectral components that are not prominent in the surface spectra are found.
Auditory filter shape
Authors: Patterson Roy D.
Published: October 2005

Threshold for a pulsed tone was measured as a function of its distance in frequency from the edge of a broad band of noise with very sharp skirts. Tone frequency was held constant at 0.5, 1.0, 2.0, 4.0, or 8.0 kHz while the position of the noise edge was varied about the frequency of the tone. The spectrum level of the noise was 40 dB. As expected, tone threshold decreased as the distance between the tone and the noise edge increased, and the rate of decrease was inversely related to tone frequency. The data were used in conjunction with a simple model of masking to derive an estimate of the shape of the auditory filter. A mathematical expression was found to describe the filter, and subsequently, this expression was used to predict the results reported by several other investigators.
How does a mynah bird imitate human speech?
Authors: Klatt Dennis H. , Stefanski Raymond A.
Published: October 2005

Broad-band spectrograms and computer-generated spectra have been obtained of a trained Indian Hill mynah bird and its tutor each saying seven English sentences composed of four to 12 phonetic segments. Comparisons of sound spectrograms indicate that the bird is able to produce good approximations to virtually any spectral or temporal detail, although energy in frequencies below about 700 Hz (in the range of the first formant) is attenuated by about 10–20 dB relative to human spectra. Fundamental frequency (F0) contours, formant transitions, and turbulent noise spectra for fricatives and plosive bursts are especially well imitated. Contour shapes are better preserved than absolute formant or F0 values. Some vowel spectra have clear formant patterns but many have multiple resonances and formant splitting effects that cannot be accounted for in terms of an acoustic tube model of formant generation. A new description of the behavior of the mynah syrinx is proposed to account for the observed acoustic patterns. One of the paired external labia in the syrinx is implicated as the source of voicing energy (analogous to the human vocal cords). Some or all of the formant resonances are produced by exciting the mechanical resonant modes of the internal tympaniform membrane in the syrinx. The five pairs of intrinsic muscles that are associated with the syrinx are capable of controlling membrane tensions and regulating the position of the external labia in the syringeal airways during sound production.
Articulatory interpretation of the “singing formant”
Authors: Sundberg Johan
Published: October 2005

The “singing formant” is a high spectrum envelope peak near 2.8 kHz characteristic of vowel sounds produced in male Western opera and concert singing. An acoustical model of the vocal tract is capable of generating such a peak provided that three conditions are met: (1) The cross-sectional area in the pharynx must be at least six times wider than that of the larynx tube opening. If so, the larynx tube is acoustically mismatched with the rest of the vocal tract, and an extra formant is added to the vocal tract transfer function. (2) The sinus Morgagni must be wide in relation to the rest of the larynx tube. This may tune the frequency of the extra formant to a value between the frequencies of the third and fourth formants in normal speech. (3) The sinus piriformes must be wide. This reduces the frequency of the fifth formant to about 3 kHz. X-ray studies of a raised and lowered larynx showed that these three conditions may be fulfilled when the larynx is lowered. Thus, the larynx lowering, typical of male professional singing, seems to explain the “singing formant” and other formant frequency differences between normal speech and male professional singing.
Self-reciprocity calibration of echo-ranging transducers
Authors: Reid John M.
Published: October 2005

The technique of calibrating transducers for available power efficiency and effective area under nearfield and farfield conditions and continuous wave and transient cases is derived. Experimental continuous wave and peak power calibrations of medical echo ranging transducers have been made. Errors estimated for this technique are approximately 30% with the equipment used to date. The ultimate accuracy is estimated to be in the vicinity of 6%. The use of calibrated transducers to establish known acoustic fields and to measure unknown acoustic fields is discussed. It is shown that this technique could be used to measure peak pulse power from a medical diagnostic apparatus by calibrating the presently used clinical transducers. The calibration of small probes to make intensity measurements in highly nonuniform fields is possible with these techniques.
Acoustic reflex and critical bandwidth
Authors: Popelka Gerald R. , Karlovich Raymond S. , Wiley Terry L.
Published: October 2005

The threshold of the acoustic reflex was measured with an electroacoustic impedance bridge in six subjects with normal hearing sensitivity. Reflex thresholds were measured as a function of the bandwidth (1, 10, 30, 100, 300, 1155, 2042 Hz) of an acoustic stimulus centered around 1 kHz, and also for broad-band noise (5780-Hz bandwidth). Acoustic-reflex thresholds were relatively constant for bandwidths between 1 and 300 Hz, and became progressively lower as the bandwidth increased (1155, 2042, 5780 Hz). The data support the idea that there is a critical-band mechanism operating for elicitation of the acoustic reflex, and that the critical bandwidth for the acoustic reflex at 1 kHz is substantially wider than that observed in psychophysical studies.
Log spectra of Gaussian signals
Authors: Gray A. H.
Published: October 2005

Expressions for the mean and variance of the log spectra of Gaussian zero-mean signals are derived, and the results discussed briefly.
Estimation of the two-dimensional spectrum of the space-time noise field for a sparse line array
Authors: Nuttall Albert H. , Carter G. Clifford , Montavon Ernest M.
Published: October 2005

For a line array immersed in a stationary homogeneous noise field composed of plane waves of differing speeds and angles of arrival, standard beamforming is not useful for estimating the noise spectrum directionality. However, the two-dimensional spectrum of the received noise field enables resolution in temporal-frequency and in spatial-frequency and can thereby indicate the temporal-frequency content and the apparent speed along the line array of plane-wave arrivals. The interrelationships and attributes of the space-time correlation, the cross-spectrum, and the two-dimensional spectrum are presented and interpreted via simple examples. A technique for estimation of the two-dimensional spectrum for a sparse line array and examples of its use and interpretation are given.
Constrained array optimization by penalty function techniques
Authors: Winkler Leonard P. , Schwartz Mischa
Published: October 2005

We investigate a stochastic penalty algorithm, which can be used to find a constrained optimum point for a concave or convex objective function subject to a nonlinear constraint which forms a connected region, even when we do not have the objective function available, but have only a noisy estimate of the objective function. When the constraint consists of one linear equation, we prove convergence to the constrained optimum value and bound the rate of convergence of the algorithm to the constrained optimum value. We then apply this algorithm to the nonlinear problem of automatically making an array of detectors form a beam in a desired direction in space when unknown interfering noise is present so as to maximize the signal-to-noise ratio subject to a constraint on the super-gain ratio.
PEST: Note on the reduction of variance of threshold estimates
Authors: Hall J. L.
Published: October 2005

There is a tradeoff in the PEST adaptive psychophysical procedure between the rule used to determine when to change the level at which the stimulus is being presented (“deviation limit”) and the rule used to determine when to terminate a series of observations (“stopping step size”). For some conditions, the average number of observations required to arrive at an estimate of threshold can be reduced with no loss of precision by decreasing both the deviation limit and the stopping step size.
Review of progress and applications in acoustic microscopy
Authors: Kessler L. W.
Published: October 2005

Acoustic microscopy is a relative newcomer to the field of acoustic imaging which will seek to discriminate micron-size structural detail and render visible mechanical microstructure. Although in an early stage of development, wide areas of application are anticipated in both the physical and biological sciences. This paper presents a discussion of recent developments in acoustic microscopy techniques and applications. Due to the resolution requirement, the present efforts to develop experimentally useful systems employ optical methods of sound-amplitude detection through various intermediate methods of coupling. The desired acoustic pattern can be displayed as a hologram or as a conventional image. Phase contrast and dark field techniques are also possible. Resolution better than 10 μm has already been reported and another order of magnitude improvement is only a few years off. Thus, acoustic resolution may soon be demonstrated that is equivalent to that obtained with optical microscopy. During the course of preliminary investigations, various interesting and meaningful contrasts have been demonstrated between acoustic and optical micrographs of the same specimens. These are presented as first examples of applications for acoustic microscopy.
Estimating refractive effects in acoustic sounding
Authors: Georges T. M. , Clifford S. F.
Published: October 2005

In an earlier paper [J. Acoust. Soc. Am. 52, 1397–1405 (1972)], we modeled the effects of atmospheric refraction on the quantities measured in bistatic acoustic-echo sounding. Here we extend those results to the case of monostatic sounding, a configuration of particular interest experimentally. To estimate refractive displacement of the scattering volume, we have to assume linear wind and temperature profiles. Two tables show numerical values of refractive corrections, calculated for both representative monostatic and bistatic geometries.
Reverberation time measurements of the scattering of sound by turbulence
Authors: Hunter G. H. , Lowson M. V.
Published: October 2005

Measurements of the reverberation time of a small (29 m3) room have been made using the Schroeder impulse response method while the air in the room was agitated by a 0.65-m-diam, 14-bladed, 2.6-kW fan and compared with similar measurements made with the fan off. The decay times were found to be shorter when the fan was on and this decay time difference is ascribed to an effective extra attenuation α1, due to scattering of the sound field by the fan-generated turbulence. Only order-of-magnitude estimates of α, are possible; α1 ∼ 10−3 m−1 and is frequency-independent from 600 Hz to 5 kHz. The results agree to an order of magnitude with recent turbulence scattering theories. Some of the implications of these measurements for present theories and future experiments are discussed.
Effect of geometrical symmetry on acoustic scattering in the shadow region
Authors: Carlson Marianne , Hunt John T.
Published: October 2005

The exterior formulation of the Helmholtz equation for a scattered wave is reduced to a line integral via the Maggi transformation. This integration is performed over the line dividing a three-dimensional scatterer into an illuminated region and a “shadow region.” The scattered wave was found for “shadow lines” with shapes of regular polygons and a circle. As the symmetry is broken, the amplitude of the scattered wave directly in back of the scatterer (on the symmetry axis) decreases.
Underwater sound transducer beam control with reflectors
Authors: McKinney C. M. , Wallace R. H.
Published: October 2005

Several underwater sound reflector-transducer systems are described, and experimental data are presented to show the relationship between aperture size, near-focal distance, depth of focus, beamwidth, minor lobe characteristics, and test distance for circular, parabolic, and elliptical converging reflectors. In addition, transducer systems using planar and diverging reflectors are described, and sets of experimental data are presented to demonstrate the beam formation characteristics of those systems.