Index of content:
Volume 73, Issue 6, June 1983

Presbycusis, sociocusis and nosocusis
View Description Hide DescriptionData and idealized curves are presented for a number of surveys on the threshold of hearing of persons who were not exposed, by and large, to intense workplace noise. From these results, and on the basis of certain assumptions, new generalized functions are presented to show pure presbycusis (aging) and sociocusis (non‐work‐noise‐induced hearing loss); typical presbycusis; typical sociocusis; and typical presbycusis‐plus‐sociocusis. Hearing level surveys, conducted in industrialized societies to reveal presbycusis, appear to reflect the joint effects of presbycusis and sociocusis, especially in males, and factory workers may suffer more sociocusis and a greater degree of presumably non‐noise‐related otological disorders (nosocusis) than are found in the general population.

A new higher order dynamic theory for thermoelastic bars. I: General theory
View Description Hide DescriptionA dynamic approximate theory capable of predicting high‐frequency behavior of cylindrical thermoelastic bars is developed using a new theory. The cross section of the bar has an arbitrary shape and contains an arbitrary number of holes. The approximate theory is valid for all of the deformation modes such as flexural, longitudinal, torsional, etc. The use of the new method permits one to eliminate any inconsistency which may occur between lateral boundary conditions and the distributions of displacements or temperature assumed over the cross section of the bar. Accordingly, the method enables one to correctly describe the reflections of the waves propagating along the bar. This, in turn, makes the dispersive characteristics of waves in bars predicted by the approximate theory agree with those obtained from the exact theory without having to introduce any matching coefficients into the approximate theory.

A new higher order dynamic theory for thermoelastic bars. II: Application to thermoelastic circular and rectangular bars
View Description Hide DescriptionIn order to show and illustrate the power of the theory proposed in Part I [J. Acoust. Soc. Am. 7 3, 1918–1922 (1983)] for the dynamic behavior of thermoelastic bars, the theory is applied to bars with circular and rectangular cross sections. In these applications, the order of the theorym is chosen to be 3. The general equations of the approximate theory governing all of the deformation modes (such as longitudinal, flexural, torsional, etc.) of circular and rectangular bars, and accomodating the thermal effects are presented. With the object of assessing the approximate theory, approximate and exact dispersion curves are compared for the flexural and longitudinal waves propagating in circular bars. A good match between these two is obtained without using any correction factors in the approximate theory. Further, experimental wave profiles are compared for longitudinal waves in rectangular bars. It is observed that the two agree quite well.

Linearity of fisheries acoustics, with addition theorems
View Description Hide DescriptionAn experiment to verify the basic linearity of fisheries acoustics is described. Herring (C l u p e a h a r e n g u s L.) was the subject fish. Acoustic measurements consisted of the echo energy from aggregations of encaged but otherwise free‐swimming fish, and the target strength functions of similar, anesthetized specimens. Periodic photographic observation of the encaged fish allowed characterization of their behavior through associated spatial and orientation distributions. The fish biology and hydrography were also measured. Computations of the echo energy from encaged aggregations, derived by exercising the linear theory with the target strength functions of anesthetized fish and gross behavioral characteristics of encaged fish, agreed well with observation. This success was obtained for each of four independent echosounders operating at frequencies from 38 to 120 kHz and at power levels from 35 W to nearly 1 kW. In addition to demonstrating the basic linearity of fisheries acoustics, the experiment verified both conventional acoustic measurements on anesthetized fish, at least for averaging purposes, and the echo integration method. Two simple theorems summarizing the meaning of linearity for use with the echo integration method are stated.

Coherent attenuation of acoustic waves by pair‐correlated random distribution of scatterers with uniform and Gaussian size distributions
View Description Hide DescriptionAcoustic wave attenuation due to multiple scattering in a two‐phase medium consisting of a fluid with embedded rigid, fluid, or elastic particles of varying sizes is discussed. The formulation, involving the exciting and scattered fields of an incident acoustic plane wave, is based on the T‐matrix method. The propagation features of coherent waves in the mixture are described by the dispersion equation which is derived by applying standard statistical approximations to the discrete random medium. Special attention is focused on the pair‐correlation function between the scatterers using the self‐consistent approximation (SCA) which seems better than the Percus‐Yevick approximation (PYA) when the volume fraction becomes significant. Besides deriving low‐frequency analytical results for coherent wave speed and attenuation, the dispersion equation has been solved numerically for higher frequencies for particles with uniform and Gaussian size distributions.

Propagation in air of N waves produced by sparks
View Description Hide DescriptionWeak sparks, of length 0.5–1.0 cm and energy per discharge 0.01–0.1 J, served to produce intense acoustic transients resembling Nwaves. Amplitude decay and waveform elongation were studied, for propagation distance up to 2 m, through the use of a wideband capacitormicrophone with essentially uniform response from dc to 1 MHz. Within the range of propagation distances for which the first (compression) phase of the Nwave was completely formed, the duration of this compression phase T and its amplitude p _{ s } were found to agree with the theoretical relations T=T _{0}[1+σ_{0} ln(r/r _{0})]^{1} ^{/} ^{2} and p _{ s } =(r _{0} p _{ s } 0/r)[1+σ_{0} ln(r/r _{0})]^{−} ^{1} ^{/} ^{2}, where σ_{0} is a parameter that depends upon the values of p _{ s } and T at a reference distance from the source r _{0}. The time required for the amplitude of the head shock to increase from 5% to 95% of peak value was observed to vary from 0.45 μs (imposed by the microphone response) to greater than 2.0 μs as the wave traveled outward and as its amplitude decreased. Finally, the microphone was calibrated through use of the variation with distance of measured values of T; this new method has led to calculation of a free‐field sensitivity that agrees within ±1 dB with the results of other calibrations.

Nonlinear mixing of surface acoustic waves propagating in opposite directions
View Description Hide DescriptionThe parametric mixing of two modulated surface acoustic waves propagating in opposite directions is studied with reference to nonlinear signal processing applications by the coupled mode theory of nonlinear surface waves. In the case of propagation in opposite directions the combination frequency wavesgenerated out of the nonlinear interaction of the two primary waves and their harmonics with one another do not satisfy the phase‐matching condition. Hence there exists no mode coupling between the primary waves. At the same time the amplitude of each combination frequency wave is proportional to the product of a harmonic amplitude of one of the interactingwaves with a harmonic amplitude of the other wave. The variation of these harmonic amplitudes as functions of the slow scale variables are governed by two sets of coupled amplitude equations, each set pertaining to one primary wave and its harmonics. It is further shown that, in addition to surface wave modes, there also exist bulk wave modes in a certain range of values of the primary wave frequency ratio. The paper concludes with indicating the relevance of the present study to the acoustical implementation of nonlinear signal processing operations like convolution, correlation, etc.

Field of a parametric focusing source
View Description Hide DescriptionAn analytical description for the field of a parametric focusing source is derived. It is valid for spherically concave sources with small aperture angle and high k a, under conditions of quasilinear interaction (strong shocks precluded). The solution furnishes computations on the phase and amplitude of difference frequency sound along the axis and in the focal plane, as well as on the width of the radiation lobe in the focal region. Underwater experiments conducted with an f/2 lens coupled to a dual, interleaved primary array are discussed. The results support the utility and validity of the analytical model for describing the distribution of sound along the acoustic axis and across the focal plane. The difference frequency radiation was found to be effectively focused, in that the width of the beam became quite narrow in the focal plane.

Time domain study of the terminated transient parametric array
View Description Hide DescriptionA spatial impulse response model of the parametric array is developed and used to give physical insight into its behavior when operated in a transient mode. Experimental measurements of the spatial dependence of the acoustic pressure waveforms produced by the transient parametric array are compared with the result of the convolution of the spatial impulse response with the specific pressure waveforms used. Particular emphasis is given to the case where the primary field is discontinuously terminated. In such cases effects due to the finite aperture of the parametric array and effects due to its termination may be seen by a point hydrophone either as separated or superposed events in time, depending on the geometry, when the parametric array is operated in the transient mode. Although the impulse response model is restricted by various assumptions, it can contribute to an understanding of the parametric array operation under more general circumstances.

Acoustic shadowing by an isolated seamount
View Description Hide DescriptionAcoustic shadowing by an isolated seamount has been studied by examining the multipath propagation measurements obtained in a shot run that passed over the seamount peak. Source depths of 24 and 196 m were used in the experiment. In the acoustic shadow, the propagation loss for the shallow 24‐m shots increased by 10–15 dB over the loss expected in the absence of the seamount. Examination of the pressure‐time history for shots deployed in the shadowing region revealed that the signals consisted of two components. The first and dominant pulse was determined to be a diffracted wave which passed over the seamount by rough‐surface forward scattering and diffraction. The subsequent group of weaker pulses was attributed to the energy which had passed over the seamount by a series of surface–bottom interactions. The shadowing loss increased by 3 dB per octave for frequencies greater than 50 Hz, in agreement with theory, but is appreciably greater than the predicted values at lower frequencies. The shadowing loss for the 196‐m shots was about 5 dB less than that observed for the shallower shots.

Normal‐mode propagation in deep‐ocean sediment channels: A sequel
View Description Hide DescriptionThe present writer has discussed various aspects of propagation in sediment channels [J. Acoust.Soc. Am. 7 0, 820–824 (1981)]. A simplifying assumption was that c _{ w }, the speed of sound in the water, is constant everywhere. In this sequel it is more realistically assumed that c _{ w } decreases slowly and linearly with height above the water–sediment interface. Consequently an acoustic barrier exists from the interface to, typically, 100–200 m above it. Acoustic energy in a signal traveling along the sediment channel can tunnel upward through the barrier, thereby causing a ‘‘leakage’’ attenuation along the channel. Equations are derived to describe the acoustic field both in and above the barrier, and a long‐known method yields the amplitude attenuation factor caused by leakage. Using numerical examples from the 1981 article, we find that the leakage factor is a negligible 1% of the factor caused by absorption in the sediment. In this case, the approximation of constant c _{ w } was justified, but for a normal mode nearer cutoff the leakage would increase considerably.

Deconvolution of the fish scattering PDF from the echo PDF for a single transducer sonar
View Description Hide DescriptionThe purpose of this paper is to deconvolve the beam pattern effect from the amplitude distribution of sonar echoes from fish to determine the scattering processes at fish. The paper is a continuation of our acoustic methods to measure fish abundance. It demonstrates a direct procedure for determining the fish density (fish/m^{3}), the probability density function (PDF) of scattering processes at fish, and the PDF of echoes. The procedure uses nonoverlapping echoes from a single transducersonar system. The integral equation for the echo PDF is in Clay and Medwin [A c o u s t i c a l O c e a n o g r a p h y (Wiley, New York, 1977), pp. 476–482]. It relates the PDFs of the sonar output w _{ E }(e), transducer beam w _{ T }(b), and scattering process at the fish w _{ F }(e). I use the transformations b=exp(−x) and e=e _{0} exp(−y) to change the integral to the standard form of the convolution integral. The derivation of expressions of the convolution and deconvolution using z transformations follow directly. We use a ‘‘home‐style’’ microcomputer for computations. Tests of the deconvolution technique on fish echoPDFs for Lake Michigan alewife show the presence of the alewife (10–12 cm length) and an unidentified group of larger fish having two to three times the length of the alewife. Deconvolution of Lake Superior data for 1978 indicate the presence of smelt and an unknown group of larger fish. Deconvolution of 1979 Lake Superior data gives an echo PDF that can be attributed to smelt. In both lakes, fish density estimates are between 10^{−} ^{4} and 10^{−} ^{3} fish/m^{3}.

Dependence of ultrasonic propagation velocities and transit times on an electric biasing field in alpha quartz
View Description Hide DescriptionThe variation of the velocity of elastic waves and of ultrasonic transit times with the direction of propagation under the influence of an externally applied dcelectric field was calculated on the basis of known elastic constants and recently determined effective electroelasticmoduli for alpha quartz. Results are presented in graphical form for propagation directions in the three planes defined by the conventional Cartesian crystal axes. For each propagation direction the three possible acoustic modes are considered in conjunction with three mutually perpendicular field configurations.

Dynamic Young’s moduli of some commercially available polyurethanes
View Description Hide DescriptionThe Young’s modulus and loss tangent have been measured in air for a number of commercially available polyurethanes. A resonance technique was used for measurements over the approximate frequency range 10^{2} to 10^{4} Hz and the approximate temperature range 40° to −5 °C. Master curves and Williams–Landel–Ferry shift constants were detemined for the materials tested. The automated data acquisition system used is described. The experimental procedure was found to be a reliable method for determining the viscoelastic constants for extensional wave propagation in elastomeric materials.

On the acoustoelastic effect
View Description Hide DescriptionA simple method is presented for obtaining the stress tensor for small displacements in nonlinearly strained material. The physics of sonic wave propagation in deformed materials and acoustoelastic effects are discussed, and a feasable experiment is suggested for early diagnosis of plastic deformation. The calculational results for surface wave velocity as a function of applied static stress are presented in tabular form convenient for the experiments.

On the three‐dimensional vibrations of the cantilevered rectangular parallelepiped
View Description Hide DescriptionA solution is presented for the three‐dimensional problem of determining the free vibration frequencies and mode shapes for a rectangular parallelepiped which is completely fixed on one face and free on the other five faces. This problem apparently is previously unsolved in the published literature. The Ritz method is used, with displacements assumed in the form of algebraic polynomials. Convergence is studied. Numerical results are given for the first five frequencies of each of the four symmetry classes of vibration, for five thick parallelepiped configurations, including the cube. Contour plots are exhibited for the modal displacements of the cube. The effects of varying Poisson’s ratio are also observed.

Nonlinear extensional vibrations of quartz rods
View Description Hide DescriptionThe one‐dimensional scalar differential equation describing the extensional motion of thin piezoelectric rods is obtained from the general nonlinear three‐dimensional description. Only the elastic nonlinearities are considered. The relations between the quadratic and cubic coefficients of the rod and the fundamental anisotropicelastic constants of various orders are derived. The quadratic rod coefficients are calculated for various orientations of quartz rods, but not the cubic rod coefficients because the fundamental elastic constants of fourth order, which are required for the calculation, are not presently known. The nonlinear equation and boundary conditions are applied in the analyses of both intermodulation and nonlinear resonance of quartz rods. In each instance a lumped parameter representation of the solution, which is valid in the vicinity of a resonance, is obtained and the influence of the external circuitry is included in the treatment.

Free vibration of circular‐segment‐shaped membranes and plates of rectangular orthotropy
View Description Hide DescriptionAn analysis is presented for the free vibration of circular‐segment‐shaped membranes and plates of rectangular orthotropy. A circular‐segment‐shaped membrane is formed on an orthotropic rectangular membrane by fixing several segments. With the reaction forces acting on the edges of an actual membrane regarded as unknown harmonic loads, the stationary response of the membrane to these loads is expressed by the use of the Green’s function. The force distribution along the edges is expanded into Fourier series with unknown coefficients, and the homogeneous equations for the coefficients are derived by restraint conditions on the edges. For a circular‐segment‐shaped plate clamped at the edges, it is formed on a rectangular plate simply supported at the edges, in which the bending moments act on the edges in addition to the reaction forces. In this case, the moments regarded as unknown harmonic loads are also expanded into Fourier series with unknown coefficients, and are included in the equations for the coefficients. The natural frequencies and the mode shapes of the actual membrane or plate are determined by calculating the eigenvalues and the eigenvectors of the equations. The method is applied to circular‐segment‐shaped membranes and plates of rectangular orthotropy, the natural frequencies and the mode shapes of the membranes and plates are calculated numerically, and the effect of the shape and orthotropy is discussed.

Sampling strategies for monitoring noise in the vicinity of airports
View Description Hide DescriptionThis paper is the third in a series dealing with the development of temporal sampling strategies for estimation of mean noise levels in the vicinity of airports. It extends the previous analysis for westcoast, one‐direction airports (due to prevailing winds) to eastcoast, multidirection airports (Boston Logan, Washington Dulles, and National). The results show that the data for many of the eastcoast airport sites are nonstationary in the mean level and the corresponding consecutive sampling requirements predicted by the Dynamic Data System (DDS) methodology are very large, at times exceeding 1/3 of a year. When the data are stationary, Monte Carlo simulations using the data produce sampling requirements comparable to the values obtained by the DDS methodology. However, the DDS methodology tends to overestimate sampling requirements for nonstationary data. The simulations demonstrate that nonconsecutive sampling strategies reduce the overall sampling requirements for nonstationary data. In general, the results reveal the following: (a) Westcoast (one‐direction); ±50% precision—four weeks, any sampling strategy, ±35% precision—eight weeks, any sampling strategy. (b) Eastcoast (multidirection); ±60% precision—four weeks, one from each quarter, ±40% precision—eight weeks, one from each eighth.

Experience with new auditorium acoustic measurements
View Description Hide DescriptionAs the inadequacy of reverberation time as a predictor of the acoustical quality of auditoria has been recognized, many new measures have been proposed. Of these, early‐to‐late sound ratios and interaural cross correlations are generally accepted as correlates of two major aspects of acoustical quality. Accordingly, the present work includes a large number of measurements of these quantities in halls ranging from 200 to 2500 seats. The purpose of the work was to improve familiarity with the newer measures, to provide more published data, and to explore the dependence of these measures on other quantities. Variations of the new measures were examined within and among halls. Halls that are apparently similar in terms of reverberation times showed clearly identifiable differences when early‐to‐late sound ratios were considered.