Volume 47, Issue 1A, January 1970

Acoustics of Powell Symphony Hall, St. Louis
View Description Hide DescriptionThe new home of the St. Louis Symphony Orchestra was inaugurated on 24 January 1968. This concert hall was reconstructed from a large motion picture theater first opened in 1925. This paper describes the major problems encountered in the reconstruction of the house, the changes that were made, the design of the stage enclosure, the finishes and furnishings, and the resulting reverberation‐time characteristics of the Hall.

Sound Transmission through Rectangular Slots of Finite Depth between Reverberant Rooms
View Description Hide DescriptionAn approximate theoretical relationship has been developed for the transmission of sound between two reverberant rooms through a connecting rectangular slot of finite depth. The theory makes use of impedance functions of rigid weightless rectangular pistons and assumes plane‐wave propagation through the slots. Slots having aspect ratios of 1, 2, 4 and 8, and depth of 12 in., were tested between two 1750‐ft^{3} reverberation chambers. Three different slots for each aspect ratio were tested, and the slot dimensions were so chosen as to have the cross‐sectional areas π/4, π, and 4π in.^{2} in each case, to compare with previously published results on circular apertures having these areas. Numerical solutions on a digital computer are compared with experimental results and the agreement is found to be excellent over the range of the parameter—wavenumber times equivalent radius of a circular section having the same area as the rectangular section—from 0.05 to 3.2.
 LETTERS TO THE EDITOR


Acoustic Waveguide Having a Variable Section
View Description Hide DescriptionA waveguide for the measurement of oblique plane‐wave reflection from absorbents has been constructed. The device operates in the 1‐kHz region. The unique feature of the guide is its moving wall, which permits a range of angles of incidence at a single frequency. Impedance of flexible polyurethane foam has been measured as a function of angle of incidence.
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 PROGRAM OF THE SEVENTY‐EIGHTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA

 Session 4B. Sound Radiation
 Contributed Papers

Transient Radiation Loading on Spherical Sonar Arrays
View Description Hide DescriptionTransient surface pressures generated by a piston set in a spherical baffle or sonar array are obtained in analytical form for velocity steps and CW pulses. Neither the wave‐harmonic series, which converges poorly at early times, nor geometric acoustics, which predicts zero pressure on passive elements, is applicable. A technique successfully used for CW impedance calculations was adapted to transient situations. On passive elements, the pressure is computed from Watson's “creeping‐wave” formulation, which fails on the active element; there, the pressure is approximated by ignoring baffle curvature. The required Laplace integrals are available in the literature. Numerical results are presented. [Sponsored by Naval Ship Systems Command, under Computer Applications, Inc. subcontract.]

Numerical Calculation of Farfield of Transducer Array near Critical Frequency
View Description Hide DescriptionFor the case of a simple box‐shaped transducer array, operating near a frequency at which the interior space of the box has a standing‐wave solution with p = 0 at the surface, one method of calculating the external radiation field has been developed and demonstrated by Schenck [J. Acoust. Soc. Amer. 44, 41–58 (1968)]. An alternative method of solution to this same problem is demonstrated, based on an approximation to the sound pressure at the surface of the array.

Some Solutions to a Mixed‐Boundary‐Value Problem
View Description Hide DescriptionMost problems in wave propagation are characterized by boundary conditions of only one type, e.g., vanishing normal‐velocity components in the case of a resonant cavity. The problem investigated by D. L. Lansing, C. E. Watkins, and G. T. Kantarges, “Oscillating Pressures within a Cylindrical Chamber that Has a Circular Piston in One End Wall” [J. Acoust. Soc. Amer. 36, 2222–2232 (1964)] is also of that type. A problem in the same vein, but with a pressure‐release surface somewhere on the cylinder surface appears to be a logical and simple extension, but this is not the case, since the boundary conditions become mixed. Numerical techniques have been employed to obtain solutions to the problem of a cylinder with a piston of smaller radius than the cylinder radius at one end, with the shoulder having either a vanishing velocity condition or pressure‐release condition imposed. Cases where the piston is inserted in the cylinder are also presented. Comparisons are made to the analytical solutions attained by Lansing et al.

New Method for Acoustical Radiation Problems with Mixed‐Boundary Values
View Description Hide DescriptionA series‐expansion method for the solution of acoustical‐radiation problems with mixed‐boundary values is presented. The condition of a given velocity on a transducer face and a given pressure or impedance on the surrounding boundary is of interest in underwater acoustics. With this mixed‐boundary condition, solutions are difficult to obtain using the usual methods in even the simplest cases. In the method presented here, a wavefunction expansion is truncated to include only the number of terms equal to the number of specified boundary values. The solution improves as this number increases, and coefficients may be evaluated through a matrix inversion as in a nearfield‐to‐farfield prediction method presented previously [J. Acoust. Soc. Amer. 44, 351 (A) (1968)]. The particular case of a radiator on a sphere is treated and results are presented that show that the sound beam is more directive if the remaining portion of the sphere is soft. [Work sponsored by the Office of Naval Research (Acoustics Programs Branch).]

Computer Display of Array Characteristics
View Description Hide DescriptionThe calculated response of a linear array of isotropic point sensors to a plane wavefront has been displayed in three‐dimensional computer plots. These plots display beamformer output as a function of signal angle and a third variable selected from frequency, beam angle, and array shading. Sidelobes appear as sharp ridges that curve across the baseplane of the plot. Changes and shifts in sidelobe structure as a function of the third variable are readily visible. General equations for contours of constant amplitude in the signal‐angle, beam‐angle, and signal‐angle frequency planes are derived. Plots of these equations can be used to extrapolate one known beam pattern to other beam angles and frequencies.

Analysis of Array with Nonlinear Amplifier/Transducer Modules
View Description Hide DescriptionProcedures for modeling the performance of a transmitting array require either an explicit or implicit definition of the velocity of each radiating element as a function of the electrical input signal and the acoustic pressure on the radiating surface. To date, most array modeling work has been restricted to linear systems where the velocities are computed from the electrical input signal and the linear equivalent circuit for each element in the array. When an array contains nonlinear amplifiers or transducers, this equivalent circuit, in general, will be a function both of the input signal and the pressure on the radiating surface, and the linear analysis techniques cannot be used. Two methods, repeated matrix inversion and iterative lookup, have been developed and applied to the hydroacoustic amplifier/transducer module. In both methods, the nonlinear operating profile characteristics of the coupled amplifier/transducer module are known, either by prediction using a simulation program for nonlinear devices or by measurement. The operating profile is defined by several equivalent Thevenin circuits in the former method and by tabular data in the latter. Several examples show that for larger arrays the latter method requires much less computer time and storage than the matrix method.

Wave Propagation in an Infinite Elastic Plate in Contact with an Inviscid Liquid Layer
View Description Hide DescriptionThe dispersion relation for straight‐crested waves in an isotropic plate in a state of plane strain that is covered by a layer of an incompressible liquid is derived and investigated in the limits of very long wavelengths (thickness‐stretch vibrations of the plate‐liquid system) and of very short wavelengths (surface waves and the solid‐liquidinterface). In the case of surface waves, there are two dispersive modes, one predominantly elastic (analogous to Rayleigh waves) and the other essentially fluid, and in the thickness‐stretch case, there are an infinite number of essentially elastic modes and one fluid mode. An approximate version of the dispersion relation valid for arbitrary wavelength is obtained by using two nonclassical plate theories to account for the extensional and flexural deformations of the plate. This relation gives rise to five modes on the real branch, which are identified as being thickness‐stretch, thickness‐shear, flexural, extensional, and fluid in character, and three modes on the imaginary branch, namely, flexure, thickness‐shear, and thickness‐stretch. Two of the five cutoff frequencies are modified by the presence of the liquid layer. A variety of numerical results are presented in graphical form.

Acoustic Radiation from Fluid‐Loaded Rectangular Plates
View Description Hide DescriptionThe acoustic radiation into a fluid‐filled infinite half‐space from a randomly excited, thin rectangular plate inserted in an infinite baffle is discussed. The analysis is based on the in vacuo modes of the plate. The modal coupling coefficients are evaluated approximately at both low and high (but below acoustic critical) frequencies. An approximate solution of the resulting infinite set of linear simultaneous equations for the plate modal velocity amplitudes is obtained in terms of modal admittances of the plate‐fluid system. These admittances describe the important modal coupling due to both fluid inertia and radiation damping effects. The effective amount of coupling, and hence the effective radiation damping acting on a mode, depends on the relative magnitudes of the structural damping—i.e., on the widths of the modal resonance peaks and on the frequency spacing of the resonances. Expressions are obtained for the spectral density of the radiated acoustic power for the particular case of excitation by a turbulent boundary layer. [Work supported by the Office of Naval Research.]

Sound Radiated by Beam‐Stiffened Plate
View Description Hide DescriptionA common structural element in aerospace and marine vehicle design consists of a relatively thin skin supported by a framework of attached beams. The present study treats this configuration as a thin elastic plate with one or more parallel beams attached. In order to find the sound pressure radiated by such a plate, the dynamic response of the plate beam system is first computed following the procedure of Lamb [J. Acoust. Soc. Amer. 33, 628–633 (1961)]. The two‐dimensional Fourier transform of the response thus obtained is used to calculate the radiated soundpressure. The resulting pressure field is then used as an indirect means of finding the significant interframe resonances. [The work presented here was supported by the Office of Naval Research Structural Mechanics Branch.]

Comparison between Theory and Experiment for a Mechanical Luneberg Lens
View Description Hide DescriptionThe first mechanical Luneberg lens was built and tested by Toulis in the latter half of the previous decade. Using the wave theory [C. A. Boyles, J. Acoust. Soc. Amer. 43, 709 (1968); G. E. Lord, J. Acoust. Soc. Amer. 43, 1177(L) (1968); G. A. Brigham, Int. Congr. Acoust., 6th, Tokyo (August 1968)] for a Luneberg lens with a monopole feed close to the nearfield, we have computed, for Toulis' test conditions, the polar response of an ideal lens. The comparison is within 4 dB throughout the 180° scanning pattern. Visual observation of Toulis' compliant‐tube lens reveals that the actual fabrication would produce some cylindrical effects in the lens. When allowances are made for this, the theory and experiment are observed to be within 2 dB of each other in the full pattern over the 2 oct test bandwidth.

Sinusoidal Horns
View Description Hide DescriptionIt is pointed out that a sinusoid satisfies Salmon's criterion for a good horn shape. Calculations have been made of the throat impedance of sinusoidal horns of various dimensions, including the case of a single globe terminating in a cusp. Depending on the relative dimensions of the mouth and throat, the device may be used as an impedance transformer. Experimental determinations of directivity of an underwater horn have been made and found to compare favorably with conical horns. Finally, it is demonstrated that several musical instruments employ sinusoidal cavities, the bell of the English horn being discussed in particular.
 Session 4C. Interaction of Light with Sound Waves I
 Invited Papers

Resonance‐Enhanced Brillouin Scattering in Crystals
View Description Hide DescriptionThe Brillouin scattering intensity exhibits resonance enhancement as the frequency of the incident radiation approaches excitonabsorption bands and the interband absorption edge. A theory of resonance‐enhancedBrillouin scattering that is analogous to that of resonance‐enhancedRaman scattering [E. Burstein, D. L. Mills, A. Pinczuk, and S. Ushioda, Phys. Rev. Lett. 22, 348 (1969)] is presented in terms of the scattering of polaritons by acoustic phonons via the exciton and continuum electron‐hole pair excitation parts of the polaritons. The theory also provides a basis for the enhancement of the electro‐optic and elasto‐optic coefficients, which is observed in II–VI compounds near the absorption edge. Two mechanisms are taken into account, that of the deformation potential coupling arising from the strain field, which gives rises to the piezo‐optic effect and, in the case of piezoelectric crystals, that of the Frölich interaction arising from the macroscopic electric field, which gives rise to the electro‐optic effect. Experimental results are presented for ZnSe and CdS. [Research supported in part by the Army Research Office—Durham and the Advanced Research Projects Agency.]

Phonon Instabilities and Interactions near Solid‐State Phase Transitions
View Description Hide DescriptionThe rôle of phonon instabilities (soft modes) in several types of solid‐state structuralphase transitions has recently been demonstrated by inelastic light‐scattering experiments. The symmetry of the soft phonon mode relates the crystal structures above and below T_{c} , and the temperature dependence of its frequency is associated with various crystal properties near T_{c} . Examples of both Brillouin zone‐center (q = 0) and zone‐boundary (q≠0) soft modes are presented. The interactions between optic and acoustic phonons respOnsible for sound‐velocity anomalies near T_{c} are discussed for several classes of phase transitions(ferroelectric, order‐disorder, etc.). While emphasis is placed on phase transitions in crystals of the perovskitestructure (e.g., ), some attention is also given to interesting transitions in other types of crystals.
 Session 4D. Speech Perception
 Contributed Papers

On the Modes and Mechanisms of Perception of Speech Sounds
View Description Hide DescriptionPrevious studies indicated the existence of categorical and continuous modes in the perception of speechsounds. It has been shown, however, that these two modes are not dichotomous, but the degree of categorical response depends largely on various factors such as acoustical properties of stimuli, context, and test procedures [H. Fujisaki and T. Kawashima, Int. Congr. Acoust., 6th, Tokyo (1968), paper B‐3‐6]. A method is described for the precise measurement and quantitative expression of a subject's ability of discriminating between two speechsounds. The perception of various categories of speechsounds including vowels, semivowels, liquids, voiced stops, and fricatives is studied experimentally and analyzed using stimuli compiled by a digital computer. A mathematical model of the process of speech perception is then presented that relates discrimination to identification, taking into account the reliability of the short‐time memories involved in the task of discrimination. The latter is shown to be affected by various stimulus attributes and test conditions, which explains the variability in the degree of categorical response to various speechsounds.

Silent Interval Duration as a Perceptual Cue of Speech Pauses
View Description Hide DescriptionThe effect of silent‐interval duration on the perception of pauses in speech was investigated. The stimuli consisted of five recorded sentences within which the words “lost” and “contact” were manipulated so that their syntactic relation to one another varied in complexity from sentence to sentence. Twelve subjects, working individually, mechanically adjusted the silent‐interval duration between the words “lost” and “contact” within each sentence in order to locate (1) the pause detection threshold, (2) optimal fluent pause duration, and (3) minimal hesitation pause duration. Across the five sentences, the mean durations were 6, 186, and 505 msec, for the three pause types, respectively. Statistical analysis, however, showed that silent interval durations for these three pause types differed significantly only when occurring between phrases. This was not true of within‐phrase pauses. Thus, contrary to usual assumptions in the literature, these results suggest that for within‐phrase pauses, at least, silent‐interval duration is an insufficient perceptual cue for differentiation of fluent and hesitation pauses. [Supported by NSF and NIH grants.]

The Glottal Stop as a Junctural Correlate in English
View Description Hide DescriptionThe fundamental‐frequency contours of English sentences have been thought to be affected by sobglottal pressure,laryngeal tension, vowel height, changes in transglottal air pressure, stress placement, and coarticulation effects. In this study, fundamental‐frequency contours in vowel‐vowel transitions have been studied for varying constituent structures, phonemic environments, and stress patterns. Transitions within words, at formative boundaries within words (re‐enter), at word boundaries, and at phrase boundaries were studied, and the fundamental‐frequency contours for these transitions were recorded. It was found that many speakers use the glottal stop to indicate juncture, and that this usage is conditioned by the position of the transition in the formative structure of the utterance. Thus the changes in fundamental frequency in vowel‐vowel transitions serve as junctural cues. Models that describe the variations in fundamental frequency in English sentences must, therefore, make provision for this effect.

A Mutually Complementary Effect of the Rate and the Amount of Formant Transition in Distinguishing Vowel, Semivowel, and Stop Consonant
View Description Hide DescriptionThe purpose of this research is to examine the effect of changes in rate and amount of a formant transition in speech sounds. Synthesized wordlike sounds /a:/, /aua/, /awa/, and /aba/ were used as the experimental materials because the motions of first formant frequency are the main cue for distinguishing them, and accordingly, the first formant frequency could be used as the only control factor in the experiment. Eight different transition patterns and 11 different target values between 250 and 790 Hz were prepared as x in a wordlike sound /axa/. The total length of each sound was 450 msec. From the results of listening tests, a distribution diagram of identification for any given sound was obtained. It was found that an increase in the rate of frequency change V reduced the frequency deviation F, necessary to switch an identification of a particular phoneme, and that the locus of boundary values between different words were represented approximately by a formula , where V _{θ}, F _{θ}, and C were constants depending on particular word pairs. [Work supported in part by grants from the Air Force Cambridge Research Laboratories and the National Institute of Health.]