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Mar 1960

Volume 32, Issue 3, pp. 311-410


Electronic Music Synthesis

H. F. Olson, H. Belar, and J. Timmens

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 311-319 (1960); (9 pages)

Online Publication Date: 11 Jul 2005

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The modern systems of communication have been applied to the electronic synthesis of music in the form of the electronic music synthesizer. The electronic music synthesizer is a machine which provides means for producing a tone with any frequency, intensity, growth, duration, decay, portamento, timbre, vibrato, and deviations. If these properties of a tone are specified, the tone can be produced by the synthesizer from a coded record. For implementing the electronic synthesis of music an improved and enlarged electronic music synthesizer Mark II has been developed and built. The new electronic music synthesizer and the use of the new synthesizer by professional musicians will be described.

Accurate Coupler Pressure Calibration of Condenser Microphones at Middle Frequencies

T. F. W. Embleton and I. R. Dagg

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 320-326 (1960); (7 pages)

Online Publication Date: 11 Jul 2005

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The technique whereby the reciprocity theorem is applied to the determination of the pressure sensitivities of microphones has been modified to improve the reliability and accuracy of the measurements. Sensitivities are measured in terms of the volume of a cavity, the capacity of a fixed condenser, and the variable setting of an accurate potentiometer. Six different pairs of measurements are made instead of three, which is the minimum possible number: this enables check to be made on the internal consistency of each calibration. The accuracy of the measured sensitivities is estimated to be ±0.05 db on an absolute scale and ±0.03 db relative to each other. This technique has been employed to measure the properties of several condenser microphones of each of three well known types over periods ranging from five months to two years. Results are given for their temperature and pressure coefficients, effective volumes due to nonrigidity of their diaphragms and drift with the passing of time.

Dependence of Acoustic Velocity in Some Aqueous Hydroxide Solutions on Temperature and Concentration

Graham W. Marks

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 327-335 (1960); (9 pages) | Cited 1 time

Online Publication Date: 11 Jul 2005

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The present work, which deals with acoustic velocity at 500 kc in aqueous solutions of LiOH, NaOH, KOH, and NH4OH and results derived therefrom, follows that which was recently reported concerning solutions of certain sulfates. It was found that the velocity vs temperature curves rise and are displaced toward lower temperatures with increase in concentration. The specific acoustic impedance varies linearly with concentration at 20°C. Adiabatic compressibilities are represented by the empirical 3/2‐power law. Results for NH4OH are at variance with those for the other hydroxides. The relative association declines with increase in concentration in solutions of NH4OH whereas it increases for the other hydroxides. From the data the apparent molal compressibilities were computed for the temperature range 15° to 35°C. Based on values of the apparent molal compressibilities at infinite dilution the solvation appears to be about six water molecules per ion.

Determination of Finite Amplitude Distortion by Light Diffraction

Bill D. Cook

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 336-337 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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The theory of a new optical method of determining the harmonic structure of progressive ultrasonic waves undergoing finite amplitude distortion is developed using Fourier transforms. The waveform is determined by measurement of the light intensity of all the orders in the diffraction pattern.

Effect of Sound Waves on Heat Transfer

Peter J. Westervelt

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 337-338 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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The suggestion is put forward that the effect of sound waves on heat transfer is dominantly result of the modification of the inner streaming boundary layer which is known to occur when the sound particle displacement amplitude s exceeds in magnitude the acoustic boundary layer thickness δac.

Scattering of Sound by Sound

J. L. S. Bellin and R. T. Beyer

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 339-341 (1960); (3 pages)

Online Publication Date: 11 Jul 2005

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An attempt was made to determine the presence of scattering resulting from the nonlinear interaction of two finite‐amplitude sources, operating in water. Experiments were performed with two beams crossed at right angles and also in the nonperpendicular case, A detector crystal, tuned to the summation frequency (13.4 Mc) of the two sources (7.4 Mc and 6.0 Mc), and pivoted about a point above the interaction region, was used to investigate the scattered field. The results indicated no scattered sound above the noise level of the detection system. The lack of scattered sound is in agreement with the theoretical considerations of Westervelt, but is contrary to the predictions of Ingard and Pridmore‐Brown.

Axisymmetric Vibrations of Shallow Elastic Spherical Shells

A. Kalnins and P. M. Naghdi

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 342-347 (1960); (6 pages) | Cited 1 time

Online Publication Date: 11 Jul 2005

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This paper contains an exact solution within the scope of the bending theory of shells for axisymmetric vibrations of thin shallow elastic spherical shells. Specifically, the solution is applied to an investigation of the natural frequencies of the free axisymmetric vibrations of spherical shell segments with various edge conditions. Comparison drawn with previously known results for transverse vibrations of shallow spherical shells, where the effect of longitudinal inertia is neglected.

Physical Equivalents of Spectral Notions

Horace M. Trent

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 348-351 (1960); (4 pages)

Online Publication Date: 11 Jul 2005

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The notion of a Fourier spectral equivalent of an arbitrary function has been known for a long time in its basic mathematical form. Calculations of these spectral quantities are conventionally based on the Fourier integral. It is not so well known that the Laplace transformation also yields a spectral notion of which the Fourier form is a special case. In addition, vibration engineers have made extensive use in recent years of the concept of a shock spectrum. Simple physical experiments are described which yield direct quantitative spectral values at specified frequencies for any of the three spectra mentioned in the foregoing. These equivalents are useful in assigning physical significance to the quantities under discussion.

Side Scattering of Sound in Shallow Water

R. J. Urick

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 351-355 (1960); (5 pages) | Cited 2 times

Online Publication Date: 11 Jul 2005

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When a sound beam travels through the sea, it is scattered in all directions by inhomegeneities of various sorts in the sea and on its boundaries. In the backward direction, the aggregate of all the scattered contributions is called “reverberation.” In other directions, the “side scattering” can be studied by using two directional transducers, trained so that the beams cross each other, to measure the sound scattered out of one beam and received on the other. This method was employed in an off‐shore area in the Gulf of Mexico having a particularly uniform bottom. Using two bottomed transducers a mile and a half apart, the intensity of scattering was measured at 22 kc for different angular orientations of the two beams. The measurements were reduced to the coefficient, scattering strength, without requiring either transducer calibrations or direct measurements of transmission loss.
The results indicate a bottom scattering strength between −30 and −40 db having no appreciable dependence on angle between the two beams. Within the angular range from the backward direction around to 150° in the forward direction, the scattering appears isotropic. This indicates that isotropic bottom scattering may be safely assumed in applications utilizing separated transmitting and receiving transducers at kilocycle frequencies.

General Theory for the Synthesis of Hydrophone Arrays

H. S. Heaps

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 356-363 (1960); (8 pages)

Online Publication Date: 11 Jul 2005

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An acoustic signal pressure and a noise background are supposed incident upon a general array of hydrophone elements whose individual outputs are combined in a linear manner by means of amplifiers and time delays. Determination is made of the optimum spatial distribution of the hydrophone elements, and also the optimum combination of their outputs, in order to produce in the combined output a maximum value of peak signal in relation to the average noise background. The incident signal is not restricted to be a continuous wave of a single frequency.

Some Effects of Velocity Structure on Low‐Frequency Propagation in Shallow Water

A. O. Williams, Jr.

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 363-371 (1960); (9 pages) | Cited 2 times

Online Publication Date: 11 Jul 2005

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Refractive conditions—variations of the velocity of sound in the water—should alter the pattern of acoustic propagation in shallow water, with respect to the homogeneous case. For small values of H/λ (water depth to acoustic wavelength), wave analysis must replace the more familiar ray treatment. If the bottom material acts like a homogeneous fluid, such changes can be computed, for a certain range of H/λ, by perturbation theory starting from the idealized Pekeris solution. The changes depend on the fractional change of sound velocity (and its structure) and on (H/λ)2. Specific calculations are made for a linear gradient and a simple sound channel, and are, in part, corroborated by a variational calculation. Limitations of the method are stated. If it is further assumed that attenuation of such transmission is proportional to the acoustic intensity near the bottom, downward refraction should lead to attenuation greater than that for isovelocity water. A few comparisons with experiment are presented; agreement is fair.

Reverberation Time Characteristics of Severence Hall

Helmut J. Ormestad, Robert S. Shankland, and Arthur H. Benade

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 371-375 (1960); (5 pages)

Online Publication Date: 11 Jul 2005

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Following the changes in the acoustical conditions made in Severance Hall during the summer of 1958 [see R. S. Shankland and E. A. Flynn, J. Acoust. Soc. Am. 31, 866 (1959)] a series of reverberation time measurements were made during the 1958–1959 concert season of the Cleveland Orchestra. Measurements were made in the empty hall, in the hall with orchestra during rehearsals, which is also the condition for recordings, and with a full audience during the regular symphony season. Measurements were made of 38‐caliber revolver shots, of fully orchestrated chords played at rehearsals by Dr. George Szell especially for our measurements, and of the endings of movements in a symphony (Mendelssohn No. 4 in A major) and a concerto (Dvořák B minor, Op. 104) during concerts. The results show a considerable increase in the reverberation time at all frequencies as compared to the conditions existing prior to 1958. The present reverberation time with a full audience is about 1.7 sec in the mid‐frequencies and rises steadily to well above 2 sec at lower frequencies. Due to the heavily upholstered seats in Severance Hall the sound absorption increment on account of a full audience is unusually low. Measurements made during rehearsals have permitted a determination of sound absorption by the orchestra. Reverberation times measured with microphone pickup on the main floor, in box seats, and in the balcony, are essentially the same. The measurements will be continued during the 1959–1960 concert season, especially to determine the effects of a new humidity control system which was installed during the summer of 1959.

Measurements of the Sound Absorption Coefficient and the Sound Transmission Loss at the Kobayasi Institute of Physical Research

Kozi Sato and Masaru Koyasu

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 376-379 (1960); (4 pages)

Online Publication Date: 11 Jul 2005

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See Also: Erratum

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During the past three years, five reverberation chambers were constructed in our institute. These chambers are now used for the measurements of the sound absorption coefficient and the transmission loss. Chamber No. 1 has a volume of 513 m3 surrounded by nonparallel walls, and the reverberation time of this chamber is greater than 20 sec at 500 cps. In this chamber, the position of the microphone and test specimens does not affect the absorption coefficient. Chambers No. 3 and No. 4, which are used for transmission loss measurements, have a volume of 164 m3, respectively. The shape of these chambers is similar to chamber No. 1. The opening between these two chambers is 3.3 m by 3.3 m. Under chamber No. 4, there is chamber No. 5, which is used for the receiving room for impact sound transmission loss measurements.

Determination of Absolute‐Intensity Thresholds and Frequency‐Difference Thresholds in Cats

Donald N. Elliott, Leon Stein, and Mary Jane Harrison

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 380-384 (1960); (5 pages) | Cited 2 times

Online Publication Date: 11 Jul 2005

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While the cat's basilar membrane is only two‐thirds the length of the human, its auditory‐frequency range is at least three times as great. Behaviorally defined absolute‐intensity and differential‐frequency thresholds have been determined for the cat and are compared with those of humans. The cat's absolute thresholds lie well below those of humans over nearly all of the frequencies the two species respond to in common. The cat's differential thresholds, however, are larger at all frequencies. But because of the cat's larger frequency range, the total number of discriminable steps appear to be about equal. Counts of ganglion cells and hair cells for the cat are reported and compared with counts for humans. The greater density of the cat's ganglion cells may explain its lower absolute thresholds, but there appears to be no direct relation between ganglion‐cell density and frequency discrimination. The lower density of hair cells for the cat, coupled with its shorter basilar membrane, may account for its poor frequency discrimination.

Masking by Octave Bands of Noise in Normal and Impaired Ears

James F. Jerger, Tom W. Tillman, and John L. Peterson

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 385-390 (1960); (6 pages) | Cited 3 times

Online Publication Date: 11 Jul 2005

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The masking of sinusoids by three octave lands of thermal noise was measured in normal and hearing‐impaired ears at each of two effective noise levels. For frequencies within the noise band results were essentially equivalent for all groups studied at either effective level. At frequencies both above and below the noise band no differences among groups were noted at the 10‐db effective level. At the 30‐db effective level, however, both presbycusics and sensori‐neural losses of presumably cochlear origin showed more masking than either normals, plugged normals, or conductives.

Temporal Irregularity of Excitations: How Much Is Accepted by the Brain for Reporting Pitch?

Max F. Meyer

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 391-393 (1960); (3 pages)

Online Publication Date: 11 Jul 2005

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For many years the only obstacle standing in the way of crediting the theory of the hydraulic‐cochlea model [M. F. Meyer, Am. J. Psychol. 72, 293–296 (1959)] as a hypothetical “theory of hearing” has been the notion that the brain reports a pitch to consciousness only when it receives excitations from the auditory sense organ in strictest temporal regularity. The test of this notion has now been accomplished by experimenting with a siren—and the obstacle has been removed.

Stereophonic and Quasi‐Stereophonic Reproduction

J. P. A. Lochner and W. de V. Keet

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 393-401 (1960); (9 pages)

Online Publication Date: 11 Jul 2005

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In stereophonic reproduction there are two distinct qualities which distinguish it from single‐channel reproduction. The first of these is a directional separation of sound sources and the second, and probably the most important characteristic of stereophonic reproduction, is the sensation of “depth” and “presence” that it creates.
It is well known that the relative amplitudes and times of arrival at an observer's ears of first sounds received from the loudspeakers determine the apparent direction of the sound sources in a stereophonic system, and it is often assumed that this is also responsible for the perception of “depth” and “presence” normally linked with this system. It appears, however, that only the former quality, directional separation, is based on the relative amplitudes and times of arrival of first sounds and that the latter quality, which we call “ambience,” is entirely on account of delayed reflections or echoes recorded and reproduced through the separate channels of the stereophonic system.
Single recording‐channel quasi‐stereophonic systems, in which these echoes were brought out as in the stereophonic system, but which could not give separation of sources, were subjectively compared with true stereophonic systems and the results are presented in this paper.

Protective Effect of the Acoustic Reflex for Impulsive Noises

John L. Fletcher and Arthur J. Riopelle

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 401-404 (1960); (4 pages)

Online Publication Date: 11 Jul 2005

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Twenty‐four male subjects were trained in the use of the Békésy audiometer. Then they were exposed to 100 rounds of machine‐gun fire, both with and without a pre‐exposure to a 1000‐cps tone for activating the acoustic reflex. Pre‐ and post‐firing audiograms, taken under both conditions, were compared to determine temporary threshold shifts. Shifts obtained with the reflex‐activating tone were found to be significantly smaller than those obtained in its absence.
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“Exploring Tones”: Discredited by a Siren Experiment

Max F. Meyer

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 405-406 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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At least four times in the history of acoustics the assertion has appeared in print that the existence “somewhere” (in the air or in the middle ear or in neuro‐chemistry) of a (not consciously heard) harmonic can be tested by the audibility of beats of an exploring tone. where an exploring tone is defined as a physical tone of nearly the same frequency as the frequency of the “hunted” tone. This assertion will be shown to be baseless and purely fictional.

Compressional Relaxation with a Tuning Fork

J. H. Andreae, C. Jupp, and D. G. Vincent

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 406-407 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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A new resonator comprising a fused quartz tuning fork with a hollow, liquid‐filled arch has been used to measure compressional loss in the liquid. Initial measurements on an aqueous solution of BeSO4 near 100 cps confirm the existence of relaxational behavior in this solution.

On the Effects of Sound Waves on Heat Transfer

Jack P. Holman

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 407-407 (1960); (1 page)

Online Publication Date: 11 Jul 2005

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A discussion is presented of the physical mechanism as proposed by Westervelt whereby heat transfer rates may be increased in the presence of intense sound fields.

Resonant Frequency of a Water‐Loaded Circular Plate

F. C. W. Olson

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 408-408 (1960); (1 page)

Online Publication Date: 11 Jul 2005

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Effect of Damping and Vibration Detector Position in Resonance Measurements

John A. Ryan

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 408-409 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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Vibrations in a finite‐length, thin rod at low frequencies are considered. Two cases are discussed. In the first, the pressure amplitude at the driven end is assumed constant and, in the other, the particle‐velocity amplitude is taken as being constant.
An oscillatory character to the amplitudes of the resonance peaks is found which is a function of detector position and attenuation.
This phenomenon may explain the observed differences in the heights of the resonance peaks, and the recurrence of groups of large and smaller peaks in rods, plates, shells, and other vibrating systems. It may also have a considerable effect on the apparent Q (or bandwidth) of the resonance curves.

Extension of the Myklestad Matrix Method to Include Rotary Inertia and Shear Deformation

Herbert Saunders

J. Acoust. Soc. Am. Volume 32, Issue 3, pp. 409-410 (1960); (2 pages)

Online Publication Date: 11 Jul 2005

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An extension to the matrix procedure of Thomson's adaptation to Myklestad's method is formulated to include both rotary inertia and shear deformation. These additions modify the frequency determination especially for the higher modes.
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