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Journal of the Acoustical Society of America

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Nov 1948

Volume 20, Issue 6, pp. 727-877


The Early History of Hearing—Observations and Theories

Georg v. Békésy and Walter A. Rosenblith

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 727-748 (1948); (22 pages) | Cited 1 time

Online Publication Date: 18 Jun 2005

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Vibration of the Head in a Sound Field and Its Role in Hearing by Bone Conduction

Georg v. Békésy

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 749-760 (1948); (12 pages) | Cited 3 times

Online Publication Date: 18 Jun 2005

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In a sound field the head is set into forced vibrations, and the vibrations are sometimes heard by bone conduction. For clinical purposes it is important to know the magnitude of these vibrations of the head so that, in cases of partial deafness, the roles of air conduction and bone conduction can be understood.
The pattern of the head vibrations and the velocity of the deformation waves traveling along the bony wall of the skull were measured. For the velocity we found c = 570 m/sec. In the course of the experiments, a new method of calibrating a vibration pick‐up with a sound level meter was developed.
It was found possible to construct an earphone that reduces the amount of “cross‐hearing” to a very low value. With this earphone, hearing thresholds can be measured in many cases without using noise to mask the ear with the better hearing, even though the difference between the sensitivities of the two ears is greater than 40 db.
It is shown that the maximal sound insulation that can be obtained with an ear plug is determined by the elastic forces acting between the skin of the ear canal and the bony wall of the ear canal.

The Role of Interaural Phase in Loudness

Ira J. Hirsh and Irwin Pollack

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 761-766 (1948); (6 pages) | Cited 2 times

Online Publication Date: 18 Jun 2005

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Recent experiments have shown that the interaural phase angle is a critical factor in the masking of pure tones and speech by white noise. The present study extends these findings to the role of interaural phase in loudness. It is found that the reduction in loudness which is effected by noise under several conditions of interaural phase parallels the masking that is produced under similar conditions. These effects are marked, however, only at signal‐to‐noise ratios in the region of the masked threshold. At higher signal‐to‐noise ratios, approximating listening in the quiet, the effect of interaural phase on loudness is nil. A convenient basis for discussion is provided by considering the masked and masking signals in terms of the figure‐ground relation between them.

The Effect of High Altitude on the Threshold of Hearing

H. W. Rudmose, K. C. Clark, F. D. Carlson, J. C. Eisenstein, and R. A. Walker

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 766-770 (1948); (5 pages)

Online Publication Date: 18 Jun 2005

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The threshold of hearing has been measured in a decompression chamber at ambient pressUres corresponding to altitudes of 35,000 feet and sea level. After the data have been corrected for the change of cushion seal and the change in response of the earphone unit with change in pressure, the results show that the shift in the average threshold of hearing for fifteen ears is within ±2.5 db of sound pressure level when the density of the air in the outer and middle ear is decreased to about one‐fourth that at sea level.

A Comparison of Artificial Ear Couplers

Joan L. Glaser and Keron C. Morrical

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 771-775 (1948); (5 pages)

Online Publication Date: 18 Jun 2005

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Comparison made of the response of several earphones measured on two different types of earphone couplers. Points of difference are noted and explained. In addition, the existence of certain characteristics which might influence the design and use of such couplers is brought out and proposed for further investigation.

The Effects of High Altitude on Speech

K. C. Clark, H. W. Rudmose, J. C. Eisenstein, F. D. Carlson, and R. A. Walker

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 776-786 (1948); (11 pages)

Online Publication Date: 18 Jun 2005

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The effects of altitude on the human voice have been determined by measuring speech spectra as a function of altitude. The apparatus simultaneously recorded the square of the sound pressure in twelve contiguous bands extending from 60 to 9000 c.p.s. Eleven talkers were used, and data were obtained in a decompression chamber at constant temperature for altitudes up to 40,000 feet. Special attention was given to the method of monitoring and phonation. Vowels, sibilants, words, and connected speech were used as test material. The results indicate that vowels and semi‐vowels exhibit a loss in mean square pressure with altitude roughly proportional to the logarithm of the density ratio, while some consonants are little affected by altitude. Measurements indicate that the number of words spoken on one breath of air is proportional to air density if constant sound pressure output is required. Normally, at 35,000 feet, it is necessary to pause for breath about two to three times as frequently as at sea level.

Quantitative Amplitude Representation in Sound Spectrograms

W. Koenig and A. E. Ruppel

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 787-795 (1948); (9 pages)

Online Publication Date: 18 Jun 2005

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The sound spectrograph shows variations in signal intensity by varying shades of gray to black which, because of the nature of the recording medium, are not susceptible to quantitative interpretation. Several methods are described in this paper for recording amplitude variations in measurable steps. These methods include contours, dot spacing, distinctive shadings, and variable area patterns.

Amplitude Cross‐Section Representation with the Sound Spectrograph

L. G. Kersta

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 796-801 (1948); (6 pages)

Online Publication Date: 18 Jun 2005

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Spectrograms as normally produced by the “sound spectrograph” are three dimensional. Time is portrayed along the length of the spectrogram paper, frequency across it, and amplitude by the blackness of the marking. The time and frequency scales thus provided are adequate for most analysis purposes. The amplitude scale, however, is poorly defined, first because inherent characteristics of the spectrogram paper limit the amplitude portrayal to a highly non‐linear and limited range, secondly, because reading degrees of blackness by eye is inaccurate. This inadequacy in determining amplitude led to the development of a method for portraying amplitude which was independent of the characteristics of the paper or of the ability of the eyes to delineate grades of blackness of marking.
The device developed and herein described provides an auxiliary presentation which portrays, at any preselected point in time, a two‐dimensional spectrogram with axes of amplitude and frequency. This device delineates a 35‐db amplitude range with the scale in uniform logarithmic steps.

Acoustic Impedance Matching by Means of Screens

Frank H. Slaymaker and Mones E. Hawley

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 802-807 (1948); (6 pages)

Online Publication Date: 18 Jun 2005

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The acoustic impedance of a transducer may be matched to that of the surrounding medium by means of a metal screen. When operating in air, transmission increases of nine decibels have been obtained by placing correctly selected and positioned screens in front of a crystal transducer. The device narrows the response curve of a sharply resonant transducer only slightly, while the directional characteristics are not measurably altered. The situation is somewhat analogous to the non‐reflection coating of optics. For purposes of analysis, a more useful analogue is that of a transmission line containing discontinuity. Experiments with woven and perforated screens of different geometric form have been performed and the results evaluated.

Instrumentation for the Measurement of Sound Pressure Level with the Western Electric 640AA Condenser Microphone

Paul S. Veneklasen

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 807-817 (1948); (11 pages)

Online Publication Date: 18 Jun 2005

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Given the pressure calibration of the W.E. 640AA microphone, certain instrumentation and complementary calibrations are needed for the convenient use of this microphone under the various conditions encountered during research work. The following aspects of this subject are discussed: (1) Considerations regarding the effect of preamplifier input impedance on the frequency response and noise threshold of a condenser microphone. (2) An a.c. operated, cathode follower type preamplifier and associated circuits. (3) A flexible extension for use with the preamplifier. (4) The use of small probe tubes. (5) Random incidence calibration and collected free field calibrations. (6) A “supercharged” cathode follower circuit and its application as a preamplifier.

Reciprocity Free Field Calibration of Microphones to 100 Kc in Air

I. Rudnick and M. N. Stein

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 818-825 (1948); (8 pages) | Cited 6 times

Online Publication Date: 18 Jun 2005

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A procedure for obtaining a free field reciprocity calibration of a W. E. 640AA transducer in the frequency range 1–100 kc is described. The basis for the calibration is investigated in some detail, particularly with regard to (a) the validity of electroacoustic reciprocity relations applying to the transducer and (b) the nature of the acoustic calibrating field. The transducers were found to be reciprocal. Factors affecting the acoustic field are the degree of approximation of the source to a point transducer, the effect of walls of the anechoic room, and the attenuation in the air. It is shown that when the separation of the transducers used in these measurements is 30 cm, the transducers are essentially points, the room produces very little effect, but the attenuation in the air can produce a significant error at high frequencies unless correction is made for it. The results of the calibration of two W. E. 640AA transducers are presented, giving their responses as speakers and microphones, the latter with and without a protective grid.

Reciprocity Calibration of Vibration Probes

Charles T. Morrow

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 826-829 (1948); (4 pages) | Cited 1 time

Online Publication Date: 18 Jun 2005

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Apparatus has been developed for calibration of vibration probes, analogous to that for reciprocity calibration of condenser microphones, except that a metallic rod instead of an air cavity couples the two transducers. The rod is assumed to act as a mechanical open circuit, whereas the air cavity is assumed to be an acoustic short circuit. The product of the sensitivities of the two transducers can be obtained from the current to the driving probe (A), the mass of the coupler, and the open circuit voltage of the pick‐up probe (B). The ratio of the sensitivities of A and B can be obtained as the ratio of their open‐circuit voltages when the coupler is driven by an auxiliary drive. From the product and the ratio, the two individual sensitivities can be calculated.

Vibrators for Measurement of Response and Compliance of Phonograph Pick‐Ups

H. A. Pearson, R. W. Carlisle, and H. Cravis

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 830-833 (1948); (4 pages)

Online Publication Date: 18 Jun 2005

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Two vibration instruments are described. The first is a vibrator having substantially constant amplitude over a wide frequency range. A small reed is milled from a solid block of steel and driven with a conventional magnetic system. A light platform with a grooved Nylon pad is attached to the end of the reed. A phonograph pick‐up is laid on this platform in the same manner as on a record, and the response from 30 to 10,000 cycles may be measured. The second is a vibrator having an armature with considerable mass and negligible stiffness. The armature is pivoted and retained by magnetic attraction with no restoring spring. A platform is provided on this armature on which to rest a pick‐up. From the frequency of resonance of the armature with the stiffness of any pick‐up or other vibrator, the stiffness of such a vibrator may be readily ascertained, as in the case of B. B. Bauer's vibrator [J. Acous. Soc. Am. 19, 319 (1947)]. Calibration data were secured from both dynamic and static measurements, the agreement of which is indicated.

Dispersion of Compressional Waves in Isotropic Rods of Rectangular Cross Section

R. W. Morse

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 833-838 (1948); (6 pages) | Cited 7 times

Online Publication Date: 18 Jun 2005

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The compressional wave velocity in rectangular brass rods is measured a function of frequency by means of standing wave patterns made visible by the use of lycopodium powder. An x‐cut quartz crystal is used as a driver between frequencies of 200 and 650 kilocycles per second. Results are obtained on rods of different width‐to‐thickness ratios, the thickness being the same in each case. The dispersion curves are made up of two branches with a discontinuity occurring one of them when the half‐wave‐length is close to the larger dimension. Each of these branches is shown to be determined by one of the lateral dimensions and a qualitative interpretation is offered in terms of a lateral resonant effect. In the case of a square rod the two branches coincide, and the dispersion is the same as that encountered in a circular rod of the same cross‐sectional area. Theoretical calculations are made for the case in which the width is much larger than the thickness. Numerical solutions are found for the dispersion curves of the first symmetrical mode for different values of Poisson's ratio. Calculated values are in good agreement with measured values when the cross‐sectional dimensions are in the ratio of 8:1 and the wave‐length is smaller than the larger dimension.

Sound Absorption and Transmission Measurements

Antonio Gigli

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 839-845 (1948); (7 pages)

Online Publication Date: 18 Jun 2005

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Report is given of the research performed in the last ten years in the field of architectural acoustics, with special reference to measurements of sound absorption coefficients of materials and sound transmission losses of partitions. The absorption of sound by systems of resonators is particularly handled.

On the Propagation of Sound over Snow

Robert B. Watson

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 846-848 (1948); (3 pages) | Cited 1 time

Online Publication Date: 18 Jun 2005

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Many qualitative observations have been made on the quieting effect of newly fallen snow. This natural phenomenon must depend on the acoustical properties of such a layer of snow. The physical constants for snow vary over a considerable range, and data for calculating the acoustic constants of snow are meager. The calculated absorption coefficient ranges uniformly front 0.25 at 100 c.p.s. to 0.75 at 2000 c.p.s. Calculations are made of the sound level at an observer's position due to sound transmitted over a layer of snow. Because of the appreciable absorption, the sound level is found to be considerably reduced at distances as small as five hundred feet from the source.

The Attenuation of Audible Sound in Fog and Smoke

Vern O. Knudsen, John V. Wilson, and Neal S. Anderson

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 849-857 (1948); (9 pages) | Cited 2 times

Online Publication Date: 18 Jun 2005

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Measurements of the rate of decay of sound in a reverberation room, first with no fog or smoke in the room and then with fog or smoke of known concentration and particle size added to the room, show that the attenuation of sound in a number of aerosols is in approximate agreement with values predicted by the theories of Sewell, Epstein, and Oswatitsch. In a water fog having a concentration of 2.0×10−6 grams/cm3 and average droplet radius of 6.25×10−4 cm, the attenuation owing to the fog increased from about 5 db/sec. at 500 c.p.s. to 13 db/sec. at 8000 c.p.s. In a quite similar fog of mineral oil, the corresponding attenuation increased from 1.6 db/sec. at 500 c.p.s. to 21 db/sec. at 8000 c.p.s. At very low frequencies, a fog of water is much more absorptive than is a fog of oil; the difference is ascribed to a “relaxation” effect of evaporation from and recondensation the droplets, which is much greater for water than for oil. The attenuation of sound in smoke may become rather high, amounting to 58 db/sec. at a frequency of 6000 c.p.s. for a moderately dense smoke of NH4Cl (180 g in a volume of 6080 cu. ft.).

The Scattering of Ultrasonic Waves in Water by Cylindrical Obstacles

Louis Bauer, Paul Tamarkin, and R. B. Lindsay

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 858-868 (1948); (11 pages) | Cited 1 time

Online Publication Date: 18 Jun 2005

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An ultrasonic beam produced in water by an oscillating quartz crystal (frequency, 1145 kc; wave‐length, 1.3 mm) is scattered by cylindrical obstacles. Three different obstacles are used: (i) a ¼″ steel rod, (ii) a ½″ steel rod, and (iii) ⅝″ hollow polystyrene tube. Lateral pressure amplitude distribution curves are obtained at different points along the axis of the beam for various positions of the obstacles on the axis. The effect of lateral displacements of the obstacles is studied. Wave‐front determinations are made with and without obstacles. The conclusion is reached that transmission through and reflection by the obstacles play an insignificant role compared with diffraction around them.

The Origin of Sound Absorption in Water and in Sea Water

L. N. Liebermann

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 868-873 (1948); (6 pages) | Cited 3 times

Online Publication Date: 18 Jun 2005

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The absorption of sound in water and in sea water has been measured in the frequency range 120 kc to 1000 kc. The fresh water values were obtained in a lake; the sea water values in the ocean. The fresh water absorption values when extrapolated as the square of the frequency are in agreement with previous values measured in the laboratory at considerably higher frequencies. It is shown that the observed absorption of water has its origin in viscous dissipation; the calculated values for the absorption agree with the observed if recently measured values for the dilatational viscosity as well as the shear viscosity are included in the calculation. The absorption processes in sea water are different. At frequencies below 100 kc the absorption is about 100 times greater than in pure water. Above 1 megacycle the absorptions are similar. It is shown that this behavior can be accounted for by introducing a relaxation mechanism with a relaxation time of 10−6 second. The nature of the relaxation mechanism is not known for certain. The proposal is made that it involves the ionic dissociation of sodium chloride in solution. Calculations are made to show that this process is a possibility.
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Remarks on Measurement of Electromotive Force of a Microphone

Richard K. Cook

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 874-874 (1948); (1 page) | Cited 1 time

Online Publication Date: 18 Jun 2005

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Plane and Circular Motion of a String

Henry Harrison

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 874-875 (1948); (2 pages) | Cited 1 time

Online Publication Date: 18 Jun 2005

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On the Performance of Cup Mouthpiece Instruments

T. H. Long

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 875-876 (1948); (2 pages)

Online Publication Date: 18 Jun 2005

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Hearing Aids

Fred W. Kranz

J. Acoust. Soc. Am. Volume 20, Issue 6, pp. 877-877 (1948); (1 page)

Online Publication Date: 18 Jun 2005

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