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Journal of the Acoustical Society of America

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Jan 1933

Volume 4, Issue 3, pp. 171-267

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Facts Developed in the Design and Construction of the Johns‐Manville Acoustical Laboratory (A)

John S. Parkinson and Paul O. Young

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 171-171 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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A brief description of the Johns‐Manville Acoustical Laboratory is given, with test data on the efficacy of various constructions employed and a description of certain modifications in test procedure.
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Measurement of Transmission Loss through Partition Walls (A)

E. H. Bedell and K. D. Swartzel, Jr.

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 171-172 (1933); (2 pages)

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This paper reviews the theory and describes the method used at Bell Telephone Laboratories of measuring the transmission loss through partition walls.
The partition to be tested is built into an opening between two adjacent but structurally isolated rooms. A loudspeaker acts as a source of sound in one room and a portion of the sound energy is transmitted into the second room through the test partition. The transmission loss is taken as
math
where L1 and L2 are the intensity levels in the source and test room respectively, expressed in db, a2 is the absorption in the test room and A is the area of the partition. The levels L1 and L2 are measured and plotted with a moving coil microphone and an automatic level recorder, and a beat frequency oscillator is used as a source of tone so that the frequency may be varied continuously. Measurements with a continuous variation in frequency enable resonances in the partition to be much more easily and quickly detected than is possible when measurements are made at discrete frequency intervals. Both pure and frequency modulated tones have been used for the measurements. Results of measurements on a few partitions are given.
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Effect of Rotating Vanes in a Reverberation Room (A)

V. L. Chrisler and Catherine E. Miller

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 172-172 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Rotating vanes have been installed in the reverberation room at the Bureau of Standards with the result that the rate of decay of sound is logarithmic even when a highly absorbent sample is in the room.
Since the vanes have been installed the change in the apparent coefficient with the size and shape of the sample is much smaller than has been previously measured. It is believed that this is due to the fact that the sound is kept more uniformly distributed by the rotating vanes.
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The Dependence of Measured Absorption Coefficients upon Position and Quantity of Material (A)

S. K. Wolf and W. J. Sette

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 172-172 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Absorption coefficients obtained from reverberation chamber measurements are dependent not only on the amount of material present but also on the distribution of the material among the chamber surfaces. Curves obtained from experimental data are given to demonstrate the influence of these factors.
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Electrically Produced Tone from String Vibration (A)

Lloyd Loar

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 172-172 (1933); (1 page)

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Several musical instruments will be demonstrated in which the small vibrations of strings are amplified to large volume.
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The Methods and Results of Supersonic Interferometry (A)

J. C. Hubbard

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 172-173 (1933); (2 pages)

Online Publication Date: 13 Jun 2005

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In the acoustics of audible sound the instruments of investigation, including sources and receivers, are generally small as compared with the wave‐length. Diffraction effects, i.e., the spreading of the waves, becomes an all important factor. On the other hand, in the optics of visible light the instruments of investigation are in general large as compared with wave‐lengths, and diffraction effects may in many cases be neglected. With Langevin's discovery of the methods of producing beams of high‐frequency compressional waves in liquids, with the comprehensive investigation of their properties by Boyle, and finally, with the development by Pierce of the acoustic interferometer, acoustics has been developed in the region of short wave‐lengths, the instruments and methods becoming analogous in many respects to those of optics. The field of acoustic research has thus been enlarged by the acquisition of interferometric methods. Aside from numerous applications of immediate practical interest the new methods are of great scientific value since they furnish a new working tool in a frequency region of significance in molecular physics. Various methods are discussed and a summary given of important conclusions.
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Some Chemical Aspects of the Dispersion and Absorption of Sound (A)

W. T. Richards

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 173-173 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Modern acoustical interferometry promises to provide a quantitative answer to several questions of importance for the collision theory of chemical reaction rates. From the dispersion and absorption of sound in nitrogen tetroxide it is, for example, possible to obtain accurate and plausible values for the rate constant, the activation energy, and the effective molecular collision diameter of the dissociation reaction. Any other rapid chemical reaction should yield similar information from acoustical measurements. Since, according to current hypothesis reaction is closely analogous to the excitation of the vibrational heat capacity, the dispersion and absorption of sound in nondissociating gases has also direct chemical bearing. Measurements on the dispersion of sound in carbon dioxide, carbon disulfide, sulfur dioxide, and ethylene at various temperatures, pressures, and frequencies are discussed from this viewpoint. The velocity of sound in mixtures of ethylene with argon, nitrogen and hydrogen is also briefly considered. It is found that while collisions with argon and nitrogen are without influence on the vibrational heat capacity of ethylene, those with hydrogen are more effective than those with ethylene itself. This result has already been foreshadowed in the study of chemical reaction rates.
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The Supersonic Interferometer and Absorption Measurements (A)

W. D. Hershberger

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 173-174 (1933); (2 pages)

Online Publication Date: 13 Jun 2005

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The previously developed theory of the supersonic interferometer is extended with the particular view of utilizing it for absorption measurements in gases. It is shown that the mechanical impedance of the interferometer is
math
where
math
math
math
.
That is, if reactance is plotted against resistance we obtain an impedance spiral with center (Acρ/tanh 2αl, 0) and radius Acρ/sinh 2αl. The action of the interferometer is studied in terms of the properties of the spiral.
Absorption measurements are effected by compensating for the changes in the equivalent series electrical resistance due to changes in 1 by adjusting a shunt resistance in the circuit so the e.m.f. across the crystal is held constant, irrespective of 1. Absorption in the medium is calculated from the values of shunt resistance for the path lengths of interest. Measurements were taken at five frequencies in the range 298.6 k.c. to 2514 k.c. The quantity 2αλ2 a as measured by the interferometric method is not constant but shows a systematic change with frequency. The possible significance of that change is pointed out.
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Velocity and Absorption Measurements at Supersonic Frequencies (A)

W. H. Pielemeier

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 174-174 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Importance of Supersonics. This field is related in varying degrees to gas theory, thermodynamics, chemistry, physical chemistry, mechanics, heat, radio engineering, navigation and biology.
The author's work in this field began in 1919 and has been confined to a search for a suitable high‐frequency source and to the measurement of velocity and absorption in air, in oxygen and in carbon dioxide. Quartz slabs, properly cut from the original crystal and sputtered on both faces with metal were found far superior to the other tested sources for measurements requiring constant frequency and intensity. With such crystals, there were obtained frequencies ranging from 300 to 2000 k.c.
The velocity in air was found to be approximately 331.6 m/sec. in this range. At the lower frequencies the absorption appeared to exceed that predicted by the earlier theory. No serious deviation from expected values were found in oxygen. With carbon dioxide the velocity was found to increase about 3 percent from 300 to 2000 k.c. The absorption greatly exceeds the values predicted by the earlier theory. Both velocity and absorption values are in good agreement with those obtained theoretically by Kneser.
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Studies in Supersonics (A)

C. D. Reid

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 174-174 (1933); (1 page)

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The paper naturally divides itself into two parts. The first deals with experiments concerning the energy distribution in a supersonic beam in water and describes a useful visual method of determining such distribution. Diffraction and interference phenomena similar to those in light are discussed. In the second part the method used for the precision measurement of supersonic velocity in air is described and the results discussed.
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The Resonant Characteristics of Soft‐Walled Cavities (A)

J. C. Cotton

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 175-175 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Resonance is undoubtedly of great importance in voice production, but little attention has been given to the resonant characteristics of such cavities as are found in the human vocal mechanism. A soft‐walled cavity obviously must react quite differently to a complex tone than does the ordinary hard‐walled resonator. X‐ray photographs showing the human vocal cavities and motion pictures of the vocal cords indicate that more than simple resonant reenforcement must be responsible in creating voice differences. Without question, absorption plays an important part.
It is now possible to determine quantitatively the effect of soft‐walled cavities on complex tones by means of an electro‐acoustical set‐up developed in the Phonetics Laboratories at Columbus. A beat‐note oscillator, a sound source of the loudspeaker type, and a potentiometer arrangement serve to produce tones of constant intensity from 75 to 10,000 cycles. A condenser microphone, a resistance coupled amplifier, and a copper oxide voltmeter indicate the sound intensity.
The cavity under investigation is coupled to the sound source and the frequency slowly varied over any portion of the afore‐mentioned frequency range. Deviations of the frequency‐response curve from a straight line indicate directly the frequency characteristics of the cavity.
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Vocal Chords Control Pitch Only and Not Vocal or Vowel Quality Demonstration (A)

John Bellamy Taylor

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 175-175 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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Vibrating columns of air associated with wind instruments are seldom simple or even single. In a typical instrument, especially of the “reed” or “brass” classification, besides the air column that is usually considered, there is a second column or cavity on the air supply side of the “check‐valve” or member which by opening and closing, releases air intermittently from bellows or lungs. This check‐valve may be recognized as reed, tongue, lips, membranes or vocal cords. This air‐column or cavity back of the check‐valve has some control over the time of vibration, as was demonstrated by the author at Cleveland meeting of the Society, December 1st, 1931.
Usually the vibrations of the supply‐side air column are heard not at all or but faintly, because of restricted opportunity for sound emission. But special devices may be employed (the stethoscope is an example) to hear sound in supply side air column and reduce or effectively suppress sound from external air column (the only one ordinarily considered).
With a microphone in close contact with an individual's chest, an amplifier and loudspeaker will make audible the sounds picked up from internal air column, and with sufficient amplification, the normal sounds of speech and singing are faint in comparison with the other. This set‐up demonstrates that while the individual has pitch control on vibrations of the internal air column, he does not and cannot change the character or quality of the supply‐side tone by any of the vocal speech or musical efforts.
This result is taken to indicate that the vocal cords have but one mode of opening and dosing (at a given pitch) and play no part in determining the character or quality of vowels and other “vocalized” sounds.
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The Interference of Subjective Harmonics (A)

Ernest K. Chapin and F. A. Firestone

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 176-176 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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The purpose of the work reviewed in this paper was to devise a techique for producing interference of subjective harmonics under controlled conditions and to investigate the nature of some of the effects of such interference.
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A New Portable Meter for Noise Measurement and Analysis (A)

W. O. Osbon and K. A. Oplinger

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 176-176 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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This article describes a new noise meter whose development is based upon several years experience in the field of industrial noise measurements. Care has been taken to make the instrument simple to operate and rugged enough for portable use.
The characteristics of noise and hearing which have been used as a basis for designing the meter are discussed. A superheterodyne analyzer attachment is described which permits analysis of noises with a high degree of selectivity.
The noise meter may also be used for vibration measurements with a moving coil type pick‐up which is described.
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Sound Measurements on Experimental Airplane Mufflers (A)

W. F. Snyder

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 176-176 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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For the past few years the Sound Section of the Bureau of Standards has been cooperating with the Aeronautics Branch of the Department of Commerce in the development of practical methods of reducing the noise in airplanes. A part of this work has been the measurement in absolute intensities of the noise emitted by an airplane engine fitted with various types of experimental mufflers.
The propeller noise was eliminated by connecting the engine to a hydraulic dynamometer instead of the propeller. The dynamometer also served for the measurement of the horsepower. A muffler made of steel barrels placed in the ground allowed measurements to be made in the absence of exhaust noises.
The sound measuring equipment consisted of a calibrated condenser microphone, a sound meter and a set of band‐pass filters. Measurements were made with no filter in the circuit and at the frequency bands 0–250, 250–500, 500–1500, 1500–3000 and 3000‐etc. The microphone was placed at six different stations ranging in distances from 2 feet to 80 feet from the engine.
It is possible to reduce the exhaust noises by 15 or 20 decibels below that of the unsilenced engine without adding too much bulk or weight to the aircraft. The propeller noise, however, must be below that of the muffled engine for the muffler to become effective.
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On Minimum Audible Sound Fields (A)

L. J. Sivian and S. D. White

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 176-177 (1933); (2 pages)

Online Publication Date: 13 Jun 2005

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The minimum audible field (M.A.F.) has been determined from data taken on 14 ears over the frequency range from 100 to 15,000 c.p.s. The observer is placed in a sound field which is substantially that of a plane progressive wave, facing the source and listening monaurally. The M.A.F. is expressed as the intensity of the free field, measured prior to the insertion of the observer. Another type of threshold data refers to minimum audible pressures (M.A.P.) as measured at the observer's eardrum. The differences obviously to be expected between M.A.F. and M.A.P. values are due to wave motion in the ear canal and to diffraction caused by the head. The M.A.F. data are discussed in relation to the M.A.P. determinations available from several sources. Some possible causes of difference between the two, which are due to experimental procedure and may add to the causes already mentioned, are pointed out. At 1000 c.p.s. the average M.A.F. observed is 1.9×10−15 watts per cm2, corresponding to 2.8×10−4 bars or 71 db below 1 bar. Data are included to show the effect of observer's azimuth with respect to the wave front.
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A Note on Supersonic Methods (A)

E. G. Richardson

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 177-177 (1933); (1 page)

Online Publication Date: 13 Jun 2005

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In collaboration with two research students, I have in hand an experimental investigation of the dispersion and absorption of supersonic waves in gases, O2, CO2, SO2, N2O, etc., with particular reference to the effects of pressure and temperature of the gases on absorption. Besides the now familiar Pierce method (for the velocity) and torsionvane method (for the absorption), methods employing hot‐wires have been developed. It has been found, for instance, that the steady resistance of a heated filament placed near a piezoelectric quartz oscillator varies with the amplitude of the supersonic waves to which it is exposed. The instrument is calibrated by keeping the filament at a fixed point relative to the quartz, and applying different alternating differences of potential to the latter. After this, the wire may be used, while the quartz is driven at constant potential, to plot the amplitude in its neighborhood, and hence the absorption coefficient for the gas may be calculated. If the velocity is required the wave‐length of the radiation is measured by means of two heated filaments, each connected to one of two primaries of a transformer, the induced current in the secondary, due to fluctuations in the two primary circuits, being measured by a thermoelement and sensitive galvanometer. If the two wires are spaced at one wave‐length apart, the two trains of fluctuations are in phase. Having determined the wave‐length by keeping one filament still, and moving the other relative to it, until maximum response of the galvanometer is attained, the frequency is measured on a wave meter, and so the average velocity of the radiation over this small space is obtained. At present, the latter method has not proved practicable above 200 kilocycles, owing to the limited response on the part of the hot wires, but with improved technique, it is hoped to use the method at higher frequencies. Further details will be published in due course.
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METHODS OF CALCULATING THE AVERAGE COEFFICIENT OF SOUND ABSORPTION

Carl F. Eyring

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 178-192 (1933); (15 pages) | Cited 2 times

Online Publication Date: 13 Jun 2005

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A NEW REVERBERATION TIME FORMULA

W. J. Sette

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 193-210 (1933); (18 pages) | Cited 4 times

Online Publication Date: 13 Jun 2005

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THE RELATIONSHIP BETWEEN LOUDNESS AND THE MINIMUM PERCEPTIBLE INCREMENT OF INTENSITY

R. R. Riesz

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 211-216 (1933); (6 pages) | Cited 2 times

Online Publication Date: 13 Jun 2005

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USE OF PRESSURE GRADIENT MICROPHONES FOR ACOUSTICAL MEASUREMENTS

Irving Wolff and Frank Massa

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 217-234 (1933); (18 pages) | Cited 3 times

Online Publication Date: 13 Jun 2005

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The operation of the pressure gradient microphone is compared with that of the pressure microphone It is shown that the pressure gradient microphone may be used to measure particle velocity in a sound wave. The advantages of the pressure gradient microphone in making loudspeaker measurements, particularly outdoors, are pointed out and experimental data are given for some arrangements which were tried out. The characteristics of the distribution of particle velocity in a complex sound field are studied theoretically and experimentally with a ribbon microphone. A method is described for measuring the energy density in a sound field and some measurements which were taken in complex sound fields in rooms are discussed. It is shown that a combination of three pressure gradient or velocity microphones with a pressure microphone, placed adjacent to each other, may be equivalent in eliminating interference patterns to four pressure microphones placed at distances large compared to the wavelength and with random distribution. A microphone for measuring energy flow in a sound field is described.
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CALIBRATION OF CONDENSER MICROPHONES FOR SOUNDMETERS

E. J. Abbot

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 235-244 (1933); (10 pages)

Online Publication Date: 13 Jun 2005

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SOME IMPROVEMENTS ON THE OPERATION OF THE BELLS OF A CARILLON

G. M. Giannini

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 245-248 (1933); (4 pages)

Online Publication Date: 13 Jun 2005

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The unsatisfactory performance of the bells of a carillon from a musical standpoint is discussed and an improvement is suggested. This is the use of a damping device to permit greater musical possibilities in the playing of carillons. The operation of the electrical apparatus which performs the damping is described.
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A NEW ANALOGY BETWEEN MECHANICAL AND ELECTRICAL SYSTEMS

F. A. Firestone

J. Acoust. Soc. Am. Volume 4, Issue 3, pp. 249-267 (1933); (19 pages) | Cited 6 times

Online Publication Date: 13 Jun 2005

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By considering each mass in a linear mechanical system as having two terminals, one fixed in the mass and one fixed to the frame of reference, every linear mechanical system is reduced to a multiplicity of closed mechanical circuits to which force and velocity relations similar to Kirchhoff's laws, may be applied. The conventional mechanical‐electrical analogy is derived from the similarity of the equations v = f/z and I = E/Z. It is incomplete the following respects which lead to difficulty in its application.
I. There is a lack of analogy in the use of the words “through” and “across” which indicates a fundamental difference in the nature of the analogous quantities, for instance, force through and e.m.f. across.
II. Mechanical elements in series must be represented by electrical elements in parallel, and vice versa.
III. Mechanical impedances in series must be combined as the reciprocal of the sum of the reciprocals while electrical impedances in series are additive.
IV. There is an incompleteness the mechanical analogues of Kirchhoff's laws.
The new analogy is derived from the similarity of the following equations: v = fz̄ and E = IZ where z̄ is the reciprocal of the mechanical impedance as usually defined. This new analogy is complete in all of the above‐mentioned respects in which the old analogy failed. It leads to analogous relations of a simple sort and permits an equivalent electrical circuit to be drawn in an easy intuitive manner.
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