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Jul 1932

Volume 4, Issue 1A, pp. 3-93

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Related Nodal Lines on Chladni Plates (A)

R. C. Colwell

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 3-3 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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No general solution of the differential equation of a square plate has ever been given; but Ritz has shown that an approximate solution may be developed. A particular case of his solution valid for the interior of the plate but not at the edges takes the form
math
. This equation is restricted to the cases in which the plate vibrates like a membrane. From it we may develop many curves which have the peculiarity that when two nodal lines cut one another, they must cut at right angles. By varying A and B, keeping m and n constant a series of nodal lines are found which resemble one another. This resemblance is due to the fact that the note of the plate is approximately the same for each figure. Some of these curves have been found experimentally with an electric valve oscillator.
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A Reed Organ to Demonstrate the Just Scale (A)

A. T. Jones

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 3-4 (1932); (2 pages)

Online Publication Date: 13 Jun 2005

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This is a “baby organ” which has been in use in the Department of Physics at Smith College for about a dozen years. There are two stops—one tuned to the equal temperament, and the other tuned in such a way that it is possible to play just scales in the four keys of c major, f major, g major, and a minor. On the special stop the white digitals give the key of c major, while the c#, d#,f#, g#, and a# digitals give respectively the d for the keys of f major and a minor, the g# for the key of a minor, the f# for the key of g major, the a for the key of g major;and the b♭ for the key of f major.
Since the d in the keys of f major and a minor is a comma flatter than the d in the key of c major, and the a in the key of g major is a comma sharper than the a in the key of c major, it is possible to give certain demonstrations of beats as well as to show the effects of certain chords and successions of chords.
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Laryngoscopic Observations on the Parabolic Action of the Epiglottis in Controlling the Directional Power of the Low, Middle and High Frequencies of the Singing Voice (A)

Louis Simmions

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 4-4 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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The speaker demonstrated laryngoscopic observations in the formation of primal sounds in the interior of his larynx and sang scales, arpeggios, intervals, trills, with the aid of a laryngoscope; he observed and reported the different elements which enter into the formation of the five fundamental singing vowels on open and covered position of the epiglottis; while making these observations he at the same time amplified these primal sounds and vowels into his own ears with a new acoustic device which he called a VOCALSCOPE.
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Short Time Variations in the Sensitivity of Condenser Transmitters (A)

E. J. Abbott

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 4-4 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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Although one decibel ordinarily represents a very minor change in loudness, it is often desirable to obtain an accuracy of measurement of a few tenths decibel. For example, in machine noise reduction it is often necessary to study the effect of a proposed change in the presence of several similar sounds. Hence the overall effect of a single change may be considerably less than a decibel, but if taken together with other similar changes the combined effect may be large.
Since the microphone represents the only part of the usual type of sound meter which cannot be calibrated fairly readily, it is usually depended upon to maintain its calibration over considerable periods of time. It appears that a microphone may maintain an average calibration, and still be subject to short time fluctuations in sensitivity which are liable to be serious in certain sound meter applications.
The literature on microphone calibration deals chiefly with the theory of various methods, and the effects of certain corrections. Little has been published concerning how well one might hope to determine the sensitivity of a particular microphone on the basis of an accepted method with accepted values for some of the uncertain constants. This paper presents data obtained in an attempt to obtain a reference standard for microphone calibration at our laboratory, and illustrates certain variations which are attributed largely to changes in microphone sensitivity. Although these variations are doubtless familiar to those who have worked with absolute microphone calibration, it is hoped that the material will be of interest to many others who use sound meters.
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An Efficient Miniature Condenser Microphone System (A)

H. C. Harrison and P. B. Flanders

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 4-5 (1932); (2 pages)

Online Publication Date: 13 Jun 2005

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This paper describes a Wente‐type condenser microphone of high efficiency and an associated coupling amplifier which are of such small size that reflection and phase‐difference effects are of negligible importance within the audible frequency range; while the cavity is so proportioned that its resonance effect is an aid rather than a detriment to uniformity of response in a constant sound field.
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Some Improvements on the Bells of a Carillon (A)

G. M. Giannini

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 5-5 (1932); (1 page)

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 two improvements are suggested. The first is to check and regulate the amplitude of the partials of the bell with respect to the amplitude of the fundamental. The second improvement is the use of a damping device which brings the bells into the class of a musical instrument. The operation of such electrical apparatus to accomplish this second improvement is described.
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The Acoustic Properties of Small Gongs (A)

J. C. Steinberg and D. W. Farnsworth

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 5-5 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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This paper gives the acoustical properties of several types of small gongs and the relations between some of these properties and the size, shape and material of the gongs.
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A New Analogy between Mechanical and Electrical Systems (A)

F. A. Firestone

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 5-5 (1932); (1 page)

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
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math
wherein velocity v is analogous to current I. It is incomplete in the following respects which lead to difficulty in its application.
The new analogy is derived from the similarity of the following equations:
math
math
wherein force f is analogous to current I and 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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The Variation of Hearing Acuity with Age (A)

J. B. Kelly and H. C. Montgomery

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 5-6 (1932); (2 pages)

Online Publication Date: 13 Jun 2005

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Measurements were made of the threshold intensity, under soundproof conditions, of over 500 ears, at 8 octave steps, from 64 to 8192 cycles, for persons between the ages of 20 and 60. At frequencies below 1024 the variations of hearing acuity over the age range are relatively small. At higher frequencies differences are found from decade to decade, becoming very pronounced at 4096 and 8192 cycles.
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The Estimation of Fractional Loudnesses (A)

P. H. Geiger and F. A. Firestone

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 6-6 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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Considerable divergence exists in the results obtained by different investigators (see abstracts 4 and 3, Journal of Acoustical Society of America, 3, p. 311 and 315, January 1932) for the reductions in intensity which observers judge to correspond to reductions in loudness of one‐half, one‐fourth, or other fractions. In order to account for this divergence in results, experiments are being made wherein observers are asked to reduce the loudness of certain sounds to different fractional values of the original. Loudness levels corresponding to 1000 cycle sensation levels of 30, 55, and 80 decibels of three sounds were used as the original sounds from which the required reductions were made. The three sounds used were a 1000 cycle tone, a 60 cycle tone, and a complex tone with components from 60 cycles to above 3000 cycles. The preliminary data show that: (1) the observer's judgment can be easily influenced by the conditions of the test; (2) a given fractional change in loudness as judged by the observers does not correspond to the same fractional change in intensity for different loudness levels or for the different sounds.
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A Relationship between Loudness and the Minimum Perceptible Increment of Intensity (A)

R. R. Riesz

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 6-6 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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Using previously reported data (Phys. Rev., Vol. 31, May, 1928) concerning the differential intensity sensitivity of the ear, the number of perceptible increments of intensity is calculated as a function of the intensity expressed in db above the auditory threshold for frequencies of 200, 1000, 3000 and 10,000 c.p.s. These curves are then used in an attempt to arrive at a logical explanation of the data presented by Laird, Taylor and Wille (Jour. Acoustical Soc., Jan., 1932 “The Apparent Reduction in Loudness”).
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Low Frequency Thresholds of Hearing and of Feeling in the Ear and Ear Mechanisms (A)

R. L. Wegel, R. R. Riesz, and R. B. Blackman

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 6-6 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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A redetermination of the hearing threshold in the frequency range 35 to 1000 cycles shows the minimum audible pressure in the ear canal to be inversely proportional to the cube of the frequency up to about 500 cycles. This is interpreted to mean that the form of vibration of the basilar membrane does not change appreciably and that the amplitude of its motion varies inversely as the square of the frequency in this range. It follows from this that the threshold stimulus for the nervous tissue is a constant acceleration. This observation also shows that the efficiency of the ear at high frequencies is principally due to the properties of nervous tissue and that the maximum mechanical efficiency occurs in the frequency range at 1000 to 2000 cycles. A redetermination of the threshold of feeling shows a nearly constant pressure at low frequencies which corresponds to a constant amplitude of motion at the ear drum and ossicles, suggesting that this sensation originates in the middle ear.
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An Experimental Determination of the Equivalent Loudness of Pure Tones (A)

W. A. Munson

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 7-7 (1932); (1 page) | Cited 1 time

Online Publication Date: 13 Jun 2005

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The intensity levels at which pure tones of different frequency sound equally loud have been determined by comparison with a thousand cycle reference tone. A frequency range from 62 to 16,000 cycles and an intensity range from near threshold to uncomfortably loud sounds was covered. The tones were impressed upon both of an observer's ears by means of telephone receivers, and were of short duration to avoid fatigue effects. The comparisons were made by eleven observers. From the intensity levels which were found to produce equality of loudness, the equivalent loudness of all points in the normal auditory sensation area were determined in terms of the 1000 cycle reference.
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Acoustic Pickup for Philadelphia Orchestra Broadcast (A)

J. P. Maxfield

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 7-7 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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This paper describes the acoustic conditions surrounding the placement of the pickup microphones and the method of compressing the volume range to meet broadcast requirements in such a manner that the greatest possible motional value is retained.
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Automatic Reverberation Meter for Sound Absorption (A)

V. L. Chrisler and W. F. Snyder

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 7-8 (1932); (2 pages)

Online Publication Date: 13 Jun 2005

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During the past several years the Sound Section of the Bureau of Standards has been endeavoring to develop an electrical method to measure reverberation times as a tool in the determination of absorption coefficients of materials. Various methods have been tried, similar to those used by other investigators, such as measurements from oscillograms, determination of end points of a decay curve and the plotting of a decay curve from measured times taken at definitely spaced arbitrary thresholds. In the measurement of absorption coefficients, great accuracy is necessary in the measurement of the rate of decay of sound and a careful analysis shows that a number of points are necessary in plotting decay curve. Since sound does not die away uniformly in a closed. space, it is necessary to determine these points statistically. To make the operation of the equipment less tedious, automatic methods have been developed and the procedure is almost entirely self operating.
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Estimating Room Errors in Loud Speaker Tests (A)

E. W. Kellogg

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 8-8 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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Reflections from the walls, ceilings and floors of loud speaker test rooms are likely to be much greater than would be judged from listening tests. Simple calculations will show whether the errors resulting from these reflections are likely to be serious, and will also indicate how they may be most easily reduced.
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A New Reverberation Formula (A)

W. J. Sette

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 8-8 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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The assumption is made that the probabilities are that any ray of energy, undergoing repeated reflection, will strike the individual surfaces of a room in proportion to the ratios of their areas to the total surface. The resulting expression for the reverberation time employs the logarithm of the geometric mean of the reflection coefficients.
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Acoustics of Broadcasting and Recording Studios (A)

G. T. Stanton and F. C. Schmid

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 8-8 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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This paper describes the acoustic design of broadcasting and recording studios wherein the type and location of acoustic treatment is selected to permit a monaural pickup to represent, when reproduced, the acoustic conditions normally anticipated for the type of program presented. Acoustic conditions surrounding musicians and performers and those surrounding the microphone more nearly conform to established ideal relation between performers and audience under actual listening conditions. Certain examples of studios treated in accordance with this plan are described.
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Some of the Factors which Affect the Measurement of Sound Absorption (A)

V. L. Chrisler, W. F. Snyder, and Catherine E. Miller

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 8-8 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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Curves have been drawn showing the effect of water vapor and temperature on the total absorption of a reverberation room. At 4096 cycles changes in barometric pressure seem to have an appreciable effect.
When highly absorbent materials are placed in the reverberation room, the rate of decay is not uniform.
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Position Finding by Underwater Sound Signals (A)

B. R. Hubbard

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 9-9 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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The ability of a navigator to fix the true position of his ship at sea under the adverse conditions of storm and fog has been made possible through synchronized radio and underwater sound signals. Hydrographic survey vessels are fixing their position with ease and accuracy by means of radio acoustic sound ranging and underwater sound spotting. The point of impact of a projectile fired from coast artillery is being determined by underwater sound spotting. Ships are checking their position at sea by taking a series of echo depth soundings. Coast defense fortifications are using underwater sound direction finding for the detection and location of distant invisible ships. In each case underwater sound signals are playing an important part. The paper describes some of the more important technical aspects of these methods of position finding by underwater sound signals.
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Resonance in Rooms (A)

Vern O. Knudsen

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 9-9 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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The observed characteristic frequencies (or eigentones) in a small room are shown to agree with the theoretical frequencies n for the vibrating volume of air in a six‐sided rectangular room, namely
math
where c is the velocity of sound, l1, l2, and l3 the dimensions of the room, and p, q, and r are integers. One or more of these integers vanish when one or more surfaces in the room are covered with absorptive material. When a tone, which is nearly of the same frequency as the frequency of one of the eigentones, is sounded and then stopped in the room, the decay, especially during the latter stages, consists of the free rather than the impressed vibration. Thus, in a room in which the fundamental frequency was calculated to be 70 cycles, oscillograms revealed that impressed frequencies of 65, 68, 70, 72, or 75 cycles all decayed at the fundamental frequency of 70 cycles. The reverberation was about 50 percent longer for the resonant frequency (70 cycles) than it was for frequencies only 5 cycles lower or higher. Similar effects were observed in the vicinity of several of the overtones for the room. The results show conclusively that volume resonance must be considered in determining the absorptivity of materials by the reverberation method, and that resonance is an important factor in determining the acoustics of small rooms.
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A Method of Measuring Acoustic Impedance (A)

P. B. Flanders

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 9-9 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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An apparatus is described whereby acoustic impedances may be measured in terms of a known acoustic impedance and the complex ratios of two electrical potentiometer readings to a third. As a known impedance is chosen the reactance of a closed tube of uniform bore which is an eighth wave‐length long. The electrical readings are obtained by balancing the amplified output of a condenser transmitter against the electrical input of the source of sound.
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Automatic Logarithmic Recorder for Frequency Response Measurements (A)

Stuart Ballantine

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 10-10 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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This instrument was designed to facilitate obtaining records of frequency‐response in cases, such as the investigation of electro‐phones, where the response varies very irregularly with frequency and the point‐by‐point method becomes prohibitively tedious. The automatic registration is photographic and both the frequency and response coordinates are logarithmic. The logarithmic frequency scale (50–10,000 cycles) is obtained by the rotation of a special condenser connected to the platten carrying the photographic paper, the plates of the condenser being so shaped as to provide a logarithmic variation of frequency of the associated beat frequency audio oscillator. A logarithmic scale of ordinates is obtained by means of a new “logarithmic voltmeter” employing variable‐mu exponential tubes which are automatically controlled. The response or sound‐pressure range covered by the present instrument is 100x, although 1000x is obtainable if necessary. Specimen records will be shown and the application of this recorder to studies of the response of loud speakers in the actual reverberant surroundings of the average home will be described.
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Acoustic Measuring Instruments (A)

R. L. Hanson

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 10-10 (1932); (1 page)

Online Publication Date: 13 Jun 2005

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During the past few years great advances have been made in various laboratories toward the development of instruments for making quantitative measurements of acoustic phenomena. Among the instruments of this type which have been developed at the Bell Telephone Laboratories, are a reverberation meter, a sound meter, an automatic level recorder, a rapid record oscillograph, and three types of audiometers. Although these instruments have previously been described in detail elsewhere this paper will be a summary of their main features and the purposes for which they are adapted. It will be followed at the close of the session by an exhibit of the instruments in operating conditions.
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NEW HORIZONS IN MUSIC

Leopold Stokowski

J. Acoust. Soc. Am. Volume 4, Issue 1A, pp. 11-19 (1932); (9 pages) | Cited 1 time

Online Publication Date: 13 Jun 2005

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