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Journal of the Acoustical Society of America

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Sep 1950

Volume 22, Issue 5, pp. 539-687

Page 1 of 4 Pages Return to All Sections Next Page
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back to top Session A: Noise
Contributed Papers
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The Threshold and Loudness of Repeated Bursts of Noise (A)

Irwin Pollack

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 671-671 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The loudness and threshold of an interrupted white noise (of constant sound‐time fraction) was studied over a wide range of interruption frequencies. White noise—alone among auditory signals—has the special property that, when interrupted, no additional audible complicating spectral products are introduced. Both at absolute threshold and at equal‐loudness above threshold, less energy is required for an interrupted white noise than for a non‐interrupted continuous white noise. In many cases, an interrupted noise (sound‐time fraction constant at 0.45) sounds louder than a continuous noise of the same amplitude (but of greater energy). The intensity required at threshold and at equal loudness is minimum for interruption rates in the region of 4–10 per second. The extent of this minimum region increases systematically as the reference loudness level is increased. A conceptual formulation which attempts to account for the results will be presented.
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Calculation and Measurement of the Loudness of Sounds (A)

J. L. Marshall, L. L. Beranek, A. L. Cudworth, and A. P. G. Peterson

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 671-671 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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In a previous paper a method was described for calculating the loudness of pure tones, combinations of tones, and continuous‐spectrum noise from measurements made with contiguous‐band analyzers. This method is supported by recently published results on loudness. The basis of the method is the hypothesis that the loudness of a noise spectrum can be obtained by dividing the spectrum into bands, replacing each band by a pure tone of equivalent r.m.s. amplitude and then determining the loudness of each tone from equal‐loudness contours and a loudness vs. loudness‐level function. The total loudness is then the sum of the loudnesses of the individual bands. Comparisons of calculated levels with experimental results of subjective loudness judgments are made assuming an analyzer with ten contiguous frequency bands, each 300 mels wide, and an analyzer with five contiguous frequency bands, each about 600 mels wide. The calculations are made using the equal loudness contours of Fletcher and those of Churcher and King. An important feature of this method is that its operations can be performed electronically, thus providing a design basis for a loudness meter. The operating principles of such a meter necessitate a set of band‐pass filters, and a non‐linear network to simulate the ear's response within each band. A meter designed and constructed for this purpose is described.
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Speech Interference Levels as Criteria for Rating Background Noise in Offices (A)

L. L. Beranek and R. B. Newman

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 671-671 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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On the basis of a number of surveys in commercial offices, criteria for tolerable office background noise levels are proposed. Questions were asked of people working in these offices regarding their ability to telephone, to confer and to perform their work under the existing noise conditions. The speech interference levels of the background noises were determined in each case. The results are presented in a chart, which rates the noise conditions as a function of speech interference levels in each of three general types of offices, (a) executive offices, (b) general clerical offices, and (c) business machines offices.
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New Techniques in the Analysis of Motor and Machine Noise (A)

R. O. Fehr and G. E. Henry

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 671-672 (1950); (2 pages)

Online Publication Date: 18 Jun 2005

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Motors and machines are acoustically complex; varied techniques are required for an analysis complete enough to be of practical use. The dynamic sound spectrograph designed by the Bell Laboratories for speech studies, can, with some modification, be used to good effect in determining the precise nature of the transient sounds which up to now have been difficult or impossible to resolve simultaneously in both frequency and time dimensions. Thus, an easy method becomes available for separating electrical from mechanical noise in motors and motor‐to‐load assembled units, without introducing an external drive. Cavity and case resonances are located by observing which frequencies recur, independently of rotor speed. A second step consists in noting the decay pattern following shock excitation of the suspected member. In most machines, frequencies forced by shaft rotation predominate over formant frequencies. Shaft rotation produces, in addition to its fundamental, an elaborate array of harmonics. Comparison of spectrograms and instantaneous pressure traces (oscillograms) is especially valuable in understanding the complete acoustic system. The limitations of the spectrograph in treatment of sounds below 1000 c.p.s. are caused by the linear frequency scale associated with the present system of heterodyne analysis. This can be overcome by the use of an external rejection filter analyzer with output fed to the marking amplifier.
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The Quieting of Transit‐Type Diesel‐Powered Coaches (A)

David C. Apps

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-672 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The problem of reduction of curb or pullaway noise of motor coaches used for city operation is attacked by the use of a magnetic wire recorder. The recordings, which will be demonstrated, are used in jury tests and for corroborative information by playback through band‐pass filters. The noise sources are attacked and reduced in their order of importance and in a form suitable for production and practical operation.
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Spectra and Loudness of Modern Automobile Horns (A)

D. B. Callaway

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-672 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Measurements were made of the sounds of three types of commonly used automobile horns. Over‐all sound levels on the axis at three feet ranged from 108 to 125 db. Loudnesses ranged from 125 to 140 phons. One type of horn gave sound levels of 88 db at 50 feet and 74 db at 300 feet, with corresponding loudness levels of 104 and 81 phons. Fundamental frequencies of all horns ranged between 160 and 380 c.p.s. Two types had harmonic overtones, with large amplitudes below about 2000 c.p.s. and smoothly decreasing amplitudes at higher frequencies. The third type, with the most unpleasant sound, had inharmonic overtones, some of which were greater in amplitude than the fundamental. Sound from a pair of horns at various distances was measured inside a closed automobile The over‐all level was 60 db (loudness, 72 phons) at 50 feet and 50 db (loudness, 53 phons) at 300 feet. Filtering out overtones above 1200 c.p.s. reduced the annoying character of horn sounds markedly and reduced the loudness by four phons at 50 feet and only one phon at 300 feet. Since the typical horn is louder than necessary at close range, use of a low pass acoustic filter on automobile horns appears desirable.
back to top Session B: Transducers, Recording
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Symmetry in the Equations for Electromechanical Coupling (A)

F. V. Hunt

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-672 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The conventional forms of the electromechanical coupling equations exhibit symmetry for electrostatic coupling and antisymmetry for electromagnetic coupling, or vice versa. Both types of coupling can be represented in symmetrical form, however, if the transduction coefficient for electromagnetic coupling includes a space‐operator k that embodies the sign convention associated with axial vectors. The same kind of conventional electric network representations can then be used for either type of coupling. There is a sound physical basis for the appearance of a space‐operator k in the transduction coefficients for electromagnetic systems in a manner completely symmetrical with the appearance of the time‐phase operator j in electrostatic coupling. Violations of reciprocity in interconnected systems, as discussed by MacMillan and others, can be dealt with analytically in a straightforward way by observing that the operators k and j do not commute, i.e., kj = − jk. Antisymmetrical coupling terms arise in the equations for all‐mechanical systems involving gyroscopes, just as in the electromagnetic case, but symmetry can be restored in these cases also by using the same kind of quaternionlike space‐operator.
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Reciprocity Calibration of Microphones Using a Pulse Technique (A)

R. L. Terry and R. B. Watson

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-672 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Acoustical calibration of a microphone may be made conveniently either by free‐field calibration or by calibration using a small cavity. Free‐field calibrations are difficult because of the necessity for establishing a space which allows for propagation of a single progressive wave, without any interference. A progressive wave may be set up in a room which will be free from interference at a given point until sound energy arrives by reflection from the nearest wall surface. By sampling the output from a microphone during this period of time, a signal may be obtained which determines the microphone response to a free progressive wave. Periodic repetition of this process gives a series of pulses from the microphone which may be used to obtain a reciprocity calibration.
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A Second‐Order Gradient Noise‐Canceling Microphone Using a Single Diaphragm (A)

A. M. Wiggins and Wayne A. Beaverson

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-672 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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A close‐talking, noise‐canceling microphone has been developed which responds to the second order of the pressure gradient and which has only one diaphragm. Since there are four sound pressures involved in a second‐order gradient microphone, it has been deemed necessary in the past to have four surfaces for the four pressures to act upon. This microphone has sound entrances to the two surfaces of a single diaphragm spaced and oriented in such a manner as to produce the second‐order effect, thereby increasing the signal‐to‐noise ratio over that obtained in a first‐order gradient microphone. Mathematical analyses are made of the microphone first as a purely theoretical microphone with infinitesimal spacing of the sound entrances, then as a microphone with dimensions between sound entrances which are practical for use in a microphone of this type.
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An Extremely Small Meter for the Measurement of Absolute Pressures (A)

Wolf W. von Wittern

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 672-673 (1950); (2 pages)

Online Publication Date: 18 Jun 2005

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A pressure meter of extremely small size for the measurement and recording of absolute pressures was developed. It is in the form of a small tube of 2.5‐mm diameter and 5‐mm length. The tube is closed by a thin iron membrane. The deflection of the membrane causes a change of the reluctance of a magnetic circuit. This reluctance change is transformed into voltages by means of a carrier frequency system. The pressure meter can be built with a maximum sensitivity of about 100 mm Hg pressure per full meter scale deflection. The sensitivity is limited by the attainable deflection of the membrane and the electrical amplification that can be applied which is limited by the “magnetic noise level” and the zero‐point stability. Using thicker membranes pressure meters of this type for higher pressure ranges can be built. The natural frequency of the membrane is higher than the carrier frequency (max. ca. 15 kc). The range of a flat frequency response characteristic is therefore not limited by the natural frequency of the membrane but by the carrier frequency and the damping of the membrane is not very important. With a carrier of 10 kc a flat frequency response characteristic from zero to about 1000 c.p.s. can be obtained. Problems concerning the sensitivity of the pressure meter for temperature variations and for accelerations and the problems of electrical and mechanical qualities and manufacture resulting from the small size of the pressure meter are discussed.
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Transient Testing of Loudspeakers (A)

Osman K. Mawardi

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 673-673 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Recent interest in the use of transient techniques to test loudspeakers springs from the inadequacy of the steady‐state pressure response to specify completely the behavior of a loudspeaker. Tone bursts have shown some promise as a useful type of electrical signal to excite loudspeakers for transient testing. It appears, however, that Heavyside's step function or Carson's unit impulse function (the delta‐function) may reveal more directly the significant characteristics of a loudspeaker. The response of loudspeakers to each of these latter functions has been examined and typical radiation spectra have been determined experimentally. The results of these analyses seem to yield a substantial amount of useful information about the performance of loudspeakers.
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High Efficiency Loudspeakers for Personal Radio Receivers (A)

H. F. Olson, J. C. Bleazey, J. Preston, and R. A. Hackley

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 673-673 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The term personal radio receiver is used to designate a complete radio receiver with self‐contained power supply, and of such physical dimensions that it can be easily carried by hand or in the pocket. The performance and compactness of personal radio receivers are limited by the efficiency with which electrical power is converted into sound power by the loudspeaker. Since the electrical power output is limited in the personal receiver, the efficiency of the loudspeaker is an important factor. A number of loudspeaker systems have been investigated, both theoretically and experimentally, as follows: direct radiator, combination direct radiator and phase inverter, horn, and combination horn and phase inverter. An efficiency of 25 percent has been obtained with the combination horn and phase inverter. This loudspeaker system has been incorporated in a complete four‐tube radio receiver, having a content of 25 cubic inches.
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Stylus‐Groove Relations in the Phonograph Playback Processes (A)

Frank G. Miller

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 673-673 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The motion of a reproducer stylus in a phonograph groove has been subjected to a mathematical analysis which includes the joint effects of tracing distortion and elastic deformation of the groove wall. The lateral motion of the stylus at fundamental frequency is obtained as a product of three factors: (1) A stylus‐groove response function which increases slowly to a major peak occurring at resonance between the compliance of the groove walls and the effective mass of the stylus, and then falls off rapidly; (2) a translation loss which is small at low frequencies but becomes complete at a cut‐off wave‐length determined by the stylus radius, the tracking force and the elastic properties of the record material; and (3) a scanning loss which arises when the dimensions of the contact surface between stylus and groove wall become significant in comparison with the recorded wave‐length. It is found to be still possible to calculate the harmonic and intermodulation distortion products on the basis of rigid‐wall tracing distortion theory provided the amplitudes of the predicted distortion terms are multiplied by both the stylus‐groove response function and the scanning loss function. Non‐linear effects of deformation turn out to be negligible in comparison with tracing distortion. Measurements made with a series of recordings programmed to exhibit these effects confirm the analysis in all important respects.
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Some Applications of Square‐Wave Testing Techniques to the Evaluation of Disk Recording Systems (A)

Samuel R. Bradshaw and Weiant Wathen‐Dunn

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 673-673 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Pertinent aspects of the theory of square‐wave testing will be discussed, and data will be presented showing how certain facts concerning the over‐all response‐frequency characteristic and equalization may be determined, as well as resonances in various parts of the system. Given an adequate recording system, a short cut of “square waves” on the outside of each record provides the user with a rapid means of determining whether or not his playback system is properly equalized and otherwise adequate for reproducing the recorded material.
back to top Session C: Hearing
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Refractory Phases in the Electrical Activity of the Auditory Nervous System (A)

Mark R. Rosenzweig and Walter A. Rosenblith

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 673-674 (1950); (2 pages)

Online Publication Date: 18 Jun 2005

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Electrophysiological responses from the auditory systems of cats show phenomena of refractoriness, that is, reduced responses to the second of a pair of successive stimuli. Thus, when two acoustic clicks are delivered in close succession (intervals from 0.2 to 500 msec.), the response to the second click varies with (a) the time interval between the clicks, and (b) the intensities of the clicks. At the round window, the microphonic components of the click response shows no refractoriness. The neural components exhibit marked recovery cycles; for moderate stimulus intensities, these may last as long as 100 msec. At the auditory cortex, the recovery cycles may be even longer and may exhibit several marked phases of sub‐ and supernormality. The cortical recovery cycles are affected by the spontaneous electrical activity of the cortex, by the level of anesthesia, and by the temperature of the animal. While some interaction between the two ears may be shown at the level of the auditory nerve, this interaction appears strikingly at the cortex.
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Short‐Duration Effects in Auditory Fatigue (A)

J. Donald Harris

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-674 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The investigation of hearing by the use of a fatiguing tone and an immediately subsequent short‐duration test tone, first used with good success by de Maré and later adapted for special problems by Lüscher and Zwislocki, Gardner, and Munson and Gardner opens a wide field for study of suprathreshold events in the ear. Among the many variables are the frequency, intensity, and duration of each of the two tones, the frequency relations between the two tones, and the recovery interval, if any, between them. Most of these variables have not been studied independently. The present paper explores fatigue as a function of (1) duration and intensity of the fatiguing tone, and (2) duration of recovery interval. Both variables will be considered with respect to the frequency of the fatiguing tone.
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A Test of the Frequency Theory of Hearing (A)

H. Davis, S. R. Silverman, and D. R. McAuliffe

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-674 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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“Tone‐pips” with a basic frequency of 2000 c.p.s. were produced by passing rectangular pulses of ¼‐msec. duration through two sound‐effects filter sections in cascade. The high pass and the low pass cut‐offs (18 db per octave) of each unit were set to 2000 c.p.s. The transducer was an Atlas PM 25 loudspeaker. The tone‐pips appear on the oscilloscope as brief trains of waves that begin gradually and reach maximum amplitude at the third wave. The amplitude then falls off only a little less rapidly. A single pip sounds like a metallic click. When the pulses were repeated at 123 per second at sensation levels from 5 to 40 db all of our subjects reported hearing a “buzz.” Other descriptive terms used were “metallic,” “high pitched,” “continuously interrupted,” and “rough.” No listener, even when directly questioned and even when a pure tone of 123 per second had been sounded a few seconds previously for comparison, ever reported any trace of a low pitched component corresponding to 123 per second. Inasmuch as the frequency of nerve impulses in each nerve fiber is 123 per second under these conditions, the absence of a sensation of low pitch is contrary to the frequency theory of pitch perception and favors the place theory even for very low tones.
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A Consideration of the Intensity‐Loudness Function and Its Bearing upon the Judgment of “Tonal Range” and “Volume Level.” (A)

Stephen E. Stuntz

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-674 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Acoustical intensity not only affects the loudness of sounds, but also profoundly influences the listener's perception of certain ranges of frequencies. The data of Fletcher and Munson demonstrate that the effective frequency response of the ear varies with signal intensity‐level. On the basis of this variation, it is possible to account for certain anomalies appearing in Eisenberg and Chinn's study of listeners' preference for frequency ranges and intensity levels in the reproduction of speech and music. It is also possible to explain the disparity between their results and those of Olson's investigation of preference for frequency ranges. For example, it can be shown that when frequency is plotted against loudness, raising the intensity level from 50 to 70 db will add more than one whole octave downward to the effective frequency response of the ear at 50 millisones loudness.
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Free‐Field Thresholds vs. Pressure Thresholds at Low Frequencies (A)

Wayne Rudmose

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-674 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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In an earlier paper data were reported indicating there was no difference between minimum audible field and minimum audible pressure at low frequencies. No satisfactory explanation was available at that time as to why these results differed from previously published data except the statement that body noises, breathing, etc., had been minimized. Further work has now produced a satisfactory explanation. Furthermore, if a well‐sealed volume of 6 to 7 cm3 is maintained invariant over the eardrum and the mechanical isolation of the signal source progresses from good to bad, the difference between MAF and MAP varies from 0 to about 16 db. Data have been obtained for deviation of MAP from MAF as the volume and mechanical isolation are kept constant, the seal being broken by measurable amounts. Finally, to study the effect for the smallest possible volume, the plugged ear was fed acoustically from a high impedance source that was well‐isolated mechanically. With this arrangement the results indicate that for the 2‐cm3 volume the difference between MAP and MAF can be made less than 4 db by carefully controlling the subject. This control involves the position of the teeth, tongue, arms, etc.
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Observations on the Effect of High Intensity Sounds in the Ear (A)

H. G. Kobrak

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-674 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The middle ear of rabbits was photographed during exposure to high intensity sounds. Extreme amplitudes of the eardrum were observed and measured. Rupture of the eardrum occurred when the signal was increased further (motion picture film). The protective devices of the ear against intense signals are discussed. The reflex of the middle ear muscles is demonstrated. Tetanic contractions of both muscles dampen the movements of the ossicles. Another mechanism which most likely acts as protection for the vulnerable inner ear is the change of axis of the stapes at high intensity signals. The stapes movements were studied in fresh temporal bones. A small mirror was attached to the vestibular side of the footplate. Acoustic stimulation was carried out through the outer ear canal. The responses are asymmetrical. The negative amplitude is greater than the positive or sometimes negative only. Signals increasing in intensity produce a gradual change of the axis of vibrations. It was also observed that the stapes may suddenly change the axis of vibration as described previously by v. Békésy. The change of axis is interpreted as a protective device. Other features of the ear which act as protection against overstimulation are discussed.
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A Warble Tone Audiometer Test Suitable for Group Administration over Loudspeakers (A)

John C. Webster

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 674-675 (1950); (2 pages)

Online Publication Date: 18 Jun 2005

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Using warble tones to reduce the effect of standing waves and utilizing a design of multiple crossings of the auditory threshold, a reliable audiometer test was developed. It was recorded on a phonograph disk and is suitable for either headset or speaker administration to large groups of people. The rate of warble is 5 c.p.s. and the extent is ± 12.5 percent at 500 c.p.s. and ± 125 c.p.s. for the frequencies 1000, 2000, 4000, and 8000 c.p.s. A modification of the usual pulsed‐tone method is utilized. Each test item consists of from zero to four pulses, but each succeeding pulse within an item is softer than the preceding pulse. The pulses are chosen to give hearing loss levels of 40, 30, 20, 10, and 0 db. Five crossings are made of any person's threshold as long as his hearing loss is between 5 and 35 db. This test was given binaurally to 200 college students over both headsets and speakers. The group pure tone test described by Harris was given binaurally over headsets as a control test. The test‐retest reliability of the warble tone test did not differ statistically from the group pure tone test. Validity measures among all of these group tests and between each of the group tests and individual tests will also be reported.
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A New Pure Tone Group Audiometer Test (A)

Ralph E. Allison and Alfred L. Larr

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 675-675 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Free‐field audiometer testing is practical. Loud speakers used in a reasonably quiet room with a five percent frequency warble on a pure tone give a relatively uniform sound pattern throughout the test room. Each person records the number of pulses he hears. A light indicates the listening period. The use of a muff over one ear makes monaural testing practical. An unweighted noise level of 40 db will allow testing at normal threshold. Eliminating the matched earphones and wires to each testing position makes the equipment trouble free and comparatively inexpensive. Many persons can be tested rapidly in an ordinary school room. A study of comparative results of the tests of public school and college students indicate that an accuracy of 5 db with reference to individual tests can be expected. The construction of the equipment will be shown by slides.
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Standardizing Auditory Tests (A)

W. A. Munson and Mark B. Gardner

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 675-675 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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An understanding of the over‐all process of hearing depends upon proper interpretation of the results of many individual experiments. In the field of subjective experimentation the problem has been complicated by the wide variety of test procedures that characterize available data. If a common technique could be applied to the many different types of auditory tests, such as thresholds of acuity, masking tests, difference limens, etc., the organization of these data would be facilitated. The purpose of the present paper is to describe a test procedure which has shown promise in this direction and to give descriptions of equipment which have been found helpful in minimizing the variability of the test results. The procedure, which we have called the “ABX” test, is a modification of the method of paired comparisons. An observer is presented with a time sequence of three signals for each judgment he is asked to make. During the first time interval he hears signal A, during the second, signal B, and finally signal X. His task is to indicate whether the sound heard during the X interval was more like that during the A interval or more like that during the B interval. For a threshold test, the A interval is quiet, the B interval is signal, and the X interval is either quiet or signal. For a masking test, A is the masking signal, B is the masking signal plus the signal being masked, and X is either A or B repeated. The apparatus for the ABX test is mechanized so all details of the method can be duplicated for each observer, and the variability of manual operation eliminated. The entire test is coded on teletype tape to reduce the time and effort of collecting large quantities of data.
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Some Limitations on Formulas for Calculating Speech Hearing Loss from an Audiogram (A)

Lee Meyerson

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 675-675 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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Recent research has confirmed the clinical observation that there is a relationship between loss of hearing for pure tones and loss of hearing for speech, and several formulas have been proposed for calculating speech hearing loss from an audiogram. These formulas must be used cautiously, however, since they do not make allowance for individual differences in ability to interpret speech stimuli or for individual differences in ability to learn to interpret partially perceived speech patterns. None of the formulas can correctly predict from the audiograms the hearing for speech of subjects who sustained severe losses of hearing before they achieved a firm command of speech and language. For hard of hearing subjects who have had intensive auricular training or who possess unusually good synthesizing ability, formula results are often misleading. Experimental evidence is presented showing a wide range of variation of the threshold for speech hearing in normally hearing subjects whose threshold audiograms did not vary significantly from the normal zero reference level. The implications of this finding are discussed.
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A Progress Report of an Acoustic Training Experiment for Profoundly Deaf Children (A)

Clarence V. Hudgins

J. Acoust. Soc. Am. Volume 22, Issue 5, pp. 675-675 (1950); (1 page)

Online Publication Date: 18 Jun 2005

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The paper reports on an experimental program in acoustic training in which profoundly deaf children, ages 9 to 14, participate. An experimental group was provided with specially designed group hearing aid equipment installed in an acoustically treated classroom. The experimental class received all of their daily instruction from the teaching staff in this specially equipped classroom. A control group, using the standard hearing aid equipment of the school and taught by the same teachers, received the same routine training as the experimental group with the exception that they did not use the special hearing aid. The purpose of the experiment is to determine: (a) whether deaf children receive greater benefits from high fidelity, specially designed hearing aids as compared to the run‐of‐the‐mill equipment now available in modern schools for the deaf; and (b) to what degree profoundly deaf children, hitherto considered beyond the reach of acoustic stimuli for all practical purposes, may benefit by acoustic training when provided with equipment capable of presenting undistorted speech signals at sufficiently high levels and at the same time protecting the ears against damage by a form of amplitude limiting. Both groups of pupils were tested periodically with achievement tests to determine their relative improvement in (1) speech perception, (2) speech intelligibility, and (3) general educational achievement. Results show significant differences in favor of the experimental group, especially in the category of speech perception where hearing is employed.
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