bluuebunny/crossref_metadata_2025 huggingface dataset:
Masking and the Perception of a Series of Successively Prominent Partials in a Vocal Sound
Authors: Lewis Don , Lichte W. H.
Published: September 2005

At the last meeting of the Society, we presented a paper dealing with a vocal sound of short duration and of essentially constant pitch and loudness whose upper partials (three to seven, inclusive) became successively and individually prominent during the course of the sound. There was no way of knowing, at the time of the previous report, whether or not masking effects were of any importance in determining how the sound was heard. Data have recently been secured on the masked absolute thresholds of each of the five crucial partials for the periods immediately preceding and immediately succeeding the period during which it was heard as prominent. Although the threshold measurements were made indirectly (that is, in relation to similar complex sounds produced with a multi-harmonic generator), the obtained values are believed to be approximate measures of the masking introduced by the vocal sound. Masking was by no means negligible; but only the fifth partial was found to be below its masked absolute threshold. It has been concluded, therefore, that any one of the partials, except the fifth, could have been heard individually during periods proximate to its period of prominence if attention had somehow been focused upon it. Possible limitations with respect to this conclusion are apparent in view of data on the typical magnitude of masked differential thresholds. However, there is little reason for doubting that attentional factors played a predominant role in determining the manner of perceiving the successively prominent partials.
Present-Day Preferences for Certain Melodic Intervals in the Natural, Equal-Tempered and Pythagorean Scales
Authors: Small A.
Published: September 2005

The chromatic steps of a piano from F2 to C4 were tuned successively to natural, equal-tempered and Pythagorean scale values. With each tuning a phonograph record was made of certain melodic and harmonic intervals in the major scale. This preliminary report presents the expressed preferences of a group of observers for the ascending and descending forms of the melodic major third (on C) and diminished fifth (on B) as given by these three tunings. A paired-comparison technique was employed in obtaining judgments.
Progress Report on Violin Research
Authors: Saunders F. A.
Published: September 2005

In continuation of work previously reported several items of progress may be mentioned. The effect of the air-body on the tone has been studied by three methods, which agree in showing that the air-body makes no considerable contribution to the tone except at the frequency of its fundamental vibration. The effect of the varnish has been studied on one instrument with results confirming those of Meinel: adding the varnish makes no important change in the response curve and only 1.5 percent change in the weight. The varnish slightly increases the damping for high tones. Changes in atmospheric humidity such as are usually encountered (20 to 70 percent) alter the weight of a violin by only 2 percent and do not affect any of its dimensions materially excepting its thickness near the bridge. This alters the stresses near the sound post and causes minor changes in the natural responses. The vibrations of the bridge have been studied by Minnaert. We are finding that the dimensions of those parts of the bridge which transmit vibrations from the strings to the feet are important and must be considered in addition to the mass of the bridge as a whole. Unsymmetrical loading of the bridge affects most the energy of those vibrations entering the body via the loaded part. Changes in the tension in the strings when symmetrical do not seem to alter the frequency of the natural responses, but when they are unsymmetrical the peaks are shifted. Transient effects in the growth or decay of a violin tone are being studied. The phases of harmonics with reference to the fundamental are found to change in a complicated way which deserves further examination. Oscillations of energy between string and body sometimes occur while the sound is decaying. The damping of the air-body can be measured, and that of some of the main body-resonant tones may be found. The damping of high harmonics is much more than that of the fundamental.
Some Measurements on a Hyperbolic Horn
Authors: Salmon V.
Published: September 2005

The coordinate system consisting of confocal ellipsoids and hyperboloids of one sheet yields a wave equation which may be separated. The resulting functions have been practically completely evaluated by Freehafer in some unpublished work at M.I.T. Rough experimental verification has been obtained for the amplitude and phase of the pressure field in a horn whose longitudinal section is a hyperbola with asymptotes 15° from the axis. A Hall type miniature condenser microphone was used; and the horn was terminated in the one bare wall of an otherwise well absorbing room. Because of the finiteness of the 6′ horn and incomplete absorption in the room at the lower frequencies, many irregularities are present in the field, but the essential features were found to have been correctly predicted. Transmission coefficient measurements are in progress, using electrical, acoustical and graphical means.
Notes on Electroacoustic Feedback Systems
Authors: Knowles H. S.
Published: September 2005

The use of feedback in the electrical portion of an electroacoustic system permits the electrical source impedance to be controlled over wide limits. Proper control of the source impedance necessitates a knowledge of the normal impedance of the loudspeaker in the system. Calculated and experimentally determined values of the normal impedance of common types of loudspeakers are given. Some of the effects of feedback from the electrical, mechanical and acoustical meshes on the steady state and transient behavior of systems are discussed.
The Degenerative Sound Analyzer
Authors: Scott H. H.
Published: September 2005

The principle of inverse feedback, or degeneration, has been applied to the problem of obtaining sharply selective circuits which do not require any inductances whatsoever and which may be tuned by merely varying resistances. Such circuits have been applied to many applications, such as oscillators and selective amplifiers for bridge measurements. Of particular interest is a new sound analyzer working on these principles. An important characteristic of the new analyzer is that the selectivity curve or band width remains a constant-percentage function of the frequency to which the device is tuned. For sound analysis this has many important advantages. Other desirable characteristics of the analyzer are its light weight and small size as compared to most other types of analyzers. A further refinement is the logarithmic vacuum tube voltmeter, which allows inclusion of the complete range on a single meter scale, thus making multipliers unnecessary. Analyzers of this sort have been found useful in many applications involving sound and vibration. Among the many problems on which the analyzer has been used are included noises made by such varied devices as watt-hour meters, fans, airplane motors, and typewriters. The unusual selectivity characteristics of this analyzer make it suitable for many applications where other types of analyzers have proved unsatisfactory.
Reverberation Time Meter
Authors: Hall W. M.
Published: September 2005

A portable direct-reading apparatus for the measurement of rate of decay of sound will be described.
Investigation of Room Acoustics by Steady State Transmission Measurements
Authors: Hunt F. V.
Published: September 2005

It should be possible to deduce the necessary acoustical information concerning the bounding surfaces of a room from steady-state measurements of the transmission between a source and a receiver appropriately placed in the room. This problem is being studied by using a small model chamber yielding discrete normal modes of vibration in the range from 200 to 1500 cycles. A small sound source having substantially constant output over this frequency range was developed and comprises a multiple capillary formed by packing a brass tube with parallel round wires, the sound from a dynamic receiver passing down the canals between the wires. Resonant pressure peaks in the chamber corresponding to the first fifty normal modes of vibration have been observed and identified. Analysis and experiment indicate that the total absorption in the chamber for a given mode of vibration can be measured by observing the width of the resonance curve at the half-intensity height. By selection of different modes of vibration, absorption coefficients are obtained as functions of both frequency and angle of incidence, the latter including grazing incidence. The decay rates predicted by these measurements have been checked experimentally. Plans will be discussed for the extension of these results to large scale rooms by an appropriate statistical analysis.
Acoustical Analysis of the Pressure Waves Accompanying Detonation in the Internal-Combustion Engine
Authors: Draper C. S. , Morse P. M.
Published: September 2005

Detonation in the internal-combustion engine is characterized by a sudden local increase in pressure in some part of the charge, which is followed by intense pressure waves within the combustion chamber. High speed pressure recorders have shown that the frequencies of these waves agree with those predicted by the ordinary acoustical theory. Recently simultaneous records have been taken of pressure fluctuations in different parts of the chamber. Theoretical analysis of the transient conditions produced by the detonation impulse indicates that these records can be used to determine the spatial distribution of the initial disturbance. Relative amplitudes of the various modes of vibration make it possible to estimate the spread of the initial disturbance; and their relative phases on the separate records locate approximately its position in the chamber. Analyses have been made for simple cylindrical and hemispherical combustion chambers and have been applied to engine records for chambers of both types.
Measurement of Acoustic Impedance
Authors: Fay R. D. , Hall W. M.
Published: September 2005

Apparatus developed for determining acoustic impedance will be described and demonstrated. The device is the acoustical equivalent of an electrical transmission line.
Resonant Frequencies of Certain Pipe Combinations
Authors: Trimmer J. D.
Published: September 2005

Computations are made of the acoustical impedance looking into an “extended” combination of pipes (i.e., one in which pipes are joined one to the next) and into a “reëntrant” system (i.e., one in which some of the pipes come back to the starting point). The resonant frequencies of such combinations are discussed. Attention is given particularly to the extended system which is the generalization of the Haskell organ pipe, namely, a pipe joined at its far end by the parallel combination of an open pipe and a closed pipe; and to the reëntrant system consisting of two pipes in parallel (a “divided path”) joined at their far juncture by a closed pipe. Comparison is made for a specimen of each of these two types between theoretical and measured values of impedance. The reentrant system is particularly interesting because, though it is a closed system, it has the same resonant frequencies as a simple open pipe.
Measurements in the Field
Authors: Stanton G. T.
Published: September 2005

“The absorption coefficients of materials as determined by field measurements, differ from those in the laboratory.” This belief appears general in the industry and is, in the author's opinion, based on a false premise.

There is some evidence to indicate that if in field measurements of reverberation due consideration is given to insuring the same degree of agreement with the definition of reverberation time as that in the laboratory, the absorption coefficients shay be determined in the field which will agree with those from the laboratory. However, the primary purpose of field reverberation measurements is to determine the acoustic conditions resulting from a given form of acoustic design, and measurements made with this end in view are not generally suitable for direct determination of absorption coefficients. The agreement between laboratory coefficient and that directly determined from the reverberation time in a practical room varies with the degree of diffusion of sound energy in the room.
Angular Distribution of Normal Modes
Authors: Bolt Richard H.
Published: September 2005

As stressed by Hunt the angular distribution of normal modes must be incorporated into an adequate evaluation of the effective absorption of material in a room. Thus, approximate theory, using the “sin θ” law of random distribution, yields an average value of acoustic impedance: z̄=z0/2, where z0 is the impedance at normal incidence. Maa derived a more accurate distribution law, in consideration of a low frequency correction reported by him and by Bolt.

A rigorous derivation of angular distribution must utilize frequency-space instead of p-space as only in the former are the directions of characteristic points identical with space-directions of the corresponding modes. A detailed consideration of frequency space reveals, at low frequencies, a discontinuous angular distribution of the general form: N(θ) = N0 +  ∫ θ1θ2f(θ)dθ+N90, where N0 and N90 count the number of modes at exactly 0° and 90° (nearly 0° and 90° in actual practice), and f(θ) approximates a stepped curve between angles θ1 and θ2. Each of these quantities has been evaluated; the resulting formula closely fits several calculated plots of angular distribution in rectangular rooms. The “smooth” part, f(θ), agrees with Maa's Eq. 17, but the present form should possess advantages, especially for incorporating absorption at grazing incidence as reported by Hunt.

This result is applied to the average impedance of a material covering an entire wall of a room, giving an explicit equation: z̄/z0 = 12 + K1/ν + K2/ν2+… where ν is frequency (up to which all modes are counted), and K1, K2, etc. involve room geometry and placement of material. Diffraction effects have not been incorporated. An apparent inconsistency is noted in the usual definition of average absorption coefficient in terms of average impedance.
Effect of an Absorbing Wall on the Decay of Normal Frequencies
Authors: Bhatt N. B.
Published: September 2005

This investigation was undertaken to study the reverberation time of a room for the first few of its normal frequencies and the effect of one absorbing surface on the decay of each individual mode. For this purpose a small chamber 49″×33.5″×19″ was constructed from 38″ thick slate in a steel frame; and to avoid wall vibrations it was backed on all sides with 2 in. thick layer of fine graded sand. Sound was let into the chamber through a 6-in. brass tube. 34 in. in diameter. It was packed full of No. 18 copper wires to avoid standing waves inside. The resonance response of the chamber and the effect of absorbing material placed on two different sides are shown. The decay time for each mode was measured by a reverberation meter constructed at the Institute. The results of the measurements in the steady state and the decay time are found to be in good agreement. The results show that the ratio between the decay coefficients of the material for the modes which are at grazing incidence and those at normal incidence, is approximately 12, which is the value predicted from exact theoretical considerations.
A Modern Concept of Acoustical Design
Authors: Potwin C. C. , Maxfield J. P.
Published: September 2005

The modern view in architecture, as it relates to the functional and utilitarian concepts of planning, has recognized the importance of a fundamental approach to the solution of acoustical problems in buildings where auditory requirements constitute a vital element of their design. Incidentally, treating acoustics as an integral part of design, rather than as a corrective measure during the course of planning, has not only produced better acoustical conditions and more efficient structures, but has also contributed to pleasing architectural form and decoration as well.

The initially important and comprehensive work of Professor Wallace Sabine and the more recent contributions of other authorities have established a basis for this modern approach to acoustical design. The coordination and practical application of the basic principles set forth have led to the development of efficient methods of combining interior form with the selection and distribution of sound absorbing materials for enclosures of widely differing types.

One method is especially described in this paper, wherein the surfaces of an audition space are shaped and coordinated with the distribution of sound-absorbing material so as to disperse the first few sound reflections of discrete and multiple types and to retain partially and control other reflections which might be termed the “long-mean-free-path” or “around-the-room” type. Particular attention is directed to the advantages derived from acoustical forms coordinated with a more scattered distribution of material than has been common in previous design practice, and also to the fact that this method of design creates good acoustics in spaces of the most unconventional basic shape.

Photographs and measurements of several recent designs will be shown, including the interesting and unusual Voder Room of the A. T. & T. Exhibit at the New York World's Fair 1939.
Auditory Patterns. A Demonstration Lecture
Authors: Fletcher Harvey
Published: September 2005

For many years physicists have been devising methods and apparatus for accurately measuring hearing, and it is now possible to describe the ear in physical terms much as other machines are described. In more recent years, auditory research has been directed more toward obtaining the relation between such a physical description and the character of the sensation evoked by a sound.

Sound waves entering the inner ear set into vibration a relatively long flexible membrane, which has distributed along its length the endings of the auditory nerve fibers. These endings are sensitive to the vibrations, and initiate a series of nerve impulses or tiny electrical currents, which travel along the nerve fibers to the brain. Such nerve messages contain the information that is used in forming the sensation of sound. By utilizing the discovery that human nerve fibers behave like busy telephone wires, relations have been obtained between the physical characteristics of a sound and the pattern of the nerve messages which it produces.

When a nerve fiber is busy carrying messages for one sound it is unable to carry messages for a second sound. In order to be heard, the intensity of the second sound must be increased until non-busy fibers can be found. From such busy tests, the fibers at different positions on the membrane that are excited by a given sound, can be charted. Such a chart is called an auditory pattern, and portrays to the eye the information that the brain must utilize in order to form sensation.

By choosing a sound which renders the fibers at different positions on the membrane uniformly busy, relations have been obtained between the pitch of a sound and the position of the excited fibers, the intensity of a sound and the rate at which messages are evoked and the changes in position and rate which accompany just noticeable changes in pitch and intensity, respectively.

In the demonstration lecture, this complicated process is vividly depicted by creating sounds and portraying the corresponding auditory patterns by means of animated charts. Deafness is artificially created and the audience sees and hears sound in the roles of both the normal hearing and the deafened.
Analysis of Transients
Authors: Kock Winston E.
Published: September 2005

A discussion is given of the frequency distribution of several types of non-periodic phenomena. The method of spectral analysis employing the Fourier integral is applied to a sine wave of short duration and it is shown that when the envelope is square-topped, noise components are present extending far to each side of the central frequency band, whereas when the envelope is sinusoidal these noise components are suppressed.
A Sound Source for Investigating Microphone Distortion
Authors: Phelps W. D.
Published: September 2005

Theoretical and experimental data are presented on a standing wave resonance system for obtaining a high pressure sound field with a prescribed harmonic eliminated. It consists of an eight-foot iron pipe ten inches in diameter, and a five-sixteenths-inch wall, with an eight-inch dynamic speaker at one end and a movable iron piston at the other. A pressure of 1000 dynes per cm2 at 100 cycles per second is readily obtained with a speaker input of less than 0.5 watt. Harmonic attenuation factors of 68 to 1 and higher are obtained. Hence the sound field is free of a given harmonic to within a few hundredths of one percent with three percent harmonic in the speaker input voltage.
Microphone Efficiency: A Discussion and Proposed Definition
Authors: Massa Frank
Published: September 2005

The microphone is treated as a converter of acoustic energy to electric energy and an expression for its absolute efficiency is derived. A definition of microphone efficiency is proposed and a family of curves has been computed to show the relation between absolute efficiency and voltage sensitivity for a microphone designed to work into any impedance.
New Microphone Providing Uniform Directivity Over an Extended Frequency Range
Authors: Marshall R. N. , Harry W. R.
Published: September 2005

A new microphone is described which consists of a moving coil pressure element combined with an improved ribbon “velocity” element to give a cardioid directional characteristic. The theory of operation is reviewed, and consideration is then given to variations in directivity caused by the size of the elements and by disparities in their phase and response characteristics. It is then shown how these variations have been largely eliminated by equalization in the electrical circuit so that the resulting directivity is practically independent of frequency throughout the range from 70 to 8000 cycles/second. The average front-to-back discrimination in this range is approximately 20 db. The use of a moving coil pressure element has made possible an efficiency of 84 db below one volt/dyne/sq. cm, while the design of an unusually rugged ribbon element provides a marked reduction in noise due to air currents and reduces sensitivity to shock.
Architectural Acoustic Testing with Electro-Thermal Noise as a Test Source
Authors: Schlenker Vesper A.
Published: September 2005

The warble-frequency test tones from a vacuum-tube oscillator have been generally used in reverberation and sound transmission measurements. The method of employing selected frequency bands of electrical thermal noise as test sources in conjunction with the high speed level recorder is presented. Typical data taken under actual “job conditions” encountered by the consulting acoustical engineer are included. The advantages of the new technique are discussed from the standpoint of simplicity of instrumentation and reliability of results.
Sound Insulation Characteristics for Ideal Partitions
Authors: Morrical Keron C.
Published: September 2005

Criteria are proposed for properly specifying the performance of sound insulating structures taking into account (1) transmission loss—frequency characteristic of the partition, (2) intensity and spectral distribution of the original sound, (3) characteristic of the human ear, (4) receiving room conditions, (5) ambient noise conditions, (6) masking, and (7) type of insulation required. On the basis of these criteria, it is possible to specify the transmission characteristic of an ideal partition, or one presenting a uniform reduction of loudness.
Conclusions from Further Measurements on Old and New Violins
Authors: Saunders F. A.
Published: September 2005

The response curves of nearly fifty violins have now been obtained, of which about a third are old instruments and over ten are of the highest quality. It is possible to pick several pairs of curves that closely resemble each other, one violin being old and the other new. Increasingly strong evidence is obtained indicating that the tone quality (for prolonged tones) of old violins can be duplicated in new instruments. A definite advantage possessed by the old instruments is that they respond for a less expenditure of work than new ones. This makes it easier for a player to execute rapid passages on an old violin than on a new, which in part justifies the high prices these violins command. Only a few listeners with the keenest ears are able to detect this characteristic. The majority are unable to tell whether a good player is using an old or a new instrument. “Blindfold” tests on audiences confirm this conclusion. The “carrying power” of violins is interpreted as an effect due to strong high harmonics which enable a violin tone to escape being masked by the accompaniment. It is connected with the “formant” mentioned by Backhaus and others as characteristic of the best violins, but it is found in both new and old instruments whose tone is characterized by musicians as “brilliant.” It is not found in instruments which are regarded as of a sweeter tone, more suitable for chamber music.
Terminology for Logarithmic Frequency Units
Authors: Young R. W.
Published: September 2005

Fletcher has proposed the use of a logarithmic frequency scale such that the frequency level equals the number of octaves, tones, or semitones that a given frequency lies above a reference frequency of 16.35 cycles/sec., a frequency which is in the neighborhood of that producing the lowest pitch audible to the average ear. The merits of such a scale are here briefly discussed, and arguments are presented in favor of this choice of reference frequency. Using frequency level as a count of octaves or semitones from the reference C0, a rational system of subscript notation follows logically for the designation of musical tones without the aid of staff notation. In addition to certain conveniences such as uniformity of characters and simplicity of subscripts (the eight C's of the piano, for example, are represented by C1 to C8) this method shows by a glance at the subscript the frequency level of a given tone counted in octaves from the reference C0 = 16.352 cycles/sec. From middle C4, frequency 261.63 cycles/sec., the interval is four octaves to the reference frequency, so that below C4 there are roughly four octaves of audible sound. Various subdivisions of the octave are considered in light of their ease of calculation and significance, and the semitone, including its hundredth part, the cent, is shown to be suitable. Consequently, for general use in which a unit smaller than the octave is necessary it is recommended that frequency level counted in semitones from the reference frequency be employed.
Characteristics and Distribution of Deafness in the Population of the United States
Authors: Beasley W. C.
Published: September 2005

An analysis is presented of threshold acuity measurements by air and bone conduction on 16,620 ears of persons drawn at random from the general population. The data were collected during a clinical investigation of hearing defects and aural pathology in the general population. The clinics were operated in twelve cities as a phase of the National Health Survey, which was completed recently by the United States Public Health Service. The audiometric data are classified according to clinical histories of hearing ability for speech, following certain arbitrary definitions of impairment. Certain sex differences in patterns of average audiograms are manifested throughout all age levels. Males always show more hearing loss on tones above 1500 cycles (by both air and bone conduction) than females of the same age range and clinical history in regard to hearing ability for speech. Females always show more hearing loss on tones below 1500 cycles (by air but not bone conduction) than males of the same age range and clinical history. The magnitude of these sex differences varies directly with age and stage of deafness—that is, the difference is larger between older age groups with a given history than between younger age groups having the same history; similarly, the difference is larger between groups of the same age but having more severe impairments. Average air conduction audiograms for males and females under 25 years of age and having a history of normal hearing for speech, or stage 1 or stage 2 deafness, show approximately uniform hearing loss on all eight tones of the Western Electric 2A Audiometer. Average audiograms for older males and females differ from those of the younger age groups in exhibiting consistently more advanced stages of hearing loss by both air and bone conduction for tones above 1500 cycles, but relatively less loss on tones below this frequency level. There is also a higher prevalence of this type of hearing loss with advancing age. Implications of these trends in relation to the most prominent features of deafness in the population are discussed. It is concluded that the typical process of aural degeneration in the general population is chronic progressive nerve deafness, which has both higher prevalence and greater severity among males.
Progressive Deafness Associated with Disorders of Vitamin A Metabolism
Authors: Josephson E. M.
Published: September 2005

Incidental to the discovery of a successful method of treatment of retinitis pigmentosa, which was previously a hopelessly blinding disease, it has been found that the deafness often associated with the disease also responds to the same treatment. The retinitis pigmentosa, with its progressive degeneration of the retina, nightblindness and eventual blindness in the untreated case, the deafness and the associated nervous disorders are associated with a failure of assimilation of carotene or vitamin A from the intestinal tract. This failure of assimilation is often associated with an impairment of liver function and bile secretion. When carotene is injected into the muscles of these cases, it is utilized by the body and serves to correct the deficiency of vitamin A resulting from failure of assimilation. As a result, the degeneration of the retina ceases and some degree of recovery takes place, vision is regained, nightblindness disappears, nervous disorders abate and eventually hearing is restored and even the failure of assimilation of the vitamin may clear up. The recovery of hearing even in the congenital cases of deafness, is sometimes quite startling in its rapidity; but it is usually slow. In the absence of any reliable criteria of the metabolism of carotene and vitamin A, it appears to be advisable to submit every case of progressive deafness to a test period of intramuscular carotene therapy.
The Parabolic Sound Concentrator
Authors: Coile R. C.
Published: September 2005

A compendium of all published experimental and theoretical work on parabolic reflector-type sound concentrators has been made. Some experiments have been carried out with a parabolic bowl to test the more recent theoretical analyses never before verified. The experimental data on amplification and directivity published in 1930 by Obata and Yosida of the Aeronautical Research Institute, Tokyo Imperial University, has been checked by the new theory. The first theoretical treatment of amplification was made by Rocard in the Revue d'acoustique in 1932. In 1935 the experimental verification of this expression for amplification was published in the Zhurnal Teknicheskoi Fiziki by Schneider, an engineer at the Moscow Radio Center. Also in 1935, Gutin, a physicist in Leningrad, derived independently the expression for amplification and went on to work out the theory of directivity which he published in the Izvestia Elektropromishlennosti Slabovo Toka. Recent measurements are described giving additional checks on the amplification theory of Rocard and Gutin, and verification of Gutin's formulas for directivity. This directivity theory has been applied to existing published directivity curves and data of Schneider, Obata and Yosida. Measurements and analyses have also been made of the sound fields inside parabolic reflectors.
Parasitic Infestations in Acoustical Materials
Authors: Brooks J. Woolson
Published: September 2005

Being a discussion of some difficulties experienced by architects in the selection and installation of acoustical materials with a few suggestions for their avoidance or remedy.
The Adaptation of Acoustical Materials to Auxiliary Functions
Authors: Parkinson John S.
Published: September 2005

With the increasing use of acoustical materials for purposes of interior finish, a number of additional uses have been found for these products. Cases are cited where the acoustical treatment has been made an integral part of the air conditioning system. The adaptation to improved lighting methods is discussed. Certain materials have such inherent architectural value that they are used primarily as interior finishes, with the acoustical function secondary. In the summary, suggestions are made to assist the architectural profession in taking advantage of these various adaptations. Details and photographs will be included.
Selective Amplification in Hearing Aids
Authors: Watson N. A.
Published: September 2005

By means of the articulation recordings and high-fidelity reproducing system described in an earlier paper, and a large variety of frequency distortion networks, the selective amplification principle in hearing aids has been tested by extensive measurements on normal and typical hard-of-hearing persons. The criterion used for evaluating the effectiveness of each type of amplification has been the standard percent syllable articulation. For all ears tested, uniform amplification, free from nonlinear distortion and adventitious noise, has proved superior to amplification “peaked” at various frequencies to provide what is often falsely called selective amplification. Carefully prescribed selective amplification, even when first tried, has proved to be better than uniform in some instances. In other cases it does not give as good results. Some hard-of-hearing persons did not hear well with either uniform or selective amplification at first, because they never had heard some of the speech sounds before, or had become unfamiliar with them owing to their impairments. However, after practice with the prescribed amplification most of them became accustomed to it, and their percentage articulation rose with successive tests. The opinion of the listener has proved to be a very poor criterion for determining the correct amplification. Many of the hard-of-hearing listeners have chosen as sounding best the types which had frequency response curves of the same general shape as their threshold curves, and have criticized as sounding very unpleasant those with which they attained the highest articulations. It is not yet always possible to prescribe immediately the best type of amplification for a given hearing impairment, but a method of prescription based on the “most comfortable equal loudness curve” has proved highly satisfactory in several cases.
Hearing Survey at the New York and San Francisco World's Fairs
Authors: Montgomery H. C.
Published: September 2005

A statistical study of hearing is being made from hearing tests at the New York and San Francisco Fairs. An acuity test for pure tones and one for spoken words were offered as part of The Bell System exhibits, and over half a million visitors permitted a photographic record to be made of their test blanks. The results of a preliminary study of these records will be presented.

About one person in seven showed a hearing loss of 25 db or more at 7040 cycles, and about one in twenty-five showed sufficient impairment at the lower frequencies to indicate a handicap in understanding speech in a public auditorium. The age and sex trends observed agree in general with those found in earlier surveys. Thresholds for certain representative groups will be gives in terms of ear canal pressure.

The results were consistent at different times of the day and from day to day. Comparison of data from New York and San Francisco indicates little difference between the groups. Certain other geographical comparisons will also be presented.
Performance of Rectangular Rooms with One Treated Surface
Authors: Beranek Leo L.
Published: September 2005

Computations are carried out for typical rooms of widely different volumes having one surface completely covered with absorbing material. The object of the computations is to demonstrate the application of the theory of normal modes of vibration of rectangular rooms to delineate the range of variation likely to be encountered in the shape of the decay curves. For each of the different rooms an ideal normal impedance curve for the treated surface is computed such that the decay curves would be logarithmic and the frequency-reverberation characteristic flat up to a certain limiting frequency. This limiting frequency depends on the dimension perpendicular to the absorbing surface. Approximate values of normal impedance of several standard acoustical materials were obtained and used in computations showing the acoustical characteristics of various rooms treated with these materials. Partial coverage of the treated surface is discussed and possible means of estimating the results from the theory of completely covered walls are suggested. The distortion of the distribution of points in frequency space caused by added absorption is discussed as a possible criterion for acoustical design.
A Review of Cardioid Type Unidirectional Microphones
Authors: Glover Ralph P.
Published: September 2005

The generalized characteristics of a unidirectional microphone whose response pattern is a cardioid of revolution are discussed with regard to pickup of reverberant energy, directional discrimination, and effect of distance and sphericity of wave on response frequency characteristic. Comparisons with the performance of the nondirectional pressure microphone and velocity microphone are made. Previous two-transducer structure for obtaining the cardioid characteristic are reviewed and a new single-transducer structure operating by acoustical phase shift is described.
Application of Piezoelectric Vibration Pickups to Measurement of Acceleration, Velocity and Displacement
Authors: Baumzweiger Benjamin
Published: September 2005

The theory and construction of the inertia-type piezoelectric vibration pickup is described. A calibration technique has been developed in which the pickup under calibration is driven by a wide range vibration actuator through a piezoelectric vibration “cell” of the inertia-type in which mechanical resonance occurs above the frequency range of the first instrument. A double integrating network and control switch permit direct readings of acceleration, velocity and displacement of vibration to be taken on a commercial sound-level meter, thus considerably extending the usefulness of the original equipment. The apparatus has found practical application in the design of quiet industrial products and in vibration studies of buildings, excavations and other civil engineering problems.
Applications of the Buchmann-Meyer Effect in the Calibration of Phonograph Recording and Reproducing Equipment
Authors: Cowan Milton , Griffith Paul
Published: September 2005

Buchmann and Meyer have shown that the optical patterns reflected from a modulated phonograph record can be evaluated quantitatively in terms of the stylus-point velocity at the time of recording. If a record is illuminated with parallel rays of light, the width of the luminous band is directly proportional to the lateral velocity. Thus, the over-all frequency-response characteristic of a recording mechanism may be readily and quickly determined. Also, the characteristic of a reproducing system may be determined from a record of known lateral velocities at various frequencies. The effect may also be used to determine the magnitude of recording turntable speed fluctuations, surface noise level of a record, and the state of the division of the particles constituting the surface of a record.

The paper develops the theory of the effect, and its practical applications will be demonstrated in the University recording laboratories.
Sound in the Theater
Authors: Burris-Meyer Harold
Published: September 2005

The showman has two principal avenues of approach to the emotions and, in rare cases, to the reason of his audience: sight and hearing. The visual component of the show depends ultimately upon the light reflected to the audience from actors, scenery, etc. Lighting instruments and control devices make it possible for the showman to employ the complete color spectrum, and to vary intensity from a level which gives only partial visibility to one which is unpleasantly bright.

Until recently the auditory component of the production has been limited in its characteristics by the limitations inherent in the source of the sound and the acoustic properties of the theater. By introducing thermionic means of sound control, it is possible to employ for dramatic purposes the whole frequency and intensity ranges to which the ear responds, and thereby give the auditory component of the show the same flexibility and susceptibility to artistry that are possessed by the visual component.

It is no longer necessary to hamper the actor by forcing him, in addition to interpreting his part, to compensate for the acoustic deficiencies of the theater, for the orchestra to misinterpret a piece to avoid drowning out the singer, or for the playwright to depend upon eleventh-century prop sound effect devices for the sound which he uses to establish locale, atmosphere and mood. It is possible to achieve with sound numerous dramatic values usually assigned to scenery, light, movement, etc. It is possible to use sound as an arbitrary independent means for stimulating predictable involuntary audience reaction; to engender by auditory means that emotional flux which will make it easy for the audience to suspend disbelief, to laugh at, weep for, or believe in something which would have seemed absurd when first the curtain went up.

The effort to devise a technique for subjecting all sound in the theater to control has been pursued for ten years. Results of that effort have already brought about some innovations in radio and legitimate production, and have made possible the development of at least one new dramatic idiom. The control of sound in the theater is now the subject of a research project underwritten by the Rockefeller Foundation. Producing organizations in the fields of motion pictures and radio as well as legitimate drama are aiding the enterprise, as are also research organizations and equipment manufacturers. Experiments in the application of the technique to a wide variety of productions will be cited. Results of experiments since the report on the subject made to the Acoustical Society (April 29, 1935) will be summarized.
Pitch as a Function of the Amount and Rate of Frequency Modulation
Authors: Pepinsky Abe
Published: September 2005

Pitch variation arising from frequency modulation was first studied by Lewis, Cowan and Fairbanks. Their stimuli consisted of short sound-pulses whose frequencies were continuously and rapidly raised or lowered. Results of their study led to the present elaboration and subsequent reinterpretation of prevalent concepts of the ear's response to modulated sounds.

Thresholds of perceived pitch change were found to vary as a function of the amount and rate of modulation. Perceived extent of pitch change was shown to depend upon the amount, rate and form of modulation. Correspondence between physical and perceived extents was much greater than expected.

It is believed that the data have an important bearing upon problems relating to the perception of the pitch element in speech.
Comments on Paper by Professor F. V. Hunt Presented at the Meeting of the Acoustical Society of America at Iowa State University
Authors: Hasbrouck H. J.
Published: September 2005

The high frequency translation losses in record reproduction which Professor Hunt has quoted from a former paper of mine apply only to soft plastic-coated recording disks such as are used for instantaneous play-back recording. They do not hold and are very much less on the relatively hard material of which commercial transcription records are pressed. The RCA reproducer was designed and primarily intended for use with these hard commercial pressings.

With reference to the frequency characteristic which is to be adopted and which is being used for the new Orthocoustic broadcast transcription records and which Professor Hunt contends represents too much high frequency pre-emphasis, let me say that this program was started solely with the idea of producing ultra-high quality disks. It seems inconsistent that such a characteristic would be used if it resulted in objectionable distortion. The direct purpose in accenting the high frequency range in recording and attenuating it in reproduction is of course to reduce surface noise. Our object in demonstrating such a record at this meeting was not only to show how far the surface or background noise can be reduced but also to direct attention to the absence of distortion.

As Mr. Robert Morris, of the National Broadcasting Company, indicated, the requirements for low surface noise on broadcast records are rather severe. Low distortion is not alone of paramount interest. The noise level too must be below a commercially acceptable value. This level is far below that which would be tolerated in home record reproduction. Assuming that it were possible to make a record totally free from wave form distortion the broadcasters would immediately insist on raising the recording level until the distortion was brought up to but not beyond the acceptable amount just mentioned. Thus the signal to noise ratio would be improved and no harm done.

I cannot argue with Professor Hunt's calculations on distortion but think perhaps he based them upon a higher recorded level than we propose to use in Orthocoustic disks. It is intended of course that the distortion will be objectionable to no one, and for all practical considerations not audible. By this method of recording it has been found possible to make ultra-high quality lateral transcription records which, in side-by-side comparison with the output from a high quality monitoring loudspeaker operating on “live” programs, defy detection, from the standpoints of frequency range, background noise and low distortion. That is all we can expect from any recording system.
A Comparison Between Piezoelectric and Electromagnetic Coupling
Authors: Van Dyke Karl S.
Published: September 2005

A development which closely parallels that which Morse gives for the equivalent network of the electromagnetic loudspeaker is carried out for piezoelectric coupling as in a supersonic generator or a piezoelectric resonator. A coupling constant may be written in mechanical ohms per electrical ohm. When combined with the mechanical impedance of a resonator it yields the usual equivalent network of the piezoelectric resonator. The series arrangement of the elements of this network which is due to the voltage-force nature of the coupling is in contrast with the parallel network where the coupling is current-force. In the one case the electrical impedance becomes greater, in the other less, as the mechanical impedance is greater. The mechanical inertia, dissipation and stiffness are each transferred in the first case to circuit elements of proportional impedance, in the second case to elements of proportional admittance.