bluuebunny/crossref_metadata_2025 huggingface dataset:
A Simple and Precise Standard of Frequency and Musical Pitch
Authors: Lamson Horatio W.
Published: September 2005

A new design of electrically driven tuning fork is loaded symmetrically by a pair of microphone buttons and energized by a small dry battery. One of these microphones drives the fork at a constant amplitude and frequency while the other supplies an alternating current quite free from harmonics. By careful design, minimum damping of the fork is secured. The use of steel of low temperature coefficient permits this fork to be adjusted and maintained at its rated pitch with a precision of one part in 10,000 or 0.01 percent. The device may be made compact, rugged and easily portable. By stroboscopic methods, all pitches of the musical scale may be measured in terms of such a tuning fork standard.
What is Measured in Sound Absorption Measurements?
Authors: Sabine Paul E.
Published: September 2005

Experimental work in various laboratories has shown that in the application of the reverberation theory to the measurement of sound absorption coefficients, certain of the fundamental assumptions of the theory are not realized and perhaps cannot be realized in practice. This paper is an attempt at a critical analysis of the points at which theory and practice diverge. What is sought as the absorption coefficient at a given frequency of a given material is a numerical value which, when applied in the reverberation formula, will give the effect on the rate of decay produced in any room by any area of that material. In small rooms, due to diffraction, with small test samples the equivalent absorption per unit area increases as the test sample area decreases, whereas with large areas localized on one surface the decibel rate of decay tends not to be linear. Both effects are functions of the absorptivity of the material and possibly of the wavelength of the sound. Various proposed methods looking to the standardization of the results of measurement in different reverberation chambers are considered.
Recent Developments in Acoustical Measuring Instruments
Authors: Wente E. C.
Published: September 2005

In this paper various acoustical instruments that have been developed in recent years will be discussed. A critical study will be presented of their limitations and their fields of application.
A Loudness Scale for Industrial Noise Measurements
Authors: Churcher B. G.
Published: September 2005

Both on technical grounds and from experience in industrial noise measurements, it is recognized that the decibel scale, used as a loudness scale, does not yield numerical values proportional to the loudness sensation. In many spheres of work this occasions great inconvenience and there is need for an agreed rule for converting the decibel observations of practical noise measurements into loudness values on a linear loudness scale. A survey has therefore been made of published data with a view to deducing the most probable law for the relation between stimulus and sensation for a 1000-cycle pure tone. Relations derived from mental estimates of loudness, from data on monaural-binaural listening and from data on the properties of tone combinations are discussed. The evidence indicates that not only does the nerve-impulse theory of audition provide an explanation of the faculty of making mental estimates of relative loudness and of the monaural-binaural listening phenomena, but that stimulus-sensation relations deduced by the two methods are in substantial quantitative agreement. On theoretical grounds it is not thought that tone combination data are admissible for this purpose and an important divergence between these and monaural-binaural data appears to exist. Consequently the suggested relation put forward is not felt to be the most probable law. For the final relation derived in the present paper from the available data, the number 100 is assigned to the loudness evoked by an intensity of 100 db above 0.0002 dyne per sq. cm reference pressure. For practical industrial noise measurements, the relation is expressed sufficiently nearly by a simple power law between the limits of 30 and 115 db. Over this range, the loudness (L) is given by L = d5×10−8, where d is the number of decibels above reference pressure. In addition to its being more in conformity with introspective judgments of relative loudness, this simple rule is thought to be preferable to the suggested curve because it is easily remembered, accurately definable and easily used with the aid of a slide rule.
The Motion of a Bar Vibrating in Flexures, Including the Effects of Rotary and Lateral Inertia
Authors: Mason W. P.
Published: September 2005

In this paper a complete theoretical solution is given for a bar vibrating in flexure taking account of rotary and lateral inertia. The solution shows that the frequency of a bar free to vibrate on both ends, is asymptotic to the frequency given by the usual solution, neglecting rotary inertia, when the ratio of width to length is small, and approaches the frequency of a bar in longitudinal vibration when the width becomes comparable to the length. The theoretical frequencies have been compared with the published results of Harrison on the frequency of a quartz crystal vibrating in flexure, and have been found to agree within one percent for a crystal whose width is less than half its length.
Velocity of High Frequency Sound in Small Tubes
Authors: Norton Gardner A.
Published: September 2005

This study of the velocity of high frequency sound in small tubes covers the range of frequency from about 10 to 80 kilocycles per second, and in diameter from 1/2″ to 3/16″. The method of G. W. Pierce, using magnetostriction oscillators, has been followed, providing high accuracy of measurement. Careful precautions in the construction were taken to eliminate the variations due to humidity, impurity, and to spurious reflections. The results tend to support definitely the Helmholtz-Kirchhoff reduction law, but provide a smaller observed value of the constant for pure air compared to the theoretical value. The value of free space velocity derived from these experiments checks that independently obtained by Grabau, using a similar method in air, to within 1 part in 4000. Hence the present tube method may be applied to delicate measurements of sound dispersion in pure gases, and their mixtures.
Effect of Intensity on Supersonic Wave Velocity
Authors: Pielemeier W. H.
Published: September 2005

It is the purpose of this paper to present further evidence that supersonic waves in air have a velocity which depends on their intensity and that this velocity approaches the limiting value (γP/ρ)12 at comparatively low intensities.
On the Principle of Uncertainty in Sound
Authors: Kock Winston E.
Published: September 2005

Following Stewart, a discussion of the application of the principle of uncertainty (ΔνΔl ≈ 1) to sound phenomena is given. Various sound phenomena are thereby explained and certain related experiments with frequency vibrato are reported. The phenomena explained are: The chromatic glissando imitation of a portamento, analysis of a formant into a Fourier series, the relation between vibrato wideness and pitch range and the pleasing effect of a frequency vibrato.
Sound Insulating Properties of Certain Building Materials
Authors: Parkinson John S.
Published: September 2005

Transmission loss data obtained in the Johns-Manville Laboratories on various building constructions are reported. Almost all this data has been obtained on “room size” floors and partitions. The relation between such tests and “panel” tests is given where data is available. Detailed studies of the vibrational properties of various constructions are also reported which show the response characteristics at various frequencies, the degree of structural isolation obtained in various double constructions, the relative importance of damping, etc.
Airplane Acoustics
Authors: Zand Stephen J.
Published: September 2005

Consideration is given to certain acoustical factors that have been heretofore underestimated by the acoustic engineer in the design of quiet commercial airplanes. The importance of proper structural preparation of an airplane to permit the application of efficient acoustic treatment is stressed. Recent experience in acoustical treatment of airplanes of French and Italian design is discussed.
Transmission of Sound Through Multiple Walls
Authors: Faggiani D.
Published: September 2005

A simplified treatment of the transmission of sound through multiple partitions is presented. On the basis of several assumptions concerning the nature of such structures an equation is derived expressing their acoustic transmission loss. According to this simplified treatment, the reduction caused by multiple structures is always less than the sum of the losses of the individual components.
Loudness Level Contours and Intensity Discrimination of Ears with Raised Auditory Thresholds
Authors: Reger Scott N.
Published: September 2005

Equal loudness level contours over the frequency range from 1000 to 4000 cycles are practically parallel with the threshold level in “normal” ears. Equal loudness level contours do not display any such “parallelism” with the threshold value of ears with approximately normal thresholds at, e.g., 2000 cycles but with markedly raised thresholds at 4000 cycles. A study of 15 persons with this type of hearing showed that if an individual had a 10 db loss at 2000 cycles and a 60 db loss at 4000 cycles, he would judge a 4000 cycle tone 10 db above his threshold equally loud as a 2000 cycle tone approximately 40 db above his threshold. Intensity discrimination studies showed that ears with raised auditory thresholds also could detect smaller increments in intensity than the normal ear at intensity levels the same number of db above the thresholds of each. The above findings are discussed in relation to the perception of speech and music—particularly amplified speech in headphones—by individuals with raised auditory thresholds.
Distribution of Peak and Root-Mean-Square Pressures in Conversational Speech
Authors: Dunn H. K. , White S. D.
Published: September 2005

Measurements made on conversational English speech are described, using the voices of six men and five women. Both peak and r.m.s. pressures are given, as measured in one-eighth-second intervals, and in twelve different bands of frequencies throughout the voice range. From these data other quantities are derived, including the frequency distribution of speech power in long intervals, and the total average voice power. The measurements being made at a distance of twelve inches from the lips, other tests on a single voice show how the speech characteristics change in going to greater and smaller distances.
Vocal Resonators
Authors: Lewis Don
Published: September 2005

A new procedure has been formulated and used to determine the nature of vocal resonators. The procedure, which is based upon the harmonic analysis of selected waves within a vibrato cycle of a sung tone, involves the following assumptions: (1) That during a sustained vowel produced by a good singer, the sound source remains essentially constant except for frequency variations (the vibrato); (2) that a good singer can hold his resonators essentially constant during the production of a sustained vowel. With changes in the fundamental frequency that typify the vibrato, the frequencies of the overtones naturally vary—by rather large amounts in the case of the higher overtones. For example, if tones near G1 (98 d.v./sec.) are used and if there is a vibrato of something over a semi-tone in extent, the overtones around the typical resonance regions for the vowel “ah” will change enough in frequency to cause them practically to overlap. The effects of the resonators on these shifting overtones are revealed by harmonic analysis. Instead of more or less isolated ordinates found in the common acoustic spectrum, many ordinates appear within fairly wide frequency bands. The data make it possible to draw inferences about the nature of the “vocal-cord spectrum” and to offer what seem to be fairly accurate descriptions of the resonators.
The Dramatic Use of Controlled Sound
Authors: Burris-Meyer Harold
Published: September 2005

The play stimulates audience response via the organs of sight and hearing. Everything which one sees in the theatre is conditioned by light which is carefully controlled for the purpose of providing visibility, establishing mood and atmosphere, and for use as an independent abstract artistic medium. What the audience hears, however, is up to the present time controlled by and limited by the human voice, the architecture of the theatre, musical instruments, eleventh century sound-producing apparatus, and, in a few cases, a public address system. It has been the purpose of the writer and his associates to control sound in the theatre as simply and effectively as light is controlled and to use it for audibility, the creation of mood and atmosphere, and as an independent artistic medium. To that end all the sound in the theatre is within certain limitations isolated at its source, carried over a switchboard similar to the switchboard used to control light and reproduced for the audience in such a manner as will best fulfill the artistic demands of the play. To carry out this purpose it is necessary to be able to produce in the theatre any sound from any source so that the audience will hear it from any apparent source, from a moving source or from no apparent source, at any intensity and with any predetermined characteristics such as pitch, quality, etc. Apparatus designed to fulfill the requirements listed has made it possible to increase the dramatic effectiveness of many plays already written and has increased the range of possibilities for the playwright. The application of the technique developed in the Stevens Theatre is discussed with respect to a number of specific plays in which the technique has been used. Projects for future research and the possibilities for commercial exploitation of the technique are discussed.
A Mechanical Bower for Violins
Authors: Abbott R. B.
Published: September 2005

A mechanical violin bower, giving a constant and continuous tone as required for recording by a crystal analyzer and sound level recorder, was made and used for measuring the “response” from violins. The report on response measurements was given at the Pittsburgh meeting. This report deals only with the mechanical bower. The bow, as now made, is composed of fine silk strands, loosely spun, and treated with a quick hardening lacquer. This hair-like thread is wound around two grooved pulleys many times, and the two ends are fastened together to form one continuous thread. Fine-toothed guides placed in front of the pulleys keep each strand in its proper place, and form a flat belt which performs like a regular violin bow. By a proper mounting of this belt on a frame, and by having a small motor to run it, the desired results are obtained. The frame holds a violin in the same manner as held by a violinist. A spring attached to the frame and violin support hold the pressure of the bow on the string at any desired constant value. The speed of the bow is regulated by an adjustable friction gear. The silk thread bow produces tones free from scratching noises, and comparable to those produced by a horse-hair bow.
A Method of Studying the Vibration of Automobile Body Panels
Authors: Young P. O. , Parkinson J. S.
Published: September 2005

Since the body of an automobile is composed largely of extensive steel panels, free and ready to radiate as sound any vibration communicated to them, no method of automobile quieting proves satisfactory until these panels are rendered ineffective as sound generators. In the work reported in this paper it has been recognized that such steel panels have two kinds of vibration communicated to them, continuous and intermittent. The paper discusses the development of a representative, duplicable, and precise test method for studying these effects. Certain general facts developed in these tests are discussed, with an outline of desirable future research in this field.
The Motion of a Bar Vibrating in Flexure Including the Effects of Rotary and Lateral Inertia
Authors: Mason W. P.
Published: September 2005

A complete theoretical solution has been obtained for a bar vibrating in flexure taking account of rotary and lateral inertia. The solution shows that the frequency of a bar free to vibrate on both ends is asymptotic to the frequency given by the usual solution, neglecting rotary inertia, when the ratio of width to length is small, and approaches the frequency of a bar in longitudinal vibration when the width becomes comparable to the length. The theoretical frequencies have been compared with the published results of Harrison (I. R. E., Dec. 1927) on the frequency of a quartz crystal vibrating in flexure and have been found to agree within one percent for the first flexural mode for a crystal whose width is less than half its length. Measured values for the second flexural mode agree within about 5 percent with the calculated frequencies.
Sound Control in Air Conditioning Equipment
Authors: Merle André
Published: September 2005

Sound control in air conditioning equipment today assumes an importance equal to that of temperature control. This paper describes some of the precautions required in the design and installation of such systems.
Acoustic Impedance of Small Orifices
Authors: Sivian L. J.
Published: September 2005

Data are presented giving the measured a.c. acoustic reactance and resistance for a number of circular orifices varying in diameter from 1 cm down to 0.034 cm, and for a rectangular orifice 1.9 cm×0.075 cm. The measurements were made for various particle velocities, the corresponding Reynolds numbers varying from 0.1 to 1000, roughly. The reactance is found substantially independent of the particle velocity; a formula for computing it is given. The resistance approaches a constant value as the velocity is sufficiently decreased; a formula for computing this “low velocity” resistance is given. At larger velocities the resistance increases with the velocity; a partial explanation is suggested.
Acoustical Planning of Catholic Churches
Authors: Möller Charles
Published: September 2005

Acoustical difficulties encountered in normal European Catholic churches are discussed relative to requirements for speech and music. Various methods for improving the conditions are suggested. These include the use of large glass screens partially separating the pulpit from the sanctuary, the use of large reflectors behind the pulpit, the introduction at will of variable acoustic absorption, and the modification of established architectural designs in building new churches.
Method for Very Rapid Analysis of Sounds
Authors: Meyer Erwin
Published: September 2005

Sound analysis by a single band pass filter requires a considerable time, which is inversely proportional to the square of the frequency discrimination. Analyzers consisting of multiple resonators are cumbersome and do not cover a continuous frequency band. The paper describes a new method based on the dispersing properties of a diffraction grating analogous to those used in optical analysis and equivalent to an infinite number of resonators. The sound frequencies are modulated by a 40-kilocycle carrier, projected by a ribbon loudspeaker and reflected by a curved grating three meters long. The frequency discrimination thus attained equals that of a 125-cycle band selector; the theoretical speed of analysis approaches 0.01 second, making it possible to obtain “moving pictures” of continuously changing sound spectra.
Production of Acoustic Wind by a Vibrating Quartz Crystal
Authors: Hight S. C.
Published: September 2005

A vibration through the thickness in an x-cut quartz crystal plate causes air to circulate away from the large surfaces and in toward the edges of the plate. The frequency of vibration may be several million cycles per second. The magnitudes of the vibrational motion (displacement, velocity, acceleration) are discussed. Equipment for demonstrating the phenomena is described.
On the Physics of Speech Sounds
Authors: Trendelenburg F.
Published: September 2005

It is difficult to determine the composition of aperiodic sound phenomena, particularly those which vary rapidly with time, as, for example, speech sounds. The methods of automatic electric analysis cannot be applied directly because of the time required. The graphic or mechanical Fourier analyses cannot be recommended because a great number of single analyses must be carried out for aperiodic processes. A very clear idea of the sound composition as a function of time is obtained when the separate octave ranges of the sound processes are recorded oscillographically by means of filters. The result of such oscillographic investigations of speech sounds is described. The oscillograms very clearly show the different harmonic and inharmonic components of speech sounds. Conclusions in regard to the voice theory are drawn from the oscillograms.
The Velocity of Sound in Ethylene Dichloride Vapor
Authors: Billhartz W. H. , Bishop F. L.
Published: September 2005

The velocity of sound in ethylene dichloride vapor at the boiling point was determined by the use of a resonance tube. The frequency of the sound was measured by comparison with the frequency of a wire of known length under known tension. Resonance was indicated by minimum reactance of the acoustical impedance of the tube of gas, on the source of sound as the length of the tube was changed by moving a piston. The precision of the apparatus was verified by preliminary measurements with air at 23.5°C and steam at 98.5°C. The values found agree to within 0.5 percent of the results of previous observers. For ethylene dichloride, said to be 99.5 percent pure and so checked by means of its boiling point, the velocity of sound was found to be 176.2 meters per second at 83.7°C.
Selective Amplification Aids to Hearing
Authors: Knudsen V. O. , Sepmeyer L. W. , Watson N. A.
Published: September 2005

The paper states the requirements for a theoretically ideal hearing aid, and describes the role which selective amplification plays in the design of aids to hearing to approximate these requirements. A description is given of the apparatus designed and built at the University of California at Los Angeles under a grant of the American Otological Society for the purpose of laboratory testing of the effect of selective amplification in aiding hearing. The results of articulation tests made with the apparatus described with specially prepared phonograph articulation records are given for several persons with low frequency impairment of hearing.
Echoes at Echo Bridge, Newton Upper Falls, Massachusetts
Authors: Jones Arthur Taber
Published: September 2005

One span of this stone arch bridge crosses the Charles River. At the abutment on one side of the river a hand clap is returned as a series of echoes of decreasing intensity. Perhaps the sound waves are roughly focused by the arch, first on one side of the river and then on the other. At any rate, the echoes seem to be produced by reflection from the arch, not from some other object.

When the source is, as usual, on the bank it is to be expected that if an observer in a boat half-way across the river hears any echoes they will succeed each other twice as rapidly as when the observer is near the source. This is not the case. The observer in the boat does hear echoes, but they succeed each other at the same rate as when heard near the source. The explanation of this fact has not yet been found.

If both source and observer are near the middle of the river it is to be expected that the echoes will succeed each other considerably more frequently than when both are on the bank. On three different occasions this was found not to be the case. The echoes heard under these circumstances succeeded each other a trifle less frequently than when source and observer were on the bank. The reason seems to involve the fact that the boat is some distance above the center of the arch. The sound reflected from the arch is again reflected from the water before it comes to a focus, and this focus is near the vertex of the arch. From this point it spreads downward, is reflected by the water and again by the arch before the first echo is heard. On one occasion when the water was low the source and observer in the boat were nearer to the center of the arch, and the echoes came with a considerably greater frequency.
Measurement of Speed Fluctuations in Sound Recording and Reproducing Equipment
Authors: Kellogg Edward W. , Morgan Adolph R.
Published: September 2005

High quality reproduction of recorded music is possible only if the speeds of recording and reproducing machines are maintained constant within very narrow limits. As improvements are made in these machines greater refinement in measurement of the variations is required in order that the progress may continue.

The development of an improved “Wow-meter” for such measurements is described, and various alternative schemes are discussed. The securing of a standard record, itself sufficiently free from imperfections, presents one of the most serious difficulties. For testing turntables a toothed steel wheel was built, in which special precautions were taken to minimize indexing and other possible errors. The current generated by means of this wheel is supplied to an electrical circuit so arranged that variations in frequency cause deflections of a galvanometer which are registered on a photographic film. The principle employed, namely, a resonant circuit slightly off tune, has been used in earlier devices. In the meter described, a push-pull arrangement has been adopted to reduce the likelihood of errors due to variations in voltage. A frequency meter of this type has certain inherent limitations in its ability to register very rapid fluctuations. Certain measures have been adopted to make the meter satisfactory in this respect, and the possibility of going further in this direction if necessary is given consideration.
Design Compromises for a Practical Sound Meter
Authors: Abbott Ernest J.
Published: September 2005

Apparently there is no ideal sound meter, and any design represents a compromise between many factors such as cost, size, weight, sensitivity, range, reliability, and convenience and flexibility of operation, etc. While meters now on the market are reasonably satisfactory for noise surveys and sales demonstrations, few if any of them are suitable for practical machinery noise reduction work.

Some time ago the author was approached and asked to write a specification for a practical sound meter for general purpose noise work. This was an unusual opportunity to allow some one else to do all the development work on the well-nigh impossible meter which I had long hoped to build for my own use, and naturally I agreed. The present paper outlines the design compromises which were made, the reasons therefor, and the meter which was the result of the specification.
Observations Bearing on the Physiology of the Human Cochlea
Authors: Guild Stacy R.
Published: September 2005

I have never held, and do not now have, any theory of hearing. There are as yet too many serious gaps in the factual knowledge of the ear to warrant theorizing. My part in this symposium will therefore be limited to the presentation of the observations made in our laboratory at Baltimore, and primarily to those made on the human ear by correlations of the records of hearing acuity with the histologic sections of the temporal bones. The observations that bear on the physiology of the cochlear part of the inner ear have already been published. (The principal paper with respect to high tones was published jointly with Drs. Crowe and Polvogt in the May, 1934, number of the Bulletin of the Johns Hopkins Hospital; and the data bearing on low tones were presented by me at a symposium of the American Otological Society last May and are published in the September, 1935, number of the Annals of Otology, Rhinology and Laryngology.)

Briefly, the evidence indicates localization for high tones (2048 cycles upward), but there is no evidence of localization in man for low tones (up to and including 1024 cycles). For the frequency of 8192 cycles the most important region of the organ of Corti is about 4 to 5 mm from the basal end of the cochlea; for 4096 cycles it is about 8 to 9 mm, and for 2048 cycles it is about 12 mm from the basal end. All tones up to and including 1024 cycles can be well heard when there is total atrophy of the organ of Corti in as much as the whole lower basal turn of the cochlea (this is about one-third of the entire length of the human cochlea). We have been unable to correlate the lesions found in the apical and middle turns with impaired hearing for low tones. No particular form of localization theory is favored by our evidence.
Physiological Acoustics; Pitch
Authors: Davis H. , Stevens S. S. , Lurie M. H.
Published: September 2005

The electrical potentials generated in the cochleas of guinea pigs were picked up by electrodes in contact with the bone or external membranes of the cochlea and the neck muscles. These potentials were studied as a function of the position of the electrodes and the condition of the organ of Corti within the cochlea in order to determine the specificity of resonance of the basilar membrane to tones of various frequencies, and thereby discover the role of the cochlea in pitch perception.

Audiograms of the electrical response were taken before and after drilling through the cochlear wall and damaging the organ of Corti at various points. The exact location and extent of each lesion were determined by subsequent microscopic study of serial sections of the cochleas and these were correlated with the losses in hearing revealed by the audiograms. Good correlations were obtained in 20 animals between the boundaries of lesions and sharp departures of the audiograms from normal.

The positions of the resonant areas for tones of various frequencies indicated by these results are confirmed by the locations derived from an integration of the most recent data for differential sensitivity to pitch in human ears. High tones are localized near the basal end of the cochlea, 2000 c.p.s. is at the middle, and the lower octaves are closely bunched toward the helicotrema.
The Relation between Loudness and Masking
Authors: Fletcher Harvey
Published: September 2005

This paper describes the derivation of a formula for calculating the loudness of any sound from the masking audiogram obtained with the observer immersed in the sound. This formula contains a new function which is dependent only on the masking audiogram. This function was derived from the loudness function G(L). The calculations by this formula are very simple and give results which agree well with those observed.
Change of Pitch with Loudness at Low Frequencies
Authors: Snow W. B.
Published: September 2005

The changes in pitch which result from changes in the loudness of low frequency tones were investigated for several frequencies between 75 and 1000 c.p.s. with a crew of 9 observers. The loudness levels covered the range 20 to 120, and both telephone receivers and a loudspeaker were used as sound sources. Fletcher's pitch standard, a pure tone of loudness level 40, was employed.

All consistent judgments gave pitch shifts downward with increasing loudness, but large differences between individuals were found. Two observers perceived no shifts at any frequency or loudness while three others experienced changes greater than 35 percent at the highest intensity. Appreciable changes with time in individual judgments were found. There appeared insignificant difference between data obtained with telephone receivers or with the loudspeaker. A set of contours of equal loudness level, plotted on coordinates frequency and pitch change in percent, is given. These curves show a pitch change small at 1000 cycles, increasing to maximum at a low frequency and decreasing for still lower frequencies. The frequency of greatest shift increased from about 100 cycles at small loudness to about 200 at loudness level 120.

The Appendix describes automatic test equipment that greatly simplified the testing routine and improved its accuracy.
A New Treatment of the Horn-Diaphragm Coupling Chamber for Receiver Measurements
Authors: Stedman C. K.
Published: September 2005

A loudspeaker may be tested by removing its horn and loading it acoustically with an air column of variable length in a closed tube. In this way one can measure the acoustic impedance of the horn and the sound power output of the speaker, under the assumption that the air chamber in front of the diaphragm can be regarded as an addition to the tube of an equivalent length r determined by experiment. Under this assumption the air load impedance ZA at the diaphragm is given by ZA = −j(A12/A2)ρc cot kx where A1 is the diaphragm area, A2, the cross section of the tube, and x the total length, i.e., actual length plus r. An analytical treatment leads to the formula ZA = −j cos2 kr[(A12/A2)ρc cot kx] −j(A12/A2)ρc sin kr cos kr. Eq. (1) leads to correct results for the measurement of acoustic impedance of the horn and sound power output, but cannot be extended to determine the mechanical impedance of the diaphragm. Eq. (2) is the basis of a new treatment which is more general. It is expressed in terms of a parameter r which can be calculated theoretically at low frequencies, or determined empirically at higher frequencies. The theory has been verified experimentally.
Change of Pitch with Loudness at Low Frequencies
Authors: Snow William B.
Published: September 2005

The changes in pitch which result from changes in the loudness of low frequency tones were investigated for several frequencies between 75 and 1000 c.p.s. with a crew of 9 observers. The loudness levels covered the range 20 to 120, and both telephone receivers and a loudspeaker were used as sound sources. Fletcher's pitch standard, a pure tone of loudness level 40, was employed. All consistent judgments gave pitch shifts downward with increasing loudness, but large differences between individuals were found. Two observers perceived no shifts at any frequency or loudness while three others experienced changes greater than 35 percent at the highest intensity. Appreciable changes with time in individual judgments were found. There appeared insignificant difference between data obtained with telephone receivers or with the loudspeaker. A set of contours of equal loudness level, plotted on coordinates frequency and pitch change in percent, is given. These curves show a pitch change small at 1000 cycles, increasing to maximum at a low frequency and decreasing for still lower frequencies. The frequency of greatest shift increased from about 100 cycles at small loudness to about 200 at loudness level 120. The Appendix describes automatic test equipment that greatly simplified the testing routine and improved its accuracy.
Apparatus and Technique for Reverberation Measurements
Authors: Hunt Frederick V.
Published: September 2005

The conventional method of timing sound decay to an adjustable threshold is made automatic by a system of relays which control the following sequence: When a predetermined sound level is attained in the chamber the source is turned off and an electric timer is started: when the sound level falls to the adjustable threshold the timer is stopped and the source is turned on again. This recurrent cycle is stopped after ten repetitions and the average time for a single decay may be read directly from the timer. The apparatus is entirely a.c.-operated and 80 db of decay can be recorded in the middle audiofrequency range. It is found that a low-pass electric wave filter can be used to eliminate the rapid fluctuations in the rectified output of the microphone amplifier without altering the recorded decay rate. This artifice, in conjunction with the warble tone, is capable of reducing the deviations from smoothness in the decay curves to a value comparable with the random timing error without resorting to rotating vanes in the sound chamber. A statistical analysis of the residual timing errors is given.
Filtration of Elastic Waves in Solid Rods with Membranes as Side Branches
Authors: Lindsay R. B. , Barnes T. G.
Published: September 2005

This paper considers theoretically the propagation of compressional and torsional waves in solid rods having membranes as side branches. An infinite cylindrical rod is loaded at equal intervals with flexible circular membranes attached at their outer edges to the inside of a circular cylinder (see Fig. 1). The assumption that longitudinal waves in the rod set up symmetrical transverse waves in the membranes leads to the conclusion that the structure is a high-pass compressional wave filter. The limiting case of an infinitely rigid membrane is also investigated. There is next considered the case of torsional waves in the rod giving rise to radial torsional waves in the attached membranes which now may be treated either as flexible or rigid diaphragms. When the latter are rigidly clamped at their outer edges, the structure is found to be a high-pass torsional wave filter. When the diaphragms are free at the outer edges, a low-pass filter results. The transmission characteristics are given for each case along with numerical illustrations.
The Present Status of the Mechanics of Sound Conduction in Its Relation to the Possible Correction of Conduction Deafness
Authors: Pohlman A. G.
Published: September 2005

E. H. Weber in 1851 interpreted the middle ear apparatus as an impedance matching transformer which balanced the resistance differences between the medium of conduction (air) and the medium of reception (liquid). The interpretation implied that the apparatus must be effective for all audiofrequency levels. It was not accepted by otologists because it was known that in conduction deafness, greater functional disability is noted for the low than for the high frequencies. Recent developments support the Weber interpretation and indicate that this low pitch disability is not dependent on frequency limitations due to the pathology of the middle ear. Evidence will be submitted to show that where the sound conduction apparatus is nonfunctional the drum membrane damps the direct conduction through the air of the middle ear. A case will be reported on the replacement of the lost drum membrane and ossicles by a prosthesis patterned after the middle ear apparatus of the bird. The possibility of creating a soft spot in the otic capsule in cases where the stapes is “frozen” to the head so that a transformer prosthesis may be applied will be considered. The accepted idea of a mass shuttling in the labyrinth liquid as the mechanical factor essential to audition is opposed.
The Legal Problems of Noise
Authors: Free E. E. , Hahn D. J.
Published: September 2005

Records obtained by standard noise meters are beginning to be accepted by American courts as legal evidence in nuisance cases, but the legal definition of what constitutes a noise nuisance is not clear. Existing and possible principles and some leading cases will be discussed. Acoustical engineers might usefully work out and suggest certain physical or physiological principles which should underlie new legal definitions in line with modern methods of noise measurement.
Application of Elastic Suspensions to High Speed Newspaper Presses
Authors: Livingston Stanley D.
Published: September 2005

The effectiveness of various types of elastic suspensions when applied to complex mechanisms has been determined from an analysis of the test data which were obtained from several multi-unit newspaper press installations. Materials used as isolation mediums were natural cork, rubber pads and steel springs. The weight of the various installations ranged from four hundred and fifty tons to nine hundred and fifty tons. A semirigid assembly of press units now being erected will have a total sprung weight of approximately twelve hundred tons.

The vital question in the case of the original installation, which was made solely for the purpose of reducing the nuisance effect of the vibration transmitted to the building structure, pertained to the degree of elasticity permissible without materially affecting the production efficiency of the presses. It has been found that the transmission of vibration can be reduced to a minimum, and, if the suspension is properly applied, the production efficiency can be materially increased. Accordingly, some suspensions are now being installed solely for economical reasons.

The writer offers for discussion the subject of the transmission of vibration by means of “carrier frequency” and questions whether this phenomenon has been given the attention it merits.
Developments in Aircraft Sound Control
Authors: Bruderlin H. , Wheaton E.
Published: September 2005

This paper describes present requirements for sound control in larger airplanes from the viewpoints of the operator, the passenger, and the manufacturer. It presents a new method of approach to the problem of satisfying these requirements, showing measures being taken toward their solution on a new aircraft project, and giving anticipated results.
Loudspeakers for High-Fidelity Large Scale Reproduction of Sound
Authors: Massa Frank
Published: September 2005

The extension of both frequency and volume range in large scale sound reproduction has imposed severe limitations on the performance characteristics of loudspeakers employed in these applications. This paper discusses some of the problems that arise under such conditions and what means have been taken for their solution. The limitations of single speakers to cover the entire frequency range are mentioned and the advantages of multi-speaker systems are pointed out.
Control of Temperature Variation in the Frequency of Tuning Forks (with demonstrations)
Authors: Eisenhour B. E.
Published: September 2005

The increasing use of tuning forks not only as frequency standards but as controlling devices for equipment requiring perfect synchronization calls either for very accurate temperature control with the ordinary steel fork, or for the development of forks in which the variation of frequency with temperature is negligibly small.

Two methods have been employed to achieve this end—either the development of metal alloys having very small frequency-temperature coefficients, or the fabrication of compensated forks from two materials having coefficients of opposite sign. While alloy steels, such as Invar and Elinvar, can be produced having coefficients of the order of one-twentieth that of ordinary steel, yet very considerable variations in coefficients are found in individual samples of these alloys even when cut from the same piece of stock.

The combination of two alloys having positive and negative temperature coefficients has proven a more practical means of producing forks of uniform qualities and with frequencies independent of temperature. Demonstrations of the thermal properties of forks of this type will be made.
Variation of Sound Absorption with Area
Authors: Chrisler V. L.
Published: September 2005

Sound absorption measurements have been made in the reverberation chamber by an intensity method on areas of 72 square feet and areas of 4 square feet. The apparent coefficient is larger for the small areas and agrees within the error of measurement with results which were obtained by the reverberation method.
Moving Pictures of the Vocal Cords in Operation
Authors: Tiffin Joseph
Published: September 2005

A 16-mm moving picture film of the human vocal cords will be shown. Several of the views were taken by means of stroboscopic illumination. The facts revealed by the pictures will be discussed briefly with reference to the theories of vocal cord vibration.
The Acoustical Planning of Broadcast Studios
Authors: McAllister G. Stanley
Published: September 2005

Radio broadcasting is aware of the very close kinship of architectural acoustics.

The growth of radio broadcasting has not only been characterized by the substantial expansion and development of its scientific and technical aspects, but the industry has been aware of and is taking advantage of the newer knowledge of architectural acoustics. Many of the attempts to utilize the knowledge have been disappointing and others have been highly satisfactory.

As in all developments of a scientific or experimental nature, the lack of information on the subject or a mis-application of the principle may bring an unfortunate result, so in the application of acoustics to the design and construction of broadcast studios this same error may occur.

The broadcast engineer and the radio production man may not master the subject of acoustics, but he fully appreciates its value and need. His contribution to the knowledge of the problem may be somewhat small and may even be “unscientific,” yet that part may be the very element which the trained expert can utilize to the fullest extent.

The acoustical problem of the broadcasting studio is of a special nature requiring specific attention to the technique of design, shape, size, use, pick-up and flexibility.
Some Data on a Room Designed for Free Field Measurements
Authors: Bedell E. H.
Published: September 2005

This paper gives some data on the absorbing material used in a room recently completed and intended for acoustical measurements under essentially free field conditions. The absorbing material, which consists of a number of layers of cloth separated by air spaces, is shown to have an absorption coefficient of the order of 98 to 99 percent over a wide frequency range. Some data are also given showing the degree of departures of the sound field in the room from the field to be expected in free space. It is shown that it may not be possible to duplicate a free field in an enclosed room, regardless of the freedom from stationary waves obtained, in the sense that the pressure may decrease more rapidly than the inverse distance law applying to a free field.
Automotive Quieting
Authors: Norris R. F.
Published: September 2005

Intake roar, exhaust noise and body resonance are discussed; methods by which these noises are attacked are explained and data showing their relative importance are given.
A Modified Tube Method for the Measurement of Sound Absorption
Authors: Morrical Keron C.
Published: September 2005

In a previous abstract, a method was described for measuring the sound absorptivity of small specimens. Sound from a loudspeaker travels down a cast-iron tube 8 inches in diameter, strikes the specimen under test at an angle of 45 degrees and is reflected down a side tube where it is measured. By measuring the sound reflected down the side tube from a thick glass plate, and by measuring the sound in the side tube when an exponential horn is substituted for the specimen, it is possible to arrive at the reflectivity and consequently the absorptivity of the specimen. The earlier apparatus has been redesigned and measurements have been taken on a large number of materials. For the frequency of 500 c.p.s. the method has given absorptivities for commercial materials that are in satisfactory agreement with those determined by reverberation measurements.
Positions of Stimulation in the Cochlea by Pure Tones
Authors: Steinberg John C.
Published: September 2005

The relation between tone frequency and position of stimulation on the basilar membrane has been calculated from data on differential pitch sensitivity. The calculations involve assumptions concerning the choice of the upper and lower pitch limits of hearing and the choice of tone levels which should be used in obtaining differential pitch sensitivity data. It is shown that for quite different assumptions the positions of stimulation for tones in the range from 500 to 10,000 cycles are not greatly affected. Outside this range the positions depend on the assumptions. The calculated positions for tones of 1000, 2000 and 4000 cycles fall, respectively, at points on the membrane about 13, 12 and 23 of its length away from the helicotrema. The calculated positions are compared with positions obtained from post-mortem studies of human cochlea and with positions obtained from electric response measurements on the cochlea of anesthetized guinea pigs. The differences between various methods for the most part are no larger than calculated differences between observers.