bluuebunny/crossref_metadata_2025_split huggingface dataset:
TRANSMISSION OF SOUND THROUGH APERTURES
Authors: Ritchie Earland 
Published: September 2005

This investigation was an attempt to obtain experimental data to justify a prediction made by Lamb concerning the fractional transmission of sound through an aperture in a very thin plate of approximately infinite boundaries. The effects upon the actual transmission of varying the lengths of the apertures, of changing the number of the apertures, and of increasing the aperture sizes were investigated.
The work was done in the Sound Absorbing Acoustic Laboratory since it approximates outdoor conditions. The purest tones available were used as sources of sound. The apertures tested varied in lengths from one thirty-second of an inch to twelve inches, and in diameters from one-fourth of an inch to one and three-fourths inches. These were circular apertures cut through large plates three feet square. Equations were established to express the observed relationships found existing for the lengths of apertures, and for a variation of the number of apertures.
The theory given by Lamb for plates of infinitesimal thicknesses was found to be in agreement with experimental results. Apertures of different lengths showed an exponential relationship when compared with the per cents of transmission. The greatest transmissivity of an aperture can be obtained by using one aperture only. Increasing the number of apertures gave an ever diminishing result per aperture. The transmission through apertures of any length is directly proportional to their respective cross-sectional areas.
INVESTIGATION OF GAMMA IN A MIXTURE OF GASES
Authors: Barnes Garnett F. 
Published: September 2005

The velocity of ultra-sonic vibrations was measured in gas mixtures and from this data the ratio of the molecular heats of the mixture was calculated. The vibrations were produced by a quartz crystal driven by a thermionic oscillator. The method employed was essentially that used by G. W. Pierce.
Mixtures of carbon dioxide and helium, air and helium, oxygen and helium, and nitrous oxide and helium were used. The molecular heat at constant pressure was taken from the International Critical Tables and the molecular heat at constant volume of the gas mixtures calculated.
It was found that the ratio of the two molecular heats of the gas mixtures as determined by experiment agrees well with that obtained by calculation.
An Efficient Miniature Condenser Microphone System
Authors: Harrison H. C. , Flanders P. B. 
Published: September 2005

It has been shown recently that microphones and contiguous amplifiers distort the sound field in which they are placed by reason of their size and the cavity external to the diaphragm of the microphone. For frequencies such that the size is large compared to the wave-length of perpendicularly incident sound, reflection causes the actuating pressure to be double that which would exist in the undisturbed field. If the direction of the incident sound be along the plane of the diaphragm, the increase of pressure due to reflection is not as great; but there may be a substantial reduction in effective pressure due to differences in phase across the diaphragm. In addition, cavity resonance produces an increase of pressure at frequencies usually within the working range of the microphone.
This paper describes a laboratory model of a Wente-type condenser microphone of high efficiency and an associated coupling amplifier which are of such small size that reflection and phase-difference effects are of negligible importance within the audible frequency range; while the cavity is so proportioned that its resonance effect is an aid rather than a detriment to uniformity of response in a constant sound field.
THE SUPERSONIC INTERFEROMETER AND ABSORPTION MEASUREMENTS
Authors: Hershberger W. D. 
Published: September 2005

The previously developed theory of the supersonic interferometer is extended with the particular view of utilizing it for absorption measurements in gases. It is shown that the mechanical impedance of the interferometer is Z = Z0 + Z(l) where Z0=j(mω − s/ω) + rZ(l)=Acρ/tanh 2αl + (Acρ/sinh 2αl)eiθ=− arc tan sin 2kl sinh 2αlcos 2kl cosh 2αl − 1.
That is, if reactance is plotted against resistance we obtain an impedance spiral with center (Acρ/tanh 2αl, 0) and radius Acρ/sinh 2αl. The action of the interferometer is studied in terms of the properties of the spiral. Absorption measurements are effected by compensating for the changes in the equivalent series electrical resistance because of changes in l by adjusting a shunt resistance across the crystal so the e.m.f. is held constant, irrespective of l. Absorption in the medium is calculated from the values of shunt resistance for the path lengths of interest. Measurements were taken at three frequencies in the range 899.0 kc to 2514 kc. The quantity 2αλ2 as measured by the interferometric method is not constant but shows a systematic change with frequency.
Physical Methods of Exploration for Oil-Bearing Structures
Authors: Shepard E. R. 
Published: September 2005

Modern scientific methods of prospecting for oil will be described and illustrated. These employ both natural and artificially produced forces. The former include gravitation, magnetism, galvanic potentials, radioactivity, and heat generation; while among the more important of the latter are seismic waves caused by an explosion and electric currents used in the study of the electrical resistivity of the earth.
A detailed description of the seismic method will be given particularly as it is used for determining the location of oil bearing salt domes on the Gulf Coast. In this method a charge of dynamite is exploded in the ground and the resulting waves through the earth are picked up by geophones at several points and recorded on an oscillograph film. The ground waves travel with different velocities, depending upon the character of the strata through which they pass. Because of the relatively high velocity of the waves through salt and stone, such mediums are easily detected.
A number of slides will depict different geologic formations with which oil is associated, while others will show seismic apparatus and the technique employed in locating the oil-bearing structures.
Sound Ranging at the U. S. Coast and Geodetic Survey
Authors: Dorsey Herbert Grove 
Published: September 2005

At this Bureau sound ranging is utilized in both the vertical and horizontal directions. The former, or echo method of depth measurement, was started in 1923 with the Sonic Depth Finder, which uses a method of regulating the rate of sending signals until the outgoing signal is binaurally heard to coincide with the incoming echo. From the rate of sending the depth is calculated. This method was displaced by the Fathometer when it was placed on the market in 1925. The Fathometer is direct reading by visual indications, the time elapsed between the outgoing signal and received echo being measured by the angle through which a neon tube has rotated during the interval. Fathometers are now used on practically all Coast Survey Ships.
The success of sound ranging in the vertical direction suggested its use in the horizontal direction and the method was developed early in 1924 with the cooperation of the Bureau of Standards. By this method a chronograph on the surveying ship records the explosion of a small bomb of TNT, the sound of which goes to two or more hydrophone stations and automatically causes the emission of radio signals which are recorded on the same chronograph. Such methods are now extensively used by Coast Survey Ships to locate their position in areas beyond the sight of land.
Minimum Audible Sound Fields
Authors: Sivian L. J. , White S. D. 
Published: September 2005

A paper by this title was presented at the last meeting of the society. It dealt principally with the thresholds for monaural hearing in an open sound field. Since that time the work has been extended to include the field thresholds for binaural hearing. The present paper is to report on the new data and to indicate how the threshold is modified by the observer's azimuth relative to the wave front of the sound field.
It also gives a further discussion of the relationship between the two types of threshold: the above minimum audible field (M.A.F.), and the minimum audible pressure (M.A.P.) as measured at the observer's ear-drum. It has been established that the two are different at frequencies so low that diffraction caused by the head and wave motion in the ear canal cannot be assigned as causes. Some new experimental evidence bearing on this point, is presented.
Discussion on the Design of a Rotating Mirror Oscilloscope
Authors: Mallina R. F. 
Published: September 2005

In the laboratory and in the classroom it is sometimes useful to project the wave form of electrical or acoustical phenomena on a screen. A rotating mirror in combination with a vibrating mirror and a light source is a convenient way of showing such waves. The problem of building an instrument for such purposes is comparatively simple if a small screen is used in a dark chamber. However, if the screen is made large enough to be viewed by a dozen people or more, many difficulties arise.
The paper describes how the various parts of the apparatus may be coordinated in order to produce a comparatively bright clearly defined wave with a small incandescent lamp in a room of average illumination. The vibrator used in the apparatus may be so constructed that its response is either inversely proportional to frequency or independent of frequency. The range covered is between 100 and 3000 cycles.
Recording Instruments for Frequency and Intensity
Authors: Hunt Frederick V. 
Published: September 2005

An inexpensive recorder which employs a spark to puncture a moving strip of chart paper has been constructed. One of the sparking electrodes is a light pointer attached to a short-period D'Arsonval galvanometer element. The other is a curved metal guide which bends the chart paper to the arc described by the tip of the pointer. In conjunction with the logarithmic vacuum-tube voltmeter already described (Rev. Sci. Inst. 4, 672, 1933) this instrument comprises a level recorder having a uniform decibel scale (60 db) and capable of following sound decay curves as steep as 150 db/sec.
A new electronic frequency meter has been developed which is capable of following rapid variations of frequency. This device employs gas-filled discharge tubes and yields an output that is strictly linear with frequency from zero to 8000 cycles and independent of the input intensity over a range of at least 35 db. The instrument is flexible and any portion of the frequency range may be fitted to the indicating instrument permitting high sensitivity to small frequency changes. In combination with the spark recorder, or any other type of recorder, this instrument places the delineation of time variations of frequency on an equal footing with time variations of intensity. For example, the melodic curves or intonation of speech and music, vibrato, and attack may be recorded directly.
Acoustics of the Rooms at the Bureau of Standards
Authors: Chrisler V. L. 
Published: September 2005

A study has been made of the acoustical treatment in two rooms of the same shape and volume. In one room the material was applied only on the ceiling. In the other room the total amount of absorption applied was smaller but the material was distributed over the upper part of the walls as well as on the ceiling. Owing to the distribution of the acoustical material, this room is acoustically the better of the two, although as usually computed, the total absorption was not as great as in the other room.
A third room which is used as a cafeteria was also studied. In this room about twice the customary amount of material was installed. Curves are given showing the variation in noise level with the number of people present, both before and after treatment.
Report of Committee on Sound-Absorption Measurements
Authors: Watson F. R. 
Published: September 2005

The Acoustical Society Committee on Sound Absorption presents a report for the information of the members of the Society. After preliminary experiments on a variety of materials, using different methods, a plan was evolved by which each of the various laboratories would be furnished a sample of the same material, with the expectation that the results obtained would be more strictly comparable than the data for different samples. The Celotex Company volunteered to make up a special run of BBB Celotex and furnish it gratis to the laboratories. The results of this experiment are shown (lantern slides) and exhibit a wide variation in the values of the coefficients. The reverberation method was used in all the tests, but there was considerable difference in the electrical instruments used. One chief reason for the variation in results was found in effect of area of material used; for instance for the frequency of 500 cycles per second, 12 sq. ft. of material gave a coefficient of 1.55, where 192 sq. ft. gave 0.44.
No standard method is approved at the present time, but certain recommendations have been adopted for guidance in absorption tests. In the meantime, several different methods are being investigated, with the expectation that a solution of the present difficulties will be found.
The Interpretation of Sound Measurements Used as a Tool in Machinery Noise Reduction
Authors: Abbott E. J. 
Published: September 2005

The recent reports of standardization committees on acoustical measurements and terminology will be of very great value in eliminating confusion which has existed on account of differences in the use of terms, in different references levels, equal loudness contours, etc. This work is highly commended. Unfortunately, however, these standardizations valuable as they are, do not eliminate all the confusions which exists; not only with workers in acoustics but more especially with engineers and executives whose primary interest is not acoustics but who are vitally interested in noise reduction and similar problems. It also appears that this confusion is hardly a matter which can be cleared away by committee action but which must be worked out in practical application.
At present there are at least seven scales used for indicating the magnitude of a sound, namely: sound pressure, sound pressure level, above threshold level (sensation level), intensity, intensity level, loudness level, and loudness. All of these scales are recognized by standardization and there seem to be definite reasons why each of these scales is valuable in practice. However, since four of them are expressed in decibels and often without further identification, great confusion results, particularly among engineers and others who are interested in noise, but who are not primarily acousticians.
This paper states the advantages and disadvantages of these various scales, together with suitable illustrations drawn from practice of the difficulties which arise in putting these scales to practical use in machinery noise reduction problems.
The Harmonic Analysis of Consecutive Waves in the Vowel “Ah” in Normal Voices and Before and After Surgical Removal of Nasal Polyps
Authors: Black John , Lierlie Dean M. , Tiffin Joseph 
Published: September 2005

Oscillograms were obtained of the word top as spoken by nine normal male voices and by five voices before and after surgical removal of nasal polyps. Every repetition of the wave pattern from the nine normals, and the first, third, fifth, etc., patterns in the sounds of the operated subjects were analyzed by means of a Henrici harmonic analyzer. A total of approximately 500 waves were considered, the analysis in each case reaching at least to the 25th component, and if necessary to the 45th.
The results justify certain conclusions relative to (a) the nature and importance of the temporal factor and wave-to-wave fluctuations in the vowel; (b) the support of the Helmholtz theory of vowel production; (c) location and variations of the three characteristic regions of energy; (d) probable reasons for certain inconsistent results found in studies of tongue position in vowel formation; (e) effect of removing nasal polyps on voice quality.
The Psychophysics of Frequency Modulation
Authors: Ramsdell Donald A. 
Published: September 2005

The auditory sensations which result from a frequency-modulated stimulus provide a method for determining certain characteristics of the auditory mechanism. A tone produced by a beat-frequency oscillator was modulated by means of a rotary condenser in order to investigate the critical rate and range of modulation at which apparent fluctuations in pitch become apparent fluctuations in loudness. The rate of modulation for ranges under thirty cycles at which observers cease to detect a change in pitch is a function of the frequency of the stimulus.
At a given frequency, 500 cycles, continuous increase in the rate of modulation shows first a critical point at about eight modulations per second followed occasionally by a second critical point at about fourteen modulations per second, beyond which changes in both pitch and loudness are detectable simultaneously. The first critical point is a linear function of the rate and range of modulation, except lot large ranges where the critical rate decreases.
The critical point phenomena can be interpreted in terms of the persistence of vibration of the basilar membrane.
Flutter in Sound Records
Authors: Shea T. E. , MacNair W. A. , Subrizi V. 
Published: September 2005

Frequency modulation of a sound signal produces some very interesting and sometimes not readily identifiable auditory sensations. Distortion of this type is caused in sound records by the nonuniform speed of the record during the recording or reproducing process.
While the physical nature of frequency modulation and some of the physiological effects produced by it are discussed, the paper consists largely of demonstrations including a demonstration of the side-band nature of flutter, the influence of room acoustics on the perception of flutter, the auditory effects of flutter in single frequency tones, and a demonstration of the auditory effects of frequency modulation in speech and music.
Apparatus and Technique for Reverberation Measurements
Authors: Hunt Frederick V. 
Published: September 2005

New apparatus has been constructed for obtaining accurate reverberation data. The conventional method of timing the 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 sound 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. If this recurrent cycle is interrupted after ten repetitions the average time for a single decay can 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.
Using this apparatus we have investigated the merits of employing a low pass electric wave filter to remove the rapid fluctuations in the rectified output of the microphone amplifier. This is approximately equivalent to the use of a recorder which is just capable of following the average decay rate. Determination of the average decay rate is not affected by the use of the filter but the average deviation from linearity in the decay curves can be reduced by a factor of at least two.
Physiological Acoustics; Loudness
Authors: Stevens S. S. , Davis H. 
Published: September 2005

Functional relationships obtained from studies of the electrophysiology of the auditory mechanism in animals may be used to determine the physical basis of the psychological aspects of hearing. Thus equal magnitudes of electrical potential are generated by the hair-cells of the inner ear when subjected to tones (of different frequency and intensity) which sound equally loud to the human observer, i.e., equal potential contours correspond to equal loudness contours. Therefore, loudness appears to be proportional to cochlear potential. Since end-organ stimulation can reach the brain only via afferent nerves which conduct series of discrete action potentials, loudness must also depend upon the number of fibers involved in the transmission of a volley of action potentials.
The relation of the size of the cochlear potential to the intensity of sound deviates from the Weber-Fechner relationship in the same manner as do the psychological functions. However, at about 60–80 db above threshold the cochlear potential begins to decrease, and a reversible depression of the response, due to overload, is shown by a “hysteresis” effect. If the overload is prolonged, microscopic degeneration of the hair-cells occurs, or if overload is too great the organ of Corti is shaken loose from the basilar membrane.
For a given tone the potential recorded from the scala vestibuli is out of phase by 180° with that recorded from the scala tympani. Therefore the potential drop is across the membrane, or from end to end of the hair-cells. The potential at the round window is in phase with that in the scala tympani, but the potential at the apex differs from the potential in the scala vestibuli by an angle which increases with the frequency of the stimulus. By moving the grid electrode along the outside of the cochlea, a point is found where the potentials which leak out of the two ends (round window and apex) cancel each other by interference.
The Position of Pure Tone Stimulation of the Basilar Membrane
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 and on the density of innervation of the membrane. 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 1000 to 4000 cycles are not greatly affected. Outside this range the positions depend on the assumptions. It appears that tones of 1000, 2000 and 4000 cycles stimulate, respectively, portions of the membrane about 1/3, 1/2 and 2/3 of its length away from the helicotrema.
Calculations made several years ago by Wegel and Lane from the differential sensitivity data reported by Knudsen gave the positions of a 1000-cycle tone in the middle of the membrane. The differences between the present positions and the earlier ones are due in part to taking account of the density of innervation of the membrane and in part to differences between the low frequency tone data on differential sensitivity reported by Knudsen and that reported later by Shower and Biddulph and used here. The latter data are believed to be more characteristic for low frequency tones.
Sound Reenforcement—An Acoustic Problem
Authors: Wolf S. K. , Stanton G. T. 
Published: September 2005

This paper discusses the approach to the subject of public address as an acoustic problem.
The primary function of a public address system is to faithfully produce, at all points in the listening area, sound of adequate loudness as heard close to its origin. The attainment of this objective is discussed in terms of the acoustic factors involved and their relation to the physical design of the apparatus.
The first of the factors is the directional-frequency characteristic of the loudspeakers involved, in terms of their relationship to the acoustic transmission of the auditorium. The tremendous complexity of computation of acoustic transmission requires, in the present state of the art, empirical determination of this factor by instrumental means. Since design limitations in the loudspeaker are such as to seldom permit securing exactly the frequency-directional characteristic required, a modification in the characteristic of electrical energy input to the speaker must be made. The requirement of attaining adequate loudness may be limited by acoustic regeneration or “feedback.” A brief discussion of the controlling factors is included.