bluuebunny/crossref_metadata_2025 huggingface dataset:
Fish Noises in the Narragansett Bay Area
Authors: Kelsey Alton S. , Beyer R. T. , Fish Marie P.
Published: September 2005

Recordings have been made of the sounds made by the various fish which inhabit the Narragansett Bay area. Of more than 25 species studied, only six produced significant amounts of noise. These were the red-winged and common sea robin, the toadfish, the long-horned sculpin, the puffer, and the burrfish. The signals from the recordings were later fed into a harmonic analyzer whose output meter was replaced by an Esterline Angus recording milliammeter. Readings were taken at intervals of 25 c/sec. throughout the entire audible frequency spectrum. Each selected portion of noise was replayed into the analyzer for the measurement at each frequency. The microphones were calibrated so that approximate intensities could be measured. The spectral distribution of the sound is reported for each of the noise-making species. A second type of noise, not previously reported, has been observed in the case of the toad fish.
Pressure in a Fluid Cylinder Due to an External Sound Field
Authors: White J. E.
Published: September 2005

Measurements of sound waves at any considerable depth in the earth must almost of necessity be made in fluid-filled boreholes, although it is a knowledge of the sound field in the absence of the borehole which is desired. This paper describes a method for computing the wave form to be expected at any point in the borehole due to a spherical wave in the earth. The same method is applied to sound in a gas-filled inner cylinder due to traveling waves in a concentric outer cylinder. It is assumed that sound pressure in the outer medium acting on an incremental length of the cylinder sets up a wave which travels away in both directions with little dispersion or attenuation. Its effect is observed at all other points along the cylinder at later times. The total pressure at any point is made up of the sum of such contributions from earlier disturbances up and down the cylinder. This is expressed as an integral, which permits easy computation of received signals in terms of wave forms in the outer medium. In general, a transient in the outer medium is measured as two arrivals, one of which may be reversed in sign. Computed arrival times and magnitudes are compared with experiment for the case of concentric cylinders.
Mutual Acoustic Impedance between Two Circular Disks
Authors: Pritchard Robert L.
Published: September 2005

A series solution has been obtained for the mutual acoustic impedance between two identical, circular disks vibrating in an infinite plane. The problem was formulated in terms of Bouwkamp's method of integrating over real and complex angles the square of the directional characteristic (relative sound pressure at a large, fixed distance) to yield the total radiation impedance. Integrals involved here are similar to a type previously evaluated by Stenzel and may be expressed in terms of a double series containing Bessel functions of integral and half-integral order. Numerical values of the mutual acoustic impedance obtained by this method for two rigid disks are in good agreement with values obtained by Klapman by direct integration of the pressure at the surfaces of the disks. The acoustic self-impedance and mutual impedance may also be calculated by the same methods for a more general type of circular disk having a prescribed radially-symmetric velocity distribution.
An Industrial Noise Problem
Authors: Reece Frederick C. , Miller Laymon N.
Published: September 2005

In a recent survey of an industrial noise problem by the Engineering Experiment Station of The Pennsylvania State College, noise level measurements were made for a large machine shop equipped with 58 high speed multiple-spindle automatic screw machines. The average audio noise level in the shop was found to be 102 db. On occasions, while listening intently to his machine to detect proper or improper operation, the operator would move his head into a region having a noise level of 115 db. Because many new employees at this company had complained of headaches and fatigue in connection with their work, it was suspected that the noise contained a large amount of ultrasonic energy. Also the design of the machines was such as to encourage rather than discourage the production of high frequency noise components. Consequently, an ultrasonic transducer was probed about the machines to determine the particularly noisy locations. Based on the audio and ultrasonic noise levels which were measured, some suggestions were made for noise reduction. The company constructed a sample enclosure to be placed around one of the machines, and a second group of noise measurements were made. Both audio and airborne ultrasonic noise levels showed a reduction of 12 to 15 db. As a result of the decreased noise levels, the company has now taken an interest in fabricating an improved enclosure. An incidental, but quite significant, advantage of the machine enclosure is the confinement of oil mist. Both from the point of view of health and shop cleanliness it is important to reduce the present high loss of cutting oil which escapes in the form of oil mist.
The Transmission of Sound through Single and Double Walls at Oblique Incidence
Authors: Beatty Ralph E. , Bolt Richard H. , Young James
Published: September 2005

Small-scale measurements of transmission loss as a function of angle of incidence will be reported and compared with theory. A 1-in. thick plywood box (4×4×2 ft.) was used as a “soundproof” chamber to exclude the incident sound. Thin, 18-in. square, test panels were mounted in an opening in the front of the box. The box, which could be rotated with respect to the fixed, 10 kc/sec. sound source to vary the angle of incidence, was lined with absorbent material to provide an anechoic space behind the test panel. The sound source and test box were placed in an anechoic chamber to provide free-field conditions on the incident side of the test panel. A rotatable microphone inside the box was used to measure the radiation pattern of the vibrating panel. The transmission loss, defined in terms of an average transmitted pressure, was found to be in rough agreement with Cremer's theory of the coincidence effect. The effects of damping and panel size will be discussed.
On the Non-Specular Reflection of Sound from Absorbent Surfaces
Authors: Twersky Victor
Published: September 2005

The non-specular reflection of plane waves of sound by certain surfaces composed of either absorbing semicylindrical or hemispherical bosses on an infinite plane has been analyzed. Solutions in terms of eigenfunctions for the problem of the single boss (with arbitrary impedance Z) on an infinite plane (of impedance Z′ = ∞, 0) and a plane wave at an arbitrary angle of incidence have been derived through consideration of a cylinder or sphere and two simultaneously incident “image waves.” The asymptotic solutions (Kr≫1) were then extended to consider certain finite (of maximum extent≪r) patterned distributions and both finite and infinite uniform random distributions of small bosses (Ka < 1), subject to the restriction that only the primary excitation be considered. (The analogous distributions of whole cylinders and spheres were also treated.) The results obtained for the various cases were then compared in the plane of incidence.
The Effect of Certain Respired Gases on the Cochlear Potential
Authors: Harris J. D. , Wing K. , Stover A. D. , Brouillette J. H.
Published: September 2005

Cochlear microphonics in response to a 4000-cps tone were recorded from cats subjected to forced respiration. Oxygen deprivation was established ranging from mild to extreme. Variables studied included amount of loss of potential, rate of decline, and ability to recover upon termination of anoxia. The range of arterial O2 concentrations in the resting anesthetized cat, as determined by us, is 11.3–15.5 cc per 100 cc of whole blood (av. = 13.6 cc). Concentrations of about 2 cc can produce a marked depression of potential which is largely or wholly reversible. Below this concentration the potentials reach their minimum somewhat more quickly and the changes are only partly reversible. In 7 cats complete and sudden anoxia was induced either by clamping the trachea, or by introducing pure nitrogen. These animals provide the limiting case against which one may compare those with low but measurable arterial O2 concentrations. Concomitant measurements of the CO2 content of the whole blood in several of the anoxic cats, and another series of cats respiring mixtures of CO2 in O2, showed that the losses under anoxia were not due to CO2. Continuous recording of electrocardiograms in all cats showed the inadequacy of observing only the pulse rate in determining the nature of cardiac activity with respect to anoxia. Instances have accumulated of loss of potential with an unchanged rate. Upon sudden anoxia, potentials decline to a first minimum of 10–20 microvolts in an average of 7.9 minutes (range 6.25–11.0), and are thereafter maintained at a much more slowly decreasing level for some hours. These results help document Wever's view that the genesis of the cochlear potential is twofold, one source relatively much more sensitive to O2 deprivation than the other. The histology of certain ears is reviewed.
Control Methods Used in a Study of the Vowels
Authors: Peterson G. E. , Barney H. L.
Published: September 2005

Relationships between a listener's identification of a spoken vowel and its properties as revealed from acoustic measurement of its sound wave have been a subject of study by many investigators. Both the utterance and the identification of a vowel involve subjective responses and are affected by the language and dialectal backgrounds and the vocal and auditory characteristics of the individuals concerned. The purpose of this paper is to discuss some of the control methods that are being used in the evaluation of these effects in a vowel study program in progress at Bell Telephone Laboratories. The plan of the study, calibration of recording and measuring equipment, and methods for checking the performance of both speakers and listeners are described. The methods are illustrated from results of tests involving some 76 speakers and 70 listeners.
Transmission Properties of the Vocal Tract—A Study Based on Analysis of Swedish Vowels and Consonants
Authors: Gunnar C. , Fant M.
Published: September 2005

Spectrum measurements on Swedish vowels made at the L. M. Ericsson Telephone Company in Stockholm are reviewed in comparison with Bell Telephone Laboratories data on English vowels. A phonetic matching of similar sounds leads to good agreement in formant frequency data. The Swedish survey provides data on consonants, including stop consonant spectra. Calculations of vocal tract transmission have been made with the purpose of supplying a theoretical basis for these measured spectra. Transmission line theory has been used assuming a system of cylindrical resonators as in the recent work by H. K. Dunn of Bell Telephone Laboratories. Speech sounds other than vowels are investigated and dissipation and formant band width are included in the theory. In some cases, calculations for a consonant can be based on those for a vowel having the same resonator network, but with a primary sound-source acting at a position higher up than the larynx. In this case the vowel formants, corresponding to poles in the system function, will also appear in the consonant spectrum but with a modification caused by the presence of a number of zeros which do not occur for the vowel sounds. This results in a partial inhibition of some of the vowel formants in the consonant spectrum.
An Automatic Device for Discriminating between Speech and Music
Authors: Clark Jones R.
Published: September 2005

An automatic electronic device will be described which sets a relay one way when the input is speech and the other way when the input is music. Actually, it is difficult to draw a line between speech and music except by arbitrary rules; patter songs certainly have elements of both. In fact, for each of the operating principles which one might use, it is possible to select a list of program materials which form a fairly continuous transition from music to speech. For the device to be described in detail, the writer has termed the variable involved in the transition from music to speech the diction, because when speech alone is involved, the current through the relay coil agrees rather well with one's subjective estimate of the distinctness of the diction. Since speech-music dichotomies are arbitrary and personal, the merit of a discriminator should be judged on the basis of the way that the relay current accords with the diction variable, rather than upon the agreement with an arbitrary speech-music dichotomy. The presentation will include a demonstration of the device.
Non-Linear Distortion in Hearing Aids
Authors: Peterson Arnold
Published: September 2005

Measurements of non-linear distortion were made on a typical hearing aid by three standard methods. These methods are: (1) the harmonic method, (2) the intermodulation method that evaluates distortion in terms of the modulation of a high frequency tone by a low frequency tone, and (3) the difference-frequency intermodulation method, which evaluates distortion in terms of the amplitude of the difference tones produced by intermodulation of two applied tones. The measurements and analysis of results on the basis of masking effects indicate that the difference-frequency intermodulation test is the most significant test for non-linear distortion in hearing aids.
An Automatic Non-Linear Distortion Analyzer
Authors: Olson H. F. , Pennie D. F.
Published: September 2005

This paper describes a system for automatically recording the non-linear distortion frequency characteristic of a loudspeaker. The system consists of the standard automatic recorder for obtaining the response frequency characteristic, coupled with a system of electronically switched high pass filters which suppress the fundamental, and pass the harmonics for obtaining the distortion frequency characteristic. Two characteristics are obtained on the same graph sheet, namely, the response frequency characteristic and the distortion frequency characteristic. The vertical displacement between the two characteristics thus obtained gives the amount of distortion at any frequency.
A Photographic Method for Displaying Sound Wave Space Patterns
Authors: Kock W. E. , Harvey F. K.
Published: September 2005

A photographic method using mechanical scanning for displaying the space patterns of sound and microwaves is described. A probe pickup scans the sound or microwave field and the amplified probe output controls the brilliance of a small lamp affixed to the probe. A camera set at time exposure records the light intensity variations of the lamp as it moves across the scanned field, forming a pattern on the film of the amplitude distribution. Phase fronts can be delineated by adding a constant amplitude signal to the probe output. Photographs are included which show: sound and microwave patterns of lenses, diffraction at a straight edge and disk, refraction by a prism, diffusion of sound by a divergent lens, and radiation from loudspeakers. Also, by transposition of source and receiver, directional patterns of transducers acting as microphones are obtained which (by reciprocity) appear identical with their radiation patterns. This provides a means for examining the directional characteristics of non-reversible transducers such as a carbon microphone. A calibration method is described which allows the relative value of the field intensities to be determined.
Equipment for the Field Measurement of Reverberation Times
Authors: Rudmose Wayne , Mims Harry
Published: September 2005

Field measurement of reverberation times in the past has required sufficient equipment to make the task somewhat undesirable. A compact set of apparatus has been developed and used which seems to lessen, somewhat, the burden. The entire source, weighing less than 5 lb., consists of a magnetic solenoid (with a moving slug) attached to a small wooden box. This impulse sound source has a wide frequency range and has sufficient acoustical level to be entirely adequate for most field measurements even for auditoriums of 400,000 cu. ft. in volume. The equipment for the measurement of reverberation time consists of a small sound level meter, a filter set, and a 3-in. cathode-ray-type reverberation meter. A 55-db logarithmic amplifier controls the vertical deflection on the persistent screen. A single frequency sweep circuit controls the horizontal deflection and is triggered by the sound level at the microphone. The filter circuit controls the frequency and the reverberation time is read directly from the calibration of the sweep circuit. For a single microphone position it requires less than 30 min. to effect the set-up, make the measurement, and repack the equipment.
Higher Order Gradient Microphones Using a Single Diaphragm
Authors: Hawley Mones E. , Kettler A. H.
Published: September 2005

In the past the construction of higher order gradient microphones has been exceedingly difficult because it was necessary to equate the frequency response characteristics, the sensitivities, and the phases of two or more pressure-sensitive units. The use of properly selected pressure pick-up points and the introduction, through suitable impedances, of sound pressures into the two sides of a single diaphragm (additive pressures on one side and subtractive pressures on the other) provides nth order operation in simple constructions. Second- and third-order microphones are feasible. A third-order microphone needs only four pick-up points, although the use of six permits easier acoustic impedance equalization. The analysis of the equivalent electrical circuit yields the ratios of the acoustical impedances involved.
Free-Field Calibration with Closely Spaced Microphones
Authors: Cox Jerome R.
Published: September 2005

In free-field reciprocity calibrations, practical considerations make a small microphone spacing desirable. For very small spacings, however, the free-field response of the microphone under test is not simply obtainable from the measurements. In this paper the effects associated with small spacings are investigated for a simple microphone (a point transducer on the surface of a hard sphere). Both theoretical and experimental results are given. The work is directed toward the determination of the minimum practical spacing consistent with the usual free-field assumptions and the formulation of corrections which will permit the use of still smaller spacings in microphone calibration.
Noise Discrimination Factor and Noise Discrimination Index: Concepts for Discussion
Authors: Wathen-Dunn Weiant
Published: September 2005

The importance of intelligible communication in noise has focused attention on noise-canceling microphones, and one of the attendant problems is that of assigning valid figures of merit to such microphones for the purpose of comparing their noise-canceling properties. Differential microphones have responses which are a function of both the direction from which the sound comes and the distance between the microphone and source. It is here proposed that a simple extension of the concept of directivity factor and directivity index would be useful as a valid figure of merit for actual microphones. Up to the present time the ability to discriminate against noise has been evaluated by taking the ratio of the on-axis response of the microphone at minimum talking distance to the on-axis response for plane waves and multiplying this by the directivity factor (modern version). This is usually a theoretical calculation; and, since real microphones do not follow accurately the theoretical decrease in response with distance, actual measurements of the response, as a function of orientation and distance for a given frequency, could be substituted in the following formula to give a noise discrimination factor, NDF: NDF =  ∫ 04π  ∫ ab drdΩ ∫ 04π  ∫ ab f2(r, Ω)drdΩ, from which the noise discrimination index would be NDI = 10log10 NDF, where f(r, Ω) is the ratio of the response of the given microphone at orientation angle Ω and distance r to its response at Ω = 0 and r = a, the minimum talking distance.
Enclosures for Direct Radiator Loudspeakers
Authors: Field William B.
Published: September 2005

In connection with the development of “talking-book” reproducers, measurements have been made at the National Bureau of Standards which show that the use of ported enclosures for loudspeakers is to be preferred over the use of totally enclosed mountings, especially with respect to the acoustic distortion at low frequencies. The discussion to be given will include a description of the experimental work carried out at the Bureau, an explanation of the cabinet design formulas, the procedure used in making an enclosure for a particular loudspeaker, the effect of absorbent material on high frequency response, and the tuning of the port or vent. A short demonstration will give an idea of how much acoustic improvement can be obtained in a portable unit by proper mounting of the loudspeaker.
Generator Impedance of Power Amplifiers Used with Horn-Loaded Loudspeakers
Authors: Levine Irving
Published: September 2005

The radiation resistance of a finite exponential horn fluctuates between wide limits in the region near the cut-off frequency. The variations in sound power output caused by these fluctuations can be minimized by choosing the correct generator impedance for the power amplifier used with a horn-loaded loudspeaker. This impedance is shown to be a function of the efficiency of the electromagnetic speaker unit. For speakers with greater than 50 percent efficiency a positive generator impedance is required, and the amplifier designer can secure the right value by a proper choice of negative feedback. For speakers with less than 50 percent efficiency a negative generator impedance is required, and this makes more severe demands on the amplifier design.
Ultra Speed Recording Technique
Authors: LeBel C. J.
Published: September 2005

The new technique permits ink recording at 5000 db per second, or ten times the pen speed possible with the high speed level recorder. This technique uses a linear-to-logarithmic converter, a linear rectifier, and a dc amplifier driving a direct writing oscillograph. Temperature stability, linearity, and transient response are discussed. The problem of achieving adequate transient performance in the logarithmic-element driving amplifier is emphasized. Examples of recordings of various types are shown, illustrating the effect of using various pen speeds between 600 and 5000 db per second.
Frequency Independent “RC” Phase Shifter
Authors: Brown Robert F.
Published: September 2005

This is a report of a study of an “RC” Phase Shifting network to develop a constant phase difference over a broad frequency range. Two channels are used which give equal output voltages nearly independent of frequency, while their phase difference is approximately constant over the design range. Some interesting properties of this circuit will be demonstrated.
A Time Constant Meter for Tuning Forks and Other High Q Devices
Authors: Morrow Charles T.
Published: September 2005

A time constant meter described operates on the principle that differentiation of an exponentially decaying rectified envelope decreases it in inverse proportion to the time constant and reverses its sign. Hence, it is possible to obtain a null by balancing the differentiated signal against a portion of the original. The circuit is simple, requiring only one amplifier tube and a tuning eye.
Depressed Sound Channels in the Ocean
Authors: Marsh H. W.
Published: September 2005

Sound channels may be expected to exist in the neighborhood of a depth at which the sound speed is a minimum. Surface channels caused by positive temperature gradients, and the sofar channel, caused by pressure effect, have been extensively studied both experimentally and theoretically. This paper treats so-called “depressed channels” caused by temperature inversions within a few hundred feet of the surface. Transmission measurements at ultrasonic frequencies are reported. In particular, these measurements are ideally suited for a determination of minimal absorption of sound energy to be expected at the frequencies studied.
Sound Absorption in Aqueous Solutions of Magnesium Sulfate and in Sea Water
Authors: Wilson O. B. , Leonard R. W.
Published: September 2005

A reverberation method has been used to measure the sound absorption in MgSO4 solutions, relative to that in water, under a wider range of conditions of temperature and concentration than for results previously reported. The relaxation frequency of the absorption process, approximately 150 kc at 25°C, showed no marked change when the concentration ranged from 0.003 to 0.02 molal. Dependence of the absorption on concentration, m, is variable, seeming to be very approximately m2 at m = 0.003 and approximately m1.3 at m = 0.02. For m = 0.01, change in relaxation frequency when the temperature was varied from 4.5–43°C indicates an apparent activation energy for the reaction of approximately 7.5 kcal per mole. The large relative absorption present for temperatures near 4° would indicate that the absorbing mechanism is not caused by a relaxation effect in the specific heat. Similar measurements on natural and synthetic sea waters agree well with each other, but give values somewhat smaller than do results of direct measurements in the sea.
Parameters of Electroacoustic Transducers
Authors: Batchelder Laurence
Published: September 2005

Electroacoustic transducers are analogous to electric networks, and may be defined by corresponding parameters. While electric networks are connected to definite terminals electroacoustic transducers usually operate in an unbounded medium. Consequently, one additional parameter, involving effective area, is required to specify the acoustic behavior. Equivalent networks are shown for the cases of electrostatic and electromagnetic coupling. The new definitions of the American Standard Acoustical Terminology are interpreted in terms of these networks, and relationships between various parameters are traced through a sort of family tree, in which reciprocity connects the branches as a vine. The basic property of a projector is its transmitting efficiency. It enters as a factor in all transmitting responses. If the transducer is reciprocal this same efficiency is the available power efficiency of the hydrophone. It is also the fraction of the total open-circuit mean-square thermal noise voltage present at the electric terminals which is contributed by thermal noise in the acoustic medium. Thus, it is a factor in determining the transducer equivalent noise pressure as well as the free-field receiving responses. A diagram is shown to aid in visualizing relationships in decibels between quantities which involve both electrical and acoustical units.
The Thermal Noise Limit in the Detection of Acoustic Signals in Water
Authors: Mellen R. H.
Published: September 2005

The factors involved in the design of an “optimum” receiving system for acoustic signals in water are considered. Formulas are derived for the minimum detectable signal level for plane waves and noise. The noise figure of the system is then defined in terms of the efficiency of the hydrophone, the noise figure of the amplifier, and the ambient water noise level.
The Standard Velocity Microphone
Authors: Kendall J. M.
Published: September 2005

A velocity microphone developed at the Naval Ordnance Laboratory early in World War II is described, which permits absolute intensity measurements of underwater sounds within the audio range. The arrangement of the microphone is such that it is easy to compute the response of the microphone to an accuracy of about 1/10 db. The microphone as built at the Naval Ordnance Laboratory consists of a rigid spherical shell which encloses a flexibly suspended magnetic system. A coil which is rigidly attached to the shell moves in the magnetic field when the particle motion of the water causes the shell to move, generating a voltage proportional to shell velocity. The weight of the shell and moving coil are made to be very nearly equal to the weight of water displaced by the shell so that shell motion is nearly that of water particle motion. When sound wavelengths become comparable to the shell diameter, the response drops off; but this effect has been computed and is allowed for.
Electroacoustical Operation of Transducers in Arrays
Authors: Pritchard Robert L.
Published: September 2005

The operation of an electroacoustical transducer in the presence of other transducers has been calculated under the assumption that each transducer can be described by two linear algebraic equations (electromechanical equations). If the mutual (mechanical) radiation impedances between transducers are considerably smaller than the internal mechanical impedance of each transducer, the radiating-surface velocity of each transducer is independent of the presence of the other units. On the other hand, for the case of a transducer at mechanical phase resonance, the velocity may be greatly dependent upon the coupling between other transducers. Under these conditions it is possible to produce 180° phase differences between velocities of adjacent transducers, such as are necessary in superdirective arrays, without requiring phase reversals between the corresponding electric currents. In special cases, no electrical connections, i.e., zero current, to one or more transducers may be required. Alternatively, for a linear array of identical transducers having negligible internal mechanical resistance and operating at mechanical phase resonance, uniform electrical current excitation produces a distribution of velocities among the transducers that is non-uniform in general and that yields a maximum directivity index.
A Reverberation Chamber with Polycylindrical Walls
Authors: Botsford J. H. , Watson R. B. , Lane R. N.
Published: September 2005

Reinforced concrete construction is employed in a reverberation chamber of moderate size to exclude extraneous noise and minimize low frequency absorption at the boundaries. High frequency absorption is sufficiently reduced by a heavily enameled interior that measurements to twelve thousand cycles per second are possible. A value for the absorption coefficient of the paint work has been obtained from data taken during construction. Cylindrical wall irregularities are fairly effective in producing diffusion above one hundred cps. In reverberation measurements, the effect of additional diffusion is obtained by commutation of the outputs of eight randomly positioned microphones. The results from pure tone data thus obtained agree with the results obtained from conventional noise band measurements using a single microphone.
Room Reverberation Study by Ultra Speed Recording
Authors: Dunbar J. Y. , LeBel C. J.
Published: September 2005

Reverberation curves, made with the high speed level recorder in studios, have heretofore shown little indication as to the excellence of a studio for broadcasting or recording. With two studios of about the same size and reverberation time, one is frequently more desirable than the other. The possibility of recording such differences by using ultra speeds up to 5000 db per second is discussed. This method seems to show the degree of diffusion of sound, during decay, with greater definition. Ultra speed ink recordings of studio reverberation at various pen speeds up to 5000 db per second are shown, and the results discussed.
An Inexpensive Acoustic Treatment for Gymnasiums, Civic Coliseums, and Similar Structures
Authors: Lane R. N. , Seay Frank , Boner C. P.
Published: September 2005

The acoustic treatment of an excessively reverberant civic coliseum is described. Before treatment, the structure, originally an aircraft hangar, had a sharply peaked reverberation time of eight seconds in the region between 600 and 800 cycles per second. Thirty-two thousand square feet of three-inch thick Fiberglas panels were suspended in horizontal V's six feet below the parabolic metal ceiling. After treatment, the reverberation time is essentially uniform from 100 cps to 8000 cps, with an average value of approximately 1.2 seconds. The method of construction and the mounting of the panels is described. Sound absorption coefficients for these panels are given, and a comparison is made between the value obtained from the coliseum installation and the value obtained for 72 square feet of identical panel hung in the Defense Research Laboratory polycylindrical reverberation chamber. The coefficients obtained from the data in the coliseum are lower than the coefficients obtained in the reverberation chamber.
An Improved Ultrasonic Interferometer for Gases and Vapors at Low Pressure
Authors: Fitzpatrick J. A.
Published: September 2005

The displacement of the reflector in the ultrasonic interferometers which we have been using has been measured by an external micrometer screw head which transmits motion by means of a rod and two balanced sylphons to the end of a cylindrical piston serving as reflector inside the system containing the gas or vapor. In the interferometer described here, the lower end of the piston rests freely in direct contact with the spindle of the micrometer screw. Motion is transmitted to the screw by a rotary crank enclosed in a stainless steel bellows sealing the system but permitting the operation of the screw inside. The load on the screw is constant, being only the weight of the reflector-piston. Readings of screw position are made through a glass window. The problem of so-called “satellite” peaks has as in all of our interferometers been completely eliminated by construction which maintains plane parallelism between source and reflector to two or three fringes of green light. This interferometer has permitted velocity determinations of a precision equalling any we have seen and has increased the precision of absorption measurements.
The Measurement of Ionic Vibration Potentials (Debye Effect) with Pulse-Modulated Ultrasonic Waves
Authors: Yeager Ernest , Dietrick Harry , Bugosh John , Hovorka Frank
Published: September 2005

If ultrasonic waves are propagated through an electrolytic solution, alternating potentials are produced within the solution as a result of the dynamical reaction of the ions to the material waves. Apparatus has been developed for the measurement of these ionic vibration potentials with pulse-modulated ultrasonic waves at frequencies from 200 to 1000 kc/sec. Preliminary measurements indicate that the amplitude of the alternating potentials is a function of the nature of the electrolyte but is essentially independent of the concentration for dilute solutions as is predicted by theory. A value of 5 microvolts per unit velocity amplitude has been found for 0.005 molar potassium chloride solution at 200 kc/sec. These results are in general agreement with the semiquantitative, relative measurements obtained with a standing wave technique during the first experimental confirmation of the effect. Ionic vibration potentials, particularly their frequency dependence, should prove especially interesting for electrolytes such as magnesium sulfate for which structural relaxation effects have been recently postulated in order to account for the abnormal absorption of sea water.
Random Noise in an Attenuating Fluid Medium
Authors: Roberson Robert E.
Published: September 2005

It is assumed that acoustic background noise is caused by a distribution of random white noise sources, whose physical mechanism is unspecified. A law expressing the amplitude-distance attenuation characteristic of the medium is also assumed. Several distributions of noise sources are considered: uniform volume distributions, uniform surface dipole distributions, and two mixed cases. The noise drop-off with frequency at a point below the surface is found for each case. For an infinite volume of noise sources, this drop-off is 6 db/octave at all frequencies. It is shown how this simple model can be generalized to other attenuation laws and other spatial and amplitude distributions of noise sources.
Mechanisms of Sound Absorption in Fluids. II
Authors: Markham Jordan J.
Published: September 2005

A great many seemingly independent approaches to the problem of relaxation absorption in fluids have been made in the last thirty years. The purpose of this paper is to group similar methods together and to indicate the relations between the various approaches to the problems. The following four classifications may be helpful: (1) method of kinetic theory, (2) method of statistical thermodynamics, (3) method of irreversible thermodynamics, and (4) the phenomenological approach. Groupings similar to these appear in other problems in the field of chemical physics. The various methods, of course, do not compete, but complement each other. For some problems, the simultaneous use of various approaches brings fruitful results.
Sound Absorption in Aqueous Solutions of Copper Acetate
Authors: Barrett R. E. , McNamara F. L. , Beyer R. T.
Published: September 2005

Ultrasonic absorption has been measured in aqueous solutions of copper acetate in the frequency range 7 to 40 mc, and at temperatures between 0°C and 60°C. The measurements were made by the radiation balance method, and they extend some earlier results obtained by one of the authors. The relaxation frequency ν0 for the extra absorption process connected with the presence of the solute lies in or near this frequency region. The experimental results make it possible to determine this relaxation frequency as a function of temperature and concentration. Preliminary measurements indicate that ν0 increases with temperature and concentration, while the maximum of the α/ν vs ν-curve (α = amplitude absorption coefficient) decreases with increasing temperature and increases with increase in concentration.
The Propagation of Sound in Carbon Dioxide near the Critical Point
Authors: Anderson N. S. , Delsasso L. P.
Published: September 2005

The expression for the normal velocity of sound in fluid becomes indeterminate at the critical point, since the coefficient of elasticity tends to zero and the specific heat at constant pressure approaches infinity. An expression has been obtained for the isentropic slope, which does not become indeterminate at the critical point. Observations were made with a Pierce-type variable path acoustic interferometer placed completely inside a pressure tank with provisions for external control. The isothermal variation of velocity and absorption was measured as a function of pressure at 572 kc in carbon dioxide. Above the critical temperature it was found that, as the pressure increases, the velocity decreases steadily, goes through a sharp minimum, and rises abruptly. Below the critical temperature a discontinuity in velocity was observed between liquid and vapor. The velocity in the liquid at 29°C was 208 meters/second and in the vapor 179 meters/second. The velocity variations away from the critical point agree with previously published results. The attenuation decreases steadily with increasing pressure and shows an abrupt rise as the critical point is reached, which would be expected from critical fluctuation scattering. Using isotherm data, two values of the velocity at the critical point were calculated, 154 and 146 meters/second. The measured value was found to be 141.6 meters/second.
Transformer Analogs of Diaphragms
Authors: Bauer Benjamin B.
Published: September 2005

The use of the conventional series R-L-C analog for diaphragms in equivalent circuits often causes serious difficulties. The action of a diaphragm is shown to be analogous to that of a system of ideal transformers, each corresponding to an area of the diaphragm. The analysis includes equivalent circuit representations of a piston diaphragm, multiple diaphragms, diaphragms with subdivided sides, and articulated diaphragms, etc., together with examples.
Sound Wave of “Stable” Form
Authors: Allen Clayton H.
Published: September 2005

Sound waves of finite amplitude are subject to progressive distortion or change in form during propagation. Theoretical analysis of this phenomenon for a plane wave neglecting dissipative forces leads ultimately to a multiple valued solution for acoustic pressure, displacement, etc. This is inconsistent with fact. R. D. Fay, introducing viscosity into the analysis, arrived at a solution in which the progressive distortion is balanced by the dissipative effects of viscosity. This wave, called the “stable” form, is essentially sawtoothed, varying in sharpness depending upon its intensity. Experimental measurements in a free spherically-diverging sound field verify the existence of the stable wave by showing the progressive distortion of an initially sinusoidal wave to a sawtoothed stable form. Comparison of the experimental results (for the diverging field) with the theoretical results (for a plane wave field) reveals good agreement as to the harmonic content of the stable form, except that a higher sound intensity is required in the diverging field. Both experimentally and theoretically, for sufficiently high intensities, the pressure amplitude of the nth harmonic relative to that of the fundamental approaches 1/n.
Acoustic Impedance in Terms of Energy Functions and the Nonlinear Reactance of Orifices
Authors: Westervelt Peter J.
Published: September 2005

Acoustical systems which are driven at a single terminal pair are considered. The acoustical driving-point impedance Z of such a system is the ratio of the pressure to the volume velocity at the driving terminal. If the system comprises a limited region R bounded by a surface S, Z can be expressed in terms of the volume integrals over R of the dissipation function, and the average lagrange density in addition to the surface integral of the complex power flowing across S. The acoustic impedance of a circular orifice, small compared with the wavelength, is evaluated by the methods discussed above. It is found that about 60 percent of the contribution to the mass reactance of a thin orifice arises from the average kinetic energy contained within the region bounded by two hemispherical caps which have radii equal to the radius of the orifice and which are placed concentrically on opposite sides of the orifice. At sound levels so great that the particle displacement amplitude through the orifice exceeds the radius of the orifice, the flow through the orifice may become jetlike in such a manner that vortex rings which form within the hemispherical caps detach themselves periodically. The coherence of the motion within the caps is destroyed by this jet-flow, so that the average kinetic energy in the caps no longer contributes to the reactance of the orifice. Measurements of the sound field in the neighborhood of the orifice indicate that the configuration of the field outside the jet region is essentially unaffected by the local jet action, thus the kinetic energy in this region will contribute to the mass reactance. The 60 percent reduction in mass reactance predicted by this theory will be compared with recent measurements performed by Ingard.
On the Generalization of the Concept of Impedance in Acoustics
Authors: Mawardi Osman K.
Published: September 2005

The conventional definitions of acoustical impedances, so useful in the investigations of the properties of idealized systems with lumped parameters, fail when applied indiscriminately to systems with distributed constants. In general, the present definitions are valid only when the specific impedance is constant on a wave front. By extending the notion of vector fields to specific impedances, the previous restriction is removed and the scope of application is considerably increased. A definition for the acoustic impedance based on energy concepts is also proposed.
Multiple Scattering by Distributions of Parallel Cylinders
Authors: Twersky Victor
Published: September 2005

A formal solution in terms of the cylindrical eigenfunctions has been obtained to the problem of the scattering of a plane wave of sound by an arbitrary distribution of parallel cylinders which takes into account all possible contributions to the excitation of a particular cylinder by the radiation scattered by the remaining cylinders. The solution is expressed as a sum of various orders of scattering. The first-order (the usual single scattering approximation) results from the excitation of each cylinder by only the plane wave or primary excitation. The second-order results from the excitation of each cylinder by the first order of scattering from the remaining cylinders, and so on to an infinite order of scattering. The nth order of scattering can therefore be expressed recursively in terms of the previous orders and finally as n products of series of the scattering coefficients of the single cylinder and hankel and trigonometric functions depending on the parameters of the distribution. Some applications to specific problems (two cylinders, grating, planes covered with semi-cylinders, etc.) have been made.
Earphone Sound Pressures in Ears
Authors: Burkhard M. D. , Corliss E. L. R.
Published: September 2005

This paper reports measurements of the sound pressure developed at the entrance to the ear canal by several earphones, and is a continuation of work previously reported on the comparison of sound pressure responses in three earphone calibration couplers. The earphones were originally applied to the ear with a 2-kg force. The sound pressure response on the ear and the statistical reliability of the response measurements have been obtained for application forces of 2, 1.5, and 1 kg. An application force of 1.5 kg was then used to obtain earphone on ear response determinations of 14 individuals. While the data are primarily for orientation for other experiments, a statistical analysis of it has given information that may be of importance in audiometry. For earphones now commercially available, differences between individuals and ears are much greater than the experimental testing precision.
A Method for the Transfer of Threshold Standards between Audiometer Earphones
Authors: Corliss E. L. R. , Burkhard M. D.
Published: September 2005

At the present time, standards of sound pressure corresponding to normal auditory threshold apply directly only to the particular type of earphone used in the original nationwide survey of hearing. Standards for new types of earphones are determined by subjective loudness-matching against earphones for which threshold standards exist. A number of skilled observers with normal hearing must perform this test, working at a level very near auditory threshold. Since auditory threshold is defined in terms of sound pressure at the entrance to the ear canal, measurement by probe techniques of the sound pressure developed by an earphone at the entrance to the ear canal seemed to offer a means of determining equivalent standards for audiometer earphones without requiring subjective judgment. Data on individual observers-obtained by both objective and subjective techniques will be compared.
On the Normalization of Formant Data
Authors: Fant C. Gunnar M.
Published: September 2005

The characteristic pattern of a vowel, described by the envelope of its frequency spectrum or by the corresponding loudness pattern on the basilar membrane, is chiefly dependent on the positions of the formant frequencies in the particular scale that is being used. Any vowel may be sufficiently defined by a set of figures related to the formant frequencies. The first three formants for female voices are, on the average, 9 percent higher in the mel scale than the corresponding formants for male voices. Different individuals produce formant patterns of the same relative form on the mel scale. There are several vowels for which significant deviations from the rule of constant mel ratios occur in the comparison of different voices. In these cases, however, the typical feature of the spectrum will be preserved in the relative position of one important formant, or of the mean value of two close formants, which carry the major part of the vowel quality. The mel scale representation is also profitable in the study of the relation between different vowels of a language. Differences of phonemic quality in Swedish vowels are associated with quantal changes of 90 mels in one or more formants.