bluuebunny/crossref_metadata_2025 huggingface dataset:
Sound Waves Observed in a Mud-Filled Well after Surface Dynamite Charges
Authors: Ording J. R. , Redding V. L.
Published: September 2005

An array of three pressure pick-ups 100 ft apart covering a vertical range of 200 ft was used to record sound waves in two wells drilled to depths exceeding 12 000 ft. Dynamite charges were exploded in an 80-ft hole at a distance of 500 ft from the well-head. A separate charge was fired with the array at each 500-ft interval in the well. The recorded events were analyzed and found to belong to two categories. The first category includes the pressure pulse arriving at the pick-up by a more or less direct route through the sedimentary rocks. The second consists of events set up in the mud column at points other than adjacent to the pick-up by the compressional wave in the sedimentary rocks. These events then travel through the mud column and are recorded as they pass the pick-up. Anomalies in the hole, such as the ends of casing strings and the bottom of the hole, cause events of larger amplitude than those set up in sections of the hole with no major anomalies.
Piezoelectric Well Hydrophones
Authors: Vogel C. B.
Published: September 2005

Information about the seismic velocity as a function of depth is normally obtained by exploding dynamite at the earth's surface and measuring travel time to a detector suspended by cable within a deep well. In such measurements errors are often introduced by vibrations transmitted along the cable or casing. Three types of piezoelectric hydrophones for use in deep wells and shallow holes have been constructed and have been found useful in discriminating against cable noise. Such hydrophones are also well suited for tandem use in measuring differential velocities, and their substantially aperiodic response facilitates resolution of late arrivals, such as shear waves, which may cause pressure variations within a bore hole. The hydrophones are described, and the results of field experiments are discussed.
The Effect of a Magnetic Field on the Phase Velocity of Sound in Electrically Conducting Bars
Authors: Robey Donald H.
Published: September 2005

Plane longitudinal sound waves traveling in an electrically conducting bar will generate complex electric currents provided there is a magnetic induction perpendicular to particle displacement. The currents react with the induction to produce a complex force which opposes the particle motion. The impedance associated with this force consists of a resistance and a stiffness reactance. The induced resistance causes a slight attenuation of the waves, while the induced stiffness increases Young's modulus and therefore increases the phase velocity. Of all the elements, it is shown that this effect is a maximum in lithium and that it is too small in ferromagnetic materials to explain the observed changes in Young's modulus with changes in induction.
A Variable Audiofrequency Inductor
Authors: Allison R. E.
Published: September 2005

A variable audiofrequency inductor is described. The inductance is controlled by the movement of a magnet to and from the cores. The inductor can be equipped with a calibrated dial. Using two cores through the coil with the flux from the magnet flowing in opposite directions through the two cores results in no increase in harmonics over the amount generated by the same cores with air gaps. This method of inductance control eliminates “electrical backlash.” In other words, the inductance returns to the same value for a given dial setting. Q's over 100 at 1000 cps and 30 at 100 cps are possible. Inductance changes of more than 30 to 1 are obtainable. Two limitations have shown up in the experimental work. First, the permeability increases, 0.66 percent per degree C on the ferrite material that is being used; second, the ferrite material saturates at 3400 gauss, limiting the power handling ability of the coil.
An Investigation of the Ultrasonic Spectrum of Cavitation Noise
Authors: Mellen Robert H.
Published: September 2005

The noise spectrum associated with tip vortex cavities produced by a stirring rod was measured in the frequency range from 10 to 3500 kc. The power spectrum density appears to vary as f−2 from 10 to 200 kc and then is flat up to 3500 kc. From incompressible fluid theory the spectrum would be expected to vary as f−2/5 above approximately 50 kc. It is proposed that the acoustic pressure waves of the form of extremely short impulses (less than 0.3 microsecond in duration) would account for the flat portion of the spectrum. Such impulses may arise if the bubble collapses on a rigid nucleus.
The Effects of Music Hall Acoustics Upon Grand Piano Tone
Authors: Martin Daniel W.
Published: September 2005

Single keys of a concert-grand piano were actuated by an automatic mechanical blow-striker. Magnetic tape recordings were made of the piano tones in Music Hall (Cincinnati), with the recording microphone located at selected positions on the concert stage and in the auditorium. A similar recording was made in an anechoic space used for acoustical measurements on pianos. High speed level recordings of the magnetic tape output reveal significant differences in scale balance at the various positions. Spectrum analyses of selected tones were also recorded vs time for the different microphone locations. The recordings show that room reverberation greatly affects the tone-wave envelope and that piano directional characteristics influence the spectrum of the tone to a limited extent.
Noise Control Measures for Test Installations
Authors: Hardy H. C.
Published: September 2005

An effort will be made in this paper to survey the various noise control measures which have been used to quiet test installations for aircraft engines and warm-up tests on complete airplanes on the ground. The economic factors in such designs will be emphasized. Under the pressure of getting quick results, somewhat more expensive and sometimes inadequate structures have been built than would otherwise have been constructed. One of the most important problems is the evaluation of the acceptance level of the noise in the neighborhood of the installation. The next important problem is obtaining reliable data on the performance of the silencing structures which have already been built. The use of scale model measurements has been very valuable in obtaining design data on proposed structures. Some of the various geometries which have been used will be discussed, and the data on their performance will be given in the cases in which they are available.
Aircraft Engine Noise Control as Viewed by the Engine Manufacturer
Authors: Hazard Donald M.
Published: September 2005

The aircraft engine manufacturer has been continually confronted with the factor of noise control in conjunction with the development and production testing of engines. The scope of this control activity has increased many fold during recent years as the result of the rapid growth in types and size of military powerplants. Presented in this paper is a review of the over-all effort including typical noise sources, control objectives, recent techniques used in the control and attenuation of aircraft powerplant noise, problems associated with the design of noise control provisions, and limitations in the existing methods. This review includes data on reciprocating, turbojet, turboprop, and ram jet powerplants, along with a description of installations used for controlling the noise both in ducted exhaust systems and in propeller-type test cells. The discussion cites cost, space, and high tolerance in design factors as being the major problems. Areas of continued endeavor are outlined for the engine manufacturer, acoustical consultant, and the noise control equipment manufacturer.
A Comparison Between Model Study Tests and Field Measurements on an Aircraft Test Cell Silencer
Authors: Calloway D. B. , Lemmerman R. D.
Published: September 2005

An acoustic model study was made of the silencer for a propeller engine test cell in which the acoustical treatment consisted of conventional splitters for high frequency silencing and thick splitters designed to give low frequency reduction. After construction of the test cell, field measurements were made of the noise reduction provided by the silencing treatment, using as a sound source both a propeller engine and loudspeakers driven by a thermal noise source. In this paper, the techniques developed for simulation in the scale model of the acoustic properties of the full scale silencer will be discussed. The model study results will be presented and compared to theoretical predictions and to the field measurements on the full scale structure.
Noise of Ventilating Fans
Authors: Peistrup C. E. , Wesler J. E.
Published: September 2005

Using the apparatus described by Reynolds, Wilson, and Beranek, measurements were made of the acoustic power in watts in twenty-four bands each one-third octave wide for three vaneaxial-type and two centrifugal-type fans of grades sizes. Formulas were derived empirically, enabling the computation of the over-all acoustic power of the noise for the exhaust end of a fan where the input electrical power, the number of blades, blade tip speed, and other design characteristics are known. The formulas are very similar to those developed for aircraft propellers by Rudmose and Beranek. The directivity pattern and acoustic power generated for each of the 24 bands was also measured at the inlet with the fan mounted in one end of a long duct outdoors. The effects of back pressure were also determined. As a second stage of this investigation, the acoustical characteristics of unlined ducts were studied. The attenuation effects of one and two 90° unlined bends placed in the 10-inch × 12-inch duct system were determined. The greatest amount of attenuation was found in those frequency bands that contained the frequencies for which the width of the duct, in the direction of the bend, was 0.5 wavelength and 1.5 wavelength.
Measurement of Vibration Amplitude at High Frequencies
Authors: Koidan Walter
Published: September 2005

The pistonphone, previously devised as a method for calibrating condenser microphones up to 200 cps, is applied to the measurement of vibration amplitudes over an extended frequency range. Vibrations of a piston, projecting into a 19.5-cc cavity, are generated by a barium titanate driver. The pressure developed in the cavity is measured by a condenser microphone previously calibrated by a reciprocity technique. The amplitude of motion of the piston is then computed from the observed sound pressure. With the microphone removed from the cavity, a capacity type vibration pick-up probe is brought in proximity to the piston surface and is calibrated against the known motion of the piston. Mechanical coupling between the driver and the main supporting structure is minimized by the use of vibration mounts and the maintenance of a small, acoustically sealed clearance between the piston and the cavity walls. Using hydrogen in the cavity to limit wave motion, calibrations from 100 to 10 000 cps have been obtained with an estimated accuracy of 5 percent. The lower detection limit of a capacity probe designed for high sensitivity is 10−10 cm peak amplitude.
Calibration of Laboratory Standard Accelerometers
Authors: Jones Earle , Rice Charles F. , Edelman Seymour
Published: September 2005

A program for design and calibration of a large number of piezoelectric accelerometers has been started. This paper describes the types of accelerometers used and the facilities used in their calibration. Sets of laboratory standard accelerometers have been constructed consisting of a number of pick-ups, each suitable for a particular range. These standards are calibrated by three methods: reciprocity, the optical method described in the next paper, and the pistonphone calibrating device described by Koidan. Calibration of accelerometers used in the field is performed on the comparison vibrator described in the paper by Rice, Jones, and Edelman by comparing the calibrated laboratory standards with unknown accelerometers. The facilities described include a large isolated concrete test block, a special vibration exciter with some novel features, and the circuit used for measurement of open circuit voltage.
Double-Ended Vibrators for Comparison Calibration of Accelerometers
Authors: Rice Charles F. , Jones Earle , Edelman Seymour
Published: September 2005

Routine calibration of an accelerometer is performed by comparing the open circuit voltage output of the unknown with the output of a laboratory standard which has been calibrated as described in the previous two papers. This comparison is performed with both accelerometers excited simultaneously in a special double-ended vibration exciter. The construction of the special vibration exciter and the precautions taken to ensure that both accelerometers are exposed to the same vibration are described. The double-ended vibration exciter is also used in part of the reciprocity calibration of laboratory standard accelerometer.
Acoustic Trauma in the Guinea Pig
Authors: Davis H. , Fernández C. , Covell W. P. , Legouix J.-P. , McAuliffe D. R.
Published: September 2005

The cochlear microphonics and the auditory action potentials of guinea pigs, under anaesthesia, were recorded with differential electrodes. The ears were exposed to pure tones of frequencies 185, 545, 2000, or 8500 cps at intensities sufficient to cause severe acoustic trauma within one to six minutes. The cochleas were immediately fixed and subsequently studied microscopically. Good correlations were obtained between the immediate depression of electrical activity and the severity of anatomical injury. Electrical depression at any given position of electrodes in the cochlea was substantially constant regardless of the frequency of the test tone. Action potentials disappeared before the cochlear microphonic. Exposures above 145 db, measured at the animal's eardrum with a probe-tube microphone, for more than half a minute regularly caused severe anatomical injury to the organ of Corti, often including gross rupture. Rupture begins at certain well-defined points in the organ of Corti. The external hair cells are the most susceptible structures, but in the middle turns of the cochlea rupture may follow closely. The injury was greatest in the apical turns from 185 and 545 cps and in the basal turn for 8500 cps.
Studies of Industrial Hearing Loss: Methodology
Authors: Wheeler D. E.
Published: September 2005

This paper deals with the following subjects relevant to the problem of industrial hearing loss: terminology, methods of research in the industrial plant, methods of research in the laboratory. Definitions of terms which constitute the basic data in field and laboratory research are considered. The increased attention being shown by many parties with differing backgrounds and interests has posed a need for uniform terminology, as closely as possible descriptive of the actual data being collected. The problems of conducting research in the industrial plant are briefly considered. Data are presented, illustrating methods of the survey type and methods representing some measure of experimental control. The implications of these methods are discussed. Some phases of the industrial hearing loss problem can be investigated in the laboratory. Illustrative methods and data are presented on the subject of ear protection. The general problem of obtaining adequate attenuation by occlusion of the ear canal is considered and some recommendations are made.
The Use of a Pulse-Type Test for Assessing Temporary Hearing Loss Occasioned by Noise
Authors: Black John W. , Tolhurst G. C. , Atkinson C. J. , Bragg V. C. , Morrill S. N.
Published: September 2005

From two to four bursts of white noise and 500-cps tone were recorded in decremental steps of two db. The recording is being employed to evaluate the amount of temporary hearing loss that accompanies different amounts of exposure to noise of various levels and spectra. The development of the testing procedure and its limitations will be discussed. Administration time of the test is 64 sec. An indoctrination experience of at least five forms of the test is required before reliable mean results can be secured from a panel of 12 listeners.
The Attenuation of Sound in Small Tubes
Authors: Kemp G. T. , Nolle A. W.
Published: September 2005

An experimental investigation of the attenuation of audiofrequency sound in two air-filled tubes of 0.238 and 0.0292 cm inside radius was conducted, and the results compared with values of attenuation calculated from the Kirchhoff theory for rigid walled tubes. This theory had not previously been verified for tubes this small. Agreement of experimental with theoretical values was found within the accuracy of the experiment. The attenuation was determined by a method which was different, in some respects, from those previously employed. The variable length, closed tube was driven with a high impedance source, and the input pressure sampled with a high impedance microphone probe. The input pressure was recorded as a function of closed tube length. Since the input pressure can be assumed to be proportional to input impedance for these conditions, the attenuation can readily be determined from the ratio of the pressure maxima or minima.
On the Diffraction of a Plane Sound Wave by a Paraboloid of Revolution. II
Authors: Horton C. W.
Published: September 2005

Some of the numerical calculations promised in an earlier paper of this same title have been carried out. Numerical values for the real and imaginary parts of nine of the low order wave functions are available to 8D for 2kξ = 0(0.1)2.0, where k = 2π/λ and ξ is the paraboloidal coordinate. Pictorial representations of two of the wave functions are shown. With the aid of the values mentioned above, a numerical study has been made of the scattering of a plane sound wave by a convex rigid paraboloid of revolution. The direction of propagation of the plane wave makes an angle of 36.9° with the axis of revolution, and the paraboloid is 2kξo = 0.5. Numerical results for the amplitudes of the low order scattered waves and for the total pressure on the surface of the paraboloid are presented.
Sources of Vorticity in Acoustic Fields
Authors: Medwin Herman , Rudnick Isadore
Published: September 2005

When a sound beam passes through a viscous fluid, vorticity is generated as a second-order effect and streaming results. The work of Eckart, which considers the vorticity generated in the medium, is extended to consider “surface sources” of vorticity which appear when the sound beam makes contact with a solid, restraining surface. Further, the way in which the results depend on the following assumptions: (1) the viscosity coefficient μ or (2) the kinematic coefficient of viscosity ν = μ/ρ, being constant for changes in density, is shown for fluids. With these generalizations, previous work on streaming by other authors is discussed and reconciled.

The streaming in two particular boundary cases is considered: (1) a plane progressive wave which contacts an enclosing cylindrical tube, and (2) a small, rigid, fixed sphere in a standing wave in air. In both cases it is shown that the predominant sources are the “surface sources.” This work was supported in part by Contract N6onr-27507.
Backward Scattering of Sound in a Fluid from the Boundary of a Granular Medium
Authors: Nolle A. W.
Published: September 2005

Backward scattering of plane-wave sound from a granular medium bounding a fluid is treated by an analysis analogous to that used for x-ray scattering by liquids. It is assumed that scattering centers are located very near to the interface. The important basic consideration is the average distribution of neighbors about a given grain or particle. Few forms of the distribution function lead to a simple analytical result. A function giving a simple result is φ(r)=A exp(−B2r2), where φ(r) is number of neighbor particles per unit area which contribute to coherent scattering. This function leads to the following expression for relative backward scattering intensity as a function of grazing angle θ: R=1 plus; (πAD/B2) exp(−G2/4B2), where D is total number of particles per unit area and G = (4π/λ) cosθ. Preliminary comparison with ultrasonic measurements of scattering from fine sand of uniform particle size shows the following: (1) The absolute intensity of backward scattering at small grazing angles is equal to the energy sum of scattering by all interfacial particles. (2) The variation of scattering intensity with angle follows approximately the expression above. These results are subject to modification by additional experimentation.
The Radiation Impedance of a Rigid Annulus in a Plane Infinite Rigid Baffle
Authors: Hudimac A. A.
Published: September 2005

The radiation impedance of a rigid annulus vibrating in an infinite rigid plane baffle has been developed: (a) in terms of cylindrical wave functions using the method of L. V. King, and (b) using the Green's function to evaluate the pressure field as was done by N. W. McLachlan. The expression for the radiation impedance is resolved into the resistive and reactive components; these are given in terms of Bessel, Struve, and hypergeometric functions. Curves giving the radiation impedance as a function of ka (where k is the wave number and a is the outside radius of the annulus) for certain ratios of the radii of the annulus are given.
A Method of Rectifying Inter-Subject Differences in Loudness Scales
Authors: Garner W. R.
Published: September 2005

Recently published data have shown that there are large differences between subjects in half-loudness judgments. One conclusion from these data has been that the concept of a subjective scale of loudness is not valid because of the inability to get uniform loudness scales. Another possible conclusion, however, is that the discrepancies between subjects is due less to real differences in the loudness scales than to the subjects' inability to verbalize correctly the loudness fraction. A technique will be described in which loudness scales can be constructed without the assumption that subjects know what constitutes one-half loudness. The technique involves acquiring two kinds of data, one of which supplies equal ratio data but with the ratio unknown, and the other of which supplies equal interval data with the zero point unknown. Two equations resulting from these data can be solved graphically to supply the unknown constants. Illustrative data will show that two loudness scales may be quite similar, even though the half-loudness judgments were quite different. Preliminary data suggest that, with correction, a greater intensity difference is required for half-loudness than subjects state verbally and than previous data in the literature suggest.
Artificial Sound Conduction in the Ear
Authors: Kobrak H. G.
Published: September 2005

There is empirical clinical knowledge available that some foreign substances (e.g., cotton pellets, rubber cigarette paper, etc.) when placed in the middle ear improve hearing in properly selected cases. The biophysical problem of the mechanism of this hearing improvement has remained unsolved. A study of this problem promises to shed light on the normal physiology of sound conduction in the ear. Experiments were carried out on animals and on fresh human cadaver specimens. The acoustic vibrations of the normal ear were recorded cinematographically and experimental lesions were produced in the sound conduction system (perforation of eardrum, extirpation of hammer and/or anvil). Acoustic prostheses were then inserted and the change in the pattern of the acoustic vibrations was noted. Observations were made on patients with similar lesions. The otoscopic findings were photographed and audiograms before and after insertion of acoustic prostheses taken. The following physical possibilities were studied: (1) reestablishment of the hydraulic ratio between eardrum and stapes footplate; (2) the mass effect of the foreign material; (3) change of phase relation between oval and round window; (4) acoustically effective sealing of one inner ear window; (5) change of resonance frequency of the sound conduction system. A motion picture demonstrating the experimental results will be shown.
Instrumentation for Studies of Sound in the Atmosphere
Authors: Pickens George O.
Published: September 2005

Explosive charges are fired on the earth's surface at points in Arizona, California, and San Clemente Island. The resulting sound waves centering at 2 cps are detected by an array of sensing units in Southwestern Arizona. This array extends 108 miles along an east-west segment of a great circle with units placed at 4-mile intervals. From these units transmission lines are routed along the ground to recording stations near Dateland and Gila Bend. A single twin-conductor field line serves from one to three units and may be as long as 40 miles. Over such a line the sensing units are turned on by relays, and the signals are transmitted to the recording station. The use of carriers has permitted the separation of multiplexed signals by means of tuning controls. Push-pull condenser-coupled amplifiers drive the Brush recording pens. Sensitivity is controlled in 6-db steps through a range from 5 to 160 dynes per sq cm peak-to-peak for full scale deflection. A pass band from 0.2 to 5 cps is set by an acoustic filter in the sensing unit. Several years of use and development have resulted in a system which has proved to be quite satisfactory.
Notes on Transmission of Sound Through Plates
Authors: Fay R. D.
Published: September 2005

The transmission of plane waves through solid plates in a liquid medium has been expressed in such a manner that the conditions for total transmission or total reflection are readily formulated. Some effects of departure from ideal conditions are indicated.
A Dimensional Analysis of Turbo Jet Noise Data
Authors: Dyer Ira
Published: September 2005

Measurements of the total power radiated by turbo jet engines have been analyzed by dimensional techniques. Under the assumption that the noise is created by an aerodynamical mechanism, the acoustic power may be set proportional to the mechanical power in the jet stream. Then the factor of proportionality must be a dimensionless function of the average properties of the jet stream. The dimensionless proportionality function may be shown to be a function of four dimensionless ratios, but physical arguments indicate that at least two of the four ratios may be relatively unimportant. The dimensionless proportionality function may be determined by plotting the acoustic power as a function of the mechanical power. Sixty-eight separate measurements on various types of turbo jet engines under both free-field and reverberant conditions have been examined. In each case the total acoustic power was determined by suitably integrating over space and frequency. The results show that the proportionality function may be written as, 3 × 10−4 [1 + (K/K0)3]; where K is essentially the ratio of the mechanical power in the jet stream to the thermal power conducted through the jet stream, and where K0 is a critical value of K chosen to fit the data. At large values of K/K0, the acoustic power is proportional to the eighth power of the jet velocity for all other variables constant, in agreement with Lighthill's work. At small values of K/K0, however, the acoustic power varies as the square of the velocity.
Distortion in Phonograph Reproduction
Authors: Roys H. E.
Published: September 2005

Three distortion methods, the harmonic, the SMPE intermodulation, and the CCIF, a difference frequency, have been studied, mainly on a theoretical basis as a means of analyzing distortion encountered in phonograph reproduction. The harmonic method is somewhat difficult to apply and some of the harmonics may be beyond the range of the system. The IM has been used in the past with considerable success and appears to be a good method of analyzing tracing distortion. The difference frequency methods appears to be somewhat insensitive to tracing distortion but offers theoretical advantages in that the analysis may be made right up to the cut-off frequency of the system; practically it is somewhat difficult to apply.
The Absorption of Sound in Air
Authors: Nyborg W. L. , Lee J. F. S. Y.
Published: September 2005

A detailed review will be presented, summarizing available data on absorption of sound in homogeneous air and its main constituents as a function of frequency, pressure, temperature, and humidity. Disagreement exists between results of the various investigators, especially when different techniques are used. It is customary to compare experimentally observed absorption coefficients αexp with theoretical values αtheor, where the latter include the effects of viscosity, heat conduction, heat radiation, diffusion, and vibrational thermal relaxation. Observed values of r = αexp/αtheor vary from slightly less than unity up to about 4 for measurements in the laboratory and up to somewhat higher values for measurements out-of-doors. Even in carefully dried air, nitrogen, and oxygen, reported values of r vary over a wide range, depending on the measurement technique employed. It is interesting that in recent measurements, using direct source-to-receiver systems where the sound field is approximately a spherical wave, r values of about 1.2 are obtained. This approaches the result expected from classical kinetic theory for rotational relaxation.
Wave Theory of Sound Transmission in a Randomly Inhomogeneous Medium
Authors: Mintzer David
Published: September 2005

Since the ray theory does not give the correct range dependence for the fluctuation of the intensity of radiation propagated in a medium in which the index of refraction varies randomly, a wave theory solution of the problem has been formulated. By means of the Born approximation to the wave equation, the coefficient of variation (ratio of standard deviation of pressure amplitude to mean pressure amplitude) has been evaluated. Using Liebermann's data, the results are compared with Sheehy's experiments, and excellent agreement is found. A discussion of the ray theory will also be given.
Discriminatory Analysis and its Application to the Identification of Vowels
Authors: Stubbs H. L. , Briana A. M.
Published: September 2005

In the problem of identifying speech sounds by means of measurable acoustical parameters, it appears that no single parameter can give a reliable identification. Hence, the statistical techniques of discriminatory analysis are appropriate to determine the optimum combination of several parameters. These techniques have been applied to the identification of vowels, where the parameters used are those fractions of the total power which are contained in certain selected frequency channels. For these parameters, a statistical distribution related to the multinomial has been assumed. This leads to a simple linear classification function whose coefficients are the logarithms of the mean values of the respective parameters. Preliminary results have been obtained which show considerable success in identifying vowels.
Discriminability of Interaural Time Difference
Authors: Klumpp Roy G.
Published: September 2005

Using earphone presentation and electrical lag lines which allow precise control of time delays, measurements were made of interaural time difference thresholds for pure tones and noise bands. The time difference threshold is here defined as the minimal change in interaural time difference which elicits a perceptible shift in the location of the sound image. Results present the discrimination threshold for interaural time delay as a function of the psychophysical method of measurement, band width and center frequency of the signal. Under optimum conditions, the mean interaural time difference threshold for the five best listeners is about six microseconds. Under similar conditions, the mean threshold for 23 listeners is about 12 microseconds.
A Simple Calibration Technique for Low Sensitivity Transducers
Authors: Galloway William J.
Published: September 2005

Increased interest in studies of high amplitude acoustic waves has made practical the use of small probe mounted transducers having extremely low sensitivities (i.e., −130 to −150 db re 1 volt/dyne/cm2). These low sensitivities make calibration by standard techniques, such as reciprocity methods, difficult to perform. In the course of some cavitation studies the radially symmetric standing wave pattern obtainable in a spherical resonator is utilized to obtain a high pressure variation. It was observed that in gassy water, under one atmosphere hydrostatic pressure, that a distinct distortion of the output wave form of the probe transducer, used to measure the sound pressure variation in the standing wave pattern, was observed at the instant the peak sound pressure exceeded one atmosphere. At the suggestion of Dr. R. W. Leonard, a careful investigation of the exact pressure at the time at which distortion occurs was made, with the possibility in mind of using this property of the medium as a means for pressure calibration of transducers. This paper shows that the accuracy and reproducibility of this phenomenon is limited only by the limits of ability to read the output voltmeter. A simple apparatus and technique for performing the measurements is described.
A Method of Sound Velocity Measurements in Solids and Liquids Using a Pulse Technique
Authors: Cedrone N. P. , Curran D. R. , Henkel J. H.
Published: September 2005

In this method a modulated pulse from a pulse generator is sent through a sample, amplified, rectified, and sent back into the pulse generator, thus triggering the next pulse. The velocity is determined from the measured pulse repetition rate, taking into account the electronic delay time. The equipment, described in a previous paper, has been improved and checked experimentally. Measurements have been made on distilled water over the temperature range 29°C to 50°C and compared with results from the other sources. An analysis of the major sources of error has been made for the equipment as it exists at present together with a discussion of the limit of accuracy obtainable by this method.
High Frequency Auditory Response of a Bottlenosed Porpoise, Tursiops Truncatus (Montagu)
Authors: Schevill W. E. , Lawrence B.
Published: September 2005

The high frequency auditory response of a bottlenosed porpoise, Tursiops truncatus (Montagu), was measured in a simple conditioned response test. The porpoise is a mammal that necessarily hears by bone conduction. Therefore, its frequency range of auditory response may be expected greatly to exceed the frequency range over which it can discriminate pitch, on the basis of what is known of hearing in man, whose auditory response by bone conduction has been reported as passing 100 kc [e.g., Pumphrey, Nature, 166, 571 (1950)]. The porpoise gave a persistent indication of an upper limit for even this presumably colorless type of response. It was exposed to tones between 0.15 and 153 kc at sound levels ranging between −20 and +28 db from 1 dyne/cm2, mostly 0 to +10 db. Above 120 kc there was a marked falling off in positive responses, and at 126 kc the porpoise responded to only 50 percent of the signals; above this the falling off continued, but never as low as 10 percent. The extreme upper frequency limit of sound production (phonation) in these animals was not found; there was still appreciable energy at 196 kc.
A Miniature Piezoelectric Microphone
Authors: Medill J.
Published: September 2005

A new Rochelle salt microphone has been developed for use as a secondary standard in production testing, sound level measurements, high quality transmission of sound, and similar applications. The diameter of the new microphone (118 inch) is half the diameter of similar units in current use. Frequency response, directional characteristics, and moisture protection have been improved without a significant loss in sensitivity.
Design of Direct-Radiator Loudspeaker Systems
Authors: Beranek Leo L.
Published: September 2005

This paper is divided into two parts, one on closed box baffles and the other on bass reflex baffles. A complete theoretical treatment will be presented including design charts for determining the power response as a function of loudspeaker constants, enclosure constants, and amplifier output impedance. Complete examples have been worked out for the two types of enclosures and are compared with curves measured in free-field and in a room.
Cadillac Mobile Television Unit—Inauguration, 1953
Authors: Weiland L.
Published: September 2005

The latest innovation in television mobile units is described. A standard seven-passenger Cadillac sedan carrying two cameras, microphones, microwave transmitter, and a power source is capable of transmitting television pictures and commentary while in motion. The operating techniques, the construction problems, and the sound isolation work are discussed with the aid of illustrations.
The Study of the Molecular Structure of Organic Liquids by Means of Ultrasonics
Authors: Karpovich John
Published: September 2005

A modified resonance and reverberation technique has been developed for the measurement of ultrasonic absorption in liquids from about 1 megacycle per second down to below 20 kilocycles per second, the limits being a function of the absorption. A spherical container is calibrated with a carefully chosen set of liquids by using the extrapolated values of absorption coefficients which have been obtained at higher frequencies by the pulse technique. The calibrated container can then be used to measure the absorption in an unknown liquid, the calibration curves being used to give the true value of the liquid's absorption (i.e., less the container wall effect). The significant features of this technique are that only one container is necessary, the nature of the container reduces the possibility of contaminating the liquid to a minimum, and quantities of liquid as small as 5 milliliters can be studied. Over 40 liquids have been measured. Hitherto unknown relaxation phenomena have been observed in 12 liquids. A mechanism which accounts for the relaxation processes is proposed.
Remarks on the Mechanism of the Photographic Effect of Ultrasonic Waves
Authors: Bennett G. S.
Published: September 2005

The production of a latent image on a photographic emulsion by ultrasonic waves was discovered in the mid 1930's by N. Marinesco and co-workers. On the basis of extensive experiments, Marinesco proposed that the explanation lay in the excitation of the halide molecules by collision under the influence of the ultrasonic wave, this view being supported by his observation that the emulsions had to be softened by soaking for the image to appear. In 1947 Pinoir and Pouradier investigated this phenomenon also, and concluded that the latent image was an indirect result, being formed by luminescence associated with cavitation produced by the ultrasonic wave. One of their important arguments is based on their statement that the luminescence should disappear if the ambient pressure is reduced to about 15 cm Hg, and their observation that no latent image is formed under this condition. This paper reports further experiments on the effect, which support the conclusions of Marinesco that the image is formed by action in the emulsion, results depending critically upon the extent to which the emulsion is softened. Pictures have been obtained at pressures as low as 2 cm Hg, in contrast to the results of Pinoir and Pouradier and seemingly ruling out any luminescence effect in this application. Properties of different types of photographic emulsions are discussed.
On the Thermal Relaxation of CO2 Molecules in Presence of H2O or D2O Molecules
Authors: Hubbard J. C. , Sette D.
Published: September 2005

None of the various suggestions till now made to explain the large effect of the presence of water molecules on the thermal relaxation of CO2 has proved entirely satisfactory. It seems useful, therefore, to collect more information on the phenomena involved. The aim of this research is to compare the effects on the relaxation of CO2 of the presence of H2O and D2O molecules measuring a part of the dispersion curve for some mixtures. Commercial CO2 was used for this comparison. The mixtures were prepared in a glass bulb and sent into an interferometer, where sound velocity was measured at a constant frequency while the pressure was decreased. The mole fractions of H2O or D2O in the mixtures studied were about 0.0082 and 0.0117. The results show a large deviation of the dispersion curves from the shape of a theoretical one relaxation time curve. The deviations increase with the water content. If this result is confirmed, it would indicate that the water molecules alter profoundly the mechanism of energy exchange in CO2. It is to be observed, however, that we have supposed that during the measurements on each mixture (a few hours) the water adsorbed on the wall of the system did not vary. If this is not the case, the humidity of the mixture would increase as the pressure decreases and this fact could account at least in part for the deviations observed. It is possible, anyway, to compare the results obtained in the mixtures containing the same mole fractions of H2O and D2O. To do this, we have shifted the dispersion curve for CO2 to pass through the experimental points of the two mixtures for various value of γ/ρ (Mc/atmos). From the curves for 0.0082 mole fractions of H2O and D2O the calculated ratio of the shifts of relaxation frequency produced by H2O and D2O is 1.85; from the curves for 0.0117 mole fraction, it is 2.55. These values show that the difference between the effects of H2O and D2O molecules can be essentially accounted for by the change in the mass effect on the probability of inelastic transitions during collisions with CO2 molecules.
Accurate Measurements of Time Delay in Ultrasonic Transmission Media
Authors: Fein Louis
Published: September 2005

By means of high speed digital counting pulse techniques, the velocity of ultrasound may be measured to 1 part in 104. The temperature coefficient of velocity may be measured to 1 part per million per degree Centigrade. A description of the method and equipment is included.
Analogies and Schematic Networks
Authors: Smith P. W.
Published: September 2005

An analytic network is defined as a topological drawing with variables (mostly unknown) assigned to its branch-points and branches, impedance-like parameters associated with the branches, and a set of rules for finding the relations between the values of the variables and the parameters. Such a network can be called the schematic network of a particular physical structure if the values of the variables and parameters of the network correspond, according to a distinct set of rules, to the values of the physical variables and parameters measured on the structure. These rules must specify some systematic way of comparing these numerical values and also the locations in structure and network with which they are associated. If two physical structures with different types of “vibrations” (i.e., electrical, mechanical, acoustical, etc.) have the same schematic network, they are analogs; they can be called direct analogs. If two structures have schematic networks which are duals, they can be called indirect analogs. The conclusions of LeCorbeiller and Yeung about duality in mechanics will be reinterpreted in this manner and contrasted with comparable conclusions for acoustical structures.
The Interaction of A Sound Wave with A Point-to-Plane Corona Discharge
Authors: Dyer I. , Blum B. W. , Ingard Uno
Published: September 2005

It is well known that the current to a point-to-plane corona discharge is sensitive to changes in the static pressure. An investigation has been undertaken of the interaction of a point-to-plane corona with dynamic pressure changes caused by a sound wave. The discharge is obtained at atmospheric pressure by the application of a potential the order of 3000 to 5000 volts to the gap between a conducting plane and a thin conducting wire held normal to the plane. Preliminary results on the dynamic pressure sensitivity of the device will be presented, and the applicability of such a device as a microphone will be discussed.
The Measurement of the Lateral Mechanical Impedance of Phonograph Pick-ups
Authors: Woodward J. G. , Halter J. B.
Published: September 2005

Instrumentation and techniques for the measurement of the lateral mechanical impedance at the stylus tip of phonograph pick-ups are described and typical results are presented. Results are given as resistance and reactance in mechanical ohms throughout the frequency range from 30 to 10 000 cps. The measured impedance characteristics show the lateral and torsional pick-up-arm resonances and antiresonances and the stylus-arm resonance, as well as various other features attributable to the mechanical system of the pick-up. Response-frequency characteristics are shown for each pick-up, also. In many cases the correlation between irregularities in response and impedance is incomplete. This lack of correspondence can be explained in terms of the analogous circuit of the mechanical system. Measured impedance characteristics for a number of pick-ups, typical of those used in home phonograph systems during the period from 1901 to 1951, show quantitatively the improvement made in pick-ups in this period.
A New Method of Obtaining a Continuous Record of Sound Transmission Loss
Authors: Waterhouse Richard V. , Cook Richard K.
Published: September 2005

An apparatus has been developed which presents a continuous record of the db difference between the sound levels in two rooms separated by the partition under test. The frequency of the input signal may be varied continuously giving a plot of transmission loss against frequency, except for a small correction for the quiet room absorption. Experimental results will be presented. A Honeywell-Brown recorder is used as a self-balancing device. The voltages produced by microphones in both the loud and quiet rooms are applied to the recorder, which drives a logarithmic attenuator which continuously reduces the loud voltage to the same value as the quiet voltage. The voltages are balanced at an attenuator setting which is proportional to the sound transmission loss and which is plotted linearly in db on an 11-in. scale. The db range may be chosen as 0–60 db or less, and the transmission loss plot is accurate to ±12 db.
Sound Transmission through Light-Weight Aggregate Walls
Authors: Ramer L. G.
Published: September 2005

A summarization is given of the sound transmission qualities of a number of light-weight aggregate structures constructed of blocks of various types, sizes, shapes, and aggregates. Sound transmission through such block walls is independent on the type of blocks and their thickness, internal shape, and porosity. Tests with surface sealing treatments indicate the relative contributions of transmission through the pores and through flexural wall vibration. Effective porosity is found to vary with shape and size of the internal cavities.
The Impedance and the Absorption of Acoustical Materials to Sound at Random Incidence
Authors: Hardy Howard C.
Published: September 2005

The boundary value problem of an infinite sheet of homogeneous acoustical material with hard backing has been set up and solved for random incidence sound. This leads to an equation for the random coefficient similar to that of Paris, except it uses, instead of the normal impedance, the impedance of the normal component which varies with angle. The admittance of the normal component is given by Y(θ)ρc = χ tanhγ1′l = iρcγ1′ tanhγ1′lωρ1′, where γ1′ = (α2 − β2 + ω2c2 sin2θ − 2iαβ)12, α and β are the propagation constants, and ρ1′ is a complex density of the medium equal, in the case of viscous damping, to ρ1[1 + i(R/ωρ1)], where R is the damping constant in dyne sec cm−4. Check with experiment, however, indicates that viscous damping is only a partial explanation of the attenuation mechanism. Even with the latter uncertainty, the propagation constants and the characteristic admittance χ can be computed by the method of Ferrero and Sacerdote. The propagation constants calculated from the above check with those given by Esmail-Begui and Naylor. The random coefficient calculated by theory agrees well with that measured in reverberation room and explains quantitatively the large discrepancy between the “statistical” and reverberation coefficient for light density materials.