bluuebunny/crossref_metadata_2025 huggingface dataset:
Evaluation of the Input Impedance of a Reinforced Plastic Plate
Authors: Bannister Ronald L.
Published: September 2005

Measurements made on a square flat plastic plate reinforced with a periodic array of six beams were checked with the theoretical input impedances of an infinite plate, an infinite beam, and an infinite orthotropic plate. Comparison shows that the beam-plate structure reacts like an infinite beam below 500 Hz. But approaches the infinite orthotropic plate prediction at higher frequencies. when excited on a rib. Excellent agreement was found with the theoretical input impedance of an infinite plate when the structure was excited between ribs at its midpoint. Comparison was also made between theoretical and measured impedances after unconstrained viscoelastic damping tile was added to the smooth side of the reinforced plate.
Some Effects of Airplane Operations and the Atmosphere on Sonic-Boom Signatures
Authors: Maglieri Domenic J.
Published: September 2005

This paper is a report on the state of knowledge of sonic-boom phenomena. The pressure buildups in the transonic-speed range and the lateral extent of the pattern in steady flight for quiescent atmospheric conditions are described. Also discussed are recent data from flight-test studies relating to atmospheric dynamic effects on the sonic-boom signatures. The acceleration and lateral-spread phenomena appear to be fairly well understood and predictable for current and future aircraft. Variations in the sonic-boom signature as a result of the effects of the atmosphere can be expected during routine operations. From the data evaluated to date, very similar variations in pressure signatures are noted for both fighter and bomber aircraft.
Laboratory Tests of Physiological-Psychological Reactions to Sonic Booms
Authors: Kryter K. D.
Published: September 2005

Investigations of the physiological psychological responses to impulsive acoustic stimuli and to sonic booms at the intensities anticipated from commercial supersonic aircraft have been conducted in the laboratory. Studies of interest include those concerned with (a) the relative subjective noisiness and loudness of booms having different wavefronts; (b) the reactions of people to booms as an auditory experience (subjective rating of booms versus other acoustical stimuli); (c) startle reactions to acoustic stimuli; and (d) arousal from sleep by acoustic stimuli. The methods and results of pertinent laboratory experiments are discussed.
Ultrasonic Absorption in Air
Authors: Rothenberg H. C. , Pielemeier W. H.
Published: September 2005

The investigation previously reported in a preliminary manner has been completed. Measurements have been made of the absorption coefficient of air for frequencies of 22, 44, 66, 88, and 110 kc, for a pressure range of 735 to 11 mm of mercury, and at humidities ranging from essentially dry air to near saturation. The velocity of propagation has been determined for frequencies of 44, 66, 88, and 110 kc for dry and saturated air at 735-mm pressure, and has also been checked at 47-mm pressure. A pulse method was used for all the measurements. The results on absorption in general show good agreement with values predicted by the classical and by Kneser's molecular theory. It appears, however, that an increase in the classical absorption coefficient of 15–20 percent is called for. This is about equal to the weighted mean of the coefficients as found by Schmidtmueller for N2 and O2. The velocity measurements show excellent agreement, on the average, with the accepted value, but no conclusive evidence of the expected very small dispersion was found.
The Design and Characteristics of a High Sensitivity Direct Current Operated Accelerometer
Authors: Lewis R. C.
Published: September 2005

The design details and operating characteristics of a newly developed accelerometer using the R.C.A. ♯5734 Mechano-Electronic Transducer tube are presented. Data is given on the selectivity and range of frequency response and sensitivity of the device. Applications to both high and low impedance indicating and recording devices are discussed and illustrated.
Accelerometer Calibration Technique
Authors: Tyzzer F. G. , Hardy H. C.
Published: September 2005

A technique has been developed for the dynamic calibration of accelerometers or other vibration measuring instruments. It is believed that the technique is more convenient than the reciprocity method for making rapid calibrations over a fairly large frequency range. For each calibration frequency the accelerometer is attached to a free-free bar driven electromagnetically at a known sinusoidal amplitude. The accelerometer output is compared in magnitude and phase with the amplitude of the bar. This is done by means of strain gauges on the bar which are calibrated periodically by direct optical measurement of bar amplitude. The importance of various design factors is discussed and also the accuracy of the technique with relation to amplitude and frequency. The error in the phase measurements is about 2 degrees and the double amplitude can be measured to about 0.003 mm. The error in measuring a 200-g accelerometer at 1000 c.p.s. is about 3 percent.
General Statistical Theory for the Masking Effect of Reverberation on the Intelligibility
Authors: MacDonald A. , Bolt R. H.
Published: September 2005

A general statistical theory is developed for the masking effect of reverberation on the intelligibility of words. Speech is considered a series of discrete pulses distributed statistically over a 30-decibel range in sound pressure level in a given frequency band. The articulation index is calculated as a function of reverberation time, using preliminary values of speech pulse lengths and spacings obtained from Visible Speech spectrograms. The percent articulation for words is then calculated from the articulation index and is compared with Knudsen's experimental values. The theoretical values agree precisely with the measured values at reverberation times less than two seconds and differ by less than 17 percent out to six seconds. The calculations are extended to include a combination of background noise and reverberation.
The Recovery of Auditory Nerve Action Potentials After Masking
Authors: Hawkins J. E. , Kniazuk M.
Published: September 2005

It is well known that the action potentials of the auditory nerve, as recorded from the round window in the cat or guinea pig in response to a train of click stimuli, are immediately reduced in amplitude in the presence of a wide band of noise of suitable intensity. We have observed that when such a masking noise is suddenly turned off, the action potentials of the click response do not regain their original size at once, but only after a period of 0.1 to 1.0 sec., depending upon the relative intensities of clicks and noise. The microphonic component of the response is similarly affected only at noise levels sufficiently intense to cause reflex contraction of the intra-aural muscles; when this occurs the recovery of the action potentials is even longer delayed. The failure of the nerve response to regain full amplitude immediately after masking appears to bear upon the nature of the masking process itself. If masking were dependent exclusively upon the all-or-none properties of the nerve fiber and the maintenance of the refractory state by the noise, recovery might be expected to be complete within a few msec. after the noise ceases. We are inclined to attribute the fact that recovery is not instantaneous rather to a temporary depletion of the mechanism responsible for the initiation of excitation in the auditory nerve. The phenomenon appears to be more closely related to auditory fatigue than to intra-cochlear inhibition, although the latter explanation has not been excluded.
A Small High Frequency Barium Titanate Microphone
Authors: Allen Clayton H.
Published: September 2005

A microphone has been constructed using a barium titanate element consisting of a hollow cylinder 116 in. in diameter, 116 in. long. The small size of the sensitive element allows its use in complex field patterns with a minimum of distortion to the field. Diffraction effects upon its response are almost negligible to 100 kc where the cylinder becomes approximately 12 wave-length in diameter. The response of this microphone in a direction normal to its axis has a general level of − 143 db re: 1 volt per dyne/cm2 and is flat to within ± 1 db from 12 to 100 kc. With an appropriate filter and sufficient amplification it has been used to measure acoustic signals having intensity levels of 90 db (re: 10−16 watt/cm2) and greater; signals as much as 10 db lower have been detected with somewhat reduced accuracy because of interference from electrical noise. The microphone might be used under water with a resulting increase in frequency range and effective sensitivity due to the greater ρc of water but this has not yet been proved by experiment.
Some Recent Engineering Developments in Group Hearing Aids
Authors: Harrison Charles E.
Published: September 2005

The engineering requirements for group hearing aids to be used with profoundly deaf children are primarily (1) a high level of maximum undistorted acoustic output (roughly 130 db), (2) suitable frequency response, (3) ease of operation by the teacher, (4) suitable acoustic treatment of the school room. The evolution of a series of instruments which attempt to satisfy these requirements will be described. The first instruments met the requirements very satisfactorily but in a subsequent series it was decided to include compression amplification. When this had been achieved it was decided to combine compression amplification with automatic volume control in an attempt to “package” speech in the relatively small auditory area available to the profoundly deaf child. This development raised the important question as to the optimum dynamics of the speech itself within the small area of audibility. The design of the series of instruments will be discussed and problems for the immediate future will be stated.
Experimental Results of the Cavity Reciprocity Calibration of Dissimilar Pressure Michophones
Authors: Benson R. W. , Morrical K. C.
Published: September 2005

The cavity reciprocity method of calibrating pressure microphones involves the use of similar WE-640AA condenser microphones in a coupler of approximately 18 cc volume. Extension of the method to allow the calibration of small diaphragm type crystal microphones was made with special emphasis on the use of dissimilar microphones in the calibrating coupler. In general, couplers of considerably smaller volume were required because of the lower sensitivity of the crystal microphone. It was found that the WE-640AA microphone could be calibrated in the coupler of 1.5 cc volume required for calibration of the crystal microphones, up to a frequency of 13 kc without the use of hydrogen in the cavity, although the errors introduced might be too great for precision work. Difficulties were encountered in calibrating the crystal microphones due to effects produced by mechanical coupling between the microphone and the coupler.
Reciprocity Calibrations in Closed Couplers
Authors: Simmons Bernard D.
Published: September 2005

The responses which are customarily defined for a transducer operating in a closed coupler do not lead to a reciprocity parameter which is independent of the acoustic impedance of the transducer unless the impedance is high compared to the impedance of the cavity. If the response of a reversible transducer used as a sound source is defined as S = pb/I, where pb is the pressure produced in the cavity for a current I into the transducer, and if the response as a microphone is defined as M = e/pg, where e is the open circuit voltage and pg is the pressure produced by a source of constant volume velocity applied to the cavity prior to the introduction of the microphone; then a reciprocity parameter may be obtained which is independent of the acoustic impedance of the transducer and the response of a microphone having a low acoustic impedance can be determined by a reciprocity calibration.
Acoustic Generation of Circulation Currents and Jet Effects
Authors: Ingard U. , Labate S.
Published: September 2005

In his theory of streaming caused by sound waves, Eckart shows that time independent streams necessarily follow as part of the solution of the complete wave equation, taking into account viscosity and second-order terms. His treatment is mainly valid for liquids and it proves that the driving force of the streams is proportional to frequency squared. The effect, therefore, is especially important in the ultrasonic region (crystal winds). However, he suggests that slow streams might also be carried in air at audiofrequencies. Studies of acoustical streaming phenomena around orifices have been made by the use of smoke particles in a three-inch diameter circular tube. Within the tube is placed transversely a thin metal plate with a diameter the same as that of the tube interior. In the center of the plate there is an orifice which may be observed through a window in the tube. These studies covered a range of orifices from thicknesses of 0.5 mm to 19 mm and diameters of 3.5 mm to 20 mm. The frequency lay between 150 to 1000 c.p.s. Velocities in the orifice cover the range of 0 to 700 cm/sec. Close studies of the flow patterns have disclosed that there exist three definite regions of flow as the particle velocity in the orifice is increased: (1) a low velocity region with laminar flow which reverses its direction above a certain level; (2) a medium velocity region in which pulsations are superposed upon the d.c. circulation; (3) a high velocity region in which the flow is only pulsatory, forming jets and vortex rings. These regions can be conveniently represented by “phase diagrams.” Photographs of the various flow patterns in each region of the “phase diagram” have been taken for a number of orifices. Under each observed condition, the acoustic impedance of the orifice is determined by a conventional standing-wave measurement in the tube. Interaction between the streams and the sound field can be seen and are always associated with additional sound absorption even at low levels. Momentum measurements were also made by means of a small disk placed in front of the orifice. These momentum measurements corroborate the photographic studies and show, in addition, that at the high velocities the forces exerted by the jet on the disk are as high as 900 dynes.
The Threshold and Loudness of Repeated Bursts of Noise
Authors: Pollack Irwin
Published: September 2005

The loudness and threshold of an interrupted white noise (of constant sound-time fraction) was studied over a wide range of interruption frequencies. White noise—alone among auditory signals—has the special property that, when interrupted, no additional audible complicating spectral products are introduced. Both at absolute threshold and at equal-loudness above threshold, less energy is required for an interrupted white noise than for a non-interrupted continuous white noise. In many cases, an interrupted noise (sound-time fraction constant at 0.45) sounds louder than a continuous noise of the same amplitude (but of greater energy). The intensity required at threshold and at equal loudness is minimum for interruption rates in the region of 4–10 per second. The extent of this minimum region increases systematically as the reference loudness level is increased. A conceptual formulation which attempts to account for the results will be presented.
Symmetry in the Equations for Electromechanical Coupling
Authors: Hunt F. V.
Published: September 2005

The conventional forms of the electromechanical coupling equations exhibit symmetry for electrostatic coupling and antisymmetry for electromagnetic coupling, or vice versa. Both types of coupling can be represented in symmetrical form, however, if the transduction coefficient for electromagnetic coupling includes a space-operator k that embodies the sign convention associated with axial vectors. The same kind of conventional electric network representations can then be used for either type of coupling. There is a sound physical basis for the appearance of a space-operator k in the transduction coefficients for electromagnetic systems in a manner completely symmetrical with the appearance of the time-phase operator j in electrostatic coupling. Violations of reciprocity in interconnected systems, as discussed by MacMillan and others, can be dealt with analytically in a straightforward way by observing that the operators k and j do not commute, i.e., kj = − jk. Antisymmetrical coupling terms arise in the equations for all-mechanical systems involving gyroscopes, just as in the electromagnetic case, but symmetry can be restored in these cases also by using the same kind of quaternionlike space-operator.
Reciprocity Calibration of Microphones Using a Pulse Technique
Authors: Terry R. L. , Watson R. B.
Published: September 2005

Acoustical calibration of a microphone may be made conveniently either by free-field calibration or by calibration using a small cavity. Free-field calibrations are difficult because of the necessity for establishing a space which allows for propagation of a single progressive wave, without any interference. A progressive wave may be set up in a room which will be free from interference at a given point until sound energy arrives by reflection from the nearest wall surface. By sampling the output from a microphone during this period of time, a signal may be obtained which determines the microphone response to a free progressive wave. Periodic repetition of this process gives a series of pulses from the microphone which may be used to obtain a reciprocity calibration.
An Extremely Small Meter for the Measurement of Absolute Pressures
Authors: von Wittern Wolf W.
Published: September 2005

A pressure meter of extremely small size for the measurement and recording of absolute pressures was developed. It is in the form of a small tube of 2.5-mm diameter and 5-mm length. The tube is closed by a thin iron membrane. The deflection of the membrane causes a change of the reluctance of a magnetic circuit. This reluctance change is transformed into voltages by means of a carrier frequency system. The pressure meter can be built with a maximum sensitivity of about 100 mm Hg pressure per full meter scale deflection. The sensitivity is limited by the attainable deflection of the membrane and the electrical amplification that can be applied which is limited by the “magnetic noise level” and the zero-point stability. Using thicker membranes pressure meters of this type for higher pressure ranges can be built. The natural frequency of the membrane is higher than the carrier frequency (max. ca. 15 kc). The range of a flat frequency response characteristic is therefore not limited by the natural frequency of the membrane but by the carrier frequency and the damping of the membrane is not very important. With a carrier of 10 kc a flat frequency response characteristic from zero to about 1000 c.p.s. can be obtained. Problems concerning the sensitivity of the pressure meter for temperature variations and for accelerations and the problems of electrical and mechanical qualities and manufacture resulting from the small size of the pressure meter are discussed.
Refractory Phases in the Electrical Activity of the Auditory Nervous System
Authors: Rosenzweig Mark R. , Rosenblith Walter A.
Published: September 2005

Electrophysiological responses from the auditory systems of cats show phenomena of refractoriness, that is, reduced responses to the second of a pair of successive stimuli. Thus, when two acoustic clicks are delivered in close succession (intervals from 0.2 to 500 msec.), the response to the second click varies with (a) the time interval between the clicks, and (b) the intensities of the clicks. At the round window, the microphonic components of the click response shows no refractoriness. The neural components exhibit marked recovery cycles; for moderate stimulus intensities, these may last as long as 100 msec. At the auditory cortex, the recovery cycles may be even longer and may exhibit several marked phases of sub- and supernormality. The cortical recovery cycles are affected by the spontaneous electrical activity of the cortex, by the level of anesthesia, and by the temperature of the animal. While some interaction between the two ears may be shown at the level of the auditory nerve, this interaction appears strikingly at the cortex.
Short-Duration Effects in Auditory Fatigue
Authors: Harris J. Donald
Published: September 2005

The investigation of hearing by the use of a fatiguing tone and an immediately subsequent short-duration test tone, first used with good success by de Maré and later adapted for special problems by Lüscher and Zwislocki, Gardner, and Munson and Gardner opens a wide field for study of suprathreshold events in the ear. Among the many variables are the frequency, intensity, and duration of each of the two tones, the frequency relations between the two tones, and the recovery interval, if any, between them. Most of these variables have not been studied independently. The present paper explores fatigue as a function of (1) duration and intensity of the fatiguing tone, and (2) duration of recovery interval. Both variables will be considered with respect to the frequency of the fatiguing tone.
A Test of the Frequency Theory of Hearing
Authors: Davis H. , Silverman S. R. , McAuliffe D. R.
Published: September 2005

“Tone-pips” with a basic frequency of 2000 c.p.s. were produced by passing rectangular pulses of 14-msec. duration through two sound-effects filter sections in cascade. The high pass and the low pass cut-offs (18 db per octave) of each unit were set to 2000 c.p.s. The transducer was an Atlas PM 25 loudspeaker. The tone-pips appear on the oscilloscope as brief trains of waves that begin gradually and reach maximum amplitude at the third wave. The amplitude then falls off only a little less rapidly. A single pip sounds like a metallic click. When the pulses were repeated at 123 per second at sensation levels from 5 to 40 db all of our subjects reported hearing a “buzz.” Other descriptive terms used were “metallic,” “high pitched,” “continuously interrupted,” and “rough.” No listener, even when directly questioned and even when a pure tone of 123 per second had been sounded a few seconds previously for comparison, ever reported any trace of a low pitched component corresponding to 123 per second. Inasmuch as the frequency of nerve impulses in each nerve fiber is 123 per second under these conditions, the absence of a sensation of low pitch is contrary to the frequency theory of pitch perception and favors the place theory even for very low tones.
A Consideration of the Intensity-Loudness Function and Its Bearing upon the Judgment of “Tonal Range” and “Volume Level.”
Authors: Stuntz Stephen E.
Published: September 2005

Acoustical intensity not only affects the loudness of sounds, but also profoundly influences the listener's perception of certain ranges of frequencies. The data of Fletcher and Munson demonstrate that the effective frequency response of the ear varies with signal intensity-level. On the basis of this variation, it is possible to account for certain anomalies appearing in Eisenberg and Chinn's study of listeners' preference for frequency ranges and intensity levels in the reproduction of speech and music. It is also possible to explain the disparity between their results and those of Olson's investigation of preference for frequency ranges. For example, it can be shown that when frequency is plotted against loudness, raising the intensity level from 50 to 70 db will add more than one whole octave downward to the effective frequency response of the ear at 50 millisones loudness.
Subharmonics Generated in Human and Animal Ears by Intense Sound
Authors: von Gierke H. E.
Published: September 2005

When subjects are exposed to intense sound fields, subharmonics radiated from the subjects eardrum are heard. The frequency of the subharmonic is exactly one-half of the frequency of the stimulating signal. Whereas these observations on humans are only possible at intensities above 140 db, subharmonics are found at the guinea pigs ear at an exposure level of about 95 db. These subharmonics will be demonstrated on guinea pigs and discussed.
Use of Barium Titanate Transducers for Producing Large Amplitudes of Motion and High Forces at Ultrasonic Frequencies
Authors: Mason W. P. , Wick R. F.
Published: September 2005

By using a barium titanate cylinder poled radially a lengthwise motion can be excited in the cylinder whose resonant frequency is controlled by the length of the cylinder. By using a 4 percent lead titanate barium titanate combination, stresses up to 1000 lb./sq. in. of cross-sectional dimension and motions up to 50 parts in 106 times the length of the cylinder are available for static or slowly varying voltages of 15,000 v/cm along the radial dimension. When such a cylinder is driven at its resonant frequency, the maximum strain appears to be limited to 10−4 by heating considerations if no cooling is used. For a cylinder 12 cm long, which resonates at 18 kc, this corresponds to a displacement on each end of 3.9 × 10−4 cm, a particle velocity of 44 cm/sec. and an acceleration of 5 × 106 cm/sec./sec. All of these quantities can be enhanced by a factor of 10 by soldering a brass “horn,” tapered exponential, to the end of the barium titanate cylinder. If the large end of the horn, which is soldered to the cylinder, is 10 times the diameter of the small end, the horn acts as a transformer to increase the particle motion by a factor of 10. Hence a 1.5-mil motion is possible with this combination at 18 kc. This structure has been made the basis of several instruments used for testing wear, for measuring magnetic flux, for testing adhesion of films and for boring odd-shaped holes. A feed-back amplifier system with a diode limiting element is used to keep the amplitude constant.
A Speech Analyzer and Synthesizer
Authors: Munson W. A. , Montgomery H. C.
Published: September 2005

This paper describes work on a resonance type of Vocoder that was started just before the war and discontinued because of war work. The project has not been renewed but the first results obtained are reported now since there is considerable interest at the present time in this type of analysis and synthesis and in the circuits used. The circuits were designed to extract the important characteristics of speech by determining the frequency and magnitude of the principal vocal resonances as continuous functions of time. Speech was split into three bands: 300 to 1100, 900 to 3000, and 3000 to 8000 cycles. In each band the frequency of axis crossings in the wave form and the total energy were measured by suitable circuits. In addition, the fundamental pitch of the cord tone and the energy in the band from 40 to 400 cycles were measured. These parameters were transmitted in eight 40 cycle bands to a synthesizing circuit which reconstructed the speech. The synthesizer contained two signal sources, a cord tone with controlled pitch and a wide band noise. These two signals were passed through resonant networks having controlled peak frequencies. The frequency responses of the networks simulated the characteristics of speech formants and the peak frequencies were shifted by variable inductance coils controlled by the axis crossing counting devices in the analyzer. Data are shown on the performance of the analyzer and the combined analyzer and synthesizer.
Preliminary Studies of Speech Produced by a Pattern Playback
Authors: Cooper Franklin S. , Liberman Alvin M. , Borst John M.
Published: September 2005

Results obtained with a sound spectrograph and pattern playback are presented in this paper. The playback synthesizes speech sounds, using modulated light transmitted through a photographic copy of an original spectrogram, or reflected from a hand-drawn version. Tests of connected speech so produced indicate that a rather high order of intelligibility is achieved. The hand-drawn spectrograms can be simplified and schematized to a considerable degree without appreciable loss. In general, either type of spectrogram can be modified in a variety of ways, and the effects of these modifications can then be evaluated by listening tests.
Ultrasonic Irradiation of Nerve Tissue
Authors: Fry W. J. , Wulff V. J.
Published: September 2005

A systematic study of the biological effects produced in nerve tissue by ultrasound is currently in progress. The contribution to the observed effects caused by temperature changes produced by absorption of the sound has been separated from that caused by other factors accompanying sound propagation. It has been shown that the observations must be correlated on the basis of factors other than temperature change occurring as the result of absorption. The completed studies include electrical measurements of reversible depression of the random activity in the excised ventral nerve cord of crayfish and ultrasonic intensity time duration relations for inducing temporary and permanent paralysis of the hind legs of frogs. The latter includes observations on summation with respect to successive periods of irradiation separated by various time intervals. Preliminary values have been obtained at 1.0 mc for the ultrasonic absorption coefficients of the biological materials of interest in this investigation.
Absorption Measurements in Electrolytic Solutions
Authors: Smith M. C. , Barrett R. , Beyer R. T.
Published: September 2005

Measurements are reported on the absorption of ultrasonic radiation in water solutions of Mg SO4. Measurements were made at 3 mc by an electrical detection method, and in the range 12–40 mc by the radiation pressure method. An attempt is made to correlate the data with the low frequency measurements of Leonard, and with the absorption theory presented by Liebermann. In particular, the results at the higher frequencies indicate that there is an additional absorption process not accounted for by the compressional relaxation in the Liebermann theory. The excess absorption varies directly with the square root of the concentration. The effect of temperature variation on the absorption is also reported.
The Velocity of Sound in Sea Water
Authors: Weissler Alfred , Del Grosso Vincent A.
Published: September 2005

In the sonar detection of underwater objects an accurate knowledge of the velocity of sound in sea water, and its variation with chemical composition and temperature, is desirable. Eight samples of Caribbean Sea water collected at various depths were studied with respect to sound velocity, density, and chemical composition. At both 20° and 30°C the velocities (determined with a 3-megacycle ultrasonic interferometer) were about 4 meters/second higher than the values in Kuwahara's tables, for which an accuracy of 3 meters/second is claimed. The salinities determined by chemical analysis agreed closely with those calculated from the densities; a slight increase of salinity with depth was noted. In another series of experiments, the sound velocity, density, and adiabatic compressibility were determined over a wide range of concentration for pure solutions of each of the seven salts which are the major constituents of sea water. It was found that the compressibility and sound velocity observed for sea water agree to 0.1 percent with the values obtained by linear summation of the effects of the individual salts, each taken at the proper concentration. Finally, removing over 90 percent of the dissolved air was found to increase the sound velocity only by about 0.5 meter/second (the order of magnitude of the experimental error) in sea water, as well as in distilled water.
Transmission of Sound in a Liquid between Concentric cylinders
Authors: Curran Daniel R.
Published: September 2005

The theoretical work of W. J. Jacobi on the propagation of sound waves along liquid cylinders has been extended to the case of sound transmission through a liquid bounded by two concentric cylinder of infinite length. Longitudinal phase velocities and radial distributions of pressure amplitude have been calculated, and the form of the Fourier-Bessel expansion coefficients has been worked out for rigid, pressure-release, and elastic wall boundary conditions. Similar calculations for the case of a single liquid filled cylinder have been made for comparison. The case of two concentric cylinders approaches that of a single cylinder as the radius of the inner cylinder approaches zero. Experimental values of phase velocity have been determined for the case of two finite concentric cylinders with elastic walls and are in good agreement with theory over parts of the range from 3 to 200 kc.
Measurement of the Mechanical Impedance of Resilient Materials
Authors: London Albert , Orlacchio Anthony W.
Published: September 2005

A method of measuring the audiofrequency mechanical impedance of resilient materials, such as rubber and felt, while under static load is described. The experimental arrangement consists of an electromagnetic driver made of a magnetic loudspeaker pot and a rigid voice coil which is supported from both above and below, by two disks made of the sample material. The motion of the coil is determined by an electrostatic variable capacity vibration detector patterned on the Van Zelst condenser microphone circuit. The ratio of the input to output voltage is measured both in magnitude and phase. To determine the mechanical impedance, it is required to make voltage and phase measurements as a function of the mass of the moving system. Results obtained on several materials using this technique and also a resonance technique will be given.
Ultrasonography
Authors: Ernst Paul J.
Published: September 2005

Marinesco was the first to describe a blackening effect of ultrasonics on photosensitive films. Whether the action is a direct or indirect one, is still open to question. Anyhow, in connection with ultrasonic lenses or my other concentration devices or even without them, the phenomenon can be used for making “ultrasonic images.” An “ultrasonic camera” is being designed for this purpose. I have the name of “ultrasonography” coined for the process since it is an ultrasonic simulation of photography. Ultrasonography has many fields of theoretical and practical application, the exploitation of which has not yet started. Some of the first “ultrasonographs” ever made will be shown.
On the Relation between the Sound Fields Radiated and Diffracted by Plane Obstacles
Authors: Wiener Francis M.
Published: September 2005

In the past, acoustic diffraction and radiation problems have been treated separately in many cases, although their intimate connection is clear from theoretical considerations. This connection becomes a useful equivalence in the case of plane piston radiators and rigid scatterers exposed to an incident plane wave. This equivalence is of practical importance since it permits, with a minimum of effort, the transition from a problem in acoustic radiation to the related diffraction problem, and vice versa, where plane surfaces are involved. The foregoing principles are applied to the important case of the circular disk.
Synthesis of Line Source Directivity Patterns
Authors: Hills Robert
Published: September 2005

The distribution of sound intensity in space (pattern function) from a line source of finite length is given by an integral involving the distribution of source strength along the line of the source (excitation function). Synthesizing a desired pattern function with a given length of source requires the solution of an integral equation for the excitation function. Practical solutions may be obtained by expressing the pattern function as a finite sum of “characteristic functions” and obtaining the excitation function as a similar sum of complementary functions. One such scheme relates the zeroes of the pattern function to the coefficients of the Fourier expansion of the excitation function. Equal-minor-lobe patterns may be approximated, but the solution is not obtained in closed form as with linear point-source arrays.
Viscosity Effects in Acoustic Inductances
Authors: Nolle A. W.
Published: September 2005

The linear acoustic inductance and resistance of narrow circular tubes, short compared to a wavelength, have usually been represented by limiting formulas valid either for very low frequencies (viscous flow) or for relatively high frequencies (pistonlike displacement). Crandall's text gives a general mathematical development, with particular stress on resistance, but variation of inductance with frequency and viscosity has not been discussed generally, nor has numerical reduction of mathematical results been generally available. The present paper describes quantitatively the dependence of inductance and resistance upon the general parameter, radius times square root of the quantity, density times frequency divided by viscosity. With increase of this parameter resistance increases, while inductance diminishes from the “static” value to the limiting “high frequency” value. Experimental checks are made to ascertain whether resistance values are strongly affected by flow-transition end-effects found in hydraulics. Impedance-tube studies are made of five tube diameters from 0.0187 to 0.750 in., at 50 to 167 c/sec. Length/diameter is approximately 10, to render inductance end-corrections relatively small. Acoustic pressures are reduced until linear behavior appears. Measured resistance is generally within five percent of calculation as resistance increases to twice the “static” value. Measured inductance generally agrees with calculation within limits of the end-correction, over the range of significant variation.
First- and Second-Order Acoustic Fields with Viscosity and Relaxation
Authors: Markham Jordan J.
Published: September 2005

The effect of viscosity on a second-order acoustic field has been studied when the time independent relation between the excess pressure and the excess density is replaced by a relaxational one. The method used is similar to that of Eckart except that some terms explicitly neglected by him are included. The introduction of relaxation indicates that steady flow caused by higher order terms is not only caused by the viscosities but is affected by the relaxational relation between the pressure and density. The calculations also indicate that quartz wind measurements are not equivalent to absorption measurements because the temperature variations of the viscosity coefficients enter into the flow problem. If these calculations are correct they suggest interesting problems on classical liquids and give a method to distinguish between relaxational and viscous effects. The introduction of relaxation also explains simply Liebermann's measurements on ethyl formate.
The Design of Small Studios
Authors: Rudmose Wayne
Published: September 2005

A design has been effected to obtain adequate acoustical conditions in smallsize rooms used chiefly as announce studios. The treatment consists of shelves and “egg-crates” intended to break up grazing modes on the walls and ceiling. Helmholtz resonators and plywood wainscot provide low frequency absorption. Midfrequency absorption is supplied by thin acoustical tile with a painted surface. The reverberation time is essentially uniform from below 100 to 8000 c/sec. with no trace of the resonant boom usually associated with such small rooms. The smallest room so treated has a volume less than 500 cu. ft.; yet the treatment does not reduce the available working space over conventional types of treatment using acoustical tile. Jury judgment and physical measurements indicate the space compares favorably with much larger studios and there is no noticeable change in quality when the studio program ends and the announcement begins. The application of this type of treatment to small practice rooms in music buildings seems promising.
Comparison of Absorption Coefficients Measured in a Reverberation Chamber with Statistical Coefficients from Impedance Values
Authors: Hardy H. C. , Tyzzer F. G. , Ramer L. G. , Ancell J. E.
Published: September 2005

As a part of an investigation of the properties of the Riverbank reverberation chamber, comparisons were made between reverberation coefficients and statistical coefficients calculated from impedance-tube data for 2- and 4-in. Fiberglas board and for resonator-type panels. One of the objectives of the tests was an investigation of materials for use as possible standards for comparison of reverberation chambers. Tests on resonator panels were suggested by Ingård and Bolt who have found that the impedance could be calculated and was independent of the angle of incidence when the air-space backing was divided into small cells. Construction details are given for the resonator panels, which consisted of perforated hard-board mounted with air-space backing and covered with cloth to obtain a resistance at resonance somewhat greater than ρc. One panel with a 2-in. air space was designed for resonance at about 700 c/sec. and the other with a 9-in. air space, for resonance at about 140 c/sec. A panel for about 350 c/sec. was also obtained by using the 2-in. air space with the facing for the low frequency panel. For Fiberglas, fairly good agreement was found, except near 500 c/sec. where the reverberation coefficient exceeded the statistical coefficient. For the resonator absorbers, however, the reverberation coefficient was considerably greater than the statistical coefficient between 300 and 700 c/sec. and was less at frequencies between 100 and 250 c/sec. The reasons for this difference between the two types of absorbers is being investigated.
Damping Effects of Porous Absorbing Units in Rooms
Authors: Roop R. W.
Published: September 2005

Unit sound absorbers, as distinguished from conventional absorbing treatment, are not limited to surface layers, but may be placed at appropriate locations throughout the volume of a room. One type of unit absorber, described by Olson, consists of two porous conical shells assembled base to base to enclose an air space. An investigation has been made of an alternative type, consisting of assemblies of layers cut from refined rockwool batts. Measurements of the absorption of porous cubes, ranging from 8 to 24 in. on a side, gave results varying from 3 to 18 sabins per unit. For the smaller cubes, bulk absorption values of about 8.5 sabins per cu. ft. of material were obtained, as compared with a value of 4.3 sabins per cu. ft. for a sample of the same material 212 in. thick in a 64-5q. ft. area on the floor. The frequency distribution of the absorption of the cubical units is more uniform than that typical of surface treatment. Within the limited range of the experiments, the absorption per unit increased somewhat as the number of units increased. A guide to the application of homogeneous unit absorbers is provided by volume perturbation theory. Perturbation methods are applied to a wave equation, containing measured values of the complex propagation constants of several samples of the materials used, to obtain approximate results comparable with experimental data.
A Large-Scale Panel-Driving Source
Authors: Baruch Jordan J. , Lang Henry C.
Published: September 2005

In testing the qualities of panels which contribute to the transmission-loss phenomenon, the need for a driving source presents a large problem. At the M.I.T. Acoustics Laboratory, a large-scale adjustable source has been built. The driver consist of a bank of 256 five-inch loudspeakers arranged in a 16-by-16 array closely coupled to the panel under test. The speakers are essentially isolated, and act individually. The individual columns of speakers may be phased independently, allowing a simulation of various wave fronts, such as cylindrical waves and plane waves of various angles of incidence.
A Wide-Range Acoustic Termination
Authors: Mawardi Osman K.
Published: September 2005

A number of practical applications in acoustics call for terminating impedances of reasonably small sizes and of values independent of frequency. A labyrinth-like structure with its passages filled with sound-absorbing materials was found to fulfill these conditions satisfactorily. The labyrinth construction is such that the flow of sound energy in any one section normal to its axis of symmetry is in a radial direction. As a result the sound path is many times longer than the over-all linear dimensions of the termination and the acoustic impedance of the termination is practically that of an infinitely long labyrinth. The impedance of such axially terminating structures have been studied as a function of the height of the passages and of the propagation constant of the absorbing material filling them. Constructional details and performance characteristics are given.
Brownian Motion and the Sense of Hearing
Authors: de Vries Hl.
Published: September 2005

The great sensitivity of sense organs leads to a consideration of the possible interference effects caused by Brownian motion in the sensory cells. The weakest audible stimulus involves energies of the order of 10−11 ergs or about 250 kT. Assuming, on the basis of v. Békésy's data, this minimum audible energy to be distributed over 1000 sensory cells, the threshold of a sensitive cell would lie in the neighborhood of 0.25 kT. Since the average thermal energy per molecule is 1.5 kT, such a threshold value would imply continuous excitation. The auditory nervous system would thus be unavailable for acoustic stimuli. Therefore a mechanism must be postulated which would concentrate the acoustic energy on a small number of sensory cells: if for example, the mechanical energy were to be transformed into electrical energy, the cells of the smallest electrical resistance would be the most effectively stimulated. This working hypothesis provides a useful viewpoint for a discussion of such phenomena as cochlear microphonics, phase relations between stimulus and electrical responses from the vestibular system, and the electrophonic effect.
New Assembly for the Measurement and Analysis of Sound
Authors: Sepmeyer L. W.
Published: September 2005

This assembly comprises a laboratory quality system for the measurement and analysis of sound over the frequency range of 20 c/sec. to 150 kc/sec. Its principal components are: (1) A hydrophone amplifier having the input characteristics of a cathode follower and a balanced line output. The response is uniform within 1 db from 10 c/sec. to 130 kc/sec. (2) A sound level meter provided with both peak and r.m.s. meters with linear db Scales. (3) A separate power supply, resulting in greater portability and allows either battery, 60 cycle or 400 cycle power to be used. (4) A calibration test set. Provision is made for inserting a half-octave filter set for analysis and for simultaneously feeding a magnetic tape recorder and a graphic level recorder.
A Mechanical Shock Tester for Instruments and Electronic Apparatus
Authors: Morrow Charles T.
Published: September 2005

A mechanical shock tester has been designed which produces high accelerations in the form of a square wave. The apparatus is described, and the logical considerations which were used as design parameters are explained. Particular attention is paid to the relation between the shocks an equipment is likely to receive in practice and the optimum type of test apparatus.
An Instrument for Measuring Correlation Coefficients
Authors: Cook R. K. , Berendt R. P. , Waterhouse R. V. , Thompson M. C.
Published: September 2005

The correlation coefficient between the sound pressures at two points in a sound field is a useful quantity for several applications. An instrument was developed for measuring and recording correlation coefficients as a function of time. A feature of this instrument is the use of a recorder's servo-mechanism to measure the ratio of two dc voltages. The results of correlation measurements in reverberant sound fields will be presented.