bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Signal Detection by Simple Correlators in the Presence of Non-Gaussian Noise. I. Signal-to-Noise Ratios and Canonical Forms
Authors: Middleton David
Published: September 2005

The detection of underwater acoustic signals by simple auto- and cross-correlation receivers in the presence of nonnormal, as well as normal background noise is examined on the basis of signal-to-noise ratios calculated from a generalized deflection criterion. Particular attention is devoted to the effects of impulse noise and mixtures of impulse and normal noise on system performance. Comparisons between system behavior vis-à-vis the two types of interference are made. For impulse noise equivalent in spectral distribution and average intensity to a Gaussian noise background it is found that the output signal-to-noise (power) ratios are related by the canonical expression (SN)I2 = (S/N)G21 + (1 − μ)Λ(S/N)G2, 0⩽μ⩽1, where Λ(⩾0) is the “impulse factor” and μ is the fraction (in average intensity) of the total noise background that is attributable to normal noise. Impulse noise always degrades system performance vis-à-vis normal noise in the autocorrelation reception of stochastic signals, characteristic of applications where passive receiving methods must be used. This degradation can be considerable [O(10 dB or more)] if the noise is highly impulsive (large Λ) and if large values of (S/N)out2(>0 dB) are required (for high accuracy of decision). On the other hand, when coherent (i.e., deterministic) signals are employed, so that cross-correlation reception is possible, the degradation may be reduced essentially to zero (i.e., Λ → 0) under realizable conditions of operation. It is observed for impulsive, as well as normal noise backgrounds, that cross-correlation receivers are linear in their dependence on signal-to-noise ratio, i.e., (S/N)out2∼(S/N)in2 if sufficiently strong injected signals are employed. The analysis is carried out largely in canonical form, so that the general results for (S/N)out2 can be applied to other, special types of nonnormal noise backgrounds. Specific relations are included, along with a detailed summary of the principal results, showing the dependence of (S/N)out2 on (S/N)in2, filtering, delay, noise and signal spectra, etc., for weak and strong inputs, little or heavy postcorrelation smoothing and for Gaussian as well as for impulse noise.
Damage-Risk Criteria for Line Spectra
Authors: Ward W. Dixon
Published: September 2005

A series of experiments designed to elucidate the differences between pure tones and octave bands of noise in terms of their ability to arouse temporary threshold shift (TTS) is described. It is shown that the critical-band concept is not relevant at high intensities, and that therefore the 10 dB correction factor currently employed, being based on the critical-band concept, must usually be incorrect. Instead, it is demonstrated that the differences in TTS producing ability of tones and noises can be attributed mainly to their differences in ability to arouse the acoustic reflex; since noises cause more sustained contraction of the middle ear muscles than do pure tones, less TTS will usually be produced by noise. Because this difference in contraction, and hence in effective attenuation, is a variable function of frequency, intensity, and time, no one single decibel correction factor is appropriate. It is suggested that damage-risk criteria for pure tones should be developed empirically by measuring TTS directly rather than by attempting to modify existing criteria for octave-band noise.
Effect of Masking Noise on Lateralization and Loudness of Clicks
Authors: Raab David H. , Osman Eli
Published: September 2005

The effects of monaural masking noise on loudness and on lateralization of clicks were compared for noise levels ranging between 35 and 65 dB SPL. For different fixed levels of unmasked clicks, sound-pressure levels of the masked clicks were adjusted by the subjects to produce centered sound images. In a second experiment, similar procedures were used to generate equal-loudness functions. For both loudness and lateralization, the effect of masking noise was greatest with high levels of noise and low intensities of click. In every case, the masking effect was greater for loudness than for lateralization.
Free-Field Threshold Shift and Temporary Threshold Shift Reduction as Measures of Efficiency of Ear Protective Devices
Authors: Fletcher J. L. , Loeb M.
Published: September 2005

The attenuation of two different earplugs and a helmet was measured by a procedure combining the free-field threshold shift and the Békésy threshold tracking methods. Subjects were then exposed to impulse noise which would produce between 12 and 64 dB TTS at 6000 cps unprotected and their TTS was subsequently measured after identical exposure during which they wore the protective devices. Following this the subjects were exposed unprotected to continuous noise which would produce a TTS at 6000 cps within ±6 dB of the TTS they experienced after their unprotected exposure to the continuous noise. Finally, they were exposed to the same continuous noise while wearing the protective devices, and their TTS following exposure was determined.

It was found that the helmet afforded significantly less attenuation of low-frequency sound than the ear plugs and roughly the same amount at higher frequencies. The three devices were found to be equally effective in eliminating the TTS following exposure to the continuous and impulsive noise. While the data did not lend themselves to definite conclusions regarding susceptibility to impulse and continuous noise, it appeared that susceptibility to one type of exposure was not necessarily significantly correlated with susceptibility to the other.
Calculation of Loudness Levels for Musical Sounds
Authors: Churcher B. G.
Published: September 2005

The application to organ tones or other sustained musical sounds of the Stevens and the Zwicker methods for loudness-level calculation from observed sound spectra is examined. It is found that both methods, although developed for dealing with noise of the continuous spectrum type, are applicable to organ tones, a particular class of discrete component sound, subject to the use in both methods of accepted equal-loudness contours. Examples of the loudness levels of some typical organ tones are given. Questions needing further investigation are noted.
Some Secondary Effects Related to Impact Wave Forms
Authors: Nisbet J. S. , Brennan J. N.
Published: September 2005

This paper considers changes in the shock spectrum that may arise from minor variations in the form of an applied pulse. In addition to the rise and decay times the nature and symmetry of the discontinuities has a profound effect on the high-frequency components. The selection of parameters in the design of a square wave accelerator is discussed. The effects of shock excited resonances in a machine are investigated together with methods of minimizing their effect.
Magnitude Estimation of the Loudness of Clicks
Authors: Raab David H. , Osman Eli
Published: September 2005

Numerical estimations of the loudness of click stimuli were found to be a power function of sound pressure. The exponent (0.49) of the function is smaller than those previously reported in studies utilizing sustained tones or noises.
Pressure-Balanced High-Pressure Hydrophone
Authors: O'Neill Edward T.
Published: September 2005

This is a hydrophone design which permits the use of cylindrical piezoelectric elements at extreme hydrostatic pressures. By means of a capillary device, the internal pressure of the hydrophone is equalized with the ambient sea pressure while still preserving the inherent sensitivity of the piezoelectric material. The technique also permits the preselection of the low-frequency cutoff point of the hydrophones, through mechanical design.
Recorded Group Audiometer Test Comparisons at the 1956 Southern California Exposition
Authors: Webster J. C. , Thompson P. O.
Published: September 2005

Recorded series of 4000 cps absolute threshold tests were administered over earphones to 1919 people in groups of 8 or less. The results suggest that: (1) test-retest reliability is increased by increasing the number of attenuation steps within a given hearing loss (HL) range; (2) use of fewer and larger steps tends to make HL scores larger; (3) warble tones are interchangeable with pure tones as test stimuli; and (4) left ears tend to show greater HL. The results of this survey for HL as a function of age agree reasonably well with results of other recorded-test hearing surveys, but not so well with survey results obtained with clinical audiometers.
Generalized Short-Time Power Spectra and Autocorrelation Functions
Authors: Schroeder M. R. , Atal B. S.
Published: September 2005

“Wiener's theorem” relating the autocorrelation function to the power spectrum of a time function has been modified and extended to the cases in which measurements are made with realizable filters having finite integration times. Similar relationships derived earlier by Fa no are valid only for the case when the power spectrum is measured by means of a bandpass filter with all impulse response e−αt cosωt or the auto-correlation function is measured by averaging through a simple R-C integrator. The generalized relationships derived in this paper are valid for integrators with arbitrary impulse responses. Several different forms of short time representations and their experimental realizations are also discussed. The emphasis in this paper is on physical realizability—not mathematical existence.
Methods for the Calculation and Use of the Articulation Index
Authors: Kryter Karl D.
Published: September 2005

Speech-intelligibility testing is an expensive and time-consuming operation that requires laboratory test conditions. In an attempt to short-cut or make unnecessary this type of testing, a procedure was developed by French and Steinberg [J. Acoust. Soc. Am. 19, 90–119 (1949)] for calculating from physical and acoustical measurements made on a communication system a measure that is indicative of the intelligibility scores that would be obtained for that system under actual test conditions. This measure is called the “Articulation Index” (AI). Methods of calculating AI have been improved and elaborated to the point where several methods for its calculation, herein reported, can be proposed for use in the evaluation of most speech communication systems.
Propagation of a Pressure Transient in a Two-Layer, Liquid Model
Authors: Knudsen William C.
Published: September 2005

The propagation of a pressure transient in a model consisting of a surface layer of liquid overlying a thick (essentially semi-infinite) bottom layer of liquid has been investigated experimentally. Attention is restricted to the behavior in and near the surface layer at a range large compared with the depth of the surface layer. The results have been analyzed to determine the group velocity curve, variation of pressure amplitude with source and receiver depth, and the rate of amplitude decay with range for the maximum envelope amplitude. The results are found to be in general agreement with the “Theory of Propagation of Explosive Sound in Shallow Water,” by C. L. Pekeris. In addition, the rate of decay with range for the first peak amplitude was measured and found to be r−2 within experimental error.
Backscattering of Explosive Sound from the Deep-Sea Bed
Authors: Urick R. J. , Saling D. S.
Published: September 2005

The return by the deep ocean bottom of the sound produced by an explosive charge consists of a decaying burst representing scattering at successively decreasing grazing angles with the bottom. An analysis of shot records at three deep-water locations between Cape Hatteras and Bermuda has yielded the backscattering strength of the sea bottom over a range of frequencies and angles between 30° and 90°. In the range 30° to about 65° the bottom appears to behave as a diffuse backscatterer of sound; between 65° and 90° (normal incidence) an increased return may represent reflection from inclined flat facets of the sea bed or from sub-bottom sediment layers. Analyses in several frequency bands between 0.5 and 8.0 kc indicate no frequency dependence of the scattering strength that could not be due to shock-wave attenuation effects in the sea. The coefficients agree with those obtained with pulsed sinusoidal sound sources.
Effect of Phase on the Quality of a Two-Component Tone
Authors: Craig James H. , Jeffress Lloyd A.
Published: September 2005

Listener responses to monaurally presented two-component stimuli (a 250-cps tone and its octave, at various intensities and phase relations) reveal striking individual differences and unexpected patterns. With certain pairs of these stimuli, that stimulus which is consistently judged higher in pitch (or louder or purer) by one subject is just as consistently judged lower (or softer or less pure) by another. When the intensity of one of the stimulus components and the phase angle between the components are held constant, reversals of phase of the entire stimulus become discriminable as soon as the intensity of the second component is increased a little above threshold. With certain combinations, as the second component is further increased, phase discrimination for one subject reaches a maximum, decreases to chance, and then increases again. For another subject under the same set of conditions, phase discrimination does not fail, but rather, monotonically increases.

No single explanation accounts for the subjects' patterns of responses and for their sensory experiences. Rather, it seems that two or more of several suggested mechanisms are involved.
Ultrasonic Velocity, Absorption, and Rotational Dispersion in Methane
Authors: Kelly Bernard Thomas
Published: September 2005

The velocity of sound was measured in methane at 3 mc in a pressure range from 50 to 2 cm Hg. The velocity, plotted according to Kneser's (V2−V02)/(V∞2−V02) = (f/fw)2/1 + (f/fw)2, showed a point of half rise, due to the relaxation of the rotational modes, at 300 mc/atmos which corresponds to a relaxation time of 1.06×10−9 sec. The dispersion was confirmed by the measurement of absorption in the relaxation region. Measurements were made on a motor-driven, Hubbard-type acoustic interferometer conjunction with a strip recorder. This instrumentation allowed the use of f/p ratios hitherto difficult to employ.
Effect of Reverberation on Assessment of Repetitive Impulse Noise
Authors: Thiessen G. J. , Subbarao K.
Published: September 2005

Reverberation is found to decrease the acceptability of impulse noise even though directional effects resulting from head diffraction are eliminated by presenting the signals by means of earphones. Four clicks per second, with artificially added reverberation corresponding to r = 1.1 sec, were presented to the subjects, who could adjust the level until it matched the same signal without reverberation. Matching was done according to “annoyance,” “noisiness,” and “speech interference.” Reverberation had no appreciable effect when the instantaneous rms level of the reference signal was below about 35 dB re 0.0002 dyn/cm2. The maximum effect occurred in the 85- to 90-dB region where it was equivalent to about 3, 4, and 8 dB, respectively, for the three criteria. The shape of the curve is somewhat different for experienced and naive subjects.
Acoustic Refraction and Scattering with Compliant Elements. I. Measurements in Water
Authors: Toulis W. J.
Published: September 2005

The velocity of sound in water may be reduced markedly with mechanical structures which effectively increase the compressibility of water. A compliant tube, formed from commercially available round tubing by deforming its cross section elliptically, is a simple example of such a structure. Compliant tubes are useful in the design of lenses at frequencies below the lowest flexural resonant frequency of a compliant tube immersed in water and reflectors for frequencies up to where the spacing between adjacent compliant tubes corresponds to a half-wavelength. Several measuring techniques were utilized to demonstrate the different aspects of compliant tubes under various conditions of interest. The analytical generalizations due to these measurements will be discussed in a second article.
Investigation of Some Parameters of the Cutaneous Threshold for Vibration
Authors: Verrillo Ronald T.
Published: September 2005

Sensitivity to vibration on the hand was determined as a function of frequency, contactor dimensions, contactor configuration, and distance of the contactor from a rigid support. It was found that each of these parameters affects the threshold in a different way. In the frequency range between 25 and 640 cps, the absolute threshold as a function of frequency yields a U-shaped curve that reaches a maximum of sensitivity in the region of 250 cps. The effect of the geometric parameters appears to be highly complex.
Improved Light Valve for the Photographic Recording of Vibrations
Authors: Sreekantath Gopala Menon
Published: September 2005

A scheme is described for modulating a beam of light by a vibrating transmission grating.
Frequency-Correlation Functions of Frequency Responses in Rooms
Authors: Schroeder M. R.
Published: September 2005

A mathematical study of the random interference of sound waves in large rooms requires statistical methods. “Statistical wave acoustics” is based on the random interference of many simultaneously excited normal modes of a room. In general, the random interference takes place for frequencies above 2000 (T60/V)12, where T60 is the reverberation time (in sec) and V is the volume (in m3) of the room. In the statistical theory, frequency responses between two points in a room are treated as random functions. The probability distributions, correlation functions, and “spectra” of these random functions are determined by physical parameters such as the distance between source and receiver, the volume and reverberation time of the room (or distribution of reverberation times), etc.

In this paper, correlation functions of frequency responses are derived for rooms with uniform reverberation time, and negligible direct sound transmission between source and receiver. Analytic formulas for the following frequency correlation functions are found: the autocorrelation functions of the real and imaginary parts, the modulus and the squared modulus of the frequency response, and the cross correlation function between real and imaginary parts of the frequency response.

The significance of these correlation functions in room acoustics is discussed. Measurement of the autocorrelation function of the real (or imaginary) part of the frequency response allows a precise determination of the distribution of reverberation times. The autocorrelation function of the modulus (or squared modulus) determines the required frequency shift in public address systems to improve their stability. For measurement of electroacoustic transducers in reverberation chambers, optimum bandwidths of noise or warble tones are obtained.
Binaural Detection of Single-Frequency Signals in the Presence of Noise
Authors: Gardner Mark B.
Published: September 2005

The effect of phase and pressure-level differences on the detectability of single-frequency signals in the presence of noise is presented for listening over of a binaural transmission system. During the several tests to be described, the two microphones were supported in free space both in the absence and in the presence of various approximations to an artificial head. The results indicate that over-all detectability is a function of the combined binaural phase relationships of both signal and noise and of the monaural intensity relationship of the two signals at the ear having the higher signal to noise ratio. Some indication was found that phase differences may influence detectability to frequencies as high as 2000 cps. Pressure-level differences, on the other hand, decrease in magnitude with decreasing frequency until only a small effect remains at 250 cps.
Measurement of Small Values of Electromechanical-Coupling Coefficient in Piezoelectric Transducers
Authors: Shibayama Kimio
Published: September 2005

The electromechanical-coupling coefficient of a piezoelectric transducer k is usually derived from the difference between resonance and antiresonance frequencies for a particular mode. However, if the mechanical Q of the transducer Qm is low, i.e., k2Qm < 2, this relationship breaks down. The region k <20% and 100 <Qm <1000 has been analyzed and the resulting formulas processed by computer. The final data are presented in graphical form, making it possible to derive accurate values of k and Q from observations of the magnitudes and frequencies of the impedance maximum and minimum.
Mechanism of Interaction between Vibrations and Heat Transfer
Authors: Fand R. M.
Published: September 2005

Several different hypotheses have been proposed in the literature to explain the physical mechanism whereby transverse vibrations increase the rate of heat transfer by free convection from horizontal cylinders. The present paper contains a discussion of the validity of these hypotheses in the light of recent experimental data.
Phase Velocity of Plane Longitudinal Waves in Infinite Plates
Authors: Diercks K. J. , McCormack K. , James D. B.
Published: September 2005

Computed curves of the dimensionless phase velocity (c/cL) of plane longitudinal waves in infinite plates for values of the parameter ν (Poisson's ratio) from 0.25 to 0.40 are presented.
Equivalent Eulerian Boundary Conditions for Finite-Amplitude Piston Radiation
Authors: Kessler Henry C.
Published: September 2005

A method is presented for replacing the Lagrangian boundary condition which occurs in the analysis of finite-amplitude radiation from vibrating pistons by an approximately equivalent condition which permits the analysis to be carried out in Eulerian form.
Relation between Strain and Velocity in Resonant Vibration
Authors: Crandall Stephen H.
Published: September 2005

In a recent paper Hunt examined the relation between strain and velocity in forced resonant motion for a wide variety of elastic bodies. He found that the maximum strain was always proportional to the ratio of the maximum vibratory velocity to the velocity of sound in the body and that the constant of proportionality appeared to be constrained to remain in a narrow range extending about an order of magnitude. Similar results were obtained independently by Ungar [see E. E. Ungar, “Maximum Stresses in Beams and Plates Vibrating at Resonance,” J. Eng. Ind. Trans. ASME 84B, 149–155 (1962)] for uniform beams and plates. In this note a similitude argument is used to establish the form of these results. It is also pointed out that because of both strain and velocity concentrations the range of possible values for the proportionality constant can be very much wider than the range found by Hunt.
Comparison of the Receiver-Operating Characteristics for Messages Received by Ear and by Eye
Authors: Carterette Edward C. , Cole Michael
Published: September 2005

Receivers were presented with equal-length words under two conditions of difficult reception: (1) by ear, against a background of white noise; and (2) by eye, for a brief period in a tachistoscope. For each word presented, the receiver recorded a message and, immediately following, gave a confidence rating with respect to his accuracy of reception. The similarities between the functions for the auditory and visual modes of reception are marked. It is found that for both auditory and visual presentation the accuracy of reception is (1) directly related to the confidence rating, (2) relatively invariant over a range of signal-to-noise ratios, and (3) not impaired by the task of rating. These results support and extend the generality of the statistical decision-making theory of the receiver.
Method of Time Normalization for Speech
Authors: Blankinship W. A.
Published: September 2005

A method of time normalization is described whereby utterances may be transcribed to a standard intrinsic scale in such a manner that those which differ only in rate of phonation will be transcribed to identical signals.
Doppler Effect in a String
Authors: Wilms E. V. , Stippes M.
Published: September 2005

The problem of a massive particle moving along a stretched string and subjected to a time-varying force perpendicular to the string is treated by the method of characteristics. If the force varies harmonically explicit expressions may be obtained; these are displayed.
Axial Vibrations of a Semiinfinite Viscoelastic Rod with External Elastic Constraint
Authors: Flügge W. , Hutchinson J. R.
Published: September 2005

This paper considers the response of a semiinfinite viscoelastic rod subject to an enforced sinusoidal displacement of its end. The rod has external elastic constraint along its length. Above a certain critical frequency, the steady-state solution consists of damped traveling waves moving away from the forced end. For lower frequencies, however, the wave travels out of the rod toward the forced end. A brief explanation of this interesting phenomenon is given by studying the work done on the rod. The transient analysis is performed, for the rod initially at rest, by applying a Fourier sine transform to the space variable. The resulting integral solution is integrated numerically for a purely viscous rod being forced at a frequency below the critical frequency. This solution shows how the disturbance is initially propagated away from the forced end and subsequently settles down to the steady-state solution of the wave traveling toward the forced end.
Articulation-Testing Methods: Consonantal Differentiation with a Closed-Response Set
Authors: House Arthur S. , Williams Carl E. , Hecker Michael H. L. , Kryter K. D.
Published: September 2005

The development and evaluation of a new speech-intelligibility test suitable for routine use by operational personnel in determining the performance level of speech-communication systems is described. The format used is similar to that described for a rhyme test but makes use of a closed-response set. An experiment was performed to determine the general reliability of the test materials when administered to U.S. Air Force enlisted personnel under a wide range of signal-to-noise ratios. Testing of 18 listeners over a period of 30 days showed that repeated exposure to the materials did not change the levels of average response in any appreciable way. Analysis of the responses to individual phonetic elements shows that the test can be useful for diagnostic study as well as for over-all evaluation of communication systems. Talker differences that appeared during the experiment and the statistical reliability and sensitivity of the materials are analyzed and discussed.
Comment on Two Papers concerning Reverberation from the Ocean Floor
Authors: Goodman R. R.
Published: September 2005

A brief analysis is given on the contribution of surface scattered sound to the reverberation measurements of Urick and Saling [J. Acoust. Soc. Am. 34, 1721 (1962)] and of Mackenzie [J. Acoust. Soc. Am. 33, 1498 (1961)]. It is demonstrated for Mackenzie's result that surface scattering intensities are the same order of magnitude as his measured reverberation level. This may account for the descrepancy in their scattering coefficients and those measured by different means.
Nonlinear Interaction of Two Sound Beams
Authors: Naze J. , Tjøtta S.
Published: September 2005

The nonlinear interaction of two sound beams propagating in the same direction is studied. Westervelt's theory for the scattering of a difference-frequency wave is extended to the case of beams with finite width. A stronger directivity in the scattered sound is obtained, in agreement with the experimental results of Bellin and Beyer.
Mechanical Impedance of Free-Free Beams
Authors: Snowdon J. C.
Published: September 2005

Discussed theoretically is the manner in which the driving-point and transfer impedances of a free-free beam depend upon the position of the driving force and upon the position along the beam at which the velocity is monitored. Also considered is the effect of one or more arbitrarily situated forces upon the driving-point impedance that is presented to a primary force at a separate location. The influence of internal damping upon the response of the beam is always considered. The influence of rotary inertia and shear displacement is usually disregarded, however, except in one example that also describes the manner in which the observed frequency dependence of the mechanical properties of the beam material—especially rubberlike materials and plastics—may be inserted into the beam equations.
Acoustic-Backing Techniques for Transducers and Radiators
Authors: Toulis W. J.
Published: September 2005

The acoustic stiffness of a liquid within a small enclosure may be reduced greatly by the introduction of compressible matter, which may be in the form of compliant tubes. This effect is due in part to the added compressibility of the compliant tubes and in part to volume resonance. The mixture can be tuned or detuned by changing either the number of compliant tubes or the type of liquid in the fill. Such flexibility permits the resonant frequency of an acoustic transducer to be altered. Additional investigations demonstrate that a simple liquid fill can also be employed successfully if the diaphragm compliance of a transducer is designed to be comparable to that presented by the fluid. The resonance width of a transducer may be broadened by reducing the thickness of a metallic diaphragm and using the liquid fill for the essential stiffness with a lesser amount of mass. However, the effective electromechanical coupling factor may increase or decrease by an amount that depends on both the relative stiffness and the specific transducer design.
Effect of Air Space on the Acoustic Characteristics of Uncoated and Coated Foams
Authors: Schwartz Manuel , Bradley Herbert D.
Published: September 2005

Air spaces between a rigid termination and a sample of foam material give absorption effects similar in some respects to the results obtained from surface coatings. Air spaces require larger thicknesses to produce equal improvement at lower frequencies. Surface coatings of increasing thickness decrease the absorption at higher frequencies, but the combination of an air space and surface coating may improve the absorption at these frequencies. The effects of air space were attributed to a considerable extent to their similarity to an equivalent thickness of foam.
Measurement of the Transmission Loss of a Finite-Depth Aperture
Authors: Wilson George P.
Published: September 2005

To provide experimental verification of an approximate solution for the diffraction of sound waves by a circular aperture in a plane rigid wall of finite thickness, a series of experiments was conducted on the transmission of reverberant sound through steel pipes inserted individually into a thick wall between two reverberation chambers. The usually recommended methods of evaluating the transmission loss proved inadequate because long, narrow apertures have sharp resonant peaks. By electronically averaging and equalizing the outputs of four microphones in each chamber and using a slowly sweeping sine wave with a small super-imposed warble, it was possible to record continuous plots of the aperture transmission loss with high resolution of frequency and amplitude. Experimental accuracy of 1 dB was possible over most of the frequency range of 300–12 000 cps, diverging to 2 dB at the frequency extremes, and for apertures with sharp resonances, diverging to about 4 dB at the peaks. The accuracy was limited by reading the “average” of the recorded fluctuating sound level, which was most difficult at resonant peaks. For larger-diameter apertures, which gave data relatively uninfluenced by flanking sound, the agreement with theoretical results was within 1 dB over most of the frequency range.
Some Preliminary Studies of Temporary Threshold Shift with an Arc-Discharge Impulse-Noise Generator
Authors: Loeb M. , Fletcher J. L. , Benson R. W.
Published: September 2005

Preliminary studies with an arc-discharge (spark-gap) impulse-noise generator produced data not entirely in line with previous experiments (employing longer pulses) with respect to the effects of variation of number and spacing of pulses and of preactivation of the acoustic reflex on temporary threshold shift (TTS). Specifically, growth of TTS with number of pulses was not linear but was less than logarithmic, and moderately loud sounds before each pulse, presumably intense enough to activate the reflex, were ineffective reducing TTS. On the other hand, when an equal number of impulses were presented at a fast repetition rate, or when more intense activating stimuli were presented at a slow pulse-repetition rate, less TTS was observed. The TTS observed was greatest at high frequencies, especially at 6000 cps and above.
Ultrasonic Relaxation and Cis-Trans Isomerization in Methyl and Ethyl Formates
Authors: Subrahmanyam S. V. , Piercy J. E.
Published: September 2005

The ultrasonic absorption of liquid methyl and ethyl formates has been measured over a frequency range of 0.6–10 Mc/sec from 60° to 140°C. The relationship with previous measurements is discussed. The absorption is consistent with the single-relaxation process of internal rotation about the carboxyl C–O bond and activation enthalpies of 7.8±0.5 and 8.0±0.4 kcal/mole for methyl and ethyl formates, respectively. The difference in energy between trans and cis isomers is estimated to be approximately 2–3 kcal/mole for both methyl and ethyl formates. Absorption measurements in dilute solutions of the formates in xylene and nitrobenzene indicate that the activation enthalpy is insensitive to molecular surroundings. The relation of the activation enthalpy to the barrier to internal rotation, bond order, and the theory of resonance is discussed.
Some Elastic Constants of Silicon Carbide
Authors: Arlt G. , Schodder G. R.
Published: September 2005

Elastic constants of silicon carbide polytype 6H have been measured by a resonance method and a double-pulse method.
Sound Absorption in Oxygen/Water-Vapor Mixtures
Authors: Calvert James B.
Published: September 2005

The relation between sound absorption in O2-H2O mixtures and vibrational relaxation in water vapor is noted, and two processes are given for vibrational relaxation in O2-H2O mixtures based on the resonant transfer hypothesis of Tuesday and Boudart. One of these processes involves the rapid dissociation of a water-vapor dimer after its excitation by resonant transfer. Both processes require a vibrational relaxation time of about 10−9 sec for water vapor at room temperature. Existing measurements on water vapor do not exclude a short relaxation time, but a choice between the relaxation processes is not possible. Further experimental measurements are necessary, including the study of O2-H2O mixtures at higher temperatures.
Vibrational and Rotational Relaxation in Water Vapor
Authors: Roesler H. , Sahm K.-F.
Published: September 2005

Measurements of the sound absorption in water vapor due to vibrational and rotational relaxation have been carried out at 50°C. The experiments yield a vibrational relaxation time of (6.0 ±2.0) ⋅ 10−9 sec, corresponding to Zvib = 73 ±25, and a rotational relaxation time of (3.2 ±0.4) ⋅ 10−10 sec, corresponding to Zrot = 4 ±0.5.
Auditory Masking in the Rat
Authors: Gourevitch George
Published: September 2005

Masked thresholds were measured with an operant tracking method at 4 frequencies between 1000 and 8000 cps and at 3–5 levels of wide-band noise. As in humans and cats, masked thresholds in the rat increased linearly with noise level. Critical ratios were calculated from the masked thresholds and found to be 10 or 11 dB greater than those in man and 5 to 6 dB greater than those in cats. Greenwood's function Δfcb = 10ax+b, relating critical bandwidths to position on the basilar membrane, was shown to fit reasonably well the data of this experiment. The constant relation shown by Fletcher between critical ratios and frequency DL's, previously found to apply to man and to cats, appears to apply to rats also.
Hearing-Loss Trend Curves and the Damage-Risk Criterion in Diesel-Engineroom Personnel
Authors: Harris J. D.
Published: September 2005

Several hundred young men were given careful audiometry before beginning duty in noise of 105–110 dB SPL at one or more of the octaves 300–600, 600–1200, 1200–2400 cps. These men were then given the same audiometric examination intervals up to five years. Less than 15% of ears had permanent threshold shifts (PTS) of more than 20 dB at any frequency. Trend curves extrapolated over log time predict a median PTS of 8 dB at 4 kc/sec for 10 years' exposure. The PTS actually found was thus 20 dB less than predicted by the ASA Z-24 Committee report; the 4-kc/sec TTS2 for an 8-h exposure to this noise was over 60 dB; use of the 4-kc/sec TTS2 index would thus vastly overpredict both the actual PTS of 8 dB and the Z-24 Committee prediction of 22 dB. Ear defenders as actually worn by this population reduce median PTS by no more than 5 dB. It is concluded that a damage-risk criterion of 100 dB SPL at any of the relevant octaves would be conservative, protecting at least 850/0 of young healthy ears from PTS of over 20 dB at any frequency.
Sound-Power Production in Wind Instruments
Authors: Bouhuys Arend
Published: September 2005

This paper presents data for output sound power PO of wind instruments relation to input power PI supplied by the player. PI was calculated as pV̇, where p equals mouth pressure and V̇ air flow rate through the instrument. PO was calculated from sound-pressure level and measurements of reverberation time in a live room of known volume. A part of the data was obtained in a room of unknown characteristics; from 15 comparable measurements on 8 different instruments in both the live and the unknown room, data were obtained that allowed calculation of PO also from other experiments in the unknown room. Measurements were made on single notes, played both pp and ff, on each instrument; one low and one high note on the scale of each instrument were chosen. The ratio PO/PI, representing the mechanical efficiency of wind instruments as sources of sound power, varies from less than 0.001% to about 2%. It appears to increase with increasing PI and, in some instruments, with frequency. The consistent results obtained for 3 different flutes played by one performer suggest that the variability noted in the other data at least partially reflects individual differences in mechanical efficiency.
Frequency Equations for the Normal Modes of Vibration for an Elliptical Ring, Including Transverse Shear and Rotary Inertia
Authors: Callahan W. R.
Published: September 2005

The research work of Mindlin, Reissner, and Uflyand on plates is extended to the actual finding of the frequency equations for the normal modes of vibrations of an elliptical ring. Product solutions are assumed for the partial differential equations of motion and it is found that infinite series of product solutions satisfies the boundary conditions; the resulting frequency equation for each boundary condition appears as an infinite determinant, equated to zero, the elements of which are infinite series of terms involving Mathieu functions whose characteristic numbers are functions of the frequency. An algorithm is given showing how to calculate the roots of the infinite determinant that gives the normal modes of vibration. The present theory is more valid for higher modes of vibrations than the classical Lagrange theory of plates since it includes coupling between flexural and shear motions, and the numerical results, if carried out on high-speed machines, should be valid for these higher modes.
Parametrically Excited Surface Waves
Authors: Brand R. P. , Nyborg Wesley L.
Published: September 2005

Experimental results are given on waves established at the upper surface of liquid in a rectangular Plexiglas vessel executing uniform vertical oscillation, with frequencies primarily in the range 50–500 cps. Comparison is made with theory originally given by Benjamin and Ursell, extended by Sorokin and Eisenmenger. Observed wave frequencies (one-half the excitation frequency) and wavelengths are in reasonable agreement with this theory, but observed values of the critical onset amplitude ξc are much greater than expected. Considerable, though insufficient, improvement results from modifying the theory so that acoustic boundary layers at the container walls are taken into account. Using this modified theory, the ratio of observed to predicted ξc is as much as 14 at low frequency, but decreases to about 2 at the upper frequency limit. It is suggested that the discrepancy may arise, at least in part, from time-dependent solid-liquid surface energy, the time-dependence resulting from oscillation of the meniscus at vessel walls.
Comparison of Theoretical and Experimental Values of Spatial Correlation
Authors: Cron Benjamin F. , Hassell Beverly C. , Keltonic Frank J.
Published: September 2005

Experimental measurements of spatial correlation were made using the top 12 elements of a 40-element vertical array. The hydrophone outputs were passed through filters in the 200- to 400-, 400- to 600-, 600- to 800-, and 800- to 1000-cps bands. Selected pairs of hydrophones were crosscorrelated. The experimental values of spatial correlation were compared with the theoretical values of spatial correlation. A good agreement of the experimental results with the theoretical results is obtained in the higher passbands. In general, the agreement is better for higher-frequency bands and higher sea states. The results indicate that (1) the noise is predominantly from the horizontal direction in the 200- to 400-cps band, (2) the noise is predominantly from the vertical direction in the other measured bands, and (3) the sources on the surface of the ocean radiate energy similar to that of a dipole source.
Aspects of Edgetone Experiment and Theory
Authors: Powell Alan
Published: September 2005

Measurements of the number of the wavelengths of the stream disturbance lying between orifice and edge are shown to be consistent with the over-all result of the assumptions used in the general feedback theory, of operation of edgetones, even though some preceding and related measurements of phase shift had suggested that one assumption was possible inadequate.
Improved Cushion for Ear Defenders
Authors: Shaw E. A. G. , Thiessen G. J.
Published: September 2005

Circumaural ear defenders require a cushion which is highly adaptable to the irregular contours of the head so as to provide a good air seal, and yet behaves like a stiff spring so as to minimize low-frequency cup vibration. These apparently contradictory requirements are met by a cushion consisting of an annulus of highly flexible yet rather inextensible material partially filled with an incompressible fluid. A theory of cushion behavior is given and is supported by experimental data. Experiments with real heads show that the attainable low-frequency attenuation is limited by the viscoelastic properties of the flesh. Values of circumaural flesh impedance derived from the experimental data are compared with the mastoid data of other workers, and the relationship between sound transmission and threshold shift data is discussed. The design of a rigid cup and flexible frame suitable for use with the cushion is also discussed.
Detection of a Doppler-Invariant FM Signal by Means of a Tapped Delay Line
Authors: Rowlands R. O.
Published: September 2005

The phenomenon of Doppler invariance in an FM signal is discussed first. This is followed by a description of how this signal may be detected by passive sampling, a variable sampling rate being chosen to make each sample correspond to a signal peak. This results in signal folding, which reduces the total number of samples required to detect the signal. Certain characteristics of the signal are described and a formula is derived for the output of the detector when a weighting function designed to reduce the sidelobes is applied to the taps. The output is a discontinuous function because the signal is not always present at all of the taps all of the time, and the nature of this function is illustrated by means of graphs drawn for a number of typical weighting functions.
Dynamic Mechanical Stability in the Variable-Reluctance and Electrostatic Transducers
Authors: Sherman Charles H.
Published: September 2005

Large displacement behavior of the variable-reluctance, and the mathematically equivalent electrostatic, transducing mechanism was analyzed in order to evaluate the importance of mechanical instability as a limiting factor in high-power sound projectors. Previous work by Hunt et al. had shown the existence of static instability. This paper first considers the effect of transients on static stability and then shows that instability can also occur under steady-state dynamic conditions even when the system is statically stable. When the excitation is increased in order to increase the amplitude of the oscillations, the average displacement also increases, which leads to collapse of the gap. This interdependence of the oscillatory motion and the average displacement, intentionally excluded from linearized treatments, is the cause of dynamic instability. Detailed calculations show the conditions for instability for typical values of mechanical Q, polarization, and frequency. Under steady-state dynamic conditions the average displacement can exceed the static limit of 13 the gap length, and the relative oscillatory displacement amplitude can reach 12 or more without collapse.
Shifts in Air-Conduction Thresholds Produced by Pulsed and Continuous Contralateral Masking
Authors: Dirks Donald D. , Malmquist Carolyn
Published: September 2005

In the present investigations, auditory threshold shifts for either constant or pulsed pure tones were observed while a steady or pulsed narrow band of white noise was delivered to the contralateral ear via an insert receiver. The narrow-band masker, centered around 4000 cps, was presented at intensity levels of 50, 70, and 90 dB SPL while thresholds were obtained from the test ear at 4000, 1000, and 250 cps. The results demonstrate, first, that larger threshold shifts occur when the test signal and the masker are pulsed simultaneously than when the masker is continuous; second, that a continuous masker may be as effective as the pulsed masker if the test tone is also continuous; third, that more contralateral masking is found when the test tone and masker are close in frequency; and, last, that a small increase in the average threshold shift occurs as the intensity level of the masker increases. Several interpretations are offered in explanation of the threshold shifts for the continuous continuous and pulsed pulsed (simultaneous) conditions.
Speech Annunciator Warning Indicator System: Preliminary Evaluation
Authors: Pollack Irwin , Tecce Joseph
Published: September 2005

The principle of a speech annunicator as a warning signal indicator was evaluated in three experiments against a master warning signal. With respect to two important criteria of performance (warning signal identification time and performance upon a concurrent visual-motor tracking test), the speech annunciator was dearly superior to the master warning indicator. With respect to two other criteria of performance (initial warning detection and performance upon a concurrent message-reproduction task), the speech annunciator was equivalent to the master warning indicator. The results suggest that a speech annunciator, perhaps coupled with a master indicator, may be a useful warning indicator system.
Standardized Communications and Message Reception
Authors: Pollack Irwin , Tecce Joseph
Published: September 2005

The reproduction of messages, selected from defined information sources, was studied in a multichannel listening task. Standardization of message procedures was controlled independently of standardization of message nomenclature. It is shown that the standardization of procedures or nomenclature is an effective determinant of message reproduction. And, the joint standardization of both nomenclature and procedure is more effective than either alone.