bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient Coding of Vocoder Channel Signals Using Linear Transformations
Authors: Crowther William R. , Rader Charles M.
Published: September 2005

The spectrum channel signals in a channel vocoder are highly correlated to each other. Kramer and Mathews have shown how this can be used to reduce the required channel capacity by transmitting not the channel signals themselves, but linear combinations of the channel signals from which the original signals can be recovered by inverse linear transformation. Using the Kramer-Mathews technique, a linear transformation matrix can be found for which the mean-squared error between the signals measured at the analyzer and the signals recovered at the synthesizer is held to a minimum for a given bit transmission rate. We originally thought to apply this technique to the logarithmically quantized channel signals, since the mean-squared error on the logarithm of the spectrum of the speech seemed to be a good error-criterion for a vocoder transmission system. Instead of the Kramer-Mathews matrix, however, we were led to use a 16×16 Hadamard matrix for the linear transformation. The implementation of this matrix by digital techniques is particularly simple, requiring only additions and subtractions, and the operation can be achieved by four identical steps of eight additions and subtractions per step, thus substantially reducing the required circuitry. Furthermore, the Hadamard matrix is its own inverse within a factor of 16, so that the transformation called for at the synthesizer is the same as that called for at the analyzer.
Ray-Path Characteristics in a Sound Channel for a Particular Velocity-Depth Profile
Authors: Dence D. F.
Published: September 2005

Various velocity-depth profiles have been analytically formulated to examine certain features of SOFAR propagation, such as the prediction of the range at which the rays converge and the travel times associated with the ray paths. Exact solutions, in terms of known functions, are presented for the ray paths and travel times associated with the velocity distribution C=C0(1+a2z2)B, with B=12, 1. These velocity profiles had formerly been examined by employing a small-angle-approximation technique. The advantage of the solutions presented herein is that the ray-parameter dependency is evident throughout the convergence zones. Also, the time dispersion of the SOFAR arrivals are determined.
Effect of Velocity-Profile Simplification upon Measured Fluctuation of Sound Propagation in Water
Authors: Leiss William J. , Whitmarsh D. C.
Published: September 2005

The Ordnance Research Laboratory has been conducting a series of underwater sound-propagation measurements at depths from the surface to 5000 ft over a range of from 2000 to 8000 yd in the frequency region of 10–40 kHz. The measurements were made with self-contained vehicles that transponded acoustically with each other as they sank slowly through the water. Amplitude fluctuations of as much as 20 dB were found in depth intervals from a few inches to a few feet. An attempt has been made to explain these fluctuations by means of intensity-loss calculations based on the sound-velocity profile. Field-test results are compared with the calculated results for combinations of source-receiver depths encountered during the measurements for a series of simplifications of the sound-velocity profile. This simplification involved approximating the actual profile in several steps by a profile consisting of from 100 to 3 layers. Typical examples of the effect of this simplification of the profile on the ray-path structure are presented also. [Work sponsored by the U. S. Navy Bureau of Weapons.]
Some Observations on Sound Fields in Large Rooms
Authors: Shankland R. S.
Published: September 2005

Acoustical observations and measurements have been made in a number of large rooms in Italy where the size, architectural detail, and decorations, especially the sculpture, produce several interesting acoustical phenomena. The wide range of air volume studied permitted special attention to be given to the facility with which sound fields can be established in them. Large variations of room shapes and extremes in the degree of acoustical coupling between airspaces also made interesting observations possible. The buildings studied afforded great variations in architecture and styles of decoration so that the scatterers for sound diffusion covered a considerable range, effecting the character of the reverberation and the effective sound absorption of complex surfaces. In the largest spaces, the effect of air absorption produced significant effects not only at the higher frequencies but also at intermediate frequencies. Measurements made with large variations in relative humidity permitted this effect to be isolated.
Model Study of the Sound Transmission over Raked Theatre Seats
Authors: West J. E. , Sessler G. M.
Published: September 2005

The propagation of sound waves traveling at grazing incidence over rows of theatre seats was studied on a 1:10 scale model for different degrees of raking of the seating and stage areas. The measurements were made with tone bursts with a duration of 4 msec spaced linearly over the frequency range from 0.75 to 8 kHz. For linear and logarithmic raking of the seating area of 15° or greater, the selective low-frequency seat attenuation [G. M. Sessler and J. E. West, J. Acoust. Soc. Am. 36, 1725–1732 (1964)] is eliminated. The measurements show no significant difference between linear and logarithmic rake. Seat attenuation can also be eliminated by raking the stage rather than the seating area; thus, concert halls with a flat main floor and more vertical space for balconies can be designed.
Achievement of Liveness in Small Rooms having Low Reverberance
Authors: Veneklasen Paul S. , Ryan James W.
Published: September 2005

The acoustical environment of small viewing or review rooms in studio or recording complexes can be controlled over wide limits even though the reverberation time is low and inherently limited in range. Echograms from model studies show that the growth period of the aural impression is controllable by orientation of sound-diffusing reflecting surfaces. Results reinforce the emerging conviction that envelopment in early echoettes is a separate factor from reverberance in determining the impression of liveness in music rooms.
Transmission Characteristics of Limp Walls in Relation to Mass Law
Authors: Sabine Hale J. , Siekman William J.
Published: September 2005

Sound-transmission (TL) loss tests on a large number of single homogeneous limp walls at Riverbank Acoustical Laboratories have shown a consistent rise in TL values at low frequencies with respect to either the field-incidence mass law (angles of incidence from 0° to 78°) or the random-incidence mass law (0°–90°). A similar rise has been noted in tests at the Owens-Corning Fiberglas Sound Laboratory on a single 22-gauge steel wall. Deviations from the field-incidence mass law at 125 Hz range from 3 to 14 dB in the two laboratories combined. The Fiberglas study shows that the deviation is independent of area from 312×9 ft to 14×9 ft, and is also independent of all variations of test conditions within the specifications of the latest proposed revision of ASTM E 90-61 T. In the Riverbank tests, the deviation varies considerably with the type of material under constant test conditions. In both laboratories, the TL at higher frequencies below coincidence agrees better with the field-incidence than with the random-incidence mass law.
Reduction of Aircraft Noise Measured in Several Single-Family Houses
Authors: Bishop Dwight E.
Published: September 2005

Noise-reduction measurements in several types of single family houses are described and compared with previous field measurements. Also described are the results of a number of laboratory sound-transmission-loss measurements of residential-type windows and doors. Windows and doors were selected for laboratory tests, since they generally constitute the “weakest links” in achieving effective noise insulation. [Work supported by the U. S. Department of Housing and Urban Development, Federal Housing Administration.]
Generation of Acoustic-Duct Modes by Internal Sources
Authors: Morfey C. L.
Published: September 2005

By means of a linearized theory for aerodynamic sound generation, the power output from sources operating in a duct is expressed in terms of duct modes. For axial fans, it is possible to infer from geometrical and cutoff considerations which are the dominant modes responsible for both broad-band and tone radiation; the inference is checked by measurements of farfield radiation patterns around fan inlets, which agree with the directivity predicted for the appropriate duct modes. With this information, different mechanisms of fan- and compressor-noise generation can be distinguished, and order-of-magnitude estimates made of the power output from each mechanism.
Effect of Duration on Detection of a Noise Signal
Authors: Wightman Frederic L. , Green David M.
Published: September 2005

The detectability of a wide-band noise signal, in the presence of a simultaneously gated, uncorrelated masking noise, was measured at seven durations from 300 μsec to 300 msec. Psychometric functions were obtained for three observers at each duration using an up-down 2AFC technique. At the 300-μsec and 100-msec durations, a rating procedure also was used to obtain receiver-operating characterisic ROC curves. With masking-noise power held constant, the signal power necessary for 75% correct detection in the forced-choice task decreased approximately 4 dB for every 1-log unit increase in duration. The psychometric functions for all observers grew progressively shallower as duration was decreased, and the slopes of the ROC curves were consistently steeper at the 100-msec duration than at the 300-μsec duration. A model based on a modified version of the familiar energy detector is proposed to account for the results. [Research supported in part by the National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Binaural Vector Model: Relative Interaural Time Differences
Authors: Levitt H. , Lundry E. A.
Published: September 2005

Further computations on the binaural vector model have been carried out [H. Levitt and E. A. Lundry, J. Acoust. Soc. Am. 39, 1232(A) (1966), and references cited therein]. The cumulative probability distribution of the phase angle between the left- and right-ear resultant vectors has been computed for the case where either the noise or the signal has been subjected to an interaural time difference. It is assumed that interaural time difference is the relevant variable for binaural signal detection under these conditions. Based on this assumption, the resolution required of the binaural system for consistency with available binaural masking-level difference (BMLD) data has been computed. An interpretation of the results in terms of short-term crosscorrelation is presented.
Rôle of Jet-Edge Asymmetry in Pipe Voicing
Authors: Elder S. A.
Published: September 2005

Observations were made, using schlieren optics with stroboscopic illumination, of jet motion in mouth region of open diapason-voiced and flute-voiced pipes. For diapason, the jet-edge system is strongly asymmetrical, the jet spending only about 17 of a period in pipe each cycle. Resulting “Class C” driving generates strong second-harmonic content evident even in the motion of the jet itself. Direct-current flow through pipe, into open end and out of the mouth, caused by Bernoulli pressure associated with average external jet flow, purges the pipe of all but about 14% of jet fluid in normal operation, making it possible to drive the pipe on CO2 with very little pitch change. Jet-edge configuration is more nearly symmetrical for flute-voicing, with even harmonics consequently weak. Driving pulse for flute-pipe lags phase of standing-wave velocity maximum only slightly, in qualitative agreement with Bechert-Cremer model. For diapason voicing, in contrast, driving pulse is very nearly in phase with pressure. This effect causes essentially the entire second harmonic of jet influx to be used in overcoming acoustic losses in diapason pipes. [Work supported by the U. S. Office of Naval Research.]
Working Theory of Trumpet Air-Column Design
Authors: Cardwell W. T.
Published: September 2005

The boundary conditions for waves in a trumpet are not simply a pressure antinode at the mouthpiece end and a pressure node at the bell end. The mouthpiece acts approximately as an infinite impedance closure at the lip plane, but viewed from its trumpet end, the mouthpiece acts as a Helmholtz resonator, and the imaginary component of its impedance moves from a high value down through zero, as the trumpet frequencies rise through their useful range. The function usually ascribed to the bell, of shifting the frequencies of the vibrational modes from those of a closed-open pipe to the musically useful modes of an open-open pipe, is significantly handled by the bell only in the lower playing modes. The necessary shifts in the upper modes of a modern trumpet are handled by the resonator action of the mouthpiece, and by an actual shortening of the over-all tube below the simple-theoretical length. Experimental resonance data are given to support the theory. The conclusions have been embodied in a playing trumpet designed for high register work in E♭ and F.
History and Theory of the Tonal Spiral
Authors: Pikler A. G.
Published: September 2005

The angular measure of musical intervals, traceable to Ptolemy (1 oct=180°; 2 oct=360°), was first determined correctly by Drobisch (1855) as 360° × log2 r, where r is the frequency ratio. Using this concept, Drobisch sketched an ascending tonal spiral (i.e., a helix) without giving its equation. Donkin (1874) provided an equation for a spiral on a plane surface, Baravallee and Tipple (1946) presented an equi-angular spiral on a plane surface to demonstrate Mercator's equal temperament of 53. Elaborating upon Euler's (1739) binary-log measure of musical intervals (log2 r) for rotational angles, we propose a helix with the equation f201.63=261.63×2ω/2π=261.63×e0.09315(ω/2π) to represent, reference middle C, the growth of frequency in the octave system as a function of the rotational angle ω/2π in radians. Applications of this equation to the invariances of the relative pitch sense (e.g., MAJOR THIRD+MINOR THIRD=PERFECT FIFTH) are discussed. Furthermore, the model is made descriptive for orientation by the absolute-pitch sense, also for diplacutic, paracutic, and Doppler shifts, and expanded to the imaginary domain. To the diameter, one can assign intensity re 0.0002 dyn/cm2. A family of nonintersecting helices can incorporate the function of equal loudness and portray the field of audition in the three dimensions of the tonal species (“chroma”), frequency and intensity with respect to normal and abnormal hearing. The equation for the helix of the fifths is f201.63=261.63×(3/2)(ω/2π); and in cyclically tempered systems 3/2 is “flattened” by the respective “schismata.” Use of a digital computer to determine the spiral points is reported.”
Effects of Pressure Gradients on Turbulent Boundary-Layer Wall-Pressure Fluctuations
Authors: Schloemer Howard H.
Published: September 2005

Spectral density, magnitude of the normalized longitudinal and lateral cross-spectral density functions, and convection velocity ratio as a function of longitudinal separation and frequency of wall-pressure fluctuations were measured with small flush-mounted transducers. These measurements were accomplished in both mild adverse and mild favorable pressure gradients in a low-turbulence subsonic wind tunnel. To establish a basis of comparison, similar measurements were made for the zero-pressure gradient, and agreement with published measurements was excellent. The effect of an adverse pressure gradient on the nondimensionalized spectral density was an increase in the low-frequency content without influencing the high-frequency portion appreciably; a sharp decrease in the high-frequency portion was observed for the favorable pressure gradient. At similar nondimensionalized longitudinal separation and frequencies the convection velocity ratio was higher in the favorable and lower in the adverse pressure gradients. The longitudinal decay of a particular eddy was more rapid in the adverse and slower in the favorable pressure gradients. No differences were found in the lateral cross-spectral density for the different pressure gradients.
Use of Building Barriers for Airport-Neighborhood Noise Control
Authors: Veneklasen Paul S.
Published: September 2005

Noise in the vicinity around airports is a multidimensional problem because of the variety of operations and mobility of the noise sources. The shielding effect of barriers for protection of airport environs must be assessed for each operation. Takeoff and landing along sloping paths are the most challenging operations. The configurations of buildings in the vicinity can be chosen to optimize effectiveness. Model measurements suggest a fruitful approach.
Implications of Automatic-Equalizer Technology for the Problem of Echo Suppression
Authors: Rudin H. R.
Published: September 2005

Long-haul voice communication has always been plagued by the problem of returned echo. The greater the delay of the echo, the more it must be attenuated to provide satisfactory service. The advent of synchronous satellite communication has increased the delay to the point where the combined effects of delay, echo, and present-day echo-suppression techniques degrade the quality of transmission. During the past few years, automatic-equalization strategies (which remove linear distortion from a transmission channel) have been under intensive investigation, particularly from the point of view of synchronous data communication. Recent work provides equalization for general communication channels over the entire channel bandwidth and is described by Lucky and Rudin [Proc. IEEE (Mar. 1966)]. The present paper discusses the utilization of the latter technique to generate a replica of the undesired echo, which replica is added to the original echo in such a manner as to cancel it. This approach is essentially identical to that of an unpublished algorithm suggested by the late J. L. Kelly, Jr. The technique is an adaptive one suited to time-varying channels and shows promise as a means for echo control.
Subjective Evaluation of Delay and Echo Suppressors in Telephone Communication
Authors: Miura Akira , Sato Rikio , Nagata Kuniichi
Published: September 2005

The effect of transmission delay upon the quality of the telephone circuit was investigated by means of psychometric methods using experimental telephone circuits. The results reveal that 600 msec of one-way transmission-time delay is well tolerable when no echo is included. Annoyance of talker and listener echo was studied. The just-tolerable minimum echo attenuation increased rapidly as the delay time increases, and, above 300 msec of roundtrip delay, the attenuation stays at the value around 20 dB. The evaluation was made on three types of conventional echo suppressors and an experimentally made cancellation-type echo suppressor. It was found that only one among the three conventional echo suppressors is good enough to give the tolerable quality up to 600 msec of one-way transmission delay. Since the cancellation-type echo suppressor in which the echo is cancelled out with the signal synthesized by convolution calculation circuit has no speech chopping, the speech quality with it was found to be better than that with all the three conventional echo suppressors.
Measurement of Noise in a High-Speed Towed Body
Authors: Stockhausen J. H. , Evensen E.
Published: September 2005

Measurements were made of the noise received with hydrophones in a streamlined body towed by a hydrofoil craft at speeds up to 30 kt. In an attempt to measure the noise due to turbulent pressure fluctuations, small hydrophones were mounted flush with the surface of the body. In order to help identify other sources of noise such as vibration of the body and sound radiated from the towing vehicle, accelerometers and larger hydrophones were mounted inside the body. The outputs from the various sensors, recorded on magnetic tape, were frequency-analyzed from 50 Hz to 20 kHz. Analysis of the data showed that the measured noise was mainly caused by mechanical vibrations of the body. In the low-frequency region, these vibrations probably originated at the towing vehicle and were transmitted by the cable. At higher frequencies, vibration seemed to originate in the body itself, mainly in the tail section. Increased noise levels encountered at high speed with short cable lengths were attributed to cavitation at the body tow point.
Pressure Nearfield and the Radiation Field in Flow Noise
Authors: Haddle Gillian P. , Skudrzyk E. J.
Published: September 2005

Theoretical computations of the sensitivity of sound receivers to flow noise are usually based on the assumption of an exponentially decreasing oscillatory correlation function. Such functions agree with measurements of the correlation of the near field when correlation is better than a few percent. Such functions are typical nearfield correlation functions. Correlation always decays exponentially to zero. Therefore, the computations exclude the effect of a sound field. The effect of true sound—that is also generated in the boundary layer therefore is excluded. Nothing is known about the shape of this function when the correlation is smaller than a few percent. The computations then show that the sensitivity of a typical hydrophone may easily decrease by 10−5 if the frequency is increased to a few kilocycles per second, or the hydrophone is lifted out of the boundary layer. In contrast to the results of such nearfield computations, the experimental findings show that the sensitivity decreases by a relatively small factor (10−1 to at most 10−2), because the radiation field (which is correlated over approximately one sound-wave length, and has been neglected in the setting up of the correlation function) then determines the noise level that is received by the hydrophone. Predictions are compared with experimental results.
Measurements of the Distortion of Ocean-Bottom-Reflected Acoustic Pulses
Authors: Santaniello S. R.
Published: September 2005

An experiment was conducted using correlation techniques to study the distortion of a one-way propagated acoustic pulse. These measurements were made over a geographically smooth, nonsloping ocean bottom area, using a deep-streamed projector and hydrophone. The transmitted signals were linear frequency-modulated pulses, 250 msec in length at 1100±50 and 3700±100 Hz. Both linear and polarity coincident correlation procedures were used to obtain the crosscorrelation functions of direct and associated bottom-reflected pulses. For angles of incidence of the bottom-reflected pulse from 25° to 77°, 80% of the polarity coincident peak correlation values exceeded 0.53 for both frequency bands. Power spectra were developed from the Fourier transform of the linear autocorrelation functions. The power spectra of the direct pulses were similar for all receptions. However, a high degree of variation occurred in the power spectra of consecutive pulses reflected off an ocean bottom where the area of insonification changed very little during the interval between the pulses.
Scattering of FM Acoustic Pluses from Metallic Spheres in Water
Authors: Diercks K. J. , Goldsberry T. G. , Hickling Robert
Published: September 2005

Experimentally measured FM echo-pulse forms are compared with computed FM echo forms for solid, air, and water-filled aluminum spheres. The nondimensionalized frequency (ka) range of the incident FM slide is 10.7–17.4. The incident-pulse length, 2Δt (=c2Δt/a, the range extent in target radii), is 10. It is further shown that for 2Δt>10 the envelope shape and spectral density of the FM echo for each sphere may be predicted from the steady-state backscattering echo function for that sphere; increased spectral densities are observed at those frequencies associated with peaks in the steady-state function. Measured and computed pressure-amplitude and spectral-density distributions for both FM up and FM down, 2Δt=11.5, 23, and 115, echo forms are shown. Correlation functions displaying the multiple peaks expected from the observed spectral distributions for the FM up and FM down, 2Δt=115, echoes are included. [Work done under contract with the U. S. Office of Naval Research, Code 463, and the U. S. Naval Ordnance Test Station, Pasadena, California.]
Acoustic Nearfield of a Metallic Spherical Shell in Water
Authors: Goldsberry T. G. , Diercks K. J.
Published: September 2005

Experimentally measured polar patterns of peak pressure and echo energy in the scattered acoustic nearfield of a thin-walled, water-filled aluminum sphere in water are presented. A pulse technique is employed. The range of r/a, the test distance in radii, is from 1 to 20. Patterns at two nondimensionalized frequencies, ka=18.7 and 56.1, are shown. A 1/r2 spreading loss in backscattered energy is obtained for r/a>5. For 1<r/a<5, the energy decays as 1/rβ, where the magnitude of β is less than 2 and is a function of r/a. Formation of the farfield lobe structure is traced through the nearfield polar patterns. A loss and reappearance of nonsurface-reflected components of the nearfield echo-pulse forms is observed; the loss of these components is related to the appearance of nulls in the nearfield lobar patterns. [Work done under contract with the U. S. Office of Naval Research, Code 463.]
Thickness-Shear and Thickness-Twist Modes in Quartz Plates with Incomplete Electrodes
Authors: Spencer W. J. , Byrne R. J.
Published: September 2005

Thin vacuum-deposited metallic electrodes on piezoelectric plates may be used to bind the acoustic energy associated with thickness-shear and thickness-twist modes to the electroded portion of the vibrating plates. In addition, by proper choice of the electrode area, the amplitude of the anharmonic series of thickness-shear and -twist modes may be substantially reduced [Mindlin and Lee, Intern. J. Solids Structures 2, 125 (1966)]. The frequency of the strong responses in rectangular AT quartz plates with rectangular electrodes have been measured and the shear displacements associated with these responses determined by x-ray-diffraction topography [W. J. Spencer, Appl. Phys. Letters 2, 133 (1963)]. The effect of the plate and electrode dimensions and the coupled flexure modes are discussed in relation to the amplitude and frequency of the anharmonic overtones of the thickness modes.
Charge Stability of Electret Microphones
Authors: Sessler G. M. , West J. E.
Published: September 2005

The sensitivity of foil-electret microphones depends largely on the surface charge of the electret; thus, the temporal stability of this charge under various environmental conditions is of interest. Since the charge decay is resistive, foils with large volume resistivity, such as fluorocarbon, are necessary for systems with high lifetime. The stability was determined by measuring both the sensitivity of microphones and the surface charge of the foil electrets over extended periods of time. Measurements at room temperature show the sensitivity of fluorocarbon-electret microphones to be constant over periods of the order of years. Extrapolation of results obtained at elevated temperatures indicates a time constant of the sensitivity of fluorocarbon microphones of 10–103 yr at room temperature, depending on the preconditioning (temperature cycling) of the systems and, to a smaller degree, on the relative humidity. Even at 50°C and high relative humidity, the time constant of a preconditioned system is still of the order of 10 yr. Typical sensitivities of electret microphones are between −50 and −60 dBV for 1 μbar. Preconditioning of the systems results in a sensitivity loss of about 10 dB.
Bessel's Solution for a Two-Tone Finite-Amplitude Source
Authors: Cooper Duane H.
Published: September 2005

The parametric statement of the Poisson-Earnshaw solution for finite-ampliude dissipationless plane-wave propagation, u(z,α)=f(ζ), z=ζ−agr;f(ζ), in which z=c0t−x, α=12(γ+1)t, and f specifies an initial-value particle-velocity waveform, provides a basis for integral relations of the form ∫g(z)uz(z,α)dz=∫g(ζ−αf)f′(ζ)dζ, with similarly corresponding limits. For g=exp(−ikz), one obtains, after partial integration, ∫exp(−ikz)u(z,α)dz=(1/ikα)∫exp(−ikζ) × [exp(ikαf)−1]dζ. This formula is a generalization of Bessel's Fourier analysis of Kepler's equation for which f=sinζ. The method is also tractable for f=ε1sink1ζ+ε2sink2ζ, resulting in sine-series coefficients 2Jm(ε1β)Jn(ε2β)/β in which β=mαk1+nαk2. The method is approximately applicable to the moving-boundary-value problem treated by Blackstock [J. Acoust. Soc. Am. 34, 9 (1962)].
Variational Method for Eletcroelastic-Vibration Analysis
Authors: Eer Nisse Errol P.
Published: September 2005

A variational approximation technique for the analysis of the electroelastic vibrations of piezoelectric devices is derived. The technique is based on the stationary property of a total Lagrangian describing the steady-state vibrations of an arbitrarily electroded, arbitrarily shaped, piezoelectric solid. Trial solutions are substituted in this Lagrangian for the electric potential distribution as well as for the mechanical displacement vector. The technique is used to calculate the short-circuit resonant frequencies and their corresponding modes of a fully electroded, BaTiO3 ceramic disk versus its thickness-to-diameter ratio. The results for a number of the lower branches of the spectrum agree with Shaw's published data to an accuracy better than past techniques. The contributions of the electrical boundary conditions and of the electromechanical coupling effects to the spectrum are demonstrated and discussed. The technique provides a method for the analysis of piezoelectric-vibration problems, which previously lacked tractable methods of solution. [Work supported by the U. S. Atomic Energy Commission.]
Laser-Beam-Induced Ultrasonic Waves in Glass-II
Authors: Lester William W.
Published: September 2005

A transient solution of the equations of motion of the medium have been obtained using electrostriction as a beam-mixing mechanism. The effect of optical absorption in producing elastic waves is also considered. The magnitude of the pressure waves generated in some glasses are calculated. Experimental work with longitudinal waves in several glasses using a Q-spoiled 1.6-μ laser verifies the predicted linear dependence of pressure amplitude on laser-spike energy. Measurements on the longitudinal wave produced in one glass verifies the predicted uniform generation of elastic waves in the volume of the sample. Either mechanism considered appears capable of producing catastrophic damage in glass in very intense laser beams.
Acoustic Amplification in a Plasma
Authors: Ingard Uno , Schulz Michael
Published: September 2005

Criteria for acoustic-wave amplification [Phys. Rev. 145, 41 (1966)] and spontaneous acoustic oscillation in a weakly ionized gas are analyzed. The mechanism is a coherent transfer of energy from electrons to neutrals. [Work supported by the U. S. Navy, Office of Naval Research, and in part by the Joint Services Electronics Program.]
Light Diffraction by Ultrasonic Surface Waves
Authors: Mayer Walter G. , Lamers G. B.
Published: September 2005

The diffraction pattern produced by monochromatic light reflected from a solid on which an ultrasonic surface wave is propagated is shown to be useful in the determination of velocity and amplitude of the surface wave. The formalism describing the interaction of light and ultrasonic surface wave is compared to the theory applicable to light diffraction by ultrasonic waves through transparent media. [Work supported by the U. S. Office of Naval Research.]
Ultrasonic Attenuation in Normal-Conducting and Mixed and Meissner Superconducting States of Niobium
Authors: Kagiwada R. , Levy M. , Rudnick Isadore
Published: September 2005

The acoustic attenuation has been measured in a pure single crystal of niobium from about 1.2°–40°K. Longitudinal waves up to a frequency of 225 Mc/sec were propagated in the [100] direction in both normal and superconducting states. In the superconducting state, measurements were made with and without the presence of an external magnetic field. In the presence of a magnetic field, measurements were made with either a fixed temperature and increasing or decreasing field or a fixed field and increasing or decreasing temperature. Ultrasonic-attenuation data obtained by increasing the magnetic field and holding temperature constant seem to obey a [Hc2(T) − H0]12 dependence near Hc2(T) as Maki has predicted, where Hc2(T) is the upper critical field and H0 is the external applied field. In the absence of an external magnetic field, αs/αn can be fitted below T/Tc=0.6 to the usual bcs expression with 2Δ=3.64±0.05 kTc. [Work supported by the U. S. Office of Naval Research.]
Subharmonic Generation in an Ultrasonic Resonant Cavity
Authors: Breazeale M. A. , McCluney Ross
Published: September 2005

The generation of subharmonics of finite-amplitude standing waves is considered in relation to parametric amplification. It is observed that certain characteristics of the cavity resonance provide amplitude and phase relationships favorable to subharmonic growth. Observations are made using both optical-diffraction patterns and electronic techniques. Subharmonics are primarily observed within the resonant cavity, although some observations are made of those transmitted through the reflector. [Research supported by the U. S. Office of Naval Research.]
Ultrastructure of the Amphibian Papilla in the Bullfrog
Authors: Flock Åke , Flock Britta
Published: September 2005

The morphology of the amphibian papilla in the bullfrog has been studied with light and electron microscopy. The hair cells in the amphibian papilla are equipped with sensory hairs, one of which is a kinocilium. The orientation of the kinocilium varies in a complicated way along the sensory epithelium. At their basal ends, the hair cells are contacted by two types of nerve endings, morphologically identified as afferent- and efferent-type terminals. Efferent-type endings are more abundant in the broader anterior portion of the sensory epithelium than in the posterior portion. In the middle portion, tight junctions have been found between axons within the epithelium. In some cases, one of these axons could be traced to an afferent-nerve ending. Tight junctions between neurons have been shown in a number of other systems to represent electrical synapses that transmit impulses with short delay.
Responses of Auditory Units in the Medulla of the Cricket Frog
Authors: Capranica Robert R. , Frishkopf Lawrence S.
Published: September 2005

Responses to acoustic stimuli were recorded with metal microelectrodes from single units in the medullae of DIAL-anesthetized cricket frogs (Acris crepitans and A. gryllus). In every animal, two disjoint regions of frequency sensitivity were found. Units of one type were most sensitive between 250 and 1000 cps. Thresholds for these units at their frequencies of maximum sensitivity ranged from 44 to 81 dB SPL (sound-pressure level). Within this population were units that were also sensitive to vibrational stimuli. Units of the other type were most sensitive between 3500 and 3800 cps. Thresholds for these units ranged from 73 to 99 dB SPL. The frequency sensitivities of the two types of units are well matched to the spectral distribution of energy in the cricket frog's mating call. Although units of both types were found close together in the medulla, we were unable to find any evidence of interaction between them. Within each population, a wide variety of adaptation rates was found, ranging from very slowly adapting units to ON units that responded only to the beginning of a stimulus.
Effect of Middle-Ear Fluid Loading on the Cochlear Microphonic in the Cat
Authors: Linnell Craig O. , Dallos Peter J.
Published: September 2005

Cochlear-microphonic (CM) magnitude and phase measurements were taken with both air- and bone-conducted stimuli, before and after filling the auditory bulla of the cat with mineral oil. The eustachian tube was blocked, and thus long-term steady-state measurements were feasible. Absolute (pressure and force) measures of the stimuli (air and bone) were obtained at the 3-μV CM level from 200 Hz to 10 kHz with both intact and fluid-filled middle ear. Relative phase measures were taken in the frequency range of 0.2–3 kHz with both type of stimulus and in both conditions of the middle ear. The experimental results indicate strong low-frequency enhancement and phase lead owing to fluid-loading with bone-conducted sound, while relatively large losses accompanied by slight phase shifts were seen with air-conducted stimuli. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Brownian Motion in the Cochlear Partition
Authors: Harris G. G.
Published: September 2005

Estimates have been made of the Brownian-pressure fluctuations at the eardrum. These are 15 dB below threshold (MAP) for 3000 cps. It is thus necessary to look into the ear itself to see whether thermal fluctuations limit the sensitivity of the ear. It is assumed that the first stage of amplification of acoustical energy takes place at the hair cell, and that it is the relative shear displacement between the top of the hair cell and the stereocilia that is the relevant parameter. Two estimates of Brownian fluctuation are made. The first assumes a rigid connection between the stereocilia and the tectorial membrane, and thus the source of noise is the fluctuation in amplitude of the basilar-membrane displacement. The second estimate assumes a connection rigid enough to provide the greatest flow of acoustical energy to a hair cell, i.e., proper impedance match, but which is loose enough so that each hair cell has independent thermal displacements. The impedance used in making these estimates were based on the in vivo measured impedances at the eardrum and the anatomy of the middle ear. The first estimate gives a signal to noise ratio of 15 dB at threshold for 3000 cps. The second estimate gives a signal to noise ratio of −37 dB. This calculation shows that it is necessary to assume that the stereocilia are attached to the tectorial membrane and that the hair cell bodies are embedded in the organ of Corti with a high degree of rigidity. There is no direct experimental evidence for the assumption of rigid attachment, although there is some indirect evidence from ultrastructural studies.
Subharmonic Squelch Effect
Authors: Dallos Peter J.
Published: September 2005

It was shown [J. Acoust. Soc. Am. 39, 1253(A) (1966)] that, between the approximate frequency limits of 750 and 3000 Hz, odd fractional subharmonics can be elicited in chinchilla ears. This type of subharmonic vibration was shown to originate in the inner ear owing to mechanical nonlinearities. Undertones were recordable both in cochlear microphonic and in the sound field radiated by the tympanic membrane. If a secondary tone coexists with the fundamental (which generates the subharmonic), then it can interfere with the subharmonic, and under appropriate conditions it can completely disrupt this nonlinear vibration. This disruption of a subharmonic oscillation by the presence of a secondary tone is termed subharmonic squelch effect. It is shown that the squelch effect is strongly dependent upon the frequency separation between the subharmonic and the secondary tone, as well as upon the intensity of the latter. Comparison is made between the squelch effect and the interference phenomenon [E. Wever, C. Bray, and M. Lawrence, J. Acoust. Soc. Am. 12, 268–280 (1940)], and the two are shown to be of completely different nature. [Work supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Acoustic Simulation of Response of Aerospace-Vehicle Skin Structure to Boundary-Layer Turbulence
Authors: White Robert W. , Crocker Malcolm J.
Published: September 2005

Acceleration-response spectra of the Apollo Spacecraft LEM Adaptor (SLA) were computed for predicted boundary-layer turbulence and for the simulated acoustic field employed in the Spacecraft Acoustic Laboratory (SAL) at NASA-MSC. For the turbulence environment, the pressure-space correlation function was assumed to have the form of an exponentially damped cosine, the parameters necessary to define the correlation function being obtained from published experimental data. The SAL acoustic field is generated in a set of 16 parallel and individually driven ducts close-coupled to the structure. For this environment, a plane-wave acoustic field was assumed for each duct. Cross correlations of the pressure fields between ducts are assumed to be zero in one case and unity in a second case. Reduction of acoustic energy along each duct is included. Based on an average response simulation, an equivalent acoustic spectrum is developed. The conical shell of the SLA was idealized to a flat plate, curvature effects being small; and approximately 400 modes of the structure were included. [Work supported by NASA-MSC.]
New United States Gypsum Company's Acoustical Research Facilities Phase I
Authors: Shiner Allen H.
Published: September 2005

The design criteria for and the construction of the United States Gypsum Company's Acoustical Research Field Facilities are described. These facilities are located on 40 acres of rural farmland, average over-all sound-pressure level 55 dB, and presently consist of four separate test structures, each representing a typical form of construction (wood, steel, and reinforced-concrete frame). Similar geometry is incorporated in each structure and consists of a two-story design with two rooms, measuring 18×16×8×12 ft and 20×6×8×12 ft, to each floor. With these room sizes, 9–10 normal modes of vibration are obtained at the 13-oct band centered at 100 Hz, offering a relatively diffuse sound field. The testing operations are performed in a central control building housing the offices, storage, and instrumentation room. Underground cables connect the measuring instrumentation with the noise-generating and microphone pickup equipment in the test buildings. The exterior faces of each structure are designed to accommodate future window and door openings, with the interior partitions both vertical and horizontal demountable, allowing for modification and reconstruction as the research programs dictate.
Low-Frequency Statistics of the Sound Field in a Reverberation Chamber
Authors: Maling George C.
Published: September 2005

The statistics of the sound field produced by pure-tone sources that excite many modes in a reverberation chamber have been studied by Waterhouse [J. Acoust. Soc. Am. 35, 1894(A) (1963)]. In this work, the spatial variations of the mean-squared pressure p2 determined from the appropriate Green's function have been studied statistically. Emphasis has been placed on the low-frequency region (below 300 Hz), where relatively few modes within the chamber are excited. At the upper end of this range, the computed p2 distributions agree well with the high-frequency approximation, although some skewness has been found towards smaller values of p2. The ratio of the acoustic power radiated by the source to the space-averaged value of p2 has also been computed as a function of source position and absorption within the chamber. The results are in good agreement with the high-frequency limit near 300 Hz, but large fluctuations occur at lower frequencies. The applicability of these results to the measurement of the low-frequency power radiated by a pure tone source is discussed.
Analytical Study of Acoustic Feedback in Sound-Reinforcement Systems
Authors: Christoff Jerry P. , Veneklasen Paul S.
Published: September 2005

The physical transduction factors expressing the components and system are quantized to derive a condition for stability. The influence of efficiency of transducers, frequency response, directivity of both microphones and loud-speakers, acoustic baffling, nearby surface reflections, and general reverberation are all included. The total electroacoustic gain capabilities of simple and complex situations can be expressed and compared with performance of complete systems.
Automatic Decay-Rate Meter
Authors: Presti A. J.
Published: September 2005

An automatic meter for measuring the decay rate in a room is described. The meter is based on a proposal by M. R. Schroeder [J. Acoust. Soc. Am. 37, 409–412 (1965)] utilizing the relationship between the integrated impulse response and the average noise response between two points in a reverberent enclosure. The meter takes voltage samples of the integrated impulse response at two freely chosen points in time. These samples are used to calculate automatically the decay rate in decibels/second for the selected time interval. The decay rate is represented by a gated pulse train in which the total number of pulses is equal to the decay rate in decibels/second. The result may be read on a digital counter or a self-contained analog pulse-count meter. Only a single measurement is required to obtain the decay rate corresponding to an average of many noise-decay records.
Ultrasonic Measurement of Elastic and Piezoelectric Coefficients of Lithium Tantalate
Authors: Smith R. T.
Published: September 2005

Monocrystalline, single-domain lithium tantalate, a synthetically grown ferroelectric and piezoelectric material in the crystal class 3m, appears attractive for use as a crystal resonator and transducer material because of its high Q and electromechanical coupling factors. The general theory of plane-elastic-wave propagation in piezoelectric materials has been specialized for particular cases of interest for the crystal class 3m. Since the electromechanical coupling factors are large for lithium tantalate, the effective elastic modulus for certain wave-propagation directions is stiffened appreciably by a piezoelectric contribution. A complete determination, including several crosschecks, of the six independent elastic and four independent piezoelectric coefficients can be obtained from measurements of the velocity of ultrasonic shear and longitudinal waves along the X, Y, and Z crystallographic axes and one rotated Y′ axis. The room-temperature values of the elastic and piezoelectric coefficients were measured by the double-pulse interferometric method of Williams and Lamb [J. Acoust. Soc. Am. 30, 308–313 (1958)] and the results are presented.
Excitation of Flat Panels by Laterally Uncorrelated Fluctuating Pressures
Authors: Boyd W. W.
Published: September 2005

The response of flat rectangular panels excited by specific acoustic fields are mathematically analyzed. The acoustic fields are assumed to be divided into an arbitrary number of “strip” pressure distributions across the width of the panel. Each strip is assumed to be continuous along the length of the panel in the propagation direction. An acoustic pressure distribution such as this permits the study of joint acceptance, squared, coefficient frequency spectra for lateral strip-pressure correlation conditions that vary between 0 and 1. An investigation of the joint acceptance, squared, coefficients for the special case of a simply supported flat panel excited by laterally uncorrelated “strip” pressures was conducted and the results were compared with a previous analysis by Bozich. [“Spatial Correlation in Structural-Acoustic Coupling,” J. Acoust. Soc. Am. 36, 52–58 (1964).] Combining Bozich's results with the present analysis yielded an upper and lower bound on the joint acceptance, squared, coefficient frequency spectra. As would be expected, the ratio of the joint acceptance, squared, coefficients for lateral strip pressure correlation conditions of 0 and 1, was highly dependent on the lateral half-wave number and pressure strip width.