bluuebunny/crossref_metadata_2025 huggingface dataset:
Loudness Changes in a Forward-Masking Stimulus Paradigm
Authors: Small Arnold M. , Canahl Julius A.
Published: September 2005

This research represented an attempt to clarify the relations between loudness changes and threshold shifts following the cessation of an auditory stimulus. A 400-msec, 1000-Hz sinusoid served as the “fatiguer” and, following a specified recovery time, a 50-msec, 1000-Hz test stimulus was presented. The test stimulus was always delivered to the ear stimulated by the 400-msec signal, but in the case of loudness judgments, simultaneous with the test stimulus, a comparison stimulus was presented to the opposite ear. The entire stimulus sequence was recycled every 4 sec. Thresholds were obtained by varying the level of the test stimulus while loudness was determined by adjusting the level of the comparison stimulus so that loudness in the two ears was equal. In general, threshold shifts were much greater than loudness shifts when both were measured in decibels. Loudness recovery proceeded more slowly than did the recovery of threshold. The sound pressure of the 400-msec stimulus produced marked changes in the amount of threshold shift, but had little effect upon loudness.
Backward Masking of Short Tones by Narrow- and Wide-Band Noise Bursts
Authors: Elliott Lois L.
Published: September 2005

Onset of a 10-msec tone (one of 11 frequencies from 250 to 4000 cps) preceded onset of a 100-msec, 70-dB-SPL noise burst (wide band or 200 cps centered at 1270 cps) by 100, 50, 35, 20, 15, and 10 msec. Masked tonal thresholds, obtained by a method of adjustment, were evaluated relative to tone thresholds in quiet and in continuous noise of equal spectra. At the longest time interval (Δt=−100 msec), both noises produced equal backward masking at all frequencies. For the wide-band masker, “backward overshoot,” a corollary to Zwicker's simultaneous phenomenon and defined as the pure-tone backward-masked threshold minus the threshold for continuous masking, was greatest at higher frequencies and occurred for intervals as long as Δt=−20 msec. The narrow-band noise produced masking for frequencies within the band at Δt=−50 msec and considerable threshold shift for these same frequencies at briefer time intervals. Backward overshoot was pronounced for frequencies above and below the narrow band, extending back to intervals of Δt=−50 msec, but was small for within-band frequencies (compared to the relatively great threshold elevation for the continuous masking). Results are interpreted in terms of temporal development of the critical band. [Supported by the National Institute of Nervous Diseases and Blindness, National Institutes of Health, Public Health Service, U. S. Department of Health, Education, and Welfare.]
Binaural Unmasking of Periodic Pulses: Effects of Interaural Time and Spectral Content
Authors: Flanagan J. L. , Watson B. J.
Published: September 2005

Binaural-masked thresholds were measured for periodic 100-μsec rectangular pulses of period T. Signal parameters were pulse rate (10, 50, 100, 250, 1000 pps), interaural time difference (0–5 msec), and spectral content (as determined by high-pass and low-pass filtering at 0, 300, 600, 1200, and 2400 cps). Broad-band, interaurally in-phase masking noise at 60 dB SL was used throughout. The signals were transduced by headphones, and the thresholds were determined by a modified Békésy technique. For all pulse rates, maximum release from masking obtains for an interaural time of about 1.5 msec or T/2, whichever is smaller. The greatest unmasking occurs for a pulse rate of 250 pps and is less at higher and lower rates. At the lowest pulse rate, severe high-pass filtering of the signal abolishes the masking-level difference, and severe low-pass filtering enhances it. The results suggest that the greatest release from masking attaches to interaurally out-of-phase motion in the vicinity of the 300-cps place on the basilar membrane.
Acoustic Properties of Solids by the Resonant-Sphere Technique
Authors: Fraser D. B.
Published: September 2005

The elastic and anelastic properties of solids may be measured by utilizing a resonant sphere. A small sample, of the order of a few millimeters in diameter, is held in place without bonding on a shear-mode transducer. The transducer is driven by a burst of rf voltage at one of the resonant frequencies of the sphere. This sets the sphere in motion and the free decay of the vibrations of the sphere is observed by switching the same transducer to a receiver. From a comparison of the frequencies of a number of excited modes with those computed for an ideal isotropic sphere, the elastic constants of the solid may be calculated. The free decay of the vibrations is related to the internal friction Q−1 of the sphere. Both elastic and anelastic properties have been studied from liquid-helium temperatures to an upper limit set by either the sample or the transducer. The computed mode spectrum is based on the assumption of an isotropic medium, and, therefore, the technique works well with materials such as glasses and fine-grained polycrystalline materials. Some limited studies of single-crystal specimens have also been successful.
Use of Inertial-Type Variable-Reluctance Transducers in Underwater Telephony
Authors: Sebesta G. J. , Mellen A. J. , Carlisle R. W.
Published: September 2005

Variable-reluctance transducers, as originally designed by E. H. Greibach and others for hearing aids, are peculiarly adaptable to swimmer's telephone headsets. They are specified in several U. S. Navy equipments as earpieces and have been used as both microphone and reproducers in equipments manufactured for Scuba divers. A new combination microphone-reproducer assembly D 519 has recently been developed by the author's company. Some details are presented, based upon a paper soon to be published in the Journal of the Audio Engineering Society.
Acoustic Interaction Effects in Arrays of Small Spheres
Authors: Weston D. E.
Published: September 2005

Multiple acoustic scattering in line and plane arrays of spheres can sometimes reduce the acoustic pressure on the sphere surfaces to well below the free-field value, especially for gas-filled spheres. However, at spacings near half a wavelength, there can be an enhancement. The resonance phenomenon is much sharper for a single spherical bubble than for a cylindrical bubble, a cylindrical vortex, a line of spheres, or a plane array of spheres. For finite arrays, the end or edge effects can be quantitatively described by additional geometrically spreading waves, but only when the above pressure reductions are small and only close to the edge. With high scattering, a modified edge wave must be used. [Hudson Laboratories of Columbia University Informal Documentation No. 79. Work supported by the U. S. Office of Naval Research.]
Computation of Farfield Radiation Patterns by Use of a General Integral Solution to the Time-Dependent Scalar Wave Equation
Authors: Ferris Horace G.
Published: September 2005

The computation of farfield radiation patterns by use of a general integral solution to the time-dependent scalar wave equation is considered. The use of this theorem in this connection appears to offer advantages that may have been overlooked. In particular, the general theorem is capable of interpretation in terms of an analogous network of linear systems whose inputs are the nearfield measured pressures and whose summed output is the desired farfield pressure. Moreover. the general theorem is valid for signals that are general functions of the time, including noise signals, as well as for signals having only a single frequency component. It may accordingly be applied to a much wider class of signals than the Helmholtz formula or the Green's formula, which have been used as the basis for most farfield computations in the past. The network interpretation of the general theorem is discussed in some detail and the forms of the network response function for both a plane and a spheroidal surface of measurement are given.
Certain Acoustic Correlates of Vocal Style
Authors: Irwin James Wesley , Perkins William H. , Yanagihara Naoaki
Published: September 2005

This paper discusses studies in progress to discover the perceptually relevant acoustic variables of three styles of atypical phonation—fry, hypertense, and hypotense—as compared to normal, hygienic phonation. For 12 steady-state vowels, waveforms for fry and hypertense phonation tend to show more polar symmetry about the time base, as well as a shorter rise time for the onset of the cycle, than do waveforms for normal and hypotense phonation. Steady-state vowels /i,ɪ,ɑ,o,ᴜ,u/ and sentences containing these vowels and diphthongs /eɪ,ɑɪ,oɪ/ have been filtered and presented to subjects for comparative style evaluation. As more high-frequency energy is rejected, fry and hypertense tend to be evaluated as normal or hypotense. As more low-frequency energy is rejected, the normal tends to be evaluated as hypertense. Fry and hypertense styles are more resistant to low-pass filtering for vowels with lower second formants. Resonances, rather than fundamental frequency, appear to be the overriding cue for these styles of phonation. [Study supported by the National Institute of Nervous Diseases and Blindness, National Institutes of Health, Public Health Service, [U. S. Department of Health, Education, and Welfare.]
Acoustic Characteristics of Space-Simulation Chambers at Low Pressures
Authors: Weichbrodt Bjorn
Published: September 2005

Three test chambers with volumes between 175 and 32 000 ft3 have been acoustically calibrated for air pressures from 760 down to 25 Torr. Such calibration presents special problems, since the normally used standard noise sources have an acoustic power output with a pressure dependence that is difficult to calculate. Therefore a special sound source was developed, using a stiff and heavy piston as radiator. This sound source, with known pressure characteristics, was used during all calibrations. Reverberation time was also measured in the chambers for all pressures. In the paper, results from the two independent calibration methods are compared to each other. The measured acoustic characteristics are also compared to theories for air damping, including effects from the humidity-dependent molecular damping. It is concluded that the chamber damping increases with decreasing chamber pressure for all tested frequencies (100–40 000 cps). At high frequencies, the measured chamber damping agrees well with the theoretically predicted air damping, thus showing that the wall damping is negligible. A general calibration curve—valid for various frequencies, air pressures, and chamber volumes—is presented.
Control-Display Time-Lag Effects with Tracking to Auditory and Visual Displays
Authors: Hodgson David A.
Published: September 2005

This study was conducted to determine the effects of 0-, 1-, and 2-sec control-display time lags using six conditions of auditory and visual displays. A two-axis sidearm control was employed for determination of performance on each control axis. The same compensatory tracking task was used for all test conditions. For the fore-aft axis, the three displays used were binaural-pitch matching; displacement of the horizontal needle in an aircraft two-axis situation indicator; and both displays simultaneously. On the lateral control axis, the displays were monotically pulsed signals; displacement of the vertical needle: and both combined. Data analysis showed performance to deteriorate with increased time lags. Greater tracking accuracy was evident in the fore-aft control axis. Training effects were established and these, in turn, interacted with the display mode effect. In all cases, the combined auditory and visual displays resulted in higher degrees of tracking proficiency.
Relation between Hearing Level and TTS from Impulse-Noise Exposure
Authors: Hodge David C. , McCommons R. Bruce
Published: September 2005

It has been suggested [W. A. Rosenblith et el., ASA Z24-X-2 Subcommittee Rept., (1954)] that persons already having hearing losses will demonstrate less TTS from a given noise exposure than persons not having hearing losses. Although we often lack definitive information about the past history of our subjects, and thus cannot really call large hearing levels losses, we hypothesized that there would be a negative correlation between preexposure hearing level and TTS. As a test of this hypothesis, 40 U. S. Army enlisted men were exposed to 50 impulses with a peak SPL of 155 dB. The hearing levels of 28 of the subjects did not exceed 15 dB re ASA zero; 12 subjects had hearing levels exceeding 15 dB. Pre- and post-exposure hearing levels were measured at 0.5, 1, 2, 3, 4, and 6 kcps with a Békésy-type audiometer, and the TTS's were converted to TTS2 for ease of comparison. All six of the correlation coefficients between hearing level and TTS2 were negative (the predicted direction), but only those for 0.5, 1, and 2 kcps were statistically significant.
Hybrid Encoding Scheme for Vocoders
Authors: Cassel Lawrence E. , Phyfe D. L.
Published: September 2005

This paper describes a method of encoding the conventional channel-vocoder parameters using a combined PCM-delta modulation scheme. The scheme takes advantage of the channel-to-channel correlation of the amplitude information without permitting the vulnerability to bit errors that one usually associates with delta modulation. This approach to efficient coding has provided improved intelligibility scores at relatively low transmission rates. The basic concept is explained and evaluation results are presented.
Subjective Evaluation of Formant-Coded Vowel Spectra Regenerated with the Aid of a Channel-Vocoder Synthesizer
Authors: Paulus E. , Rothauser E. H.
Published: September 2005

A channel-vocoder synthesizer controlled by a digital computer has been utilized to regenerate formant-coded speech spectra. Paired comparison tests similar to those reported by J. L. Flanagan [“Difference Limen for Vowel Formant Frequency and Amplitude,” J. Acoust. Soc. Am. 27, 613–617 (1955); J. Speech Hearing Disorders 22, 205–212 (1957)] were conducted in order to measure difference limens for amplitude and frequency variations of formants. It was found that slight variations of the formant data may result in a variety of subjectively discriminable spectra, even if the variations of the formant data are considerably smaller than the difference limens reported from conventional formant synthesizers. This effect can be explained as a result of the quantization in amplitude and frequency of the spectrum of typical channel-vocoder output signals. Test results and estimates of the difference limens in this context are given.
Investigation of the Time Autocorrelation of Sonic Pulses Propagated in a Medium of Random Temperature Microstructure
Authors: Campanella S. J.
Published: September 2005

Measurements were made of the random variation in the amplitude of sonic pulses at frequencies of 480 and 1420 kc/sec in a water medium perturbed in refractive index by thermally induced temperature microstructure. The received pulse-amplitude variation was analyzed to determine time autocorrelation and variance over the transmitter to receiver separations ranging from 1633 to 7655 in. It was found that the time autocorrelation of sonic pulse amplitude was the same as that observed for the temperature microstructure, and that the variance varied as the square of separation distance. The above findings are compared with the theoretical findings of Mintzer and Bergmann. The observed equality in temperature microstructure and pulse amplitude autocorrelation indeed is predicted by Mintzer. However, neither Mintzer's nor Bergmann's theoretical developments predict the dependence of variance on the square of range. The observed departure of variance from the theoretical predictions is explained in terms of the nature of the distribution function of phase angle of the scattered arrivals.
Comparative Study of Deep-Ocean Ambient Noise
Authors: King Louis A.
Published: September 2005

Ambient-noise-spectrum measurements for a period in excess of one year were made south of Bermuda using omnidirectional hydrophones fixed at various depths from 3000 to 15 000 ft. The bulk of the data was processed through logit filters from 100 to 1500 cps. It was found that measurable spectrum-level differences occurred between the shallow and deep receivers, particularly at frequencies above 800 cps. It is reasoned that these differences arise primarily as a result of the presence of two noise spectra: one due to locally generated noise that correlates very well with local surface conditions, the other due to distributed noise generated at a distance that influences the receivers via multiple reflections and/or refraction paths. The resultant spectrum in the vicinity of any receiver is then a consequence of the manner in which the respective energies are propagated to it. These studies show that the noise spectrum in the region of a hydrophone depends upon the depth of the hydrophone, a parameter that determines the weight assigned to each of the two identified noise spectra.
Acoustic Turbulent-Flow Water Tunnel
Authors: Carey George F. , Chlupsa John E. , Schloemer Howard H.
Published: September 2005

This unique closed-loop tunnel has a clear plastic-pipe test section (312 in. i.d.), through which water is pumped at centerline velocities ranging from 8.5 to 48 kt. Noise-reduction techniques have adequately prevented pump and piping noises from entering the test section either through structural or fluid paths. Measurements at centerline velocities between 8.5 and 44 kt with flush-mounted hydrophones at several longitudinal spacings show that the ratio of convection velocity to centerline velocity ranges from 0.89 to 0.63. The increase of this ratio with transducer spacing and the decrease with frequency agree with published measurements by Bull and Corcos. The curve of maximum space-time correlation in frequency bands versus transducer spacing in wavelengths is in excellent agreement with those reported by Bakewell et al. and Willmarth. Frequency spectra measured from 100 to 12 500 H coincided when nondimensionalized with respect to centerline velocity and boundary-layer thickness. When corrected for hydrophone size, the spectral curve was similar to those reported for turbulent airpipe flow and rising and falling bodies in water.
Air-Flow Measurement during the Production of Speech Sounds
Authors: Klatt Dennis H. , Stevens Kenneth N. , Mead Jere
Published: September 2005

The volume velocity of the airstream during the production of a number of vowels and consonants has been measured in a limited set of phonetic environments. Flow is determined indirectly by measuring the pressure drop across a face mask containing a low-resistance, wire-mesh-covered port. Accuracy and limitations of this technique are discussed. A set of 21 English consonants has been rank-ordered according to air volume expended during production by three speakers. The air volume utilized is greatest for voiceless consonants and least for voiced consonants and vowels, but systematic effects of place and manner of production are also observed. Detailed waveforms are shown and some effects of context and stress are discussed. Two test sentences were spoken at several speech power levels; results indicate wide variations in volume velocity among speakers and little correlation between speech power and long-term-average volume velocity.
Decay Patterns of Harpsichord Strings
Authors: Pyle Robert W. , Schultz Theodore J.
Published: September 2005

The decay of single-plucked harpsichord strings has been observed experimentally to be characterized in general by a fast initial decay relative to the ultimate decay rate. Although the higher modes of the string generally decay at faster rates than the lower, this does not account for the observed behavior. Rather, it appears that the impedance presented to the string by the bridge varies somewhat with the polarization of the string vibration, giving rise to at least two “fundamental” modes, two “second harmonics,” etc. The “fundamentals” differ very slightly in frequency and often substantially in decay rate. Observed decay patterns may be qualitatively explained by beats between nearly isochronous modes. This effect also appears to account for certain features of harpsichord tone quality. [Work sponsored in part by The Cannon Guild, Cambridge, Mass.]
Solution of Radiation and Scattering Problems by Integral Equations
Authors: Chertock George
Published: September 2005

Several recent methods for the calculation of the radiation field of an arbitrary vibrating surface, or the field scattered by a rigid obstacle are shown to reduce to solutions of integral equations, where the kernel function and the surface of integration are the same in all methods. The kernel function is usually replaced by a matrix of terms that are defined at only a finite number of stations, and thus the integral equation is approximated by a set of simultaneous algebraic equations. Hence, the comparative accuracy of the different methods depends mostly on the procedures used in selecting the stations and evaluating the matrix terms. A new method is described in which the surface stations are selected with arbitrary spacing, and the surface element about each point is approximated by a spherical cap whose curvature, inclination, and area match those of the local surface element. The method is illustrated by the problem of a vibrating piston on a sphere, and compared with solutions based on triangular and ringshaped surface elements.
Theory of Reflection from an Infinite Array of Compliant Tubes in an Aqueous Medium
Authors: Lubell Alan H.
Published: September 2005

This paper attempts to explain the observed phenomenon of acoustic reflection from an array of “soft” tubes in an aqueous medium. [W. J. Toulis, J. Acoust. Soc. Am. 29, 773(A), 1021–1026, 1027–1033 (1957)] in terms of fundamental array and diffraction theory. Both diffraction and radiation effects are investigated for infinitely long cylindrical tubes of circular cross section as a function of s/r and ks. For ks (s/r)−2<1, zero and first-order diffraction terms together with the corresponding radiation terms suffice. Furthermore, for kr<0.3, the zero-order radiation term is dominant. Hence, a simple solution for the surface velocity of the typical tube of an infinite array can be found by applying Newton's second and third laws to the tube surface. The infinite series thus obtained bears a strong resemblance to the Fresnel integral. Machine computation is used in a novel way to estimate the sum of this series.
Ultrasonic-Velocity and Absorption Measurements in Liquids at High Pressures
Authors: Holton Gerald
Published: September 2005

A review of recent work in our laboratory, including techniques and experimental results on water, alcohols, and acetates to about 10 000 atm pressure. The interpretation of these data in terms of molecular relaxation processes is discussed.
A CW Phase System for Measurement of Small Changes of Ultrasonic Velocity in Liquids and Gases
Authors: Noble Frank W.
Published: September 2005

A continuous radio-frequency signal is applied to a sending transducer located at one end of a pipe containing the sample fluid. The frequency and the pipe length are chosen to result in an attenuation of at least 60% so that reflected waves are reduced to negligible proportions. The phase angle between the voltage driving the sender and the voltage produced by a receiver transducer located at the other end of the pipe is measured by means of a phasemeter having a full-scale sensitivity of 1.8°. A system presently in use operates at 20 MHz, with a pathlength of 1 in. in water. The resolution at twice noise level is 0.4-cm/sec change in sound velocity. As a result of the “foldover” characteristic of the phasemeter, it is possible to measure phase changes of thousands of degrees without ambiguity and without sacrifice in resolution.
Action of Energy-rich Phosphate Compounds on Cochlear Potentials
Authors: Tanaka Yasuo , Brown Peter G.
Published: September 2005

Endocochlear potential (EP), cochlear microphonics (CM), and action potentials N1 were recorded from the basal turn of the guinea pig's cochlea to which various energy-rich phosphate (∼P) compounds and metabolic inhibitors were applied by microinjection and ionophoretic techniques. The administration of some ∼P compounds, such as adenosine triphosphate, into the scala media produced a prompt depression, followed by recovery, and then a gradual decrease in the cochlear potentials. The EP dropped to 30.9% to 60.5% of the original level within 2 min after injection of adenosine triphosphate and returned to 75.5% to 100%. Other substances, similar in structure or in charge to ∼P compounds, were tested for their effects. In another group of experiments, anoxia brought about the usual reduction in cochlear potentials during and after the application of ∼P compounds. The metabolic inhibitors that block adenosine triphosphate production and utilization acted as a depressant on these potentials. A possible rôle of metabolic energy in maintaining oxygen-sensitive cochlear potentials is discussed, and the prompt depression of EP induced by ∼P compounds is analyzed.
Long-Term Intracochlear Electrodes in Cats: Electrophysiological Observations
Authors: Simmons F. Blair
Published: September 2005

Multiple stainless-steel electrodes permanently placed at different distances along the scala tympani and the modiolus of cats reflect CM and N responses that (1) confirm the Békésy-Davis-Fernández-Tasaki concepts of “localized” CM generators isolated electrically from distant areas of the cochlea (even during monopolar-type measurements), wherein the high-frequency-generated microphonic decreases both in sensitivity and amplitude at electrodes placed more apically in the cochlea; (2) confirm that the N1–2 complex is mainly (but not invariably) a volume-conduced electrical potential from a “distant” source; (3) demonstrate that the cochlea will indeed tolerate such electrode placements for periods in excess of eight months. Preliminary data on CM input-output functions, phase shifts, click-stimulus time delays, selective-frequency sound fatigue, neural responses, and behavioral responses are presented, together with histological observations. [Work supported by the National Institute of Neurological Diseases and Blindness, National Institutes of Health, O. S. Department of Health, Education, and Welfare.]
Numerical Methods for General Acoustic Radiation Problems: A Survey
Authors: Schenck Harry A.
Published: September 2005

Rapid growth in the capability and availability of high-speed electronic computers has stimulated interest in methods for the analysis of acoustic radiation from bodies of arbitrary shape. Either a differential or integral formulation of these acoustic radiation problems provides a basis for the numerical methods discussed in this survey. Various discrete approximations can be applied to either formulation to produce a system of linear algebraic equations. Because this system of equations is usually very large, it is necessary to make use of the special properties of the system in order to obtain a solution economically. Recently-developed techniques for constructing and solving these equations in typical problems are reviewed. It is also shown that these numerical methods can be extended to mixed boundary-value problems with little additional complexity.
Tolerance Analysis Study
Authors: Vande Bossche R. Y. , Akervold O. L.
Published: September 2005

A tolerance analysis study has recently been completed on a complicated planar array. The array consisted of 48 ceramic elements that were tuned, voltage-shaded, and controlled by a multitransformer network. The main objective of the study was to arrive at the tolerance limits of the element parameters and transformer parameters that would have to be maintained during fabrication in order to control the end performance of the transducer. Successful beam formation of this array is dependent upon three main parameter groups. These are radiation-loading, individual-element parameters, and transformer-network parameters. Based upon practical limitations and previous experience with arrays of this design, simplifying assumptions were made in regard to radiation-loading. This left the beam-formation control dependent upon element amplitude, phase, and physical placement. The errors that could be tolerated in these three parameters were computed. The maximum allowed variations in element and transformer-network parameters were then directly related to the allowable errors in amplitude and phase. This paper shows the methods used, the assumptions made, and the results achieved.
Measurement of Very Small Changes in the Velocity of Sound in Solids
Authors: McSkimin H. J. , Andreatch P.
Published: September 2005

Apparatus for measuring very small changes in delay time or velocity of ultrasonic waves in solids is described. The long-term stability of the electronic system and a resolution of approximately one part in ten million for high-Q materials extend the usefulness of the equipment. By way of illustration, some results for delay-time variations for ultrasonic waves in single crystals under small uniaxial stress are presented. Also, the determination of shear mechanical properties of low-viscosity liquids by the shear-reflectance method is described.
Effects of Suspended Panels on Reverberation
Authors: Knudsen V. O.
Published: September 2005

After reviewing the work of American acousticians during the 1930's in respect of the application of normal modes to reverberation, and the second work at UCLA on the diffraction of sound by an array of rectangular reflective panels, this paper gives a preliminary report on an investigation, now in progress, of the effects of suspended panels on the decay of sound in a rectangular reverberation room (19×30×24 ft high), with and without the floor covered with absorptive material. The array consists of 96 panels of plywood 1×3 ft × 12 in. thick located in a horizontal plane midway between the floor and ceiling. The panels appear to be completely nonabsorptive at frequencies below about 250 cps. Their absorption increases progressively at higher frequencies. At 4000 cps, they add 23 sabins to the reverberation room, which would correspond to an absorption coefficient of 0.08, if this coefficient is calculated in the usual manner by dividing the added number of sabins by the area of the panels. The absorption coefficient for the array would be 0.04 at 4000 cps, and it diminishes progressively at lower frequencies. As is well known, the covering of the floor with absorptive material results in nonlinear decay rates unless the sound field is diffuse. In the experiments conducted to date, there is no artificial diffusion in the room, except that added by the panels under investigation. The decay curves are characterized by an initial high rate of decay followed by progressively lower rates of decay. The panel array introduces other complications in the decay, and decay rates depend greatly on the positions of the sound source and microphone. We have not yet attempted to explain the findings, but the methods of wave acoustics and normal modes should be able to account for most of the experimental findings. The results to date, however, have a bearing on how suspended panels influence the decay of sound in auditoriums that lack adequate diffusion and have highly reflective walls and ceilings.
Some Computations Relevant to the Webster-Jeffress Model for Binaural Signal Detection
Authors: Robinson Donald E.
Published: September 2005

In 1956, Jeffress, Blodgett, Sandel, and Wood published an extension and elaboration of Webster's 1951 hypothesis that the important stimulus for signal detection under dichotic conditions is the interaural phase (or time) shift that occurs when the signal is added to the masker. This paper is a summary of some computations based on that hypothesis. A few of the more important interaural conditions are investigated, using a computer to obtain the probability distributions of the interaural phase shifts. In general, the Webster-Jeffress model is found to be in agreement with the available data. [Research partially supported by the U. S. Air Force Office of Scientific Research.]
Tests of Basal Cochlear Contribution to Temporal Processing
Authors: Tobias Jerry V. , Shank Kennon H.
Published: September 2005

The question is sometimes raised as to whether the temporal aspects of acoustic signals are analyzed solely at the basal end of the organ of Corti. Three series of experiments were performed on the differential masking of stimuli known to be analyzed by the auditory system on the basis of temporal characteristics. First, a masking-level difference (MLD) experiment was performed. Binaural masked thresholds (under S0 and Sπ conditions) of a 500-Hz tone were measured and compared to similar thresholds taken while a loud high-pass noise, cut off at 800, 1000, 1200, 1600, 2400, or 4800 Hz, was simultaneously presented. Any basal cochlear contribution to the MLD was predicted to be at least partially disrupted by the extra masker (since it would be serving to keep the high-frequency segments of the basilar membrane busy). Similarly, perception of the Wood effect (a monaural phase effect) and of binaural beats was tested with and without such high-pass bands of noise. Except for those cutoff frequencies that allowed noise energy to interfere directly with the signal, the influence of the extra masking was negligible. Because a fatigued ear might behave differently, the experiments were repeated following intense high-frequency exposures (and, in one case, with a subject having a precipitous high-frequency hearing loss). The results were similar. Implications of these findings are discussed. [Investigation supported in part by the National Institute of Neurological Diseases and Blindness, National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Transmission of Acoustic Data for Analog Beam Forming
Authors: Forster Carle A.
Published: September 2005

The transmission of analog data, from individual elements of an acoustic array for beam-forming, places stringent requirements on the transmission system. A 40-channel telemetry system has been developed, utilizing synchronous sideband frequency-division multiplexing techniques. The transmitted carrier frequencies are synchronously generated with a PRN generator driven by a master clock. The master-clock frequency and two unused carrier frequencies are transmitted with the data channels. The receiver carrier frequencies are generated with another PRN generator, driven by a signal at the recovered master-clock frequency, and are phase-locked with the two recovered carriers. This technique minimizes the required transmission bandwidth, and affords a dynamic range greater than 40 dB. Measurement and performance data indicate that the transmission system does not affect the generation of beam patterns. [This work was performed under contract with the U. S. Department of the Navy, Bureau of Naval Weapons.]
Analysis of Side-Looking Sonar Performance in the Near Field under Dynamic Conditions
Authors: Collins A. D. , Kness E. F.
Published: September 2005

A detailed analysis has been performed of a side-looking sonar working in the near field where the platform is permitted to move through three rotation angles and three displacement vectors during the transit time of each sonar pulse. The polar diagram of the side-looking sonar was calculated in the near field on a digital computer for various combinations of the aforementioned dynamics. Detection and target recognition criteria were established using the signal characteristics of the sonar transducer. The detection operation is performed on the shadow function displayed to the operator on a film strip. The complicated nature of the transducer polar diagram was combined with signal-detection theory to obtain a family of detection- and recognition-probability curves as a function of ocean-bottom geometry and the dynamic behavior of the sonar platform. The analysis included consideration of bottom-reverberation characteristics, sea attenuation, thermal-noise target characteristic, and sonar performance parameters.
Investigation of Linear End-Fire Arrays
Authors: Flad F. R. , Gordon Robert S.
Published: September 2005

This paper presents the results of an investigation aimed at obtaining symmetrical beams of high directivity from linear end-fire arrays. A principal deterrent to the use of such arrays is the marked beam distortion and loss of symmetry as steering angles of 60° and greater are reached (90° being the full end-fire position), for free-line or baffle-mounted arrays. An array configuration is described that produces a symmetrical beam at the true end-fire position. Methods of increasing the directivity of these arrays were also examined. In particular, an analysis of the Schelkunoff polynomial synthesis was made, and experiments with the Hansen-Woodyard technique were performed with favorable results. Additional results of the investigation showed that of all the constraints on achieving end-fire radiation, edge diffraction is the most significant for linear arrays. Experimental results also established some general transducer and array-design criteria to aid in end-fire-array applications.
Experimental Investigation of Finite-Amplitude Standing Waves in Air-Filled Tubes
Authors: Sanders J. V. , Coppens A. B.
Published: September 2005

The air in a rigid-walled tube of fixed length was excited into vibration by means of a piston driven by an electrodynamic shaker. At the fundamental frequency (100 Hz), or one of the overtones of the tube, the pressure at the fixed end was analyzed to determine the harmonic distortion. From these data, the attenuation coefficient for each of the resonance frequencies up to that of the fifth overtone of the tube was calculated using an extension of the Keck-Beyer theory. These results compare favorably with attenuation coefficients determined directly from the infinitesimal-amplitude pressure and particle acceleration measured at the piston. Photographs of the distorted waveform lend additional weight to the validity of this perturbation analysis for standing waves. [Work supported in part by the U. S. Office of Naval Research and the Bureau of Ships.]
Experiments on the Sondhauss Thermoacoustical Phenomenon
Authors: Feldman Karl Thomas , Hirsch H. , Carier R. L.
Published: September 2005

When heat is added steadily to the gas in the closed end of a pipe having only one closed end, a large-amplitude pressure oscillation occurs. Such heat-generated sounds are known as Sondhauss thermoacoustical oscillations, after the German physicist, C. Sondhauss (1850). A physical analysis of the heat-exchange mechanism driving the Sondhauss oscillator indicates that it operates like a heat engine having a specified thermodynamic-engine cycle. Experimental measurements of sound-pressure level and velocity of the heat-driven acoustic wave have been made to define the thermodynamic cycle. Other measurements of the various geometric and energy flow parameters of the system have been compiled. A theoretical model of the Sondhauss oscillator has been derived and solved. Theoretical solutions predict the sound-pressure levels generated for specified heat inputs with less than 4% deviation from the experimental results.
Parametric Application of Ultrasonic Waves
Authors: Cook Bill D.
Published: September 2005

The nonlinear wave equation describing the propagation of ultrasonic waves in liquids predicts parametric amplification, i.e., the amplification of lower-frequency waves by intense higher-frequency waves. This amplification is limited by the interaction of higher-order sum and difference frequencies. In this paper, the parametric amplification is placed in the mathematical formulation used for the investigation of plane waves of finite amplitude. The results show for the dissipationless situation that a subharmonic of half the fundamental frequency can be amplified approximately 6 dB. In addition, several of the higher-order sum and difference frequencies become comparable in amplitude to that of the subharmonic. [This work is supported by the U. S. Office of Naval Research.]
Stable and Transient Acoustical Cavitation in Water and in Liquid Helium
Authors: Jarman Peter D.
Published: September 2005

The occurrence of stable and transient acoustical cavitation in liquid helium has been reported recently by Finch et al. and by Jarman and Taylor. It appears to be similar to acoustical cavitation in unfiltered gassy water. Solutions to the non-dissipative incompressible differential equations for the motion of gaseous and/or vaporous cavities in water and liquid helium have been obtained on an analog computer, and these will be related to experimental data. [Work supported by a research grant from The University of Western Australia and by the U. S. Office of Naval Research.]
Review of Mechanical Immittance and Transmission Matrix Concepts
Authors: Rubin S.
Published: September 2005

The concept of immittance (impedance or admittance) and transmission matrices for application to the vibration of mechanical systems is reviewed. The experimental measurement of the elements of the matrices is explored from a conceptual standpoint. Included is a discussion of the correction of the data taken under other than desired condition of constraint. Some general applications of the matrices are described.
Some Measurements of the Effect of Geometric Scale on Structural Impedance and Radiated Sound
Authors: Schloss Fred , Reader Wayne T.
Published: September 2005

Two wooden structures resembling flower boxes and geometrically scaled in the ratio of four to one were driven in air and water with sinusoidal and random excitation, and transfer impedance and radiated sound measurements were made. It was found that (1) the resonant frequencies of the lower modes were in the ratio of one to four within a few percent, and the frequencies at which the impedance is a maximum and the resonant frequencies at the higher modes do not scale in any obvious pattern; (2) impedance measurements at symmetrical points of the same structure are identical only at the lower frequencies; (3) reciprocal transfer impedance measurements are identical at all frequencies; (4) the impedance magnitude scaled in the ratio of 16 to one only at low frequencies, but the impedance averaged over small frequency ranges and the impedance using random excitation in 13-oct bands scaled at all frequencies.
Structural and Electromechanical Interaction in the Multiple Exciter Technique for Random Vibration Testing
Authors: Trubert Marc R.
Published: September 2005

Imposing difficulties arise in the proper generation of the simultaneous driving random forces in the multiple-exciter vibration-testing technique since, due to structural feedback, each shaker is strongly influenced by any of the others. A general analysis has been worked for a ρ degree-of-freedom structure excited by N electrodynamic exciters (ρ⩾N) in order to determine the armature voltages e1, e2, …, eN needed to produce specified accelerations ü1, ü2, …, üN of the structure. The analysis includes the mechanical and electrical properties of the exciters and leads to a system of differential equations representing a multiple input/output interacting electromechanical system. The transfer matrix H(ω) that transforms the multiple known base accelerations ü1, ü2, …, üN to the multiple desired exciter voltages e1, e2, …, eN is determined. Then the crosspower spectral densities of the voltages is deduced from the crosspower spectral densities of the accelerations. Finally, as an illustration, the analysis is applied to a uniform flexible beam, tied to the armatures of two exciters, but otherwise free. Correlated and uncorrelated random base accelerations ü1 and ü2 are considered. In both cases, the crosspower spectral densities of the voltages e1 and e2 are determined. These crosspower spectral densities represent the fundamental requirement for the multiple equalization and control system. [Work sponsored by the National Aeronautics and Space Administration.]
Correlation of the Dynamic Response of a Complex Plastic Model with its Prototype
Authors: Bannister R. L.
Published: September 2005

Experimental vibration characteristics of two-turbine generator sets on a common bedplate were studied, utilizing a plastic model. Acceleration readings were recorded at many locations on the model and prototype while driving the system simultaneously with known sinusoidal forces. Symmetrical and antisymmetrical modes were excited by using two electrodynamic shakers at symmetrical locations. A single sinusoidal force may excite a majority of all the modes, but the response could be distorted and misleading. Instrumentation used to collect the data terms of g's/pound is described. Comparing the response of the model and prototype, a detailed mode-shape correlation was established for the first 9 major flexing modes. The results show that the natural frequencies and mode shapes of heavy machinery can be determined quite accurately from scaled plastic models. [Work supported by the Bureau of Ships, U. S. Navy.]
Temporal Effects in Speech Analysis and Synthesis
Authors: Scott Robert J.
Published: September 2005

Experiments in adjusting the time dimension of natural speech have been carried out with a hybrid computing facility. The distribution of spectral energy for successive time samples was derived by scanning the output of a channel-vocoder analyzer, and the relationship between the analytic and synthetic sampling rate was modified in various ways. Time normalization of utterances was done by both linear and nonlinear methods; the nonlinear, arc-length method may be better for automatic speech recognition. The perceptual effects of time adjustment were investigated in an intelligibility test. A dichotic method for time compression of speech was investigated in which odd-numbered time samples were presented to one ear and even-numbered samples to the other ear. Potential applications for time-adjusted speech and possibilities for further research are suggested.
Analysis of Speech in a Helium-Oxygen Mixture under Pressure
Authors: MacLean D. J.
Published: September 2005

Tape recordings made in the helium-oxygen atmosphere of the U. S. Navy's SEALAB II have been analyzed by spectrographic techniques. The divers breathing this gas mixture have an unusual voice quality often characterized as “Donald Duck” speech. The Sealab experiment permitted speech analysis of divers living in such an atmosphere for several days. A preliminary study of the recorded data has led to the following observations: (1) formant shifts are responsible for the unusual quality of the helium-oxygen speech; (2) the formant shifts are nonlinear—the frequency shift of the first formant is greater than the frequency shifts of the higher order formants; (3) relative formant amplitudes are often changed radically; (4) pitch or fundamental frequency changes are not significant; (5) after several days in this new atmosphere, changes occurred in the speech quality that made it sound more natural. These changes most likely have been affected by modifications of the vocal-tract gestures.