bluuebunny/crossref_metadata_2025 huggingface dataset:
Selection and Evaluation of Isolating Structures and Room-Acoustics Treatment at The Hopkins Center, Dartmouth College
Authors: Klepper David L.
Published: November 2005

The Hopkins Center comprises extensive facilities for the creative and performing arts. These facilities include a multiuse auditorium, an experimental and a proscenium theatre, and numerous practice-teaching and rehearsal rooms. Since these spaces will often be used simultaneously, sound-isolating structures were chosen to prevent interference between rooms. This paper discusses design considerations in the Center, with particular attention to the selection of sound-isolating structures, subsequent measurements in the Center, and acoustical evaluations of the project. Room acoustics design is also discussed, with special reference to the unusual multiuse auditorium. The Center's architects are Harrison and Abramovitz of New York.
Balloon-Borne Acoustic Interferometer for Upper-Atmospheric Measurements
Authors: McDonald Carlos
Published: November 2005

A balloon-borne acoustic interferometer for determining the local virtual air temperature of the upper atmosphere (up to 45 km) through phase-velocity measurements of sound is described. The spacing between a plane-wave emitter and a receiver-reflector is held fixed while the frequency of the emitter input is periodically varied between 24 and 30 kc/sec. A standing wave is generated between the emitter and receiver; and the receiver output, consisting of a frequency-amplitude modulated waveform, is telemetered to a ground station. The phase velocity of sound is determined by an amplitude-frequency measurement of the received signal, and the virtual air temperature is then calculated. Under certain conditions, measurements of sound absorption and specific acoustic impedance are possible by amplitude and frequency bandwidth measurements of the received signal. These measurements can then be used to determine the air density and coefficient of air viscosity at high altitudes. The effects of wind, atmospheric pressure, and other end effects of the sound transducers are described. The results of contemplated balloon flights are summarized. [Supported in part by U. S. Army Signal Corps Grant No. DA-SIG-36-039-62-G17 and Air Force Cambridge Research Laboratories.]
More about New Instrumentation for Real-Time Spectrographic Analysis of Speech
Authors: Wood D. E.
Published: November 2005

A new instrumentation for spectrographic analysis of speech was described to the Society on 24 May of last year. The capabilities of this real-time system have since been increased. New functions are described and illustrated from films made on the analyzer. This instrumentation was designed both for economical mass recording of spectral patterns and for practical experimentation in the automatic processing of speech features. A new method of pitch extraction is presented as an illustration of processing experiments.
Distinctive-Feature Logic for the Recognition of the Speech of a Single Speaker
Authors: Hemdal John F. , Hughes George W.
Published: November 2005

A computer-recognition scheme, based on the detection of distinctive features, is presented in which attention is focused on the utterances of a single speaker. Spectral data pertaining to a list of some 250 CVC nonsense words and several short sentences have been examined. That computer logic is described that extracts sufficient information from the speech data to signal the presence or absence of several distinctive features. Information concerning the features sonorant-nonsonorant, consonantal-nonconsonantal, continuant-interrupted, and tense-lax is first extracted. This initial segmentation is accomplished on a time-independent basis; i.e., no contextual information is used to improve the reliability of the segmentation. The accuracy of the initial classification is about 90%. Accuracy is defined as the percentage of time intervals classified in agreement with the intent of the speaker. After formant-tracking, the program applies peak smoothing and classification smoothing, as well as simple linguistic constraints, in order to improve the accuracy. Further tracking of other distinctive features is described, that requires a departure from time-independent measurements [The research reported in this paper was sponsored by the U. S. Air Force Cambridge Research Laboratories, Office of Aerospace Research, under contract AF 19(628)-305.]
Radiation from Orthotropic Plates, including the Effects of Acoustic Loading
Authors: Maidanik Gideon , Kerwin Edward M.
Published: November 2005

This paper covers the acoustic radiation from point- or line-driven, infinite, orthotropic plates. The analysis includes the influence of acoustic loading on plate response. The radiation comprises (a) forced-wave radiation from the forced, nearfield vibration around the point of excitation, and (b) free-wave radiation from the free, propagating flexural waves. Acoustic loading reduces the forced-wave radiation significantly if ρ0c0/ωm>1 (ρ0, c0=fluid density and speed of sound; ω=circular frequency; m=plate surface mass). The forced-wave radiation is insensitive to the mechanical-loss factor η, if η<1. In an orthotropic plate, the free flexural wavespeed varies from a maximum value in the “stiff” direction (1) to a minimum value in the “soft” direction (2). The wavespeeds in these directions equal c0 at the critical frequencies f1 and f2, respectively, (f2>f1). For ff2, all free waves radiate with unit efficiency. Between f1 and f2, the radiation efficiency rises monotonically from 0 to 1.0, as more and more of the free waves become radiating. [Work supported by U. S. Bureau of Ships.]
Analog and Digital-Analysis Methods for Determining Phase Relationships between Complex Acoustical Signals
Authors: Collier Robert D. , Summers Agnes C.
Published: November 2005

The phase relationships between the vibration spectra of different parts of a distributed mechanical system under complex, external excitation are investigated over a range of limited frequencies. Results of experimental phase-time relationships with a recently design multichannel analog correlator are compared with digital crosscorrelation and phase analyses obtained with a digital computer. The phase relationships at specific frequencies are used in the study of mode shapes and distributed damping. A mathematical model of the distributed mechanical system with variable damping and controlled forcing functions is analyzed on an analog computer. The results provide phase/damping relationships as a function of frequency and include several of the calculated normal modes. Comparisons between the mathematical model and full-scale experimental data are discussed, including the effect of exciting the system at different points, phase stability as a function of time, and modal response for selected damping coefficients.
Crest and Extremal Statistics of a “Cube-Law” Element Driven by Random Noise
Authors: Smits Talivaldis I.
Published: November 2005

A method of analyzing directly the probability distributions of output extrema (maxima and minima) and crests in terms of the input crest and extremal statistics [J. Acoust. Soc. Am. 34, 1859–1864 (1962)] is applied to a quasi cube-law negative-resistance element. The statistics are predicted for random-noise excitations of various bandwidths. The theory predicts symmetry of the “output” probability densities for the maxima and the minima, provided the “input” process has this symmetry (i.e., Wmax[η]=Wmin[−η]), as is true for Gaussian processes. A jump (i.e., a “spike” in the probability density) is predicted for both the probability distributions of the output maxima and minima, at values determined (for each distribution) by the nonlinear transfer characteristic. The crest distribution also exhibits a jump. However, the crest statistics, unlike the extremal statistics, do not depend on the input bandwidth for the Gaussian inputs quantitatively investigated here. The theory is compared with experimental data taken on a “cube-law” characteristic simulated here by means of a coupled pair of tunnel diodes. These data were obtained electronically by means of a specially designed “peak discriminator” used in conjunction with a standard electronic counter. [The research was supported by the Aeronautical Systems Division, Air Force Systems Command, U. S. Air Force, under contract AF 33(657)-7453.]
Investigation of the Glottal Waveshape by Automatic Inverse Filtering
Authors: Miller Joan E. , Mathews M. V.
Published: November 2005

Considerable attention has been given of late to the source function, its properties and significance. Consequently, a method of pitch-synchronous analysis, reported on previously, has been improved and applied more extensively to gather additional data on the volume-velocity function of the glottis. The technique arises from the model of vocalic sounds in which the spectra are characterized by a separation of vocal-tract poles from glottal-source zeros. A Fourier analysis is made on one period of the pressure wave, the formants are located and removed from the spectrum, and the glottal waveform is computed from the residual by Fourier synthesis. This approach requires digital recordings free from phase distortion and with a high signal-to-noise ratio. Data from six male talkers in varying contexts and at different pitches and intensities have been studied with attention to shape, phase with respect to the speech wave, duty factor and degree of closure as a function of talker, sound, pitch, and intensity.
Some Measurements of the Glottal-Area Waveform
Authors: Soron Henry I. , Lieberman Philip
Published: November 2005

High-speed motion pictures of the larynx were exposed by the techniques of indirect laryngoscopy at approximately 10 000 frames/sec. The acoustic waveform at the speaker's lips was also optically recorded on the film. The area of the glottal opening and amplitude of the acoustic waveform were measured, with the aid of a digital computer, for each frame of a film in which the speaker uttered /ɑ/ for approximately 0.3 sec. This short-voiced sound is about the duration of the voiced segments that normally occur in fluent speech. The changes of the glottal-area waveform are correlated with the beginning and end of phonation and the positions of the arytenoid cartilages.
Detectability of Missing Pitch Periods in Speech
Authors: Michaels Sheldon B.
Published: November 2005

The ability of listeners to detect missing pitch periods in human speech has been investigated. The detectability data are presented in relation to the following factors: (1) voiced and unvoiced fricative boundaries, (2) voiced and unvoiced stop boundaries, (3) abrupt fundamental frequency changes, and (4) rapid formant changes. The relationships between these factors and detectability are described and results are compared with previous data that used monotone excitation of a fixed POVO-type vowel simulator. This comparison shows that, while the signal in this experiment is complex and information-bearing, listener ability to detect missing pitch periods is not decreased with respect to monotone-excited fixed-vowel detectability.
Comparison of the Spectra of the Voices of Twins
Authors: Alpert M. , Kurtzberg R. L. , Pilot M. , Friedhoff A. J.
Published: November 2005

Differences between identical and fraternal twins have long been examined in attempts to separate characteristics determined by nature from those resulting from nurturing. This paper describes a study of the vocal spectra pairs of monozygotic, dizygotic, and nontwin age- and sex-matched controls. The results are based on a statistical comparison of the relative energy of the voices of pairs of individuals at each of a number of spectral points. The monozygotic twin pairs were found to be significantly more alike in the range from 670 to 2000 cps but not in the range below 400 cps. These data are consistent with previous findings in this laboratory that the lower-frequency range is more sensitive to changes that accompany emotion-evoking stimuli. Thus, the lower section of the spectrum is more variable whereas the higher section is more stable. The data support the hypothesis that the vocal spectrum is, at least in part, determined by genetic factors. [This research was supported by Public Health Service grant MH-04664, U. S. Department of Health, Education, and Welfare.]
Condenser Microphones with Electret Foil
Authors: Sessler G. M. , West J. E.
Published: November 2005

Condenser microphones using electret foil are discussed in this paper. Frequency response, sensitivity, and distortion of these systems have been described previously. During the past year, the stability of electret microphones has been measured. Over this period, the sensitivity has not changed more than ±1.5 dB. An independent study of the surface charge of electret foils has been conducted in order to better understand the mechanism of polarization, as well as the relation between the change of this surface charge and the stability of the microphone. A theoretical analysis makes it possible to determine the parameters that influence the sensitivity of the microphone. In addition, the use of transistorized preamplifiers in conjunction with this microphone is discussed.
Transmission-Velocity Stability of SOFAR Signals
Authors: Hamilton G. R. , Drake M. E. , Hartdegen C.
Published: November 2005

In May 1961, 98 SOFAR charges were detonated during a 24-hour period at sound-channel axis depths off Antigua. Here, the Atlantic missile range's target array of bottom hydrophones makes it possible to precisely determine their detonation time, depth, and relative position. The resulting SOFAR signals were recorded by axis or near-axis hydrophones at Bermuda and the Bahamas. The SOFAR signal's sound velocity at the cutoff point was computed for these 1000-nm transmission paths. The measured hour-to-hour variations were within ±0.1 ft/sec, with the total variation over the 24-hour period being as much as 0.4 ft/sec. There is some evidence of periodic cycling. For a better understanding of the extent and possible cause of these velocity variations, an extended exercise consisting of shots fired every hour for a week was conducted in March 1963. The data for this exercise are presently being computed and the results are to be included in this paper. [This program was supported by the U. S. Office of Naval Research's Acoustics Programs.]
20-cps Pulsed Signals of Probable Biological Origin at Bermuda
Authors: Patterson Brian , Hamilton G. R. , Grayston P. H.
Published: November 2005

Pure-tone pulses, at a frequency close to 20 cps, have been received on deep-water hydrophones at Bermuda, each year during the months November through March, since monitoring began in 1951. The pulses occur at regular intervals, several times per minute for about 15 min, then stop for 2 to 3 min. This sequence often continues for hours with no preference for day or night. The source of these pulses has been tracked, using several hydrophones at average speeds of 1 to 4 knots. The source normally meanders throughout the tracking area but occasionally moves in a straight line. The estimated source level is 1 to 8 W. There is generally only one source pulsing at a time in a listening area of 300 square miles. Similar signals have been heard throughout the North Atlantic and in the Pacific. The pulses are believed to be of biological origin with the cetacean the most probable source. No definitive data on source depth are yet available. [Supported by the U. S. Office of Naval Research's Acoustics Programs.]
Effect on Auditory Functioning of Repeated Exposure to Temporary Fatigue
Authors: Riach Winifred , Elliott Donald N. , Frazier Larry
Published: November 2005

The experiments reported assess (1) the effect of repeated high-intensity stimulation on the threshold of audition and on intensity discrimination and (2) the effect of recovery time on intensity discrimination, holding degree of TTS constant. The first experiment exposed Ss to a 2-Kc-sec tone presented at 105 dB SL for 2 min. Pre- and post-exposure measurements of the threshold of audition and intensity discrimination were obtained for 20 sessions. The second experiment varied the duration and level of the high-intensity fatiguing stimulus so that a given TTS (10 or 20 dB) could be obtained at a specific time period after exposure. Pre- and post-measurements of intensity discrimination were obtained. The results showed a trend, possibly indicative of learning, toward a lower pre- and post-exposure threshold—but this trend was not supported statistically. Consequently, it can be concluded that repeated high-intensity stimulation similar to that in the experiment did not result in any systematic shift in sensitivity. Additionally, it appears that the degree of TTS is the determiner of any change that occurs in intensity discrimination, rather than the time of recovery at which the measurement is obtained.
Absence of Central Factors in Auditory Fatigue
Authors: Ward W. Dixon , Sweet David F.
Published: November 2005

At the last Society Meeting, Wernick and Tobias reported that listeners consistently showed greater temporary threshold shift (TTS) when a fatiguing tone was presented during a “mental task” than when they simply sat quietly (“reverie”). We cannot confirm this report. Twelve listeners were exposed to a 4000-cps tone at 100 dB SPL for 3 min under two conditions: (1) sitting quietly and (2) adding columns of figures. Pre- and post-exposure thresholds at 5600 cps were determined with Békésy audiometer, interrupted tones. Order was balanced, initial postexposure setting was at preexposure threshold, and instructions to the subjects were neutral in regard to expected outcome. Indeed, the person actually running the subjects was unaware of the outcome of Wernick and Tobias' study. No significant differences in TTS were found at any time after exposure; in fact, the greatest mean difference at any time was in the opposite direction: the TTS at 2 min 15 sec was 14 dB for the “reverie” condition, 12 dB for the “mental task.” It is concluded that the efferent system need not be invoked to account for any aspects of auditory fatigue. [Supported by grants from the Public Health Service, U. S. Department of Health, Education, and Welfare.]
Loudness of Time-Varying Sounds
Authors: Connor W. K.
Published: November 2005

Loudness balances by the method of adjustment were made between two alternately repeated short samples of narrow-band noise, one of which changed in level with respect to time. The rate of change of a given sample was constant at ±9.0 or ±30 phons/sec, and the steady and varying samples were both of either 0.5 or 1.0 sec duration. The steady sample was presented at a loudness level of approximately 74, 85, or 91 phons. The data of 220 judgments indicate that the loudness level of the time-varying sample corresponds to its time-average loudness. Similar balances between a fixed 1000-Hz tone and a glissando tone of steady level that changed frequency symmetrically about 1000 Hz at a rate of ±0.70 octave/sec indicate that the two are equally loud when their SPL's are equal. [This work was performed at Southern Methodist University and supported in part by the Callier Trust.]
Relaxation Time in CO2 as a Function of H2 and D2 Concentration at Several Temperatures
Authors: Winter T. G.
Published: November 2005

It is well-known that small amounts of impurities shift the relaxation frequency of a gas linearly with concentration and that the amount of this shift is a measure of the efficiency of energy exchange in A-B collisions. The influence of temperature and mass on the efficiency of vibrational energy exchange in CO2-H2 and CO2-D2 collisions was determined by the shift of relaxation frequencies. Hydrogen was found to be 2.4 times more effective than D2 in quenching the vibration of CO2 at both 47° and 154°C as expected, but, surprisingly, it was found that 15% to 20% more c collisions were required to transfer energy at 154°C than at 47 C for both H2 and D2. No satisfactory explanation of this phenomenon has yet been offered. [This work was performed at The Catholic University of America and was supported by the U. S. Office of Naval Research under contract Nonr 2249(02).]
Ultrasonic Technique for the Melting Transition and Melt of Polymers
Authors: Eby R. K.
Published: November 2005

An extension of McSkimins' technique [J. Acoust. Soc. Am. 23, 429–434 (1951)] to polymer melts or amorphous polymers above their softening temperature is reported. For 12-Mc/sec longitudinal waves, the modulus and internal friction are presented for the melting, supercooling, annealing or recrystallization, and melt of polyethylene.
Measurement of Ultrasonic Attenuation in Solids by a Reverberation Technique
Authors: Lange James N.
Published: November 2005

The measurement of ultrasonic attenuation has long been plagued by the experimental difficulties involved in obtaining measurements of the absolute values of the acoustical absorption. A technique was investigated that would provide accurate measurements of the ultrasonic attenuation. This technique is very similar to the method of measurement of reverberation times in architectural acoustics. Sound is introduced into the specimen through a quartz transducer excited by an rf pulse. The radio frequency of the pulse is warbled and the pulse duration is longer than the amount of time that it takes for the initial wavefront to travel to one of the reflecting surfaces of the specimen. The energy is reflected many times from the nonparallel surfaces of the specimen until a statistical equilibrium situation is approached and the sound field can be considered diffused. The resulting decay will be quite complicated, but when the frequency is warbled an average is presented on the oscilloscope and the slope of the decay is found to be exponential. Preliminary measurements indicate a loss factor for aluminum approximately 10 times less than previously measured due to the absence of any apparent attenuation due to grain scattering. [This research was supported by the U. S. Air Force Office of Scientific Research.]
Vertical Directionality of Deep-Ocean Noise
Authors: VonWinkle William A.
Published: November 2005

Using a 300-ft vertical array of 40 receivers mounted near the ocean floor in 2400 f, an experimental program has been completed from which the vertical directionality of deep-ocean noise as a function of frequency and sea-surface condition can be inferred. Data are presented for the frequency range 100–2000 cps, based on logit band measurements, as a function of surface-wind speed and waveheight corresponding to sea-state numbers from one through six. The ability to electrically steer the array through a variety of angles of elevation provides a reasonably well-defined distribution. A comparison of these data with theoretical models of the distribution is presented.
Ambient Noise Field in Relation to the Directional Properties of Surface-Noise Sources
Authors: Talham Robert J.
Published: November 2005

Since much low-frequency acoustic energy is surface-generated, attempts to account for the directional ambient-noise field usually hypothesize a surface distribution of noise sources. It is to be expected that the induced-noise field will depend on any directional properties attributed to the source elements. To obtain a measure of this dependence, an investigation is made of the effects of various directional source patterns on the resultant ambient field when account is taken of refraction, bottom and surface reflection, volume absorption, frequency, and sea state. The results are viewed in the light of ambient-noise measurements made recently in the deep ocean. [This work was supported by the Bureau of Ships, U. S. Navy.]
Space-Time Correlation in Isotropic Noise Fields
Authors: Usher Theron
Published: November 2005

The crosscorrelation between signals produced by two omnidirectional transducers located in a field of many scattered noise sources is considered. Both spherical, three-dimensional distributions and circular, two-dimensional distributions are analyzed. Graphical interpretations of the general equations used for computing the crosscorrelation are given. Specific results for a Markov-type noise spectrum and a narrow-bandpass noise spectrum are included. Upper limits of the crosscorrelation for both spectra are computed. A technique for determining the ridges and valleys of a map of the crosscorrelation as a function of transducer separation and electrical time delay is also developed for the case of the narrow-bandpass noise spectrum.
Comparison of Theoretical and Experimental Values of Spatial Correlation
Authors: Keltonic F. , Hassell B. , Cron B.
Published: November 2005

A surface-noise model has been developed. This noise model consists of noise sources uniformly distributed on a large circular area of a plane. The noise sources are assumed to be directional. The spatial correlation is obtained as a function of the directionality of the noise sources. Experimental measurements were conducted using some of the elements of a 300-ft vertical linear array of 40 hydrophones in about 15 000 ft of water. The data were passed through filters in the 200- to 400-, 400- to 600-, 600- to 800-, and 800- to 1000-cps bands. The theoretical and experimental values were compared. The results indicate that the noise is from a horizontal direction in the 200- to 400-cps and from a vertical direction in the other frequency bands. A good agreement of the experimental results and the theoretical results is obtained in the higher passbands. In general, the agreement is better for higher frequencies and sea states. The results indicate that the sources on the surface radiate similar to that of a dipole source.
Aspects of Structural Excitation by Sound
Authors: Powell Alan
Published: November 2005

The role of the pressure exciting a mode of vibration of a structure may be expressed in terms of the generalized force, which involves the two-point space-time pressure correlation over the exposed surface of the structure. This is illustrated in the one-dimensional case, the significance of scale being pointed out. The general two-point correlation is needed for other cases, except in the important special case of the generalized force for plane waves exciting orthogonal modes of a rectangular surface when the product of instantaneous correlations taken parallel to the edge suffices. Response of structures large as compared to the scale of the pressure field may be found approximately from a corresponding infinite structure, regardless of the magnitude of the structural damping, provided the few lowest modes are not highly excited. When more than a single mode is excited, the correlation between the motions of the modes may become important, especially in determining maxima of the response: this is particularly so for cylindrical and spherical structures. The adequate determination of the pressure correlation in many practical situations is very laborious; also, there is often a lack of detailed knowledge of the relevant structural-response characteristics: model test work may be most useful, provided that the ratio of excitation to natural frequencies, and of excitation scale to structural scale, is preserved. If nonlinear effects are present in either the presure field or in the structure, the amplitude must also be appropriately scaled.
Use of Dynamic Models to Determine Structural Response to High-Intensity Noise
Authors: Roberts W. H. , Eldred K. M.
Published: November 2005

A search for an approval to the very complex problem of determining the structural response to acoustic loads shows that only a few analytical or experimental tools are available. The experimental tool arising from dynamically scaled models is explained. The need for an experimental capability is established by presenting recent problems in structural dynamics and reviewing the state of the art. New loadings, combined loadings, and the new phenomena in fatigue are presented. The serious nature of the problems occurring in the field affects structural integrity and equipment reliability and requires reassessment of our basic procedure. Material properties show loss in strength, loss in stiffness, and sensitivity to random load. Although the scaling relationships are straightforward, the accuracy of the final answers is dependent on the design and construction technique. Guidelines are presented based on the results of several models. Structural qualification for combined loads, accelerated testing, fatigue scaling, engine scaling, and thermal scaling are capabilities possessed. Integration of the damage from several failure modes is also accomplished.
Noise-and-Vibration Characteristics of Large, Solid Rocket Motors with Thrust-Vector Control
Authors: Franken Peter A. , Keast David N. , Newbrough Dan E.
Published: November 2005

Noise-and-vibration measurements have been made during static firing of three solid rocket motors. The thrust level of the largest motor was approximately 106 lb. Far- and near-field acoustic data show fair agreement with data scaled from smaller motors, but raise some questions concerning assumed acoustic equivalences between solid- and liquid-fuel systems. The effects of liquid-injection thrust-vector control are visible in acoustic and vibration data. These effects are in line with the hypothesis that thrust-vector control tends to relocate the sources of nearfield noise closer to the exhaust nozzle. [This work was supported in part by subcontract with Aerospace Corporation.]
Impact-Noise Measurements of Floor Constructions
Authors: Kodaras Michael J. , Hansen Robert A.
Published: November 2005

The Federal Housing Administration Rept. No. 750, entitled “Impact Noise Control in Multifamily Dwellings,” has focused a considerable amount of attention on this noise problem. The FHA Guide was prepared by Dr. T. J. Schultz of Bolt Beranek and Newman Inc. This paper sub-bits data of several standard and special floor constructions with a range of impact-noise ratings of −15 to 0.
Effects of Room Geometry on Reverberation Measurements of Absorption Coefficients
Authors: Johnson Roger P.
Published: November 2005

A test program has been carried out in a 10 000-cu-ft reverberation room to determine the effects of room variables on absorption-coefficient measurements of a single, highly absorptive sample. The experimental conditions include fixed diffusing elements, a fixed or rotating vane of variable shape, position of sample, and microphone position. The sample tested is a duplicate of the Sillan used in ISO round robins of European and Canadian laboratories. The results of this study are compared with other experimental data and with the theoretical values calculated from impedance-tube data according to the method developed by Northwood.
Some Preliminary Results on the Design of Scattering Panels with Minimal Directivity Effects
Authors: Drushel M. E. , Wittenborn A. F.
Published: November 2005

At the last two meetings of the Acoustical Society of America, some results were presented of a digital-computer simulation of the scattering of sound pulses from slatted surfaces. It was shown that the computed directivity pattern of the scattering surfaces agreed with experimental measurement, and audible results for a number of different bandwidth-time products were compared to the direct pulse for a subjective comparison. In this paper, scatterers of a more complex structure are examined with the simulation technique, with a view toward broadening the directivity pattern while at the same time avoiding subjectively objectionable sounds due to the scattered pulse or the interaction of the direct and scattered pulses.
Slow-Motion X-Ray Pictures with Stretched Speech as a Research Tool
Authors: Abramson Arthur S. , Cooper Franklin S.
Published: November 2005

X-ray films in slow motion are useful for getting a notion of gross articulatory movements in speech and for planning electromyographic studies. Synchronized sound added to the picture enables the viewer to track the speech gestures with good reference to the sounds. This can be realized by means of a vocoder used with a multitrack tape recorder to stretch the speech and maintain synchronization with the picture. A short film demonstration accompanies the paper. [This work was supported in part by Public Health Service research grant DE-01774, National Institute of Dental Research, National Institutes of Health, U. S. Department of Health, Education, and Welfare; and in part by contract SAE-8324 with the U. S. Office of Education.]
Vowel Identification and Phonetic Contexts
Authors: Fujimura Osamu , Ochiai Kazuo
Published: November 2005

Confusions in the perceptual identification of vowel samples taken out of various phonetic environments have been examined. Japanese words were uttered by a female speaker. The central portions of vowels within the words were electronically gated out for a 50-msec duration, including tapered ends. For each of five Japanese vowels, fifteen samples out of different environments were prepared, and 75 samples in total were arranged in randomized orders for forced-judgment-identification tests. The result showed a considerable amount of confusion for some vowels uttered in certain phonetic environments. Some appreciable effects upon the score were also observed when the subjects had been trained in different ways immediately preceding the listening tests. The result, in general, conforms with explanations in terms of articulatory movements, previously reported formant data, and some other factors that would influence the subjects' judgments.
Human Recognition of Sustained Phonemes
Authors: Focht Louis R.
Published: November 2005

The capability of the human to resolve isolated phonemes was investigated by a series of forced-choice listening tests. Sustained utterances of 20 phonemes (11 voiced, 5 unvoiced, and 4 voiced fricatives) as spoken by 5 speakers were recorded and edited to eliminate all contextual clues and presented to a listening team. It was found that correct-phoneme-recognition scores averaged 62%. Control tests carried out with the same listeners and equipment, but using phonemes in context, were also performed. The control experiment yielded recognition scores of 96% and greater. However, when certain isolated phonemes were lumped together to form less than one-half as many classes of sounds as previously used, recognition scores rose to 95%. Details of both the experimental procedure and the experimental results are given.
Chambered-Pipe Application of Basic Theory to Exhaust-System Design
Authors: Lentz E. C. , Walker J. C.
Published: November 2005

This paper presents a summary of development and testing of the concept of “chambered-pipe” exhaust-system design. Current automotive-engineering advancements requiring solutions to many problems are discussed. The limited capability of conventional exhaust systems to handle these problems and a research program going from basic theory to design parameters is discussed. Experimental confirmation of these parameters in the troublesome exhaust frequency range of 40 to 600 cps, using hot-gas flow, is discussed and results shown. Comparisons of optimum placement of small acoustic elements to form the distributed exhaust system are made to conventional systems with regard to supporting means and also for extension of corrosion life. Conclusions are made that the distribution of elements made possible by the chambered-pipe concept will make possible acoustic treatment of engine-exhaust gases where space does not now permit, that lower system weights are practical, that more-specific tuning of systems can be accomplished, that over-all sound levels can be established over a wider practical range than now possible, and that secondary acoustic sound generations should also be reduced. Further, the developers point to this application as the start of more-complex methods of analysis.
Acoustics and the Automobile
Authors: Scott W. N. , Farnham J. R.
Published: November 2005

The increased reliability and ease of operation of today's automobile allows the customer to make his choice based largely on comfort and aesthetic factors. Since we react strongly to consumer demands, the industry has responded with a major emphasis on sound-and-vibration attenuation. The noise-and-vibration characteristics of an automobile are especially challenging because, as we lower the general noise level, we encourage our customers to become more demanding—what was considered quiet yesterday is too noisy today. As we have increased our knowledge of the vehicle vibration system, its complexity has become more apparent. It has, therefore, been necessary to treat everyday engineering problems with the methods and techniques formally associated with research science. This paper examines the nature of the complexity of the automotive noise problems and the means that have been developed to deal with them.
Instrumenting an Impact Pendulum for the Evaluation of Energy-Absorbing Materials
Authors: March N. E.
Published: November 2005

Injuries sustained by automobile passengers during collision have made it imperative that we develop an improvement in the energy-absorbing capabilities of the padding materials in automotive interiors. An impact pendulum has been developed for the determination of the energy absorption of experimental padding materials. The instrumentation required for measuring impacting and rebound velocities, material indentation, pendulum acceleration and jerk, and pressure on the material is described.
Automating Mechanical-Response Testing
Authors: Clements R. W.
Published: November 2005

A system is described for experimentally obtaining the mechanical-response characteristics of a complex structure for instantaneous comparison with computed data obtained from a mathematical model of the structure.
Backscattering of Short-Gated CW Pulses from a Statistically Varying Rough-Ocean Surface
Authors: Saenger R. Alfred
Published: November 2005

A general formula for the back-scattered pressure p(A) developed in another paper [R. A. Saenger, Paper L1, this meeting] is used as a theoretical basis for analyzing the following specific problem: a series of monochromatic isotropic spherical pulses initiated at A reflect from a one-dimensional narrow-band noise-type ocean surface. In the specular region, the succession of reflecting patches is considered sinusoidal with random amplitude h and phase δ. During the period when the specular component po is present, certain approximations are employed that make it possible to express the total pressure p(A) as po⋅𝔐〈t〉, where 𝔐 involves a surface integral over a time-dependent region within the reflecting patch. For high-frequency pulses as normally filtered, the quasi steady-state, pulse amplitude P can be derived explicitly. It depends on the value of the roughness parameter, the phase of the surface, and, to some extent, the surface wavelength. If P2 is taken as a measure of reflected energy, then it can be shown that the average P2 equals the squared-amplitude value PM2 obtained in mirror-surface reflection. The limits of fluctuation of P2 above and below PM2 depend on the rms roughness parameter. These results may offer a partial explanation for the high rough-surface reflectivities observed by M. V. Brown and others. [Hudson Laboratories, Columbia University Informal Documentation No. 32. This work was supported by the U. S. Office of Naval Research.]
Fluctuations in Surface-Reflected Pulses
Authors: Nichols R. H. , Senko A.
Published: November 2005

A series of statistical measurements of the variability of underwater-pulse amplitudes caused by reflection from the ocean surface has been carried out during the months of December, January, February, and June. Pulses 500 msec long, at frequencies ranging from 350 to 1500 cps, were generated by a bottomed source at 2400 f. The singly reflected pulses were received on bottomed hydrophones so located that the grazing angles at the surface were 18°, 31°, and 85°. Early results indicate that variability reaches a limiting value as frequency increases, and increases with grazing angle at low frequencies. The observed effects of frequency, grazing angle, and sea state are presented and discussed in comparison with recently published theoretical results. [This work was supported by the Bureau of Ships, U. S. Navy.]
Generalized Scattering Theory for One Dimension
Authors: Harrison Mark
Published: November 2005

If one is interested in computing reflection and transmission coefficients for a plane wave in a medium where the propagation function varies continuously, one may not have at his disposal the usual boundary-condition problem in a sufficiently simple form as to easily yield a solution. In this case, the WKB method is often resorted to. In this paper, another technique is developed that is analogous to the partial-wave method of treating two- and three-dimensional scattering. It is shown that the problem may be cast into an integral-equation form where the first iterated solution corresponds to the weak-scattering Born approximation and which may be used to compute the reflection and transmission coefficients when the properties of the medium vary slightly in an arbitrary way. Further, the reflected and transmitted wave can be viewed as a particular superposition of partial waves that can be obtained by an integral-equation analysis and that yields not only the Born approximation in the case of weak scattering, but also an exact solution in some cases of interest. [This work was supported by the U. S. Office of Naval Research, under contract.]
Estimating Noise Hazard with the Sound-Level Meter
Authors: Flanagan J. L. , Guttman Newman
Published: November 2005

A simple and rapid measurement procedure is suggested for surveying nonimpulsive, continuous-spectrum acoustic noise. The procedure includes rules for relating the measurements to contemporary damage-risk criteria. The standard A, B, and C frequency weightings of the sound-level meter are exploited to make a limited estimate of the noise spectrum. On the basis of analytical approximations to the weighting functions, scale-difference readings are calculated for a number of input-noise spectra. The procedure utilizes the measured and calculated scale differences to indicate whether more-detailed measurements, such as octave-band levels, are to be made.
Digital Simulation of the Cochlea
Authors: Hause A. Dickson
Published: November 2005

Several digital-computer simulations of the human cochlea are described. The underlying fluid-mechanical model assumes one-dimensional flows in the scales coupled to one-(transverse)dimensional motion of the cochlear partition. The simulation output mode normally employed is a time sequence of microfilm plots of displacement vs location along the partition. Experimentation with these simulations is facilitated by expressing the relevant data as physically measurable constants and parameters that are punched on control cards as decimal constants or FORTRAN formulas. With such flexibility, these programmed models should also be useful for simulating the cochleas of experimental animals. A number of simulations are discussed that exhibit, in response to impulse or sinusoidal excitation, the effects of varying the following parameters: the number and spacing of discrete partition elements, the sampling rate, the velocity of plane waves in the scala fluid, the mass, stiffness, and damping of the partition, including coupling between adjacent elements by stiffness and viscous forces, and the effective cross section of the scalas.
Some Quantitative Consequences of Hearing Loss from the Standpoint of Communication Theory
Authors: Corliss Edith L. R.
Published: November 2005

A model based upon simple elements permits summary description of many experimental observations on hearing. Only two mechanisms are required: One element emits unit responses whose number is proportional to the amplitude of the sound. It is followed by a selector mechanism, analogous to a resonant circuit, that integrates the responses. Correspondingly, just two parameters are involved: the threshold of hearing and the “Q” of the selector mechanism. Experimental evidence from noise-masked audiometry [T. Palva, A. Goodman, and I. J. Hirsh, Laryngoscope 63, 842–860 (1953)] indicates that the selector mechanism is unimpaired in many cases of sensorineural loss. The prevalent type of loss reflects a depression in the number of unit responses to sound of a particular amplitude. Loss with recruitment implies a basic number of spontaneous unit responses. The influence of hearing loss upon the perception of frequency differences and intensity changes can be computed. When noise is presented with the signal, its influence upon recognition of signals, the perception of frequency differences, and intensity fluctuations can be predicted. The model indicates quantitatively what has been recognized qualitatively: that amplification does not restore full discrimination in the presence of sensorineural loss. [This work was begun under sponsorship of the U. S. Office of Naval Research, and continued while the author was a guest at Imperial College.]
Effects of Two Kinds of Noise on Auditory Discrimination
Authors: Stewart John L.
Published: November 2005

Upon stimulation, each patch of cells along the organ of Corti gives rise to a train of neural impulses. The temporal rate of these impulses provides a partial-stimulus measure. When combined with cell-patch signals over the entire inner ear, allowing for interactions between cell-patch signals, there results a time-space pattern of neural activity that specifies the complete stimulus. During receipt of a sound, the entire surface due to the sound is subject to random fluctuations. These fluctuations, which constitute neural noise, limit ability to discriminate between alternate stimuli and, hence, limit recognition. Understanding of the nature of neural noise can be promoted by studying the neural signal from a single patch of sensory cells. There may be identified two kinds of noise, one with a uniform spectrum from zero frequency to the kilocycle range, and the other that has intense low-frequency components but that becomes unimportant above a few cycles per second. The intensity of the noise increases with the average neural pulse rate. The time-space pattern of neural activity is made uncertain in proportion to its height with slowly varying portions being especially difficult to discriminate. Certain bounds on discriminability are identified and discussed specifically.
Transverse Vibration of Internally Damped Beams with Rotary Inertia and Shear
Authors: Snowdon J. C.
Published: November 2005

Discussed briefly is the manner in which the Timoshenko equation may be extended to predict the response of internally damped beams to vibration. The Timoshenko equation describes how rotary inertia and shear displacement influence beam vibration when the bending wavelength is not large compared with the beam thickness. Center-driven free-free and simply clamped beams have been considered as specific examples. In the case of the free-free beam, the individual influence of the damping factors δE and δG associated with the Young's modulus and the shear modulus of the beam material has been distinguished by equating each damping factor to zero in turn. In the case of the simply clamped beam, the driving-point impedance, the moment impedance, and the force and moment transmissibilities across the beam have been determined with the assumption that the damping factors δE and δG possess equal values. Normally, this assumption is well-justified in the case of plastic and rubberlike materials. [This investigation was sponsored jointly by the U. S. Bureau of Naval Weapons, the U. S. Bureau of Ships, and the U. S. Office of Naval Research.]