bluuebunny/crossref_metadata_2025 huggingface dataset:
Acoustic Wavefunctions and Multipole Sources
Authors: Skudrzyk Eugen
Published: November 2005

Certain difficulties have been caused in acoustics by the untraditional introduction of dipol, quadrupole, and other source fields of higher order. In this paper, the fundamental properties of the wavefunctions and the acoustic and electric multipole fields are discussed in detail and the definitions actually reviewed.
Surface Waves in a Fluid-Solid Interface near a Discontinuity
Authors: Yip T. , Middleton F. H.
Published: November 2005

In an effort to further explain some unexpected experimental results (obtained by Feder and Middleton), this paper considers the problem of surface wavepropagation in a fluid-solid boundary. The boundary conditions are complicated by the introduction of a wedge-shaped discontinuity in the solid material. The process of acoustic-energy radiation into the fluid medium is obviously of primary concern. Considerable work is reported in the literature on the similar physical situation of a solid medium bounded by a vacuum. The presence of the liquid changes the boundary conditions in such a way that, instead of vanishing, the normal component of stress at the boundary must be continuous. An iteration procedure that has proved successful in the vacuum-boundary case is employed in the present study. The first iteration produces the diffracted wave in an integral form. Subsequent evaluation of these integrals by contours in the complex plane gives useful results in terms of the three waves transmitted through the discontinuity.
Statistical Properties of Reverberant Soundfields
Authors: Waterhouse Richard V.
Published: November 2005

In connection with a study of the statistical properties of reverberant soundfields in enclosures, the distributions of various kinds of scalar wavefield are considered. The wavefield is derived from either (a) waves of one frequency and random phase, or (b) a warble tone, or (c) a band of white noise obtained with an ideal filter. The distributions of mean-squared pressure are found for repeated sampling at one or more points in the field. Such sampling is done, for example, in finding the average energy density of the field of a sound source and, hence, the power output of the source. The applications of the theoretical results to soundfields in actual enclosures is discussed, and some experimental results are given. [This work was supported by the U. S. Office of Naval Research, under contract.].
Logarithmic Computer-Plotter for Mechanical and Acoustical Impedances
Authors: Cousins E. L. , Kahlbau J. V. , Hixson E. L.
Published: November 2005

An electrical-analog device to simplify measurement of mechanical and acoustical impedances has been built. It is intended for use with several of the types of two-channel vibration-and-sound transducers generically known as impedance heads. This equipment facilitates continuous measuring and plotting of mechanical or acoustical impedances or their reciprocals, mobility and admittance. The computer features externally adjustable compensation for mass or inertance inherent in many impedance heads, independent logarithmic compression of both impedance-head signals for wide dynamic range (approximately 60 dB over the frequency range 20–2000 cps), and relative phase measurement after logarithmic compression to insure that phase-meter input signals from both information channels are of acceptable level. Computations are effected by a summing network that produces a linear combination of dc voltages proportional to the logarithms of the two impedance-head signals, the logarithm of frequency, and a constant representing combined-scale factors. By appropriate choice of impedance head and algebraic signs of the summed voltages, a dc voltage proportional to magnitude of the measured quantity is produced. Both this magnitude and a phase-angle signal can be recorded vs the logarithm of frequency by an x-y plotter with two sweeps of the frequency interval. This paper describes the computer, discusses its capability, and compares automatically-plotted impedance curves with ideal curves and point-by-point plotted measurements for certain mechanical structures and acoustical systems. [This work was sponsored by the U. S. Navy Bureau of Ships.]
Quincke-Tube Acoustic Filter for Fluid Ducts
Authors: Hixson E. L. , Kahlbau J. V.
Published: November 2005

The general problem of acoustic wavepropagation through parallel ducts is approached by two-port network theory. This theory allows the combination to be considered as a single two-port element represented by admittance parameters that are summations of the corresponding admittance parameters of each of the several parallel paths. Transmission-line methods are used to calculate the required parameters and the transmission loss introduced by the parallel paths. The Quincke-tube acoustic filter uses two parallel paths. A particular choice of duct lengths can produce an infinity of transmission loss at one frequency and every one of its harmonics. This result is unique among acoustic filters. The transmission-loss characteristics of several other variations of duct sizes and lengths, along with some very limited experimental data, are presented. [This work was sponsored by the U. S. Navy Bureau of Ships.]
Learning in Psychophysical Experiments
Authors: Tanner W. P. , Rivette C. L.
Published: November 2005

When one attempts to construct a model of the human auditory system, consideration must be given to the relation between psychophysical behavior and previous experience. In this context, it is of interest to conduct psychophysical experiments in which learning is involved. In the experiment reported, six observers were asked to judge the position of a 10-msec signal in a 110-sec interval. While they were unable to make the judgment initially, after several hundred attempts their performance improved and continued to improve until at least 12 000 judgments had been made. These data are interpreted in terms of the development of subjective scales through experience. [This research was supported by the Advanced Research Projects Agency and was monitored by the U. S. Air Force Office of Scientific Research, under contract No. AF 49(638)-1233.]
Effect of Pedestals on the Detection of Signals in the Absence of External Noise
Authors: Pfafflin Sheila M.
Published: November 2005

Using a two-interval, forced-choice procedure, subjects were asked to choose the interval containing a 1000-cps signal when pedestals (1000-cps sinusoids of equal amplitude) were present in both intervals of the experiment. There was no external-noise source; the experiment was thus equivalent to an intensity-discrimination task for pure tones. Pedestals both in phase with the signal and 90° out of phase with it were used. In-phase pedestals produced an initial improvement in detection, followed by a loss in detectability at higher pedestal intensities. This result is similar to that found in pedestal experiments when external noise is present. The pedestal value that resulted in maximum detectability varied for different subjects; when external noise was added, this difference disappeared. Detectability with 90° out-of-phase pedestals also decreased with increasing pedestal in a manner similar to that found when external noise is present.
Frequency Resolution at 1000 and 4000 cps
Authors: Anderson Charles V. , Bilger Robert C.
Published: November 2005

Frequency discrimination as a function of signal duration was investigated with five trained, paid observers who demonstrated normal hearing and seven observers who demonstrated cochlear damage at one or both of the center frequencies of 1000 and 4000 cps. Frequency separations were 4, 8, and 16 cps at 1000 cps and 16, 32, and 64 at 4000 cps. The signal durations were 16, 32, 64, 128, and 256 msec. All signals were presented in a background of band-limited, 100- to 6000-cps, random noise. Using the two-alternative, forced-choice technique, the performance of each observer on 400 trials for each experimental condition was evaluated with d′ as a discrimination index. The individual performance of observers indicated improved performance with longer-duration, narrower bandwidth signals at center frequencies where hearing was normal. At center frequencies where cochlear damage was demonstrated only at the widest frequency separations did performance improve with increased signal duration.
Response of a Model of the Peripheral Auditory System to Sinusoidal Stimuli
Authors: Weiss Thomas F.
Published: November 2005

A model of the peripheral auditory system, which relates the firing patterns of single auditory-nerve fibers to acoustic stimuli, is discussed. Two aspects of the model's response to sinusoidal stimuli are compared with electrophysiological data obtained [N. Y.-S. Kiang, personal communications (1961–1963)] from single auditory-nerve fibers of the cat: (1) the equal response or “tuning” curves of individual fibers and (2) the sensitivity of a population of fibers as a function of frequency when each fiber responds to sinusoidal stimuli delivered at the “characteristic frequency” of the fiber. The model is composed of three elements: (1) a linear system intended to represent the outer, middle, and the mechanical part of the inner ear, (2) a nonlinear transducer intended to represent the sensory cells, and (3) a simplified representation of a nerve fiber that is probabilistic and contains a threshold and a refractory period. The model's responses to a variety of stimuli and its spontaneous activity were investigated with the aid of a digital computer (the TX-2 computer of the Lincoln Laboratory MIT). [Supported in part by the U. S. Army, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; and in part by the National Science Foundation (grant G-16526); and the National Institutes of Health, U. S. Department of Health, Education, and Welfare (grant MH-04737-03).]
Search for High-Q Liquid-Filled Systems
Authors: Simon Murray M.
Published: November 2005

The bulk modulus and its associated loss factor for small viscoelastic specimens can be determined by placing the sample at a velocity node of a liquid-filled system. The Q of this system must be high in order to obtain accurate results. Thus, to develop systems of high Q with the aim in mind of eventually measuring the Q of test specimens, the frequency response and Q of several systems were determined, including tubes and spheres of metal or glass containing liquids of various viscosity and density. [This work was supported by the U. S. Air Force Office of Scientific Research.]
Modal Characteristics of Composite Elastic Structures
Authors: Coale Charles W.
Published: November 2005

Analysis of the dynamic response of complex structures requires knowledge of the dynamic characteristics of the structure. In many cases, a structure is composed of several sections, each having a known or determinable set of modal characteristics. In this paper, a matrix eigenvalue equation is derived for determination of the modal characteristics of the composite structure in terms of the characteristics of its sections. Use is made of functional vector modes to describe the modal behavior of the sections in three-dimensional space. The problem is then formulated in terms of the modal- and rigid-body coordinates of the sections. The eigenvalue equation is derived by application of Lagrange's equations. The connection conditions between sections provide relations between the coordinates that are used to reduce the size of the matrices involved. Both direct and elastic connection of sections are considered. Several arrangements of the sections are treated, including tandem and multibranch configurations. As an illustration of the application of the above equations, the dynamic characteristics of a satellite with flexible solar panels are determined.
Influence of Boundary Conditions on the Modal Characteristics of Thin Cylindrical Shells
Authors: Forsberg Kevin
Published: November 2005

The modal characteristics of thin cylindrical shells have previously been determined for only three sets of boundary conditions. In the present analysis, all sixteen sets of homogeneous boundary conditions are considered, at each end of the shell (each set contains four conditions). The equations of motion of thin, circular, cylindrical shells developed by Flügge are used. The general solution to these equations can easily be written down. The difficulty arises in evaluating the constants of integration, and this apparently is the reason no one has followed this approach to its ultimate conclusion. One can assume a circumferential nodal pattern, eight boundary conditions, and a frequency of vibration, and then iterate numerically to find the length of shell that will meet these conditions. The advantage of this approach is that one can obtain a solution to the basic equations for any boundary conditions desired. Results indicate that the condition placed on the longitudinal displacement μ in many cases is more influential than restrictions on the slope or moment. It has been found that even for long cylinders the minimum natural frequency may differ by as much as a factor of two, depending upon whether, at both ends, μ=0 or the longitudinal stress resultant Nx=0.
Modified Isopreference Method for Audio-Quality Measurements
Authors: Rothauser E. H.
Published: November 2005

The audio quality of some speech-processing systems has been evaluated by isopreference tests. The isopreference method [W. A. Munson and J. E. Karlin, J. Acoust. Soc. Am. 34, 762 (1962)] could be simplified and was adapted to the special purpose so that the complexity of the required measurements was reduced. The principal interest has been concentrated on the reproducibility and on the transitivity of the measurements, rather than on absolute evaluation of the speech signals themselves. Instead of a “real speaker,” only a high-quality recording of such a speaker was used as a reference signal. The values of the evaluation scale were related to the reference signal used. The test signals were presented over headphones with a loudness corresponding to the “optimum speech level.” The accuracy and reproducibility of the results obtained by the modified method is believed to be sufficient for many evaluation purposes.
Study of the Nature of Speech-Transmission-Circuit Quality by Means of the Direct Production of Equivalent Impairments
Authors: Bricker Peter D.
Published: November 2005

Fifty-one listeners were asked to match the over-all quality of a variety of voice circuits with fixed parameters by adjusting either the speech level or the noise level on a reference circuit. Thus, they were required to produce “equivalent impairments” directly, whereas such equivalents are usually arrived at by inference from subjective judgments of a variety of circuits. It was found that (1) individual listeners generally found the task difficult and exhibited 10 times more variance on heterogeneous matches (where a speech-level difference was balanced by a noise-level difference) than on homogeneous matches (where speech levels and noise levels could be matched exactly); (2) listeners nevertheless agreed with themselves better than with each other, so that interindividual differences cannot be dismissed as error; (3) a reference circuit-speech level that is too loud for a substantial portion of the listeners can lead to results that are uninterpretable in terms of a single dimension of “quality.” The results suggest that a statement about the relative over-all qualities of two heterogeneously paired circuits is meaningful only if it is a statement of a large difference.
Psychoacoustic Speech Tests: A Modified Rhyme Test
Authors: House Arthur S. , Williams Carl , Hecker Michael H. L. , Kryter Karl D.
Published: November 2005

An attempt has been made to develop and evaluate an intelligibility test that can be used routinely by operational personnel to evaluate the condition of communication systems. The format used is similar in general respects to that described by Fairbanks as a rhyme test. Six lists of fifty monosyllabic words were constructed in such a way as to form fifty ensembles, each composed of six related words. Any given ensemble is characterized by one vowel that is the nucleus of each word; all of the words in a given ensemble either are initiated or terminated by the same consonantal phoneme. The listener is asked to select from each ensemble the word being transmitted. An experiment was performed to determine the general reliability and acceptability of this new test when administered under a wide range of signal-to-noise ratios to U. S. Air Force enlisted personnel. Testing of 18 subjects over a period of 30 days showed that repeated exposure to the materials did not change the average response levels in any appreciable way. Analyses of responses to individual phonetic elements suggest that the test may be useful for diagnostic purposes, as well as for over-all evaluation of communication systems. [This work has been supported by the Decision Sciences Laboratory, Electronic Systems Division, U. S. Air Force.]
Intelligibility of Excerpts from Conversation
Authors: Pollack Irwin , Pickett J. M.
Published: November 2005

Unrehearsed conversation was recorded from four talkers. Excerpts representing one or more words were then made from fluent portions of the conversations. The excerpts were presented to listeners in intelligibility tests. Average word intelligibility was calculated and examined as a function of average duration of excerpt. Excerpts ranged from 10 csec average duration, 14% correct, to 200 csec, 92% correct. For a given duration of excerpt, fast utterance was just as intelligible as slow utterance.
Reaction Time to Synthetic Stop Consonants and Vowels at Phoneme Centers and at Phoneme Boundaries
Authors: Studdert-Kennedy M. , Liberman A. M. , Stevens K. N.
Published: November 2005

The purpose of this study was to determine how quickly and consistently listeners can identify synthetic stops and vowels, depending on where they lie on an acoustic continuum that connects the center of one phoneme class with the center of the next adjacent one. All stimuli were produced on OVE II at the Royal Institute of Technology in Stockholm; they consisted of (1) thirteen consonant-vowel syllables in which the second- and third-formant transitions varied in such a way as to produce /b,d,g/ and (2) thirteen vowels in which the first three formants varied in approximately equal log steps through /i,ɪ,ɛ/. Listeners were instructed to identify each stimulus phonemically by pressing one of three buttons in one condition and by making an appropriate vocal response in another. For both stops and vowels, voice and button-press reaction times were lower near phoneme centers than in the vicinity of phoneme boundaries. In other respects, the results for stops and vowels differed, supporting the conclusion that the stops are the more readily identified. This difference is viewed in the light of other data that show gross differences in the shape and level of the discrimination functions for these two sets of signals. [This study was supported in part by the National Science Foundation.]
Effect of Competing Speech on Aided Discrimination of Monosyllabic Words
Authors: Tillman Tom W. , Carhart Raymond
Published: November 2005

PB50 lists were presented under three unaided and three aided conditions to 12 monaural hearers, 12 cases of conductive loss, 12 young adults with sensorineural loss, and 12 presbycysics. All items were presented in a sound field at a sensation level of 30 dB for the condition of the moment. The nontest ear was occluded to assure monaural response. The test ear, or the ear-level hearing-aid during aided listening, was at 45° azimuth to the loudspeaker emitting PB items. Two tests (one unaided and one aided) were given in quiet, two more while competing sentences at 12 dB SL came from a second loudspeaker (135° azimuth), and the final pair while the competing sentences were at 24 dB SL. All groups experienced slight deterioration of unaided discrimination and substantial deterioration of aided discrimination when the competing message was added. Moreover, the aided discrimination was always the poorer whether in quiet or not. Finally, deterioration of aided discrimination in the presence of competing speech was much more severe for the two sensorineural groups than for the other two groups.
Speech-Interference Criteria
Authors: Webster J. C.
Published: November 2005

An attempt has been made to show the similarities between three ostensibly different methods of rating noises for speech interference. The three basic methods are: sound-level meter (SLM) readings, using various frequency-weighting networks; noise criteria contours, where spectral peaks of noise become tangent to one of a family of rating curves; and dB-averaging methods, the articulation index (AI) being the most sophisticated method and the speech-interference level (SIL) being the simplest to use. A speech-interference (SI) curve has been evolved that, when used as a frequency-weighting network in a SLM, or as a noise-rating curve, or as a curve-fitting method of arriving at an SIL, greatly reduces the spread of scores among the three measurement methods when rating the speech-interfering properties of noise. Based on a literature review of speech intelligibility in noise, a family of SI contours was evolved to encompass greater ranges of noise levels (and intelligibility scores). These contours are compared to a theoretical treatment of the AI in idealized noises. Many similarities are noted. One potential use of the SI curve (as a frequency-weighting network in a SLM) is discussed: namely, a method of locating potentially objectionable noise environments from SLM readings alone.
Vibration of the Clarinet Body and its Contribution to the Clarinet Tone
Authors: Backus John
Published: November 2005

An artificially blown clarinet with all its tone holes closed was coupled tightly to one end of a large metal pipe so that all the sound produced was radiated into the pipe. Porous urethane foam stuffed into the other end absorbed the sound while allowing sufficient steady air flow to operate the clarinet. The internal sound wave in the instrument was monitored by means of a microphone in the mouthpiece. Under these conditions, the clarinet was practically inaudible; the level as read on a General Radio SPL meter placed nearby increased only two to three dB above the laboratory background of about 46–48 dB, and this increase was mostly due to sound radiated from the pipe rather than from the clarinet body. By using plastic tube in place of the more-rigid clarinet body, the sound radiating from it could be approximately measured, and was found to be some 45 dB below the sound radiated in the normal manner under the same blowing conditions when the sound-absorbing pipe was removed. It appears that the vibration of the clarinet body has no effect whatever on the tone of the instrument.
Characteristics of the Tone Quality of Wind Instruments
Authors: Hall Jody C. , Lockwood Clyde E.
Published: November 2005

Tests reported at previous meetings of the Acoustical Society of America have been extended to include a correlation of tone analyses with the terms used by musicians to describe tone quality. The characteristic harmonic patterns of the entire family of wind instruments are reviewed, as well as the factors that differentiate between tones judged by musicians to be acceptable or unacceptable. Tape recordings and slides are used to illustrate the characteristics of sounds that musicians refer to by such terms as “bright,” “dark,” “edgy,” “stuffy,” “round,” and “thin.”
Experimental Study of Self-Reciprocity Calibrations of Underwater Electroacoustics Transducers
Authors: Diercks K. J.
Published: November 2005

The present study is derived from the self-reciprocity method advanced by Carstensen in 1947 [J. Acoust. Soc. Am. 19, 961 (1947)]. Self-reciprocity calibrations for transducers covering the frequency range from 10 to 500 kc/sec are compared with calibrations obtained using more-conventional methods. In general, agreements to within 1 dB or less were obtained. Self-reciprocity calibrations obtained within the limit of the Fresnel region—i.e., in the nearfield of the transducer—in addition to those obtained at distances where the beamwidth exceeds the dimensions of the reflector (4×4 in.) are described. Five practical (inexpensive and readily available) reflectors were studied: 1-in.-thick commercial styrofoam (expanded polystyrene) alone; styrofoam bonded to aluminum (increased rigidity and manageability); 12-in.-thick Armstrong DC-100 corprene (corkneoprene) bonded to aluminum; 18-in.-thick Armstrong DC-167 corprene bonded to aluminum; and 1-in.-thick Kopper's Dylite bonded to aluminum. The expanded plastics, it is shown, are nearly acoustically perfect reflectors, but display some undesirable “handling” characteristics (are easily scarred and/or deformed). The corprenes, on the other hand, exhibit the desired physical characteristics but tend to be “lossy” (scattering and/or absorption), especially at the higher frequencies. The electronic apparatus, appreciably simplified with respect to Carstensen's, is described. [This work was supported by the U. S. Office of Naval Research.]
Use of Compliance Loading as a Transducer-Design Technique
Authors: Lubell Alan H.
Published: November 2005

The addition of a pair of compliance elements to the “Tonpilz” configuration may be viewed as a means of matching the impedance of an electrostrictive ceramic stack to that of the surrounding medium. The application of Thevenin's theorem allows a simple analysis of the electrical equivalent circuit of this vibrating system. It is shown that this technique can be used either to reduce the size of a low-frequency transducer or to simultaneously reduce the Q and increase the power output of a mechanically limited, energy converter. Applying the latter design approach to the source described in another paper [A. H. Lubell, Paper R4, this meeting], the combination mass loads and radiating plates are trimmed in mass to the smallest value compatible with control of flexural modes of vibration. Compliance elements are then inserted between the ends of the stack and the radiating plates to bring the fundamental resonant frequency back to its original value. Because of the lower mechanical Q, higher electrical drive may be applied without exceeding the strain limitation of the ceramic stack, providing that low-loss, high-coupling, electrostrictive ceramics are employed. [This work was undertaken as part of the Hughes company-sponsored acoustic-radiation-research program.]
Approximate Method for Estimating and Scaling the Energy Spectra of End-Detonated Line Charges
Authors: Slifko John P.
Published: November 2005

An approximate method is discussed for estimating the energy per unit area spectral density of the shock-wave pulse from an end-detonated underwater explosive line charge of any weight and length, and at any angle of emission and range. This method requires only that the following quantities, which can be estimated, be known: (a) the impulse of an equivalent weight “point” charge at the same range; (b) the shock-wave pulse duration; (c) a frequency function for the approximate waveform generated at the emission angle of interest. Experimental and calculated results are shown for a 40-g, 5-ft-long charge and for a 2-lb, 10-ft-long charge. The calculated values are in good agreement with experimental results for all angles of emission, except for angles in the sector ±10° from the beam angle. A simple method of directly scaling measured energy spectra to other sets of experimental conditions is also described. Good results were obtained for all angles of emission when the 40-g, 5-ft charge results were scaled to the energy values measured for the 2-lb, 10-ft charge.
Propagation of Transient Pressure Pulses in Water
Authors: Carome E. F. , Mraz S. J. , Parks P. E.
Published: November 2005

A study has been made of the propagation in water of low-amplitude, unidirectional pressure pulses of widths between 0.1 and 3.0 μsec. Piezoelectric plates were employed as acoustic sources and receivers, and the travel time through them was longer than the pulse width. The experimental data are compared with the results of recent theoretical studies by various workers. This includes the relationships between the time profiles of the voltage pulse applied to the source and of the pressure pulse produced in the liquid, and also between the time profiles of the receiver-output voltage and of the stress wave incident on the receiver. In addition, consideration is given to transient processes in the acoustic field of a piston source and the way these affect the shape of the received signal at different pathlengths. [This work is supported in part by the U. S. Office of Naval Research.]
Optically Induced Acoustic Transients
Authors: Carome E. F. , Clark N. A. , Moeller C. E.
Published: November 2005

The intense optical impulses produced by a laser have been used to generate acoustic transients in both liquids and solids. The optical impulses, which are less than 1 μsec wide, produce transient heating at the surface of an optically absorbing material. The time profile of the resulting elastic disturbance has been studied as a function of the acoustic-boundary conditions at the absorbing interface. The results of a number of other preliminary experiments indicate the usefulness of this optico-acoustic technique for various physical-acoustic studies. [This work is supported in part by the U. S. Office of Naval Research.]
Frequency-Band Radiation Patterns for the Linear Array
Authors: Bailey R. P.
Published: November 2005

The integrated response of an array over a band of frequencies, plotted as a function of direction from the array, is known as a band pattern. It is shown that the computation of such patterns is much simplified by the use of a table of values of a certain function Hn(Z). The directional gain for the classical single-frequency pattern is also obtained directly from the table. General properties of band patterns for the linear array are discussed and illustrated, both for the case of uniform amplitude noise and amplitude decreasing 6 dB per octave. [This work was performed for Chesapeake Instrument Corporation, Shadyside, Maryland, under a contract from the Acoustics Branch, U. S. Office of Naval Research.]
Farfield Radiation from a Solid Circular Cone Undergoing Steady-State Longitudinal Vibration
Authors: MacKinnon R. F.
Published: November 2005

Equations for the farfield pressure due to a vibrating cone have been derived under the assumptions that diffraction effects may be neglected and that the vibration is solely longitudinal. The former assumption limits the validity of the derived equations to cases of high and low frequency. The latter assumption entails a neglect of Poisson effects. Directivity patterns are presented for a variety of cases for both full and truncated cones. The ratio of the pressure on the axis of the cone due to the curved surface of a full cone to that due to the plane circular end set in an infinite baffle is given analytically as a function, dependent upon the mode of vibration, frequency, and velocity mismatch between the vibrating body and the medium.
Auditory-Threshold Determinations, Using Continuous and Stepped Attenuation
Authors: Silbiger Herman R. , Elliott Donald N.
Published: November 2005

A comparison was made between auditory thresholds obtained by means of a recording attenuator (Békésy method), using the usual stepless continuous attenuation and a method whereby the recording attenuator increased or decreased attenuation in discrete steps of 1 dB. Thresholds were obtained at 2800 cps, using both continuous tones and interrupted tones with five different combinations of periods and duty cycles. Thresholds were also obtained after introduction of 20 dB of auditory fatigue. The results do not show any difference in threshold location ascribable to the continuous or stepped attenuation either before or during fatigue. The interval of uncertainty is reduced to approximately 2 dB instead of the 5 to 10 dB found with continuous attenuation. The large differences between individuals and within individuals in pen-excursion size during threshold determinations disappear when the stepped-attenuation method is used. The reduction in pen-excursion size with continuous tones during auditory fatigue is not in evidence with stepped attenuation. The findings indicate that, when only threshold location is required, there are definite advantages to using stepped instead of continuous attenuation, since it gives a clearer indication of the threshold location and eliminates the influence of factors affecting the pen-excursion size. [This work was done at Wayne State University with support of the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]
Audibility Curve of Chinchilla
Authors: Miller James D.
Published: November 2005

The chinchilla can be readily trained to respond to tones by the method of avoidance conditioning in a shuttle box. In addition, they can be trained for the threshold tests in about the same amount of time as required to train cats. The method for threshold tests is as previously described for cats, with the addition of adding feedback for responses to very weak tones so that the animal knows whether his response was correct. The binaural-audibility curve of chinchilla has been carefully determined at 12-octave steps for six highly trained animals. Below 1000 cps, sensitivity appears to be better than man's; above 2000 cps, it is similar to man's but extends to slightly higher frequencies, that is, about 32 kc/sec. Between 1000 and 2000 cps, chinchillas have narrow regions of low sensitivity; these dips vary in location from animal to animal but are reliable and stable for each.
Binaural Interaction in the Accessory Superior-Olivary Nucleus of the Cat
Authors: Hall Joseph L.
Published: November 2005

In an effort to understand the neural encoding of binaurally presented stimuli, clicks were presented through earphones to the two ears of anesthetized cats and the electrical response activity of single cells in the accessory superior-olivary nucleus was studied. Stimulus parameters investigated included interaural time difference, interaural intensity difference, and average intensity. Attention was focused on cells that were excited by stimulation of the contralateral ear and inhibited by stimulation of the ipsilateral ear. A model is suggested in which localization judgments are obtained on the basis of activity in the accessory nuclei. In the model, the position of the virtual image is determined by a comparison of the amount of response activity in the two accessory nuclei. Incorporation of empirical data into the model yields predictions that are in agreement with results from human psychophysics. The model predicts that the virtual image should be localized toward the side receiving more-intense or prior stimulation. A time-intensity trading relationship that is in agreement with results from “centering” experiments is derived. The model predicts minimum detectable changes in interaural time difference of 5–10 μsec and minimum detectable changes in interaural intensity difference of 0.1–0.5 dB. [This work was supported in part by the U. S. Army, the U. S. Air Force Office of Scientific Research, and the U. S. Office of Naval Research; and in part by the National Science Foundation (grant G-16526) and the National Institutes of Health, U. S. Department of Health, Education, and Welfare (grant MH-04737-03).]
Use of the Békésy Audiometer in Animal Research
Authors: Voots R. J. , Reger S. N. , Hinchcliffe R. , Watson J. E.
Published: November 2005

The Békésy audiometer has been adapted to our needs in animal research by substituting for their organic counterparts an extracorporeal decision-maker and button-pusher. In this system, the electrical response to a continuing tonal stimulus from the Békésy audiometer is picked up from any suitable cochlear electrode(s), amplified as usual, and submitted to the decision-maker. This device, functioning as an autocorrelating coherence detector, operates a relay substitute for the button-pusher. As the expected signal rises above or falls below the predetermined threshold level, the relay feeds back this information to the Békésy attenuator motor, thus controlling the stimulus level as usual in Békésy audiometry. This system permits continuous tracking of “thresholds” at levels well below the background noise and is expected to facilitate study of recovery from temporary threshold shift following various types of cochlear insult.
Computer Program for Automatic Composition and Generation of Music
Authors: Mathews M. V. , Miller Joan E.
Published: November 2005

A new computer music program with greatly simplified notation and expanded capabilities is described. The new program makes the handling of computer music much easier for the noncomputer-oriented musician. Both the definition of computer instruments and the preparation of a score have been simplified. Instruments are designed first in diagram form, and descriptions are prepared for the computer by merely listing each of the elements of the diagram, together with its input specifications. Each such list, which defines an instrument, is named, and, thus, several instruments of the same type may be compiled by mentioning the name only. In addition, many potentialities for computer-aided composition have been added. The former program required the composer to write the parameters of each note to be played. With the new routines, the computer can be used to generate note parameters. For example, once a theme with many notes is written, it may be repeated by a single instruction. The notes can be modified in simple ways, such as transposing the pitch, playing upon other instruments, and changing tempo or loudness. Single voices can be harmonized according to simple rules. Examples of these transformations are presented.
Puzzling Origin of Javanese Tuning Systems
Authors: Barbour J. Murray
Published: November 2005

The Javanese sléndro system is a pentatonic scale of approximately equal intervals of 240 ± 20 cents. Three consecutive intervals constitute the sléndro fifth of about 720 cents, although it is less stable than might be expected. In the heptatonic pélog system, there are five small intervals and two that are about twice as large, all of these intervals being unstable. Pélog fifths that contain two large and three small intervals average about 780 cents. The normal pélog fifth, comprising one large and four small intervals, is remarkably stable at about 665 cents. Although gongs, metallophones, and xylophones form an integral part of the Javanese orchestra, there is no evidence that their inharmonic partials have affected these tuning systems. Nor does Erich von Hornbostel's theory of a Blasquinte of 678 cents have a bearing on the tuning, for his theory was completely discredited 25 years ago. Thus, the origin of the sléndro fifth of 720 cents and the pélog fifths of 665 and 780 cents remains a mystery.
Effect of Pressure on the Absorption Coefficient of an Electrolytic Solution with Water-Methanol Solvent
Authors: El-Dosokey Hamdy , Beyer Robert T.
Published: November 2005

The sound-absorption coefficient has been measured by a pulse technique at a temperature of 30°C and under various pressures up to 15 000 psi in the frequency range 15 to 65 MHz. The observed data show that the absorption coefficient per wavelength decreases slightly as the pressure is increased in the frequency range measured. The relaxation frequency of the process appears to increase as the pressure is increased (from 67 MHz at 1 atmosphere to 86 MHz at 1000 atmospheres). The results here made by Fisher [J. Acoust. Soc. Am. 30, 442 (1958)] are compared with similar measurements on 0.5 molal MgSO4 in a pure-water solvent, studying the low-frequency peak. The decrease in the size of the absorption coefficient here was much smaller. Sound-velocity measurements were also made in this research. These indicate a nearly constant gradient of +17.3 cm/sec per atmosphere, close to the value for pure water. [This work was supported in part by the U. S. Office of Naval Research.]
Thermal Relaxation Processes in Gases
Authors: Shields F. D. , Lee K. P.
Published: November 2005

Sound-absorption and velocity measurements have been made in O2 with added amounts of H2, D2, and He. The number of collisions, Z10(AB), necessary to deexcite the first vibrational state of O2 has been calculated from the measured relaxation times. At 100°C: Z10(O2-H2)=2.0×104, Z10(O2-D2)=2.5×105. At 200°C: Z10(O2-H2)=1.1×104, Z10(O2-D2)=1.5×105, Z10(O2-He)=7×104. At 300°C: Z10(O2-He)=3.8×104. These values are in general agreement with values reported by Parker; Holmes, Smith, and Tempest; and White and Millikan. When log Z10(AB) is plotted vs the cube root of the reduced mass times the square of the vibrational frequency divided by the absolute temperature, a linear relationship is found between the O2-H2 and the O2-He data. However, Z10(O2-D2) is unexpectedly bigger than Z10(O2-He). When the collision numbers Z10 for pure O2 and N2 are plotted in this way, they fall along a single curve. [This work was supported by the U. S. Office of Naval Research under contract Nonr 3078(00).]
Evaluation of the Effects of Dynamic Encoding on Vocoder Performance
Authors: Cassel Lawrence E. , Steele Robert W.
Published: November 2005

The concept of dynamic encoding and decoding was presented at the May 1963 Meeting of the Acoustical Society of America. As a follow on to this presentation, this paper is concerned with demonstrating the degree of vocoder improvement obtainable, using dynamic encoding from both an intelligibility and quality viewpoint. An RT (rhyme test) word-testing technique developed by Grant Fairbanks was employed to determine the intelligibility improvement, and an A-B comparison test was employed for quality evaluations. The tests were run by using dynamic encoding at both the 2400- and 1200-bits/sec rates and were compared directly to the conventional 2400- and 1200-bits/sec rates. At 2400 bits/sec, the intelligibility scores average approximately 4%–6% higher with dynamic encoding and at 1200 bits/sec the scores average from 7%–10% higher. The difference in quality is significant in both options. A demonstration tape is played illustrating the differences. This tape also illustrates the remarkable ability of dynamic encoding to provide vocoder performance very close to that obtained in the analog-to-analog mode.
Speech Synthesis by Rule Controlled by a Small, Low-Speed Digital Computer
Authors: Holmes J. N. , Shearme J. N.
Published: November 2005

Computer synthesis of speech by rule has already been demonstrated by workers at the Bell Telephone Laboratories, using a large high-speed computer to perform the entire process. This paper describes a way of achieving a similar result by the use of a small computer, in conjuction with a moving-resonance speech synthesizer. The computer program is fairly simple, and consists of instructions for interpreting a table of phoneme data that has been previously fed into the computer store. The sequence of phonemes corresponding to the speech required, together with associated larynx frequencies, is then fed in from a punched tape. Durations are not specified separately, but are calculated from the tables; however, if variations of duration, intensity, or other properties are required to produce variations of stress, etc., additional characters may be added immediately prior to any phoneme symbol. These characters cause the stored table of properties to be modified for that one occurrence of the associated phoneme. This use of modifying characters enables the program to be easily used for experimental changes of the synthesis rules. These are needed mainly for perception experiments leading to further improvements of the rules.
Computer-Simulated Analyzer for a Formant Vocoder
Authors: Coker C. H.
Published: November 2005

A formant-vocoder analyzer has been programmed for a large-scale digital computer. The rectified and smoothed outputs of a 24-channel, contiguous filterbank are multiplexed and digitalized for computer analysis. The program extracts a voiced-unvoiced decision, four poles and one zero for voiced sounds, and one pole and a zero for fricatives. Poles are located by a technique of interpolative peak-picking within certain frequency ranges. Confusion within overlapping boundaries is resolved by a method of fitting stored resonance curves to adjacent poles. Accuracy of the extracted parameters is checked by resynthesis and audition, using a computer-programmed synthesizer described previously [J. L. Flanagan, C. H. Coker, and Carol M. Bird, J. Acoust. Soc. Am. 34, 2003(A) (1962)]. A magnetic-tape demonstration of the complete analysis-synthesis system is presented.
Speech Analysis with Computer-Simulated Filter Bank
Authors: Crystal T. H.
Published: November 2005

A 165-filter basilar-membrane model is used to analyze speech signals. In an attempt to take a new approach, logical and crossfilter operations are performed instead of the customary time-averaging. The model simulation and logical operations are programmed on an IBM-7090 and the results plotted on microfilm with a Stromberg-Carlson 4020. Applications to pitch and formant tracking are described.
Measurements of Noise Generated by Centrifugal Blowers
Authors: Maling G. C.
Published: November 2005

A plenum chamber of lightweight vinyl plastic has been used to make reverberation-chamber measurements of the total acoustic power radiated by a homologous series of centrifugal blowers. The experimentally determined sound-power levels have been reduced to dimensionless form by applying dimensional analysis to the variables that influence the acoustic power radiated [G. C. Maling, Jr., J. Acoust. Soc. Am. 35, 1556 (1963)]. The variables chosen are an acoustic parameter θ = E/ρc2D3, a frequency parameter s = f/n, the tip-speed Mach number M = πDN/c, and the flow coefficient φ = Q/πD3N. N is the speed of the impeller, D is the impeller diameter, Q is the delivered volume flow, and ρ and c are the density of air and the speed of sound, respectively. It is shown that a dimensionless spectral-density function can be used to characterize the acoustic power radiated by the series of blowers.
Variations in the Eddy-Convection Speeds in Rocket-Exhaust Flows and Their Influence on the Radiated Noise
Authors: Ffowcs-Williams John E.
Published: November 2005

When turbulent eddies are convected supersonically, they give rise to a highly directional radiation that has been termed a Mach wave emission. This type of radiation is probably the main contributor to rocket-noise fields. The theory describing the mechanism of Mach wavegeneration has so far neglected the way in which changes in the convection speeds can affect the noise field. The work described is aimed at answering some of the unresolved questions regarding these speed changes so that the theory can be more useful in understanding the noise of high-velocity rocket-exhaust flows. [This research has been supported by the National Aeronautics and Space Administration.]