Volume 35, Issue 11, November 1963
Index of content:
- PROGRAM OF THE SIXTY‐SIXTH MEETING OF THE ACOUSTICAL SOCIETY OF AMERICA
- Session A. Shock and Vibration I
- Contributed Papers
35(1963); http://dx.doi.org/10.1121/1.1937487View Description Hide Description
A study was undertaken to investigate the decay of simple electromagnetically driven mass‐loaded systems by measurements of the bandwidth and of the decay time, where either the loss resistance or the loss factor was frequency‐dependent. Results indicated, however, that it is extremely difficult to design a system that acts like a simple point‐mass compliant‐element vibrator. Unless great care is taken, the system does not produce the simple frequency curve that one would expect, but many resonances are observed that can be attributed to the system supports and the driving mechanism. Because of the difficulty experienced in eliminating the coupling to the supporting apparatus and the driver, a detailed study of simple vibrating systems became necessary. A series of mass‐loaded systems that gave progressively simpler frequency curves was developed, including one in which the driving magnet acts as the mass loading. A description of each is presented, along with its frequency curve. [This work was supported by the U. S. Air Force Office of Scientific Research.]
35(1963); http://dx.doi.org/10.1121/1.1937488View Description Hide Description
The dynamic response of a homogeneous, isotropic, elastic disk due to rigid‐body motion of its boundary is treated. Asymptotic values of the displacements and stresses are obtained for small times. The specific problem of impulsive applied accelerations is treated numerically and analytically; more‐general motions can be built up from this by integration. This problem has applications to propellant‐grain stress analysis and to other problems of interest to machine designers.
35(1963); http://dx.doi.org/10.1121/1.1937489View Description Hide Description
Approximate solutions are presented for the thickness and vibrational amplitude of a long thin bar vibrating in lateral motion under the condition of uniform stress along its length. It is shown that, rather than one unique shape dependent upon the choice of dimensionless frequency, there is a family of shapes that depends upon the choice of dimensionless stress. Attention is given to the problem of properly terminating such a bar. The predictions of the theory are compared with the results of experiment.
35(1963); http://dx.doi.org/10.1121/1.1937490View Description Hide Description
Previous studies conducted in this laboratory on the vibrations of plates with joints were concerned primarily with rigid bar joints presenting essentially a one‐dimensional constraint. Photographs of this system's nodal patterns clearly demonstrate transmission of those modes having nodal lines parallel to the joint, in agreement with theory, while for more complex patterns only the component parallel to the joint is transmitted. Present work centers about an investigation of multiple‐joint and joint‐stiffener rib combinations that approximate a two‐dimensional constraint. Measurements made of the velocity distribution of freely suspended plates with such joints are discussed.
35(1963); http://dx.doi.org/10.1121/1.2142598View Description Hide Description
A comparison is made of the two different types of vibration testing: modal and environmental. Their application to the determination of the flight‐safety characteristics of a flight vehicle is discussed. A brief history is included of the development of the equipment and techniques for modal or resonancevibration testing, which is so important before first flight. An example is given of a modal vibration test on an unusually complex aircraft structure, the Lockheed WV‐2E, that shows the problems of separation of modes closely spaced in frequency and the difficulties in obtaining all of the modes, clean. The significance of mode shapes, location of mode lines, and mode‐frequency ratios are discussed as to how they affect dynamic responses and flutter susceptibilities.
35(1963); http://dx.doi.org/10.1121/1.2142599View Description Hide Description
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 ρ0 c 0/ωm>1 (ρ0, c 0=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 c 0 at the critical frequencies f 1 and f 2, respectively, (f 2>f 1). For f<f 1, no free waves radiate; for f>f 2, all free waves radiate with unit efficiency. Between f 1 and f 2, 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 Signals35(1963); http://dx.doi.org/10.1121/1.2142600View Description Hide Description
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.
35(1963); http://dx.doi.org/10.1121/1.2142601View Description Hide Description
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., ), 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.]
- Session B. Speech Communication I: Source Characteristics
35(1963); http://dx.doi.org/10.1121/1.2142602View Description Hide Description
An information‐theory approach is used to evaluate the information rate necessary to accurately transmit the pitch information of connected speech. An IBM‐1620 is programmed to scan experimentally obtained pitch data and evaluate transitional probabilities, which are used to determine the conditional entropy. The conditional entropy decreases monotonically as higher‐order transitional probabilities are considered. For transitional probabilities of sufficiently high order, the minimum entropy for the pitch signal is obtained. Numerical values for the pitch‐information rate, based on experimental data, are presented as a function of the transitional probabilities. [The work reported was sponsored by the National Science Foundation under grant GP‐590.]
35(1963); http://dx.doi.org/10.1121/1.2142603View Description Hide Description
This paper presents quantitative information concerning the shifts in pitch that occur when a talker changes the power level of his voice from “normal” to “loud” or from “normal” to “soft” under natural speaking conditions; in addition, data are given of the shift in frequency of the first formant (F1) for an increase in speech power level. The shifts were measured for the following sets of words: (1) a group of recordings of the same word, each spoken by a different talker, and (2) a group of different words spoken by the same talker. For each word, the shifts accompanying the change in speech power level were computed for five points along the pitch and formant tracks—from the beginning to the end of the word. For a change in speech power level from “normal” to “loud,” the average change in pitch for all of the data was approximately 40%, and the change in F1 was approximately 12%. For a change in speech power level from “normal” to “soft,” the over‐all average decrease in pitch was approximately 12%.
35(1963); http://dx.doi.org/10.1121/1.2142604View Description Hide Description
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 pressurewave, 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 speechwave, duty factor and degree of closure as a function of talker, sound, pitch, and intensity.
35(1963); http://dx.doi.org/10.1121/1.2142605View Description Hide Description
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.
35(1963); http://dx.doi.org/10.1121/1.2142606View Description Hide Description
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.
35(1963); http://dx.doi.org/10.1121/1.2142607View Description Hide Description
Recent perceptual studies employing analysis of natural vowels and synthesized complex waves have suggested that spectral parameters other than fundamental frequency may be operative in pitch perception. The present study was designed to investigate the extent to which high‐pitched male subjects and males with normal vocal pitch could be distinguished by characteristic resonant frequencies and amplitudes, as well as fundamental frequency. Pitch judgments scaled by the pair‐comparison techniques were related to spectral parameters. Data were collected from 1500‐msec midvocalic segments of /i/ vowels produced by 25 subjects. The data suggested that some form of physiologic changes are manifest for the two groups such that the characteristics of the acoustic resonators are different for males with abnormally high‐pitched voices. These subjects utilized a resonating system wherein the second formant was approximately 200 cps higher than was apparent for persons of normal vocal pitch. No differences in formant amplitudes were found. Inconsistencies in the fundamental frequencies and listener pitch‐judgment data demonstrated the need for expanded knowledge of the relation of listener perception of pitch to parameters of the acoustic signal.
35(1963); http://dx.doi.org/10.1121/1.2142608View Description Hide Description
This paper describes a talker‐recognition procedure that selects a small subset of features from a much larger body of data and bases recognition on this subset. The subset is chosen as those features having small variation between utterances of a given talker as compared to the variation among utterances of different talkers. This procedure is applied to materials consisting of quantized spectrographic information from a group of ten talkers uttering 10 different words seven times each; modified materials averaging the spectrographic information are also used for recognition. Results are computed as a function of the number of features used. These results are compared with those obtained by simple pattern matching and by a procedure that selects features by means of multidimensional analysis of variance. Although we have treated talker recognition only, this procedure is general and can be applied to other recognition problems where it is desirable to use a simple, cheap, and fast method to select a few important features from a much larger set that can be in the thousands.
35(1963); http://dx.doi.org/10.1121/1.2142609View Description Hide Description
The use of the voice as a means for identifying an individual is limited to a great extent by marked variability of trial‐retrial responses. This paper discusses several techniques designed to reduce this variability. A spectral analysis series of 10 measurement points in the frequency range from 500 to 2000 cps with passbands 1 cps in width is employed for the vocal analysis. Data are presented from a series of 5 experiments with 70 subjects. Results of these studies are presented: (1) Frequencies below 500 cps are highly labile. They are shown to vary as a function of mild stress, time, and simple stimuli. (2) The energy distribution above 2000 cps depends more upon the spoken sound than upon the individual characteristics of the speaker. (3) Subjects were instructed to match the fundamental frequency to a standard tone (125 cps for males, 250 cps for females). (4) Each subject matched the intensity of his voice to a standard. Thus, fundamental frequency and intensity of the voice sample can be controlled. These techniques eliminate the major sources of variability in intrasubject vocal analysis. The extent to which these techniques permit discriminations among individuals on the basis of their speech is discussed.
35(1963); http://dx.doi.org/10.1121/1.2142610View Description Hide Description
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.]
- Session C. Electroacoustics
- Invited Paper
35(1963); http://dx.doi.org/10.1121/1.2142611View Description Hide Description
The RCA Victor “DYNAGROOVE” system is a planned evolution of improvements in all aspects and elements of sound recording by means of disk records. The main objective has been to provide a distinct improvement in performance by the development of a new cohesive and integrated system from the artist's conception of the music to the reproduction of the sound as perceived by the listener.
- Contributed Papers
35(1963); http://dx.doi.org/10.1121/1.2142612View Description Hide Description
Condensermicrophones 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 electretmicrophones 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.
35(1963); http://dx.doi.org/10.1121/1.2142613View Description Hide Description
This paper considers the radiation impedances of various sizes of elements forming a plane array. The mutual‐interaction impedance for various shapes of radiators and types of baffles is discussed in order to form a basis for computation of the total interaction impedances. Erroneous results can be obtained if the wrong theoretical model is used for the element; specific limitations of the circular piston and the pulsating hemisphere are described. Suitable techniques are discussed and results are compared with those of Stenzel and Pritchard. It is shown that the radiation impedances reported at the November 1962 Meeting were erroneous. The general behavior of radiation impedance is summarized.