摘要:

Dispersed high‐order modes have been observed at frequencies as high as 300 Hz and at ranges of 600 km for shots detonated and received on the axis of a SOFAR channel located in the western Mediterranean Sea. Spectrum analysis of shot records has revealed as many as five identifiable group‐velocity profiles that correlate with modes as high as 70. Accurate prediction of observed group‐velocity profiles is obtained by applying WKB mode theory to sound‐velocity data. In addition, dispersion of individual resolved multipath arrivals, for which low frequencies tend to arrive later, is observed and analyzed by a modified ray theory including diffraction effects.

ISSN:0001-4966    

DOI:10.1121/1.1913317

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The Trott nearfield calibration array (NFCA) is an experimentally proven concept for determining the farfield acoustic radiation of large underwater transducers from measurements in the nearfield. Existing successful NFCAs are large planar configurations of small reciprocal transducers whose responses are amplitude‐shaded to produce a nearly uniform plane wave directed normal to the NFCA throughout the volume to be occupied by the unknown transducer. Trott obtained effective shading coefficients by the use of semiempirical methods that are applicable to linear or planar arrays. In this paper a rigorous derivation of the NFCA reciprocity principle is presented for the first time. The results allow for both amplitude and phase shading and are applicable to NFCAs of any configuration. A numerical technique based on this principle is described which produces an optimum set of shading coefficients for any NFCA configuration with a prescribed plane wave direction, volume, and frequency domain. Numerical examples are presented and discussed. Included is the design of a cylindrical NFCA suitable for calibrating an enclosed cylindrical transducer without mechanical rotation.

ISSN:0001-4966    

DOI:10.1121/1.1913318

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The response of an impact damper system to an excitation with approximately white‐power spectral density and Gaussian probability distribution is determined, using two independent methods: digital computer and electronic‐analog techniques. Results are given for mean‐squared level, power spectral density, probability density, probability distribution, and amplitude probability density of the response. The impact damper is found to be a practical and efficient device for reducing the response amplitude of systems subjected to random excitation.

ISSN:0001-4966    

DOI:10.1121/1.1913319

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The possibility that velopharyngeal opening may cause the transglottal pressure drop necessary for the production of normal English non‐nasal voiced stop consonants was investigated. Nasal airflow rate and intraoral pressure were measured during the production of a selected speech sample, produced by three normal adult females. Results suggest that nasal airflow is not uncommon during the production of non‐nasal stops by normal English speakers but that the observed airflow is most likely not due to velopharyngeal opening and therefore a velopharyngeal leak represents the least probable single mechanism for the generation of a transglottal pressure drop. The hypothesis is presented that the observed nasal airflow is due to active movements of the soft palate changing the volume of the nasal cavity. The possibility that a velopharyngeal leak mightcontribute, in an occassional and selective manner, to transglottal flow is recognized.

ISSN:0001-4966    

DOI:10.1121/1.1913320

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An attempt has been made to evaluate the performance of the simplest type of liquid‐solid lens, i.e., a hemispherical surface between the liquid and solid. The nature of the image allowing for the effects of refraction, absorption, and mode conversion has been determined for an equally spaced object and image. It appears that the diffraction effects are the only important ones and that geometric aberration is unimportant.

ISSN:0001-4966    

DOI:10.1121/1.1913321

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Investigators have suggested several internal noises that affect absolute thresholds (e.g., heart sounds, circulatory pulsations, muscle tremors). Furthermore, it has been suggested that blood flow may modulate aural noise in the external canal. Since mental blood vessels cannot expand outward due to bone encasing the canal, an inward expansion is suggested which induces an increase in aural noise by decreasing mental volume under the earphone. In short, the meatal pulsation hypothesis (MPH) suggests a modulation of aural noise as a function of blood flow through the ear canal. This study examines the MPH under three conditions (tight and normal fitting supraaural cushions and an insert earmold) as a function of the cardiac cycle. Three dependent measures were obtained, viz., EKG, blood flow at the earlobe, and pressure changes within the ear canal (positive pressure indicating, according to the MPH, an inward expansion of the blood vessels). The EKG R‐wave keyed a signal averaging computer which in turn averaged the data over 32 separate heartbeats. Results indicate: (1) a maximum positive pressure approximately 225–250 msec after the R‐wave with rapid decreases prior to and immediately after the maximum (tight fitting earphones); (2) no systematic pressure change with normally fitting earphones; (3) an inverse relationship between blood flow at the earlobe and pressure change within the meatus. The maximumnegativepressure occurring near 225–250 msec after the R‐wave.

ISSN:0001-4966    

DOI:10.1121/1.1982164

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

When chinchillas are continuously exposed for more than 24 h to an octave band of noise centered at 500 Hz, the behavioral TTS for 715‐Hz tone stabilizes at an asymptotic value proportional to band level [Carder and Miller, Trans. Amer. Acad. Ophthal. Otolaryng.75, 1346 (1971)]. Recovery to normal thresholds requires from two to seven days. Chinchillas were exposed to this same noise for two days at 65, 75, 85, or 95 dB SPL. The organ of Corti was immediately fixed and prepared as a flat, whole‐mount specimen in plastic suitable for both phase contrast and electron microscopy. Other ears exposed at 95 dB SPL were allowed to recover 7, 28, or 70 days before fixation. The number of cisternae in the peripheral membrane system of many outer hair cells was increased from three to six to as many as 30. Similar membranes appeared as whorls within the cells. The proportion of altered cells was greatest in upper second and lower third turns and increased with exposure levels. Recovery toward normal membrane configuration was evident at seven days and only minor variations remained after 28 and 70 days.

ISSN:0001-4966    

DOI:10.1121/1.1982166

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This method is based on the acoustic tube model of the vocal tract in which the tube is divided into a finite number of sections with equal lengths. The volume velocity is defined in each section. Input impedance at the front end of the tube (corresponding to the lips) can be computed as the ratio of the pressure and the volume velocity there, providing that the volume velocity and the pressure are continuous at each boundary between two adjacent sections. This input impedance is shown to be of the formD(z)/G(z), whereD(z) andG(z) are polynomials inz−1. It is also shown thatD(z) andG(z) are constructed as a difference and a sum, respectively, of two polynomials whose coefficients can be determined from the reflection coefficients of the acoustic tube model. Since a method for obtaining the reflection coefficients from the speech wave is already established [H. Wakita, SCRL Monogr. No. 9 (July 1972)],D(z) and G(z) can thus be obtained from the speech wave. Input impedance singularities obtained with area functions for five Russian vowels by Fant were in very good agreement with Mermelstein's results [J. Acoust. Soc. Amer.41, 1283–1294 (1967)]. [The Office of Naval Research supported this work.]

ISSN:0001-4966    

DOI:10.1121/1.1982173

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

It has been shown by Flanagan and Landgraf [IEEE Trans. Audio Electroacoust.16, No. 1, 57–64 (1968)] that in the transformation between glottal area and glottal volume velocity during voiced vowels, the effect of the interaction between the acoustic impedance of the glottis and that of the supraglottal vocal tract cannot always be neglected. When there is such interaction, the glottal‐supraglottal acoustic system must be considered a nonlinear system with time‐varying parameters. Thus, any inverse‐filtering process designed to extract the glottal area waveform from measurements of supraglottal pressure or air flow must also be nonlinear. This paper reports initial efforts to determine the conditions under which a nonlinear inverse‐filtering process exists that will yield a function directly related to glottal area from recordings of oral volume velocity, and how such a nonlinear inverse filter could be implemented.

ISSN:0001-4966    

DOI:10.1121/1.1982176

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Most previous electromyographic studies of tongue muscles have been limited to those extrinsic muscles which are easily accessible: the genioglossus and palatoglossus. Recent experiments have provided access to the styloglossus, among the extrinsic muscles, and to the intrinsic fibers of the tongue. Thus, a fuller picture of muscular synergisms in the positioning and shaping of the tongue is beginning to appear. This study reports findings from three subjects who spoke 10 American English vowels in a labial consonant frame preceded by schwa. All electromyographic activity was recorded from hooked‐wire electrodes inserted into the various muscles by means of hypodermic needles. The results reveal as many differences as similarities between the articulatory strategies of the subjects. It appears that the similar articulatory configurations that underlie the linguistically relevant acoustic structures of the vowels can be achieved by a variety of muscular patterning. [This research was supported by the National Institute of Dental Research.]

ISSN:0001-4966    

DOI:10.1121/1.1982182

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP