摘要:

The duration of speech segments as a function of position in utterances (initial, medial, final) was studied. Seven English speakers read nonsense utterances of the form “say a bab, say a babab, say a babab,” etc. Spectrograms were used to determine the duration of speech segments in the readings. Final syllables were found to be longer than nonfinal syllables. Final‐syllable vowel increments were about 100 msec. Final‐syllable consonant increments were less than vowel increments, for instance, 20 msec for absolute final consonants. Also word‐initial consonants were found to be lengthened by 20–30 msec. It is suggested that durational studies in general should be interpreted in the light of findings concerning position‐in‐utterance lengthening. Explanations of lengthening effects are discussed. One theory suggests that lengthening in certain utterance positions is a learned aspect of languages which cues listeners concerning the segmentation of utterances into words, phrases, or sentences. Explanations based on hypothesized properties of the articulatory control system are also discussed.

ISSN:0001-4966    

DOI:10.1121/1.1975561

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

In March in the Gulf of Mexico in 3180 m of water, seven acoustic runs were conducted over a two‐day period. A directional source was suspended, at 80‐ and 360‐m depth and below a duct, from a surface ship that was essentially in a drift mode. An omnidirectional receiving hydrophone was towed at 3 kt at depths between 70 and 330 m and from 0.8 to 12 km. The acoustic energy was propagated in the form of 120‐msec CW pulses at 380 and 258 Hz, alternately, every 15 sec. During these opening and closing range trials,X‐BT's were taken at the receiving ship. Analysis for the received pulse levels was restricted to those coming via the refracted only and surface‐reflected propagated modes. Comparisons made of ray‐trace calculations from several models of the predicted acoustic signal levels with experimental results show good agreement through the Lloyd mirror interference regions with somewhat lesser accuracies for single path arrivals at the maximum ranges.

ISSN:0001-4966    

DOI:10.1121/1.1975571

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Two contributions are made to ray‐theory techniques for propagation through continuously stratified media. The first makes use of spline polynomials to approximate speed of sound profiles smoothly. The second eliminates the singularity occurring in the usual range integral. A versatile automatic numerical procedure for solving a wide variety of acoustic propagation problems results.

ISSN:0001-4966    

DOI:10.1121/1.1975577

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The widespread use of snowmobiles as recreational and utilitarian vehicles has resulted in a new and significant noise problem. A survey of 50 snowmobiles in typical operation indicated that an “average” snowmobile, when cruising, produces a sound level of approximately 90 dBAat 15 ft. The range of levels was 79–102 dBA. Operators of snowmobiles are exposed to sound levels in the vicinity of 105–120 dBA, at which levels there is a serious risk of hearing damage. A representative snowmobile was examined in detail, the major noise sources were resolved and, using standard techniques and materials, the noise output of the machine was reduced by 9 dBAwithout affecting its mechanical performance. The modified machine produced a maximum sound level of 85 dBAat 15 ft and 103 dBAat the driver's ear. The latter level particularly is still excessive. The implications of the findings of this study are discussed with respect to the snowmobile operator, the manufacturer, and the community. [A more extensive discussion of this material is found in NRC report APS‐477.]

ISSN:0001-4966    

DOI:10.1121/1.1975597

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Acoustic fields, set up in ducts carrying fluids, are modified owing to viscosity and heat conduction. These distortions are more prominent near the walls of the ducts. As a result, the field near a wall could be regarded as an acoustic boundary layer. In this paper, an account of the attenuation due to this boundary layer is presented. Included also is a discussion about the possible interacting influence of the flow boundary layer on the attenuation due to acoustic boundary layer.

ISSN:0001-4966    

DOI:10.1121/1.1975613

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A general method has been investigated for simultaneously solving a system of equations for the elastic constants and orientation of single crystals from measured wave velocities. Applicability of the method to cubic crystals has been studied in detail. The minimum number of velocity measurements required is equal in number to three for orientation parameters plus the number of elastic constants inherent to the crystal. Additional velocity measurements and a least‐squares minimization of the equations decrease the influence of individual random errors in the velocity measurements.

ISSN:0001-4966    

DOI:10.1121/1.1975623

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

A theory is developed for the propagation of sound waves in a rigid, isotropic, and homogeneous porous medium filled with a compressible fluid, including both the effect of viscous dissipation and the effect of thermal comduction. With a capillaric model assumed, an expression for the permeability as a function of the frequency is also given. For very low frequencies (isothermal case) and very high frequencies (adiabatic case), the results reduce to those of a theory presented by Morse [J. Acoust. Soc. Amer.24, 696 (1952)]. The present theory can be used to determine the structural parameters of a porous system at a given frequency. Attenuation and phase factors are plotted as functions of a nondimensional frequency parameter for various combinations of the characteristic constants.

ISSN:0001-4966    

DOI:10.1121/1.1975631

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The amplitude of the vertex potential (N1P2component) evoked by alternately presented sounds was studied as a function of the azimuth separation between the sound sources. A 1000‐ 67‐dB‐SPL tone served as the standard stimulus. It was located at 270° azimuth and was presented on every odd second throughout 200 sec. A variable stimulus of similar physical characteristics was presented on every even second. Its location, however, was either 270°, 315°, 0° or 90° azimuth. TwentySswere tested four times on each combination of standard stimulus‐variable stimulus location. The amplitude of the evoked responses summed for 100 standard and 100 variable stimuli differed significantly (p<0.01) among the various conditions of spatial separation. Response amplitudes were least when the sound sources were near one another. It is suggested that alternately presented stimuli originating close together in space activate a common pool one neurons, thereby promoting habituation. When alternately presented stimuli are widely separated in space, the stimuli from each location activate a different pool of neurons; the habituating effect of repetitive stimuli is reduced.

ISSN:0001-4966    

DOI:10.1121/1.1975641

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The distribution of spontaneous discharge rates for auditory‐nerve fibers recorded from the guinea pig modiolus suggests that there is a greater number of fibers in the 10–30 discharges/sec range than in the cat. Some tentative groupings on the basis of discharge rates has been possible from an inspection of the cumulative frequency distribution. Three groups are suggested, with means of 10, 24, and 71 discharges/sec. The standard deviations are 2.8, 2.3 and 2.7 discharges/sec, respectively. The spontaneous discharges are reduced by COCB stimulation. The “high‐rate” group shows less reduction by COCB than the two “low‐rate” groups. For nerve fibers with best frequencies above 1 kHz, the effect of the COCB on spontaneous discharges varies as Δuvaries with frequency. Below 1 kHz, there is more COCB effect on spontaneous discharges than would be expected from Δu.

ISSN:0001-4966    

DOI:10.1121/1.1975658

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The purposes, problems, and progress of radiated‐noise, self‐noise, and ambient‐noise research are reviewed. Purposes are related primarily to national defense, but applications to fishery and to the utilization of other natural resources are also noted. Basic problems, most of which were recognized 20 years or more ago, involve ascertainment of properties of the noise, identification of noise sources and mechanisms of noise generation, and the discovery and definition of noise dependencies on environmental factors. Many radiated‐ and self‐noise sources and mechanisms have been identified. Major problems are those of noise measurement, and noise reduction and prevention. In the field of ambient noise, most measurements have been of sound‐pressure level.Someof the noise sources and environmental factors have been identified, and a capability for qualitative and gross prediction has been achieved. Recommended are further investigations of the variation of ambient noise with receiver depth, directionality of the noise field, statistics of both noise level and instantaneous noise values, additional work at frequencies below 10 Hz, and additional geographic coverage, making full use of current knowledge to fashion noise models for experimental guidance. Challenging problems exist in procedures and instrumentation for noise studies.

ISSN:0001-4966    

DOI:10.1121/1.1975666

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP