摘要:

Much interest has centered in recent years in measurements of the noise of large machines as installed. Free‐field conditions above a reflecting plane are desired, and a means for evaluating conditionsin situare a necessary part of the measurement process. A current trend in drafting ISO and ANSI standards is to employ the method of enveloping surfaces. [G. Hubner, “Qualification procedures for free‐field conditions for sound power determination of sound sources,” inInternoise 73 Proceedings(Copenhagen, August 1973).] It has been found that spaces which fail to qualify by this method often pass a criterion like that of American National Standard ANSI S1.13‐1971, which requires only that the sound pressure level measured at one or more points in a direction away from the machine be at least 6 dB less than that at 1 m. It is argued that the latter criterion insures adequate accuracy for engineering measurements, and that the former one requires an unnecessary number of measurements.

ISSN:0001-4966    

DOI:10.1121/1.2003794

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A nonlinear theory for the long‐range propagation of sonic booms through the thermosphere has been developed. A realistic atmosphere is employed, and consideration is given to such factors as nonlinear stretching and decay of the wave, the effects of the caustic, the winds, the linear acoustic attenuation, and the increase in Mach number due to the decreasing density at high altitudes. Detailed results are presented for the case of the Concorde SST in straight, level, and steady flight at 17.5 km and a velocity of Mach 2. We predict maximum ground level pressures of 0.3 Pa with anN‐wave “period” of about 10 s. The sound level is a minimum along the flight track with the maximum signal strength occurring about 300 km off the flight track. The strongest received signal travels initially downward and reflects off the surface of the ocean to thermosphere. The wave turns around at an altitude of 160 km and is returned back to the ground at a horizontal distance of 320 km from the launch point. The acoustic Mach number of the wave never exceeds 0.2. Ninety percent of the wave's energy is attenuated below 100 km, with 99% attenuated by the time the wave reaches the turning point.

ISSN:0001-4966    

DOI:10.1121/1.2003848

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Considerable attention has been given to finite‐amplitude waves in aerosols, principally by G. A. Davidson and D. S. Scott [(J. Acoust. Soc. Am.54, 1331 (1973) and J. Aerosol Sci.5, 55 (1974)], who derived and analyzed a single model equation for unidirectional plane waves. This note seeks to correct an error in their analysis for the case in which the thermal and momentum relaxation times of the particular phase are equal. The correct result is that the medium in that case is a relaxing gas of precisely the kind considered by a number of other authors, with equilibrium and frozen sound speeds and a bulk viscosity all capable of simple interpretation. Possibilities not previously recognized are then opened up; specifically that partly dispersed shock waves will occur under appropriate conditions at low frequencies, while at high frequencies the model equation may be reduced to the familiar Varley—Rogers equation, which demonstrates that at a given frequency shock formation may be altogether precluded if the properties of the aerosol are suitably chosen.

ISSN:0001-4966    

DOI:10.1121/1.2003900

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper will discuss performance data of various mammalian ears, i.e., their overall sensitivities, frequency ranges, points of maximal sensitivity, directional patterns, localization by the binaural system, etc., in the light of a number of physical factors, such as head size, length of the ear canal, area of the tympanic membrane, and others. In general, these physical factors were found to be quite critical in determining the performance of the ear. Some must clearly be the result of a compromise between conflicting requirements: (a) to collect an optimal amount of acoustic energy over a wide frequency range, (b) to bring sensitivity close to its optimal value, (c) to avoid creation of dead zones in the directional pattern of hearing, and (d) to facilitate auditory localization both in the horizontal planes and in the vertical one. Its performance makes the ear an excellent early warning device, superior in this respect to all other sense organs. [Supported by NIH grants.]

ISSN:0001-4966    

DOI:10.1121/1.2003947

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The organization of mammalian auditory cortex shows species‐specific specializations as well as organizational rules common to all studied mammals. Electrophysiological mapping of the tonotopic representation in several species indicates that features common to AI include (1) orderly representation of the entire cochlea within AI, (2) representation of a one‐dimensional cochlear segment by a two‐dimensional cortical belt crossing AI, and (3) radial organization of sharply tuned neurons of similar best frequency through the depth of the middle cortical layers. For some species, the AI representations resemble scaled models of one another. In most species, there are one or more orderly cochlear representations adjacent to AI. Surrounding these highly ordered fields are other fields (the “belt region”) in which neurons may not be as sharply tuned for frequency, or in which the cochlear representation may not be as orderly. “Association” fields may represent further abstractions of acoustic information, and sometimes may integrate polysensory information. Comparisons of the cortical cytoarchitecture of many species suggest expansion of “association” cortex through mammalian evolution. A most interesting species‐specific specialization is human speech and its associated hemispheric lateralization.

ISSN:0001-4966    

DOI:10.1121/1.2004003

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Kunisaki and Fujisaki [Ann. Bull. RILP11, 85–91 (1977)] have reported that perception of fricatives from a synthetic [s]‐[∫] continuum depends on the nature of the following vowel: Listeners give more [s]responses when the vowel is rounded than when it is unrounded. After replicating their basic finding using 100‐ms fricative noises followed by either [a] or [u](with appropriate formant transitions), we have begun to investigate the limits of this contextual dependency. Our experimental manipulations include (1) extending the duration of the fricative noise, (2) introducing silent intervals of varying length between the fricative noise and the vocalic portion (so that a fricative‐stop‐vowel sequence is heard), and (3) preceding the fricative‐stop‐vowel stimuli with another vowel (thereby introducing a syllable boundary between the fricative and the stop). We have also preceded and/or followed the fricative noises with steady‐state vowels, and we have systematically varied the formant transitions of the following vowel, in order to dissociate contextual effects due to the transitions themselves from those due to the vowel. By comparing our perceptual results with measurements of natural speech, we will examine to which extent contextual dependencies in perception (and their changes in the various experimental conditions) parallel coarticulation effects in the production of analogous utterances. [Work supported by NICHD and BRSG.]

ISSN:0001-4966    

DOI:10.1121/1.2004052

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The fricative‐affricate distinction is signalled by a set of diverse acoustic features. To account for the integration of these features in perception, it is presumed that we perceive the articulatory act from which their coherence is derived. In the present research, our aim is to learn more about conditions which determine whether a particular set of acoustic cues is perceived as the consequence of a fricative or affricate production. To this end, we have examined the significance of short durations of silence for distinguishing word‐initial fricative from affricate following precursors which provide various degrees of utterance continuity. Results suggest that continuity of utterance affects the meaning of silence for the fricative‐affricate contrast.

ISSN:0001-4966    

DOI:10.1121/1.2004079

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This study investigates the effect of noise marking on the identification of nasal consonants [m, n, ŋ] in VC syllables, in which V is [i, e, a, o, u]. These VC syllables, spoken by male phoneticians, were masked with white noise (60–4000 Hz), and played to subjects who were professors and graduate students of phonetics. There were four listening conditions with different signal‐to‐noise ratios. Preliminary results suggest three principal findings: (1) Nasals are correctly identified after [a] even in the noisiest condition, (2) [m]tends to be identified as [n] after the front vowels [i, e]and, less strongly, (3) [n] tends to be identified as [m]after the back rounded vowels [o, u]. These misidentifications of [m]and [n] occur more frequently in the noisier conditions. The results will be discussed in relation to patterns of sound change in syllable final nasals. [Research supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2004083

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Ten studies between 1829 and 1919 ordered the vowels /u, o, a, e, i/ from low to high pitch, respectively. More recent research is consistent with this rank order. Peterson and Asp reported a rank order for prevocalic consonants based on pitch differences. From these studies and clinical experience, a hypothetical pitch (“tonality”) model was constructed that divided consonants, vowels, and diphthongs into pitch categories. From this model, 30 monosyllabic words were selected, ten each from the low, middle, and high pitch categories. The phonemes within each word were from the same category, e.g., /rum/ for low pitch and /sis/ for high pitch. The 30 words were recorded in 435 pairs. Nineteen normal hearing listeners selected the word from each pair that was higher in pitch. Using a matrix, the 30 words were rank ordered from low to high pitch. The rank order agreed with the proposed model. Statistical analysis separated the words into groups that corresponded to the low‐, middle‐, and high‐pitch categories. [Work supported in part by Biomedical Science Support Grant.]

ISSN:0001-4966    

DOI:10.1121/1.2004096

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

One of the few characteristics shared by most of the proposed algorithms for vowel normalization is their utilization of the mean formant frequency values of the vowel system as a correction factor for individual vowels. This reflects the accepted view that the quality of a particular vowel depends less on the absolute formant values than on the relations between these values and the general range of the speaker's formants. While such approaches very satisfactorily reduce the dispersion within a single language, they are unsatisfactory for cross‐linguistic comparisons, since the means can differ drastically from language to language when the vowel systems are different. For example, the overall mean of theF2values of Danish, which has two sets of front vowels (rounded and unrounded) but only one set of back vowels, is significantly higher than that of English; moreover, the overall meanF1of Danish is over 100 Hz lower than that of English. Using overall means to normalize in these cases confounds phonetic differences with systemic differences. A method of comparing vowels across languages which avoids this problem will be discussed. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2004101

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP