摘要:

The influence of spectral cues on discrimination peaks in the region of the phonetic voicing boundary was examined. The discriminability of voice onset time (VOT) differences of the same temporal magnitude was assessed using stimuli from labial and velar consonant–vowel VOT continua that differed in the timing of spectral changes associated with the first formant (F1) transition, and in the location of the phonetic boundary. Subjects were initially given labeling tests and fixed‐standard AX and all‐step discrimination tests on both series. Half the subjects then received all‐step discrimination training on one series and half received training on the other series. Finally, all subjects were again given the labeling and discrimination tests on both series. Just noticeable differences (jnds) in VOT were estimated from the all‐step functions before and after training. Initial jnds showed that VOT discrimination was most accurate around the voicing boundary on the two continua, where differences inF1 onset frequency accompany variations in VOT. jnds on both series decreased significantly after training, although these regions of greater sensitivity remained. No evidence was seen of increased sensitivity around ±20‐ms VOT, as expected if auditory processing constraints were influencing temporal order judgments. Comparisons of post‐training jnds within and across series indicated that spectral components of VOT, primarilyF1 onset frequency differences, exert a substantial influence on discrimination, and, along with other spectral cues provided by source differences at stimulus onset, can account for the discontinuities in discrimination often reported in research with VOT continua. Large phonetic effects also were seen in the initial performance of all subjects: jnds decreased consistently as standards drew nearer the voicing boundary. However, these effects were absent in the final jnds for most subjects. Implications of these findings for the understanding of basic auditory and attentional processes in speech perception are discussed.

ISSN:0001-4966    

DOI:10.1121/1.389539

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The monaural free‐field speech‐reception threshold (SRT) without and with a hearing aid was investigated for conversational sentences presented to 50 hearing‐impaired listeners. SRT without a hearing aid was measured in quiet and in noise at levels of 40, 55, 70, and 85 dBA. SRT with a hearing aid was obtained in quiet and at noise levels of 25, 40, 55, and 70 dBA. The noise had a long‐term average spectrum equal to that of the sentences. The 50 subjects were equally distributed over five degrees of pure‐tone hearing loss and five types of hearing impairment (sensorineural high‐frequency losses, with or without recruitment; flat audiogram of a sensorineural, mixed, or conductive origin). It is shown that a model of SRT as a function of noise level, developed by Plomp [J. Acoust. Soc. Am.63, 533–549 (1978)] gives a good description of the SRT values measured, both without and with a hearing aid. The data illustrate that, generally, current hearing aids do not improve speech intelligibility in noise beyond, roughly, 60 dBA.

ISSN:0001-4966    

DOI:10.1121/1.389540

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Lossless bowed strings have usually been thought to possess a motion discovered by Helmholtz in 1863. However, it was shown [Acustica44, 194–206 (1980)] by the author that a more complicated standing wave motion, theSmotion, exists on such strings provided both the bowing distance and bowing force are above certain minimum values. This paper exploresS‐motion harmonics which give arise to waveforms of considerable complexity on very thin strings. Equations are found which describe the experimentally determined waveforms as a function of bow position, bow velocity, and observation point. In the special case of square velocity waves at the bow point, the equations give quantized values for the bow/string sticking duration. That result agrees with Raman’s [Proc. Ind. Assoc. Adv. Sci.15, 1–158 (1918)] prediction. In general, however, the waveforms have rounded corners.

ISSN:0001-4966    

DOI:10.1121/1.389541

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A compact, portable instrument has been developed to measure the acoustic impedance of the ground, or other surfaces, by direct pressure‐volume velocity measurement. A Helmholtz resonator, constructed of heavy‐walled stainless steel but open at the bottom, is positioned over the surface having the unknown impedance. The sound source, a cam‐driven piston of known stroke and thus known volume velocity, is located in the neck of the resonator. The cam speed is variable up to a maximum 3600 rpm, and since the cam has five lobes, the maximum acoustic frequency is 300 Hz. The sound pressure at the test surface is measured by means of a microphone flush mounted in the wall of the chamber. An optical monitor of the piston displacement permits measurement of the phase angle between the volume velocity and the sound pressure, from which the real and imaginary parts of the impedance can be evaluated. The prototype instrument can measure specific ground impedance at normal incidence up to 50 times the specific impedance of air. Detailed design criteria and results of measurements on an uncultivated grass field are presented.

ISSN:0001-4966    

DOI:10.1121/1.389542

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Vibration transducers do not faithfully follow the ground motion at high frequencies, since a resonant system is formed by the weight of the vibration transducer and the contact compliance of a placing point. Particularly, the contact resonances cause errors in measurement and place restrictions on the measurement frequency range. The characteristics of the effect of ground coupling depend on the type and condition of the ground surface and the method of planting the transducer. This paper examines the characteristics of the frequency response of the vibration transducer placed on the ground and provides the optimum relationships between the base area and the weight of the transducer for decreasing the effect of ground coupling under all conditions. The relationships are represented in the figures for the user’s convenience. When the vibration transducers designed to satisfy the relationship proposed here are employed for the measurement of the ground vibration, it is shown that the errors in measurement caused by the ground coupling decrease considerably. As compared with the old vibration transducers the measurement frequency ranges are markedly spread out.

ISSN:0001-4966    

DOI:10.1121/1.389543

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

Graphical experimental data in the form of passive receiving scanning beam patterns is presented for several high resolution acoustic lens–acoustic filter plate combinations. They show the comparative properties of various types of flat and curved filter plates when used in such acoustic antennas. Experimental data relating the achieved frequency‐independent constant beamwidth of the several lens–filter plate combinations to the governing parameters of the filter plates are summarized for empirical design purposes. The basic experiments reported were conducted over the frequency range from 25 to 1000 kHz but the results can be scaled to any frequency range of the corresponding scaled width. As a receiving antenna, the acoustic lens–acoustic filter plate device eliminates the distortion imposed on the spectral content of a received multifrequency signal as a function of angle‐off‐boresight which is inherent in the use of conventional variable beamwidth directional receiving antennas.

ISSN:0001-4966    

DOI:10.1121/1.389544

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

The theory of a broadband constant beamwidth transducer (CBT) which is based on Legendre function shading of a spherical cap was described in a previous report [P. H. Rogers and A. L. Van Buren, J. Acoust. Soc. Am.64, 38–43 (1978)]. Theoretical calculations showed the CBT to have uniform acoustic loading, extremely low side lobes, virtually no nearfield, an essentially constant beam pattern for all frequencies above a certain cutoff frequency, and a flat transmitting current response over a broadband for piezoelectric drive. In this paper we present experimental results obtained for a prototype CBT based on fifth‐order Legendre function shading. The transducer is a spherical cap with a diameter of 30.5 cm and a total cap angle of 50°. Measurements on the CBT showed it to possess very low side lobes and a nearly constant beamwidth over the frequency range from 20 to 140 kHz for ambient pressures up to 3.4 MPa. We also present formulas useful in the design of a CBT which is to be used as a transmitter and/or receiver. The formulas involve simple algebraic and trigonometric expressions which can be readily evaluated using a pocket calculator.

ISSN:0001-4966    

DOI:10.1121/1.389545

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

An experimental investigation was conducted to determine the effects of different edge conditions and face mount backing conditions on the electrical response of strongly coupled piezoelectric disks with electroded faces on which spatially nonuniform forces are applied by a pencil lead breaking mechanism. Various mounting schemes were employed to simulate traction‐free, simply supported, and fixed edge conditions. The response was found to be relatively insensitive to changes in the edge conditions. Experiments were also conducted on a commercially available transducer in various stages of dismantlement. It was revealed that the main structural element for controlling the electrical output was the impedance matched backing that is epoxied to the inner face of the crystal. It was concluded that mathematical models for characterizing transducers subject to nonuniform face loadings can incorporate the analytically most convenient edge conditions but must also include a suitable model for the backing.

ISSN:0001-4966    

DOI:10.1121/1.389546

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A laser has been used to determine acoustic wave paths from a source, located between parallel noise barriers, to the top of each barrier. Various barrier designs have been studied, and conclusions drawn on the likely effect of parallel siting on sound levels at a protected receiver for a typical traffic noise geometry.

ISSN:0001-4966    

DOI:10.1121/1.389548

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP

摘要:

A subject who had a tinnitus with 10 000‐Hz pitch equivalent in the left ear and no tinnitus in the right ear was exposed in the left ear to a steady tone of 2000 Hz, 107 dB SPL, for 10 min. This exposure resulted in a permanent tinnitus in both ears with similar pitch of approximately 10 000 Hz and loudness of 50–55 SPL (5–10 dB SL). When the left ear of this subject was exposed to a steady 500‐Hz pure tone at 121 dB SPL for 21 min, tinnitus disappeared temporarily from the stimulated ear but was heard in the nonstimulated ear. In the left ear: 3 h after stimulation, tinnitus reappeared as a mixture of multiple pitches superimposed upon broadband noise and/or low‐pass filtered noise; 24 h after stimulation, tinnitus pitch changed to 3260 Hz, two days later to 5100 Hz, three days later to 8310 Hz and one week later to the original 10 000 Hz and has remained there since. In the nonstimulated right ear: Immediately after cessation of stimulation, tinnitus pitch was 6700–8000 Hz for 48 h; thereafter, tinnitus has been fluctuating between 8000–9000‐Hz tone and a narrow‐band noise centered around 7986 Hz with a bandwidth of 2710 Hz; the tinnitus did not return to the previous pre‐exposure pitch of 10 000 Hz until about four weeks after exposure. We suggest that these contralateral effects of tinnitus are mediated by the central auditory system.

ISSN:0001-4966    

DOI:10.1121/1.389549

出版商:Acoustical Society of America    

年代:1983

数据来源: AIP