摘要:

For 20 patients with tinnitus, we found that the intensity of broadband noise required to mask the tinnitus increased (by as much as 45 dB) during 30 rain of noise exposure. in contrast, the intensity required to mask an external tone remained nearly constant. Some speculations which might account for these results are offered. We posit that excess neural activity is the physiological determinant of tinnitus, and that the excess activity is central, generated in the brainstem postsynaptic to the eighth nerve. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2018318

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

It is well known that train operations on an elevated structure are much noisier than those on a grade level roadbed. For the composite type of bridge structure made up of a concrete deck on a steel box girder, theoretical and experimental studies show that the steel web plates are a major source of noise radiated from the structure. This paper will summarize some of the work done over the last 15 years to reduce this source of noise by damping the steel box girder of such structures. Both homogeneous type damping and shear type, or constrained layer damping materials have been used successfully. The noise reduction on one type of structure with homogeneous damping mateddais will be described, including scale model and full scale tests. In another type of structure, a partial damping treatment with shear type damping material was developed to reduce the very disturbing low frequency noise radiated by the steel box girder plates. Full scale field tests will be described in which noise and vibration measurements were made on damped and undamped sections of the elevated structure during train passage at several speeds. The effect of damping on the noise and vibration levels will be detailed.

ISSN:0001-4966    

DOI:10.1121/1.2018324

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Transmission of vibrations through the key structural elements in the path between the rails and the ground was measured on a concrete elevated structure of the Port Authority Transportation Corporation (PATCO) rail transit system in Camden County, New Jersey. Results are compared with similar, but less complete measurements taken at sites in New York City, San Francisco, and Atlanta. Generalizations of the results are applied to the new concrete elevated transit structures under design for the Metropolitan Dade County Rapid Transit System. [Work supported by Urban Mass Transportation Administration (various contracts).]

ISSN:0001-4966    

DOI:10.1121/1.2018327

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In a previous study of stress perception using nine disyllables, it was found that the ratio of duration of the first vowel to that of the second which distinguished first and second syllable stress (the stress boundary) was not independent of the identity of the two vowels. [Smith, J. Acoust. Soc. Am. Suppl.1 66,S87 (1979)]. The present study had two purposes: first, to determine if the observed relative distribution of boundaries was specific only to the durations used in that experiment, and second, to test the hypothesis that stress boundaries could be expressed as a ratio that would be invariant with respect to changes in rate. The same nine disyllables of the form /s_ds_d/with fixed formant patterns for each of the vowels /i/, /I/, and /ɝ/ were synthesized. For each form the duration of the first vowel was varied in 10 ms steps across three ranges: the original 50 to 150 ms, 80 to 240 ms, and 110 to 330 ms. Listeners reported the stress of isolated words presented in a block design with one range per block. The relative ordering of boundaries was not preserved entirely across the three ranges. The ratio description of stress boundaries describes the data only for the three words in which both syllables contain the same vowel.

ISSN:0001-4966    

DOI:10.1121/1.2018334

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous studies have shown that supraglottal air pressure (P10) is greater for stressed than unstressed stops and for voiceless than voiced stops. The present study examined theseP10contrasts as a function of utterance length and position within the utterance. Eight subjects read nonsense utterances consisting of from one to five /bábá/s or/pápá/s (5 times each) with the intonation of an English declarative sentence (e.g., “Bábá bábá Bábá”). PeakP10was sensed via a pressure tube inserted in the mouth and measured from osciiiographic traces.P10in utterance‐initial words increased as number of following words increased.P10was greater for /p/ than /b/ except for stops initiating the 2‐ and 5‐word utterances.P10was always greater for stressed than unstressed /b/; it was also greater for stressed than unstressed /p/ except in utterance‐initial words where pressure for the initial stressed Ipl was less than that of the following unstressed /p/. This reversal of the expectedP10contrast for stress appears to reflect the length of time necessary for subglottal pressure (P8) to rise to peak level at onset of phonation. Even though stressed /p/ was longer in utterance‐initial than ‐medial positions it was probably shorter than the minimal time necessary forP8to reach peak level at onset of phonation. It thus appears thatP10for stressed /p/ in utterance‐initial position represents risingP8, while a following unstressed /p/ reflectsP8which has already reached peak level.

ISSN:0001-4966    

DOI:10.1121/1.2018338

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In this paper, we investigate the relationship between the physical characteristics of randomly rough surfaces and the surface roughness spectrum (i.e., wavenumber spectrum). This spectrum is important because at low grazing angles (i.e., far from normal incidence), the backscattered field is proportional to the surface roughness spectrum. Consequently, both the frequency dependence and the level of the backscattered field are determined by the surface roughness spectrum. [Part of this work was performed at the University of Paris VII, Paris, France.]

ISSN:0001-4966    

DOI:10.1121/1.2018342

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

TheR‐matrix theory of acoustic scattering, developed by us earlier [G. Gaunaurd and H. Überall, J. Acoust. Soc. Am. Suppl. 166,S81 (1979)] is here applied to the case of sound scattering from an absorbing bubble. The mechanical impedance of the scatterer is a meromorphic function of frequency, belonging to the class of Wigner'sRfunctions [E. P. Wigner, Ann. Math. Stat.53,36 (1951)] which have poles on the real axis. Developing theSmatrix (which contains theRfunctions) in the one‐level approximation leads to a Breit‐Wigner resonance formula with a frequency shift and a resonance width. The effect of absorption in the bubble consists in a further shift of the resonance frequency and a broadening of the resonance width. Both of these effects (in particular the broadening of the widths) are suitable means for determining the absorption, which is crucial for the echo reduction of a target. [H. Überall is also at Catholic University, Washington, DC 20064, additionally supported by Code 421 of ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2018346

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A transfer‐function method is described of measuring the acoustic intensity of plane waves in a duct with flow. In this method, the transfer function between two locations in the duct is used to determine the reflection coefficient. Acoustic intensity in a duct with flow is then determined from the reflection coefficient using an expression developed by Morfey. In the case of no flow, the transfer‐function formulation reduces to a cross‐spectral relation similar to the relation used to measure acoustic intensity in three dimensions. In contrast to the relation in three dimensions, however, the cross‐spectral formulation for a duct is not limited in accuracy by the microphone spacing. Laboratory tests have been conducted in which the transfer‐function method was used inside the pipe to evaluate the net sound power transmitted toward the open end of the pipe. The three‐dimensional cross‐spectral method of measuring acoustic intensity was used outside the pipe to evaluate the total radiated sound power. The acoustic power‐loss during the radiation process was then determined by comparing the two results.

ISSN:0001-4966    

DOI:10.1121/1.2018349

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Sound intensity is a vector that predicts sound power when integrated over a closed surface. Since only the integral is directly related to local physical constraints such as conservation of energy, the local intensity may be subject to considerable variations, depending on the acoustical environment of the radiating system. Limitations in the use of acoustical intensity data, quite apart from those that result from the accuracy of the measurement, will be discussed.

ISSN:0001-4966    

DOI:10.1121/1.2018361

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An important parameter in the use of the surface acoustic method for sound power measurement or sound power accounting of sources is a knowledge of the behavior of the spatial coherence or incoherence of the surface motion viewed as an acoustic source. If the machine surface can be treated as a collection of incoherent sources with some scale determined by a correlation length then considerable simplification in the power measurements may result. Measurement of the coherence of surface vibrations on a large machine are discussed with a view toward establishing a correlation length and hence the determination of the number of measurement points.

ISSN:0001-4966    

DOI:10.1121/1.2018364

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP