摘要:

A broad‐band acoustic instrument consisting of a white‐noise generator and a damped piezoelectric receiver has been used to analyze the frequency spectra of 0–3 MHz acoustic surface waves on complex structures. By varying the path length, the frequency dependence of attenuation can be obtained. This attenuation data are used in the design of acoustic emission monitoring systems, where the frequency‐dependent characteristics of the acoustic paths between possible acoustic emission sources and the detection transducer are needed. In addition, the data can be directly used in characterizing structures such as honeycomb sandwich panels where defects produce changes in the surface wave attenuation. The system used to make these measurements are described and results for a variety of structures are presented.

ISSN:0001-4966    

DOI:10.1121/1.3437499

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The power flow and energy relationships between a cello, the stage supporting it, and the air in a reverberant room are experimentally investigated by measuring the power flowing into the cello from a shaker attached at the cello bridge, the power flow through the cello endpin into the stage, and the acoustic radiation from the cello and the stage. The objective of the study is to evaluate the significance of radiation from the stage relative to the radiation from the cello alone to determine the feasibility of enhancing the total radiated sound by altering the cello‐stage coupling and/or changing the stage radiation properties. Experimental techniques employed include direct measurement of power flow between the two structures and acoustic power measurements in13‐octave bands. Four different stage configurations are investigated including a concrete floor, simple unbaffled wooden panel, a baffled panel of the same dimensions, and a special soloist's podiu m which incorporates a sounding board connected to the podinto top by a sound post. [This research has been supported by the National Science Foundation.]

ISSN:0001-4966    

DOI:10.1121/1.3437505

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The apparent acoustic length of the mouthpiece‐leaderpipe combination increases with frequency through the normal playing frequency range. For example, the apparent length may increase from 23 cm at 165 Hz to 35 cm at 1100 Hz. At higher frequencies it declines. Theory indicates that, at frequencies low enough for losses to be neglected, the apparent acoustic length,l, should be related to the total internal volume of the mouthpiece‐leaderpipe combination,V, the cross‐sectional area of the main cylindrical tubing to which the leaderpipe is attached,S, the resonances and antiresonances of the mouthpiece‐leaderpipe combination, Ω, and Ψn, by the equation:ctn(ωlc) = ScVΩ1[(Ω12−ω)Ψ12(Ω22−ω2)Ψ22(Ω32−ω2)Ψ32(Ω42−ω2)…ωΩ1(Ψ12−ω2)Ω22(Ψ22−ω2)Ω32(Ψ32−ω2)Ω42…].Experiments show that the tuning behavior of the mouthpiece‐leaderpipe combination can be quantitatively predicted with this equation in the frequency range from zero to 1000 Hz.

ISSN:0001-4966    

DOI:10.1121/1.3437508

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

TheAplysiastatocyst is a spherical organ, approximately 200 μm in diameter, filled with fluid and small (6–20 μm), dense statoconia. The wall of the statocyst consists mainly of 13 large receptor cells. Light, transmission‐ and scanning‐electron microscopy have shown that each receptor cell bears many (500–1000) true cilia which project into the cyst lumen. The fine structure of the cilia and their associated basal bodies appear similar to those of vertebrate hair cells, suggesting that similar transduction mechanisms may be operative. The statocyst receptor cells were penetrated with micro‐pipette electrodes in a preparation mounted on a table which allows a physiologic stimulus to be applied by tilting so that the statoconia roll to deflect cilia on the cell. Such a stimulus causes depolarizations from 0 to 15 mV and conductance increases from 0 to double the resting conductance. At rest, there are ongoing fluctuations in membrane potential from 2 to 15 mV peak‐to‐peak amplitude. These fluctuations increase as the recorded cell is tilted downward. Most of the energy in the baseline fluctuations lies at frequencies below 10 Hz.

ISSN:0001-4966    

DOI:10.1121/1.3437909

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Several reports in the literature have represented the sensitivity of the alternating cochlear potential as being easily degraded by cooling. Our attempts to replicate these findings in the guinea pig failed to confirm them; hence we have conducted a thorough investigation in which careful attention was given to (1) optimal physiological condition of the preparation, (2) accurate quantification of sound, and (3) precise measurement of intracochlear temperature. At low levels of cochlear output (1–10 μV) the sensitivity of the normal cochlea was found to be invariant down to at least 30° C. This invariance does not appear to hold for the cochlear output at higher levels, close to bendover. Possible theoretical implications of these findings are discussed.

ISSN:0001-4966    

DOI:10.1121/1.3437915

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

In previously reported experiments we have shown that an intense sound exposure can temporarily depress the cochlear nerve evoked potential (N1) while not affecting the alternating current cochlear potential [J. Acoust. Soc. Am. S3, 326 (1973)]. Sodium salicylate was likewise found to produce a temporary effect on N1 only. In this experiment it was found that when these agents are given together they produced a greater change inN1than either agent alone, but not more than would be expected from a simple summation. This combined effect‐ of both agents onN1‐was also temporary. The interaction of these agents did not affect the ac cochlear potential. This interaction—of intense sound and sodium salicylate‐does not produce the permanent damaging interaction effects reported for other ototoxic drugs.

ISSN:0001-4966    

DOI:10.1121/1.3437916

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The effects of reverberation time (RT) upon monaural and binaural speech discrimination were investigated for normal‐hearing and hearing‐impaired subjects. After preliminary tests, the Modified Rhyme Test was administered through headphones at RTs of 0, 1, 2 and 3 sec, monaurally and binaurally. For all conditions, the normals performed significantly better than the impaired group, although a similar trend was evident for both groups. Binaural scores were significantly higher at each RT for both groups (in spite of homophasic conditions). For both groups, monaural and binaural scores decreased with increasing RT. Monaural scores decreased at a faster rate with RT than binaural (this effect was more marked for normals). Increasing the monaural presentation levels to simulate binaural loudness gain did not result in higher scores. It was concluded that speech discrimination under reverberation is superior binaurally to monaurally for both normal and hearing‐impaired persons. This is due, at least partly, to the ability of the binaural system to squelch the effects of reverberation. A theoretical model is suggested for the binaural squelch of reverberation.

ISSN:0001-4966    

DOI:10.1121/1.3437922

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Speaker identification techniques which extract speaker characteristics from single sound units can be applicable to both text‐dependent and text‐independent speech. Experiments have shown that identification accuracy improves if decisions are based upon combined information from several different sound units. With such techniques, it would be helpful if potential sound units could be rank ordered according to how much each contributes toward successful speaker identification. In text‐independent speaker identification there is no control over the number of sound units in the test speech sample, so it would be beneficial if the probability of success could be predicted not only from the population size but also from the number and type of sound units available. Speech samples from ten male speakers are being used to evaluate ten non‐diphthongized vowels and three nasals. Experimental results are presented on rank ordering these sounds and the determination of conditional probabilities based upon the selection of sounds. [Sponsored by Air Force Systems Command, Rome Air Development Center, Griffiss Air Force Base, New York 13441.]

ISSN:0001-4966    

DOI:10.1121/1.3437931

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The evidence presented in two recent California “voiceprint” cases is reviewed. In one, the defendant, Nehemiah Jackson, was accused of making a telephone call to the Riverside police station as a result of which two policemen were murdered. The call was recorded on a 24‐hour tape recorder with a very low signal/noise ratio and an apparent upper frequency limit of about 2300 Hz. Copies of the recordings will be played, and the spectrograms which were used for comparing the voices of the accused and the unknown caller will be displayed. The case ended in a hung jury. In the other case the defendant, Stephen Chapter, was accused of making a bomb threat. The Court found the defendant not guilty, and the evidence “not reliable in this particular case due to: (a) Mistakes and errors in preparation of the spectrograms used in making the identification. (b) Failure to ascertain the existence of such errors. (c) Demonstrated listening errors in court while under cross‐examination. (d) Tentative misidentification of the court ordered exemplar. (e) Failure to maintain adequate records/logs during conducting of tests.” These two cases raise the issue of how to extrapolate from laboratory studies to forensic situations.

ISSN:0001-4966    

DOI:10.1121/1.3437934

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The components of human reaction to noise have been studied extensively in the laboratory, but have been less assessed in the real world. This paper describes a theoretical framework and practical application of some novel techniques for assessing human reaction under field conditions. Data collection techniques never before applied in this context included (1) 24‐hour diary (recall), and (2) paired‐comparison method to determine an individual's relative value of noise/ quiet. These techniques were utilized as part of a survey instrument, or questionnaire, which was administered to a small group of subjects in a preliminary test. The survey was tested in four different residential sites in conjunction with a pilot test of a system for assessing community noise and individual noise exposure and reaction to this exposure. [The study was supported jointly by the Department of Transportation and the Environmental Protection Agency.]

ISSN:0001-4966    

DOI:10.1121/1.3437939

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP