摘要:

A fundamental study of noise generation in high‐speed mechanical systems is undertaken. The objective being the development of modeling techniques for the prediction of mechanical system noise levels. Recently developed dynamical procedures are used to obtain the motions of linked mechanical systems with elastic elements and connection clearances. The ranges of critical system parameters are identified and classical acoustical analysis methods are used in determining the most significant acoustic sources. Detailed acoustic models are analytically developed for these significant sources. These methods and models are then used to predict the farfield radiation of a simple, yet representative, mechanical system; an elastic link with connection clearances in a nominal motion container.

ISSN:0001-4966    

DOI:10.1121/1.383921

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The reciprocal of the reverberation timeTis expressed as a power series in the absorptivity of the enclosure. The leading term of the series is found to be the Sabine–Franklin expression, and the procedure is thus interpreted, for weakly absorbing enclosures, as a new derivation and confirmation of that still controversial expression. The next term of the series then provides a correction to the Sabine–Franklin value in many practical cases of intermediate absorptivity where the Sabine–Franklin value is reasonably accurate but not accurate enough. Four other formulas which have been advanced as improvements on Sabine–Franklin are shown to yield unreliable corrections which are even of the wrong sign in some enclosures. Finally, it is shown thatTbears a simple relation to the gaingof a laser, and, thus, existing evaluations of eithergorTare immediately interpreted as evaluations of the other.

ISSN:0001-4966    

DOI:10.1121/1.383922

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

One of the causes of the deviation of the signal‐to‐noise array gain from its ideal value is the existence of random amplitude and phase fluctuations of the signal and noise waveforms arriving at the elements of the array. The effect of normally distributed fluctuations on both the signal and noise gains is examined in this paper. An equation is developed which gives the gain, when there are fluctuations, as a function of the ideal gain for both the signal and noise. The expressions for the signal and noise gains used in this paper are valid for all single‐frequency fluctuations arising between the source and the point in the array where the output is measured. It is shown that under certain conditions the total signal gain degradation due to fluctuations can be approximated by the sum of the degradation due to fluctuations in the medium and the degradation due to fluctuations in the equipment.

ISSN:0001-4966    

DOI:10.1121/1.383923

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Space‐frequency equivalence, a 1958 concept involving either electromagnetic or acoustic detection systems, states that the physical complexity of a system is interchangeable with the frequency complexity of the system so that the use of a multiplicity of discrete frequencies permits a significant reduction in the physical (space) extent of the system. The implications of combining this equivalence with holography are here examined.

ISSN:0001-4966    

DOI:10.1121/1.383934

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The discrete Fourier transform (DFT) inherently accepts complex data; yet signals to be processed are usually real. This necessitates special accommodations if efficient computation is to be achieved. Further accommodation is necessary for efficiency when processing bandpass data. Both accommodations can be made by generating analytic signals using Hilbert transforms. The generation of such signals around zero frequency can be accomplished by analytic band translation where the bandpass can afterwards be defined at baseband by a pair of matched filters. After baseband processing, the spectrum can be translated back up to an arbitrary frequency or can enter after Hilbert sampling directly into the complex DFT for the most efficient spectrum analysis. The analytic translation to the zero‐centered baseband frequencies provides the most conveniently normalized spectrum and facilitates the most efficient use of computational resources. The analytic band translator applies to either digital or analog implementation and is useful in both spectrum analysis and other processes.

ISSN:0001-4966    

DOI:10.1121/1.383935

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The threshold of the acoustic reflex (TAR) and the magnitude of middle‐ear muscle response were measured for a homophasic (0°) and an antiphasic (180°) 550‐Hz tone in a background of in‐phase noise. Signal‐to‐noise ratio ranged from −20 dB to +15 dB. Whereas previously reported data shows an effect of phase on the percept of loudness, no evidence of a phase effect was measured for acoustic‐reflex responses. These results are interpreted as evidence against a relation between loudness and acoustic reflex for binaurally presented signals.

ISSN:0001-4966    

DOI:10.1121/1.383830

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Psychophysical performance was measured in a number of different tasks in order to compare performance under different masking conditions. With the noise masker set to provide a given amount of masking, frequency discrimination of a 4‐kHz tone was shown to be worse in a lowpass noise than in a wideband noise. Discrimination of the intensity of the tone under these two masking conditions was comparable except at the lowest level of tone. Finally, the growth of detectability with level was measured in a detection task, with a greater slope being found in lowpass noise than in wideband noise. The results are discussed in light of the differences in physiological responses observed under similar masking conditions.

ISSN:0001-4966    

DOI:10.1121/1.383936

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

When one tone burst (the conditioner) preceeds another (the target) by 100 ms, target loudness is enhanced if the conditioner is more intense and decreased if it is less intense. We show here that similar loudness enhancements and decrements occur when the conditioner follows the target. In all instances, monaural loudness enhancements (in which the conditioner and target are delivered to the same ear) are greater than the dichotic enhancements (in which the conditioner is presented contralaterally), but the decrements, which are smaller than the enhancements, are similar in magnitude. Loudness enhancements and decrements are similar to sequential loudness effects and central tendency effects; the major difference is the relatively very large increases in loudness obtainable in loudness enhancement experiments. We outline a mechanism to account for these loudness phenomena and suggest that this mechanism is responsible for similar perceptual effects that occur in other stimulus dimensions and modalities.

ISSN:0001-4966    

DOI:10.1121/1.383937

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In general, the detectability of a signal preceded and followed by noise maskers is less than the prediction based on a simple addition of the effects of the maskers (i.e., an intensity sum). Data verifying and extending this finding were collected in a variety of conditions in which the two maskers either surrounded the signal in time or preceded it. These data are used to support two related claims. First, the failure of the intensity‐sum argument is likely to be due to nonlinearities in the coding of intensity. Second, the signal threshold is a monotonic measure of the internal percept at essentially the same time relative to the signal for different masking conditions. This latter result negates the integrator‐movement hypothesis (which holds that the time varies) and provides important support for the chain of derivations obtained by Penner and Shiffrin [J. Acoust. Soc. Am. 67, 617–627 (1980)].

ISSN:0001-4966    

DOI:10.1121/1.383938

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A model of temporal summation and intensity coding relates the subject’s internal percepty(t) to the stimulus inputx(t) by the equationy(t) =g{Ft−∞ f[x(τ)]h[t,τ,x(τ)] dτ}. In words, some transformationf[x(t)] of the stimulus intensity is weighted by a functionhand integrated; the result is transformed into the internal percept by a functiong. This system postulates a linear integral operator preceded and followed by transformations which may be nonlinear. Based on forward masking of clicks by white noise, we (1) show that the above characterization of the model is appropriate (which involves showing that there is a linear temporal summation stage), and (2) derive certain characteristics of the system’s nonlinearities. In particular, the integral ofhtimesfis shown to be a nonlinear function of the input intensity exhibiting more compression than a power function. It is also shown thathmust depend upon the intensity of the stimulus.

ISSN:0001-4966    

DOI:10.1121/1.383885

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP