摘要:

A mathematical study of the random interference of sound waves in large rooms requires statistical methods. “Statistical wave acoustics” is based on the random interference of many simultaneously excited normal modes of a room. In general, the random interference takes place for frequencies above 2000(T60/V)12, whereT60is the reverberation time (in sec) andVis the volume (in m3) of the room. In the statistical theory, frequency responses between two points in a room are treated as random functions. The probability distributions, correlation functions, and “spectra” of these random functions are determined by physical parameters such as the distance between source and receiver, the volume and reverberation time of the room (or distribution of reverberation times), etc.In this paper, correlation functions of frequency responses are derived for rooms with uniform reverberation time, and negligible direct sound transmission between source and receiver. Analytic formulas for the following frequency correlation functions are found: the autocorrelation functions of the real and imaginary parts, the modulus and the squared modulus of the frequency response, and the cross correlation function between real and imaginary parts of the frequency response.The significance of these correlation functions in room acoustics is discussed. Measurement of the autocorrelation function of the real (or imaginary) part of the frequency response allows a precise determination of the distribution of reverberation times. The autocorrelation function of the modulus (or squared modulus) determines the required frequency shift in public address systems to improve their stability. For measurement of electroacoustic transducers in reverberation chambers, optimum bandwidths of noise or warble tones are obtained.

ISSN:0001-4966    

DOI:10.1121/1.1909136

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The effect of phase and pressure‐level differences on the detectability of single‐frequency signals in the presence of noise is presented for listening over of a binaural transmission system. During the several tests to be described, the two microphones were supported in free space both in the absence and in the presence of various approximations to an artificial head. The results indicate that over‐all detectability is a function of the combined binaural phase relationships of both signal and noise and of the monaural intensity relationship of the two signals at the ear having the higher signal to noise ratio. Some indication was found that phase differences may influence detectability to frequencies as high as 2000 cps. Pressure‐level differences, on the other hand, decrease in magnitude with decreasing frequency until only a small effect remains at 250 cps.

ISSN:0001-4966    

DOI:10.1121/1.1909137

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The lateral‐line organ of killifish is shown to be sensitive to a linear function of water displacements associated with the near‐field of sound sources, with the displacement probably being the most important factor rather than velocity or acceleration. The near‐field effect is discussed and is shown to be important not only for the lateral‐line organs but also for the acoustical and vestibular organs. It is emphasized that the near‐field effect introduces considerable complications into the study of the acoustico‐lateralis system, and is of conceptual importance for the theory of hearing and the study of schooling fish.

ISSN:0001-4966    

DOI:10.1121/1.1909138

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

In the auditory detection of a sinusoidal signal in the presence of random noise, it has previously been demonstrated that the presence of a “pedestal” or background sinusoid of the same frequency and phase as the signal increases detectability. This increase was confirmed in a two‐interval forced choice experiment in which a 1000‐cps sinusoid was present in one of two 0.1‐sec intervals, and the noise plus pedestal were present in both intervals. Pedestals of moderate intensity in phase with the signal increased detectability. Pedestals in quadrature (90° out of phase) with the signal did not improve detectability. Very large pedestals decreased detectability irrespective of phase. A simple energy‐detection model was developed and its performance compared with the experimental results. The model consists of a bandpass filter, a square‐law element, and an integrator. The probability of correct detection varies with signal level in a manner similar to the auditory results. Detectability is improved by an in‐phase pedestal and approaches that of a correlation detector in the limit of infinite pedestal. Detectability is not improved by quadrate pedestals. The model can be modified to predict the decreasing detectability with large pedestals.

ISSN:0001-4966    

DOI:10.1121/1.1909139

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Bursts of high‐pass filtered thermal noise coming from two different sources in space were alternated in time (with no time gap between bursts). Separation angles between sources from 5 to 50 deg were used, and alternation rates from 2 to 14 per sec. Duration of bursts was also varied. Subjects indicated for each sound perceived whether it was steady or intermittent, and where it was located.When the angle between sources is small, some subjects may hear only one continuous sound, provided that the repetition rate is relatively high. More commonly, however, our subjects tend to hear one steady sound and one intermittent sound when the separation angle between sources is small; they tend to hear this pattern at wider separation angles when the duration of one of the stimuli is short. When one of the bursts has short duration, and sources are separated by 30 to 50 deg, it appears to many subjects that the short burst is markedly displaced in location. For wider angles of separation between sources, and various conditions of duration, many subjects can also hear a third steady sound between the other two. Occurrence of this latter sound has especially interesting implications for a theory of sound‐localization mechanisms.

ISSN:0001-4966    

DOI:10.1121/1.1909140

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Theoretical analysis of the crest and extremal statistics of a square‐law‐derived random process is presented. The differences between the crest and the extremal statistics, particularly the bandwidth dependence of the latter, are illustrated for the Gaussian‐derived case. The theory is applied to the statistical response of a uniform bar in tension. Particular attention is paid to the crest distributions which deviate from the integrated Rayleigh distributions in a predictable way at large amplitudes of vibration. Experimental distributions obtained from the strain response of a uniform bar forced in its fundamental mode by band‐limited Gaussian white‐noise signals are in excellent agreement with calculated values.

ISSN:0001-4966    

DOI:10.1121/1.1909141

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The sound spectra of nasal murmurs in various vowel contexts have been studied by use of an analysis‐by‐synthesis scheme. The acoustic characteristics are described in terms of format‐antiformant distributions (pole‐zero locations of the transfer function for the articulatory system) in the frequency domain. It is shown that the location of the antiformant characterizes the murmur of each consonant within the class. The spectral structures are discussed with reference to the articulatory features, and acoustical interpretations of the observed characteristics of the formants and antiformant are given. Also suggested is the existence of certain gross spectral features that are characteristic of nasals as a class.

ISSN:0001-4966    

DOI:10.1121/1.1909142

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

In a series of experiments, listeners were asked to make judgments of the relative duration, loudness, and stress associated with the components of stimuli consisting of sequences of two noise bursts. The over‐all duration of each stimulus was the same, and the two components were given various relative intensities and durations. All response sets demonstrate marked asymmetry, particularly those requiring a judgment of the stress pattern of the sequence.

ISSN:0001-4966    

DOI:10.1121/1.1909143

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The results of an experimental investigation into the techniques of coupling the transducer to the specimen in making ultrasonic measurements are presented. Two major couplants, glycerine and phenyl salicylate, were subjected to tests. As a result of these tests, a bonding clamp was developed that greatly increased the reproducibility and accuracy of the measurements.

ISSN:0001-4966    

DOI:10.1121/1.1909144

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The electromechanical‐coupling coefficient of a piezoelectric transducerkis usually derived from the difference between resonance and antiresonance frequencies for a particular mode. However, if the mechanicalQof the transducerQmis low, i.e.,k2Qm < 2, this relationship breaks down. The regionk<20% and 100

ISSN:0001-4966    

DOI:10.1121/1.1909145

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP