摘要:

A feedback oscillator, consisting of an active device with transconductanceA, and a damped resonator of impedanceZ, is operated at constant amplitude by an external driver. The oscillation runs at an energy “profit” or “loss” ifZAis above or below breakeven (ZA= 1). The rate of energy gain or loss, as a function ofZA, is largest in the feedback regions just above or below the energy breakeven value. In the nonlinear regenerative oscillations of reed wind instruments, energy is transferred via heterodyne effects between several frequencies. In this case,Zis dominated by the sum of the input impedances of the air columns upstream and downstream of the reed. At each component frequency, the energy balance is describable in terms of the single frequency oscillator. If (ZA)nis below breakeven at the frequency of thenth spectral component, and the magnitude OfZnis decreased, the energy balance at this frequency causeslessof a drain on the overall oscillation; if (ZA)nabove breakeven, and the magnitude ofZnis increased, there is less energy production at this frequency. Finally, the effect on the spectral component of the pressure signal on one side of the reed at the frequency of thenth partial, when the input impedance is varied on the opposite side of the reed, can only be large when (ZA)nis near breakeven. Experimental evidence will be presented. Musical implications will be summarized. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2021756

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Some master violin makers are expert at “tuning” a bridge to a particular instrument. Others tend to cut bridges to a given set of dimensions. A demonstration discussion will be presented using a violin with several differently cut bridges, based on hologram studies of Reinicke, to show the effect on violin tone of changing bending stiffnesses at various points.

ISSN:0001-4966    

DOI:10.1121/1.2021758

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

According to classical acoustic theory, the Doppler shift associated with an acoustic source moving at constant velocity induces the following straining of the time coordinate:t′ =t|1‐M cos α|. Heret′ denotes the time coordinate in the fixed frame of reference (receiver),Mis the Mach number of the source, and α is the angle between the direction of motion and the direction of observation. At transonic velocitiest′ can assume a value of 0, in which case all the acoustic energy is received in an infinitesimal increment of time. This implies a transfer of infinite power so it is not physically realizable. We have used the method of characteristics to find the exact Doppler shift to a transonic source and the corresponding maximum amplitude observable at the receiver. Two cases are considered: a point source and a line source, both moving rectilinearly above a point receiver. [Work supported by the Office of Naval Research ONR.]

ISSN:0001-4966    

DOI:10.1121/1.2021766

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The results of a model study of the diffraction of transients from blasting caps over barriers are reported. A prediction technique based on Oberhettinger time domain notation was developed [J. Res. Natl. Bur. Stand.61,5 (1957)]. The results of this calculation are compared to the data. Finite wave effects were incorporated into the prediction and were shown to be small for the geometries and charge size employed in the model study. The finite wave effects on diffraction of transient may be important for shorter duration pulses such asNwave from sparks.

ISSN:0001-4966    

DOI:10.1121/1.2021771

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This presentation describes the development of a system that provides real‐time determination of the location and spectra of transient underwater sounds. The system is computer‐based and field‐portable. Sound source location is determined by time‐arrival‐difference analysis on sounds detected at a long baseline array of three or more hydrophones. The arrival‐time differences are calculated from digital cross‐correlation analysis of each possible pair of the received pressure time histories. Signal spectra are determined from a Fast Fourier Transform (FFT) analysis. The system was field tested off Point Barrow, Alaska during the Spring 1984 bowhead whale migration as an adjunct to an ongoing visual census effort conducted annually by the North Slope Borough. During this period sounds were received at an array of three sonobouys and transmitted to a nearby field camp for recording and processing. The localization and spectrum analyses were applied successfully to a wide variety of transient sounds including those of bowhead whales, beluga whales, bearded seals, and a variety of ice noises. [This research was supported by the North Slope Borough, Alaska.]

ISSN:0001-4966    

DOI:10.1121/1.2021774

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The bispectrum of several measured ocean acoustic ambient noise processes was estimated and used to test for the linearity and Gaussianity of the processes. A linear process has a constant bispectrum, while a Gaussian process has a zero bispectrum. Both linearity and Gaussianity could be easily rejected for several common ambient noise processes, even though in some cases the processes tested to be univariate Gaussian. These results suggest that autoregressive models, since they are linear models, may not be the most appropriate models for ocean acoustic ambient noise. Some possible explanations for the causes of the observed nonlinear behavior will be suggested. [Work supported by the Office of Naval Research, Code 411.]

ISSN:0001-4966    

DOI:10.1121/1.2021779

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Native English speakers show a trading relation and perceptual integration of a temporal cue (F1transition duration) and spectral cues (F3andF2onset and transitions) differentiating the liquids /r/‐/l/ [L. Polka and W. Strange, J. Acoust. Soc. Am. Suppl. 173,S53 (1983)]. To investigate the effects of linguistic experience on these perceptual phenomena, native Japanese speakers learning English completed forced‐choice identification and oddity discrimination tasks, using two synthetic /rak/‐/lak/ series in which the temporal and spectral cues were varied orthogonally. Identification functions of Japanese who could consistently label the /r/‐/l/ series showed a trading relation (a predictable shift in the identification category boundary) and perceptual integration of temporal and spectral cues. Discrimination of pairs differing on both cues was significantly better than spectral‐cue‐alone pairs only when the combination of cue values facilitated phonemic differentiation. Preliminary results with less advanced Japanese English learners showed no advantage in discrimination performance of two‐cue pairs over one‐cue pairs, suggesting that the perceptual integration of cues is a function of language‐specific phonetic processing. [Work supported by NIMH.]

ISSN:0001-4966    

DOI:10.1121/1.2021783

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Identification and discrimination procedures were used with nonspeech stimuli to investigate a possible auditory basis for categorical perception of place of articulation. One sinewave series consisted of linear frequency transitions (varying in onset frequency) followed by a steady‐state portion. A second series was produced by combining each of the stimuli from the first series with a second tone (a rising initial transition followed by a steady state). The stimuli were modeled after the second and third formants of a stop consonant series varying in place of articulation. Subjects reliably sorted the one‐tone‐component series into three categories corresponding roughly to rising, flat, and falling transitions. The local maxima of subjects' discrimination functions fell near the labeling category boundaries. With the inclusion of the second tone, subjects reliably sorted the continuum into two, rather than three, categories. Further, a single discrimination maximum, located in the vicinity of the category boundary, was found for the two‐component stimuli. The results suggest that auditory categories may underlie the perception of an analogous stop place series and that information is not extracted independently for each transition. Rather, the pattern of formant transitions seems to be the critical information that underlies the stop‐place categories. [Work supported by NINCDS.]

ISSN:0001-4966    

DOI:10.1121/1.2021786

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This is an extension of the investigator's previous work [J. Acoust. Soc. Am. Suppl. 171,S105; and72,S16 (1982)]. A series of spoken /sɪsi,sisɑ/ tokens was modified using a PCM speech editor. The /s/‐noise segments were excised. The original intervocalic /ɪ‐i,ɪ‐ɑ/ contexts and the /ɪ,i,ɑ/ vowels in isolation were assembled into a perceptual identification test and low‐pass filtered at 3 kHz with an attenuation slope of 48 dB/oct. As a consequence, the noise and transient energy coextensive in time but higher in frequency than the vocalic formant structures was removed more completely than before. Subjects identified the consonants heard adjacent to the vocalic segments. There was better agreement as to thelabialstop frequently heard in the intervocalic /ɪ‐i/ context than previously. As before,dental‐alveolarstops were frequency heard in /ɪ‐ɑ/. These results reflect perceptual integration over the arresting and releasing transition and silent interval duration cues. [Haskins Laboratories provided valuable assistance in the preparation of stimuli on NIGHD Contract No. NIH‐71‐2420.]

ISSN:0001-4966    

DOI:10.1121/1.2021793

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

The propagation of strong pressure pulses in bubbly liquids, the transition to chaotic behavior in dynamical systems, and the development of new experimental methods of investigation motivate recent interest in large‐amplitude forced bubble oscillations. The results of some numerical and analytical investigations of simple mechanical models of the phenomenon will be reviewed. Physical processes not accounted for in these studies, namely the compressibility of the liquid and the complex thermal processes taking place in the bubble, will then be discussed by means of suitable modification of the available theoretical formulations. Numerical results will be presented showing the importance of these effects in large‐amplitude motion. An application to the damping of pressure pulses in bubbly liquids concludes the presentation. [Work supported in part by ONR and NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2021800

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP