摘要:

The sound radiation from convex and concave rigid diaphragms represented by portions of a spherical surface was investigated for the purpose of modeling a dome loudspeaker. Pressure responses, radiation impedances, directivity patterns, and some other characteristics were obtained and compared with those of a circular flat diaphragm of the same radius. While the on‐axis pressure response of the rigid flat piston remains constant, the response of the convex dome decreases for aboutka≥ 1 as the height of the dome increases. The concave dome has a wide smooth peak aroundka= 1.5 and many peaks and dips for larger values ofka. The radiation resistance of the convex dome increases by the rate of 12 dB/oct or less up to aboutka= 2.0 and remains almost constant in higher frequency regions. On the other hand, the radiation resistance of the concave dome has its largest peak at the frequency corresponding to the peak of sound pressure response and shows many peaks and dips in higher frequency region. The radiation reactance of the convex dome is smooth and always positive, while the concave dome also exhibits negative reactance due to the resonance in its cavity. The directivity patterns of either the convex or concave dome do not have minima with zero sound pressure and their radiation patterns are generally wider than those of the circular plate.

ISSN:0001-4966    

DOI:10.1121/1.2018095

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous work has considered the effect of free body resonances on the scattering of an incident plane wave by a cylindrical target in water and has related the major features of the theoretical form function resonances to the experimentally obtained farfield reflection patterns. Excitation of these free body resonances is here observed for a glass cylinder in water utilizing a birefringence imaging technique. A fused quartz cylinder is insonified by a long plane propagating pulse and images of the internal stress pattern at resonance frequencies obtained under polarized light. The experimental data are in agreement with a normal mode theoretical computation of the resonance locations and predicted stress distributions for the particular modes.

ISSN:0001-4966    

DOI:10.1121/1.2018152

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The impedance formulation developed by Junger [J. Acoust. Soc. Am.24,366–373 (1952)] to describe a thin elastic shell is used for an eigenfunction expansion solution to the plane wave scattering from two elastic cylindrical shells in fluid. The two‐dimensional approach employs the addition theorem as first reported by Twersky [J. Acoust. Soc. Am.24,42–46 (1952)]. The effects of the resonances of the shell are shown by comparison with the cases of scattering from two acoustically soft or two acoustically rigid cylinders. The interaction between the cylindrical shells is discussed. Finally, the method of images is used to investigate the scattering of a plane wave from a cylindrical shell near an infinite plane.

ISSN:0001-4966    

DOI:10.1121/1.2018205

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Previous studies have shown that an inverted‐velocity‐profile coaxial nozzle for use with supersonic cruise aircraft produces less jet noise than an equivalent conical nozzle. Furthermore, decreasing the annulus height (increasing radius ratio with constant flow) results in noise reduction benefits. In the present model‐scale study, the annulus was shaped by an eccentric mounting of the annular nozzle with respect to the conical core nozzle. Acoustic measurements were made in the flyover plane below the narrowest portion of the annulus and at 90° and 180° from this point. The model‐scale spectra are scaled up to engine size (1.07‐m diameter) and the perceived noise levels for the eccentric and concentric inverted‐velocity‐profile coaxial nozzles are compared ovcr a range of operating conditions. The implications of the acoustic benefits derived from the eccentric nozzle to practical applications are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2018250

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

In a two‐interval, forced‐choice task, observers were to discriminate a binaural noise whose interaural correlation,r, varied according to the functionr(t) = m cos 2πfmtfrom an interaurally uncorrelated noise[NU; r(t) = 0.0]. The former stimulus produces a perceptual binaural “flutter,” where the flutter rate is equal to the modulation frequencyfm, and the amount of flutter corresponds tom. The stimuli were narrowband Gaussian noises with center frequencies of 0.5, 1.0, 2.0, or 4.0 kHz. Presentation level was 75 dB SPL; duration was 1.0 s. For a given modulation frequency, modulation “depth,”m, was varied in a blocked procedure, and thresholds were estimated from the psychometric functions as that value ofmrequired for 75% discdminability. For the 0.5‐kHz stimulus. thresholds increased fromm= 0.28 atfm= 1 Hz tom= 0.78 atfm= 50 Hz. For higher‐frequency stimuli, discrimination was generally poorer and the function relating thresholdmtofmwas flatter: thus, for 2 kHz,m= 0.56 atfm= 1 Hz, andm= 0.71 atfm= 20 Hz: for 4 kHz,m= 0.80 atfm= 1 Hz, but no thresholds could be determined forfm<5 Hz. The data will be discussed in relation to previous work on dynamic binaural processing. [Supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2018312

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A system for imposing static (fixed‐head) localization cues on an artificial sound source is described. The system is based on the measurement of the peripheral binaural impulse responses at a series of target source positions using small microphones in the subject's ear canals. A computer with associated waveform processing software convolves these impulse responses with widehand noise bursts and plays the results to the subject over headphones. The headphone impulse responses are also measured and deconvolved out of the waveforms in advance by the computer. Both live and simulated localization trials have been carried out, using an identification paradigm with unconstrained source and subject‐response positions. Two‐dimensional, weighted error analysis is used to derive performance scores. Psychophysical localization performance with the simulator is compared to equivalent live performance.

ISSN:0001-4966    

DOI:10.1121/1.2018354

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Single tones at frequencies of 250, 1000, and 3000 Hz were added to white noise to determine the effect of tonal components on judgments of overall loudness, noisiness, and annoyance. Binaural measurements were obtained by magnitude estimation without designated standards. To obtain a reference function for the group of ten normal‐hearing listeners, the loudness of the noise was judged both with and without tonal components. When tonal components were added, the SPLs of the tone and noise were independently varied over a 30‐dB range between 70 and 100 dB SPL. Within this range, tone‐to‐noise ratios of +5, +10, +15, +20, +25, and +30 dB relative to the appropriate one‐third octave‐band pressure level were produced and evaluated. Tentative data analysis indicates that in order to adequately assess the perceived magnitude of noise‐tone complexes, the effects of mutual interaction between noise and tone need to be considered. Such interaction seems to depend on frequency, tone‐to‐noise ratio, and overall SPL of the noise. [Work supported by NASA‐Langley Research Center.]

ISSN:0001-4966    

DOI:10.1121/1.2018411

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A simple computational model was devised to predict the results of forward masking experiments which use tonal probes and maskers. Using straight‐line approximations for the hypothetical underlying excitation patterns and a fixed “detection” criterion, the model predicts “masked threshold” for a given combination of masker and probe parameters. Discussion will center upon the validity of the simplifying assumptions and the comparisons between predicted and observed values. [Work supported by a David Ross Fellowship from Purdue University and grants from N.I.H.]

ISSN:0001-4966    

DOI:10.1121/1.2018467

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Habitually exposing the hands to vibrations may lead to recurring episodes of finger blanching and numbness, with reduction in manual dexterity, tactile sensitivity, and damage to soft tissue occurring in severe cases. By systematically analysing retrospective studies of workers occupationally exposed to vibration, it can be shown that the duration of employment (and hence exposure) determines, on the average, both the appearance of the initial vascular symptoms, and the transition from reversible to irreversible disorders in groups using similar tools. A power law relating vibration amplitude and duration of exposure can then be deduced for occupations involving near‐daily exposure, provided an equinoxious contour is selected to frequency‐weight vibration spectra. In this way both the appearance and progression of subjectivity reported symptoms can be related to the vibration experienced by the hands. If it is then assumed that an individual's susceptibility remains unchanged during the course of the disorders, tolerable vibration exposures for the whole population can be predicted. The vibration limits so derived compare favorably with those proposed for day‐long exposure by the ISO.

ISSN:0001-4966    

DOI:10.1121/1.2018523

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A precise statistical analysis has been carried out for the steady‐state response of a general one‐dimensional wave‐bearing system formed of two identical subsystems coupled together at an end. The statistics correspond approximately to averaging in frequency. Cross correlation between the wave fields incident on the coupling from the two subsystems (neglected in most statistical analyses) strongly affects the magnitude of the coupling power and, for dissipative couplings, the dissipative power. Asymmetry of the wave field in each subsystem (also usually neglected) can have a significant additional effect even when the dissipative loss factor is small. These results from a scattering analysis are compared with prior results [T. D. Scharton and R. H. Lyon, J. Acoust. Soc. Am.43,1332–1343 (1968)] from a modal analysis of a particular system.

ISSN:0001-4966    

DOI:10.1121/1.2018050

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP