摘要:

In the measurement of the transmission properties of panels it is usually desirable to make the test panel as small as possible, consistent with the avoidance of edge‐diffracted signals at the receiving sensor. The transient response of the panel will delay the attainment of a steady‐state transmitted signal. Such a delay shortens the time window available for measurement before the arrival of the signals diffracted from the panel edges. The effect is illustrated analytically for a panel to be tested in water, and comprising a mass sheet (a plate below its critical frequency) and an attached compliant layer. Several sets of systems parameters are chosen, and the approach to steady state is determined as a function of the number of cycles of the excitation. The more sluggish the panel response (due, say, to a lower resonance frequency of the plate mass with the layer stiffness), the more slowly the panel achieves steady‐state response at any given frequency. Thus a sluggish panel would have to be larger to be free of edge‐diffraction effects.

ISSN:0001-4966    

DOI:10.1121/1.2016504

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper extends the author's previous paper (presented at the 94th meeting of ASA) on the prediction of farfield sound radiation from a vibrating rectangular boxlike structure resting on the ground from surface acceleration measurements. The lowest‐order approximation of the Green's function which was used earlier can describe farfield radiation only for certain ideal points. An improved approximation to the Green's function (with Neumann boundary conditions) can be fabricated to predict the entire far field radiation pattern from the corresponding Helmholtz integral equation solution for the same problem based on techniques related to the geometrical theory of diffraction. The resulting approximate Green's function takes into account the direct waves and the diffracted waves with the assumption that the sound diffracted by more than one edge of the box makes a negligible contribution to the farfield. The diffracted waves are derived from the uniformly valid asymptotic expression for diffraction of point‐source‐generated waves by a semi‐infinite right‐angled rigid wedge. The agreement of the theoretically calculated SPL in the farfield with those measured values gives a substantial verification of the applicability of the geometrical theory of diffraction to the experimental example of a 130‐cm × 76‐cm × 152‐cm water‐filled steel tank excited at 265 Hz by two underwater speakers within the tank.

ISSN:0001-4966    

DOI:10.1121/1.2016509

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The reproductive system of the mouse and the pregnant mouse uterus studied under both pulsed and continuous wave regimes display a spectrum of responses. There is generally an increased incidence of response as the time average intensity is increased. Some notable exceptions exist to this general trend. These studies have used focused beams of 2 and 4‐mm diameter at the 6‐dB points. A given organ is covered by multiple‐site exposure in a serial time sequence. In this way more nearly organ‐specific irradiations can be conducted and paralysis due to spinal cord irradiation or anal musculature destruction is avoided for exposure at average intensities necessary to elicit the bioeffects observed in the study. A variety of ultrasound regimes have been studied and the time average intensity and exposure times reduced to the levels at which no statistically significant difference exists between exposed and control animals for the bioeffects being scored. Solid tumors grown in the hamster flank by innoculation with cells derived from a Simian medulloblastoma have been irradiated with 720‐W/cm2focused ultrasound. At 7‐s continuous wave irradiation, it is possible to produce tumor extinction, regarded as a cure rate of 33%. The exposure regime has not been optimized.

ISSN:0001-4966    

DOI:10.1121/1.2016512

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Onset of cavitation is monitored at ultrasound frequencies between 0.75 and 3 MHz, in both aerated and degassed media. Three different classes of criteria are used: physical effects (subharmonic generation and sonoluminescence), chemical effects (iodine release and ferrous ion oxidation), and biological effects (cell lysis and other forms of cell death). The effect of pulsing the field on these phenomena is illustrated and discussed.

ISSN:0001-4966    

DOI:10.1121/1.2016515

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

One outgrowth of our theory of intensity resolution is the following prediction concerning the relation of loudness matches to intensity discrimination: Two stimuli are matched in loudness if and only if their intensities divide their respective dynamic ranges proportionately in terms of number of JNDs [J. S. Lim, W. M. Rabinowitz, L. D. Braida, and N. I. Durlach, J. Acoust. Soc. Am.62, 1256–1267 (1977)]. This prediction, which is essentially the same as that proposed by Riesz [R. R. Riesz, J. Acoust. Soc. Am.5, 211–216 (1932)], is derived from our theory by assuming that loudness is the predominant cue used to discriminate intensity and that all stimuli are equally loud at the tops and bottoms of their dynamic ranges. This prediction is consistent with a wide variety of functions relating loudness to intensity (including the power law); all that is required is that loudness be a monotonically increasing function of the proportional JND factor and that this function be the same for all stimuli. This prediction does not, however, take account of the effects of context on loudness. In this paper, we discuss this prediction in detail and comment on its relation to other concepts concerning discrimination and loudness and on its consistency with experimental data. [Work supported by NIH and NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2016519

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Judgments of comparative loudness (e.g., loudness‐ratio judgments or judgments of loudness relative to a reference sound) show a high degree of repeatability and loudness scales developed from such judgments have been found to be reasonably similar for different subjects. These scales, however, have typically been derived from a limited subset of a much larger matrix of comparative judgments. The scaling of loudness by the method of loudness doubling, for example, concentrates observations on only one side and close to the diagonal in the matrix of possible loudness‐ratio judgments. A loudness scale obtained solely by the method of loudness doubling differs systematically from that obtained by loudness halving, and both scales differ from that obtained by loudness quadrupling. Thus, although the judgments are reasonably repeatable, the exact form of the loudness scale depends on which subset of judgments is used. In this paper, a general approach to loudness scaling based on a complete matrix of loudness‐ratio judgments is developed and the results obtained from three separate implementations of the approach are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2016520

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Scaling annoyance is different from scaling loudness. The exponent of the annoyance function is more labile than the exponent of the loudness function. However, there is a general truth: If one physical parameter is varied then subjects will use those variations to represent values of the dimension they are asked to respond to. This clearly induces correlations between things like annoyance and loudness.They can only be untangled when annoyance judgments vary, as with spectral differences, but loudness does not. Not only are scales of annoyance different from perceptual scales, the notion of “annoyance” derives from a social response to noise. Community response is commonly represented by proportions of respondents replying to partition scale descriptors. Evidence that community annoyance is not represented by such frequency tables is shown by the discrepancy between survey response data for attitudes toward the Concorde, and the annoyance scales for aircraft overflight sounds based on a utility comparison scale (cross‐modality matching). These data demonstrate that although everyone in a community may report that they are annoyed by the sounds of aircraft overflights, the magnitude of the annoyance is neither uniform across individuals, nor is it reflected in the proportions of annoyed people in the community. [Work supported by NASA.]

ISSN:0001-4966    

DOI:10.1121/1.2016524

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Variability in magnitude estimates, both within and among observers, will be discussed. Over a group of 20 subjects the power‐law exponents may vary from 0.1 to 0.4 (power units). Repeated judgments for a single individual of a given intensity show coefficients of variation (ratio of standard deviation to mean) of 0.1–0.4. Magnitude production data show similar values. Although such variability has been known to exist for some time, there is still no adequate theory to account for it nor empirical techniques to minimize it. For practical application of this technique there is no alternative but to use large numbers of subjects. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2016530

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Polish is traditionally described as using the prevoiced and short‐lag categories to contrast its voiced and voiceless stops. However, Moslin and Keating [J. Acoust. Soc. Am.62, S27 (A) (1977)] have shown that some speakers of Polish make use of the long‐lag, aspirated voicing category. Preliminary results for six speakers of Polish on a/da/‐/ta/continuum with VOT from −20 to +80 ms indicate that all speakers, regardless of how they produce their apical stops, show a labeling boundary and discrimination peak at about 35 ms. That is, speakers who rarely if ever produce long‐lag stops themselves place their category boundary between the short‐ and long‐lag regions, thus showing a dissociation between production and perception. Further work will vary the test conditions and/or subjects' response categories to determine if a boundary exists between the prevoiced and short‐lag regions of the continuum.

ISSN:0001-4966    

DOI:10.1121/1.2016532

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The amount of intervocalic silence needed to perceive two different stop consonants in stimuli of the type /V1b−gV2/(type 1 boundary), and two identical stops in stimuli of the type /V1b−bV2/ (type 2 boundary), was determined as a function of different vowel contexts (V1,V2= /a/, /i/, /u/) and of different durations of the initial and final vowels (120, 180, and 240 ms). It was predicted that changes in the vowels, and thus in the extent of the formant transitions into and/or out of the closure period, would affect type 1 boundaries more than type 2 boundaries. On the other hand, changes in vowel duration, which effectively change the perceived speaking rate, were expected to affect type 2 boundaries more than type 1 boundaries. Preliminary data tend to confirm these hypotheses, and thus support the view that type 1 and type 2 boundaries reflect temporal integration at different levels of processing. [Work supported by NICHD.]

ISSN:0001-4966    

DOI:10.1121/1.2016545

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP