摘要:

Early studies of ultrasound induced optical birefringence in liquids were performed in the near optical field of the ultrasonic grating. More recently, a farfield method has been developed for studying the effect. The range of experimental conditions under which the respective methods may be accurately applied vary significantly. In addition, the methods differ considerably in their abilities to provide measurements from which theories for the effect can be directly evaluated. Experimental results obtained from each method in castor oil are compared to illustrate the significant differences which occur and to clarify the advantages and limitations of each method.

ISSN:0001-4966    

DOI:10.1121/1.2015912

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

In an earlier paper [H. S. C. Wang, J. Acoust. Soc. Am.57, 1076 (1975)], it was demonstrated that amplitude shading of a transducer array can be derived from the minimum property of the total received power except that through a slice of main beam. We show here that in the special and fundamentally important case of linear arrays, the formulation can be simplified by considering the power or object function (OF) to be minimized as a function of a generalized variableu = cosθ − cosθ0, where θ denotes the colatitude angle and θ0the steered direction. Although the total visible range of a linear array covers −2⩽u⩽2, the OF needs only to be minimized in 0⩽u⩽2 due to symmetry of the directivity function. Furthermore, the space 0⩽u⩽2 can be sub‐divided into various regions of different weights to form multiparameter OF for the control of individual sidelobes. As an illustrative example, an endfire array of 12 elements logarithmically spaced over an aperture of 4.4 wavelengths is shown to have an unshaded sidelobe level of −10.4 dB, which was improved to −14.8 dB when synthesized with a single parameter OF and to −23.1 dB with a multiparameter OF.

ISSN:0001-4966    

DOI:10.1121/1.2015920

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The cross‐spectral matrices of signal and noise were recorded for a superdirective array in shallow water. Well defined beam shapes were formed from the 4‐min cross‐spectral averages. Endfire configurations of three hydrophones equally spaced by 0.2 wavelengths enabled an array gain of 8.5 dB to be achieved at 136 and 230 Hz. The array weights used were adapted to an average measured noise field. If weights are optimized for an isotropic noise field an array gain of 7.5 dB is obtained.

ISSN:0001-4966    

DOI:10.1121/1.2015924

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A general approach is presented to evaluate the acoustic radiation and interaction impedances for the nonuniform velocity of a vibrating surface on an infinite cylinder. The approach is based on the use of a Green's function and Fourier transform technique. General integral expressions are developed for both the acoustic radiation and interaction impedances for a general velocity distribution on the cylindrical surface. The expressions are shown to reduce to previously developed expressions for the radiation and mutual impedances for several uniform velocity problems of interest. As a particular nonuniform velocity of interest, the radiation and interaction impedances are addressed for thein vacuomodes of a simply supported finite cylindrical shell. Simple expressions are presented as a function of the circumferential and axial mode number for both the low‐ and high‐frequency behavior of the radiation and interaction impedances. Numerical results are presented to illustrate the general behavior of the radiation and interaction impedances of the low‐order mode of interest.

ISSN:0001-4966    

DOI:10.1121/1.2015930

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The noise attenuation due to a barrier constructed parallel to a building facade has been studied to test for filling in of sound in the semireverberant space between the barrier and building. The excess attenuation in each13‐octaveband from 125 to 4000 Hz was measured and compared with the predictions of Maekawa. Measurements were also done with the barrier in a free‐field configuration, remote from the house. Results show that there is negligible filling in of sound and that the excess attenuation agrees well with the Maekawa predictions in both cases. The barrier was relatively light (2.5 kg/m2) and, although the performance was therefore limited by the transmission loss, the maximum excess attenuation ofA‐weighted levels was found to be greater than 19 dB.

ISSN:0001-4966    

DOI:10.1121/1.2015938

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A set of computer programs, called Integrated Noise Model (INM), has been developed to compute noise exposure values due to aircraft at various locations around airports. The INM evolved from an earlier computer model used for investigating noise around 23 U. S. airports in terms of NEF. The INM consists of three independent routines: (1) Contour Analysis Model, (2) Grid Analysis Model, and (3) Contour Plotting Pack.age. INM will compute noise exposure values for the following: Noise Exposure Forecast (NEF); Day—Night Average Sound Level (Ldn); Community Noise Equivalent Level (CNEL); Aircraft Sound Description System (ASDS); and Daily Overall Sound Exposure (DOSE, an experimental noise metric). The calculations are sensitive to details of fleet mix data and flight operational procedures. The Contour Analysis Model develops points on curves of equal noise exposure. The Grid Analysis Model computes exposure levels at user‐specified points. Optional output allows examination of the noise contribution from each flight. The Contour Plotting Package retrieves contour point locations from mass storage and plots them. [Work supported by U. S. Department of Transportation.]

ISSN:0001-4966    

DOI:10.1121/1.2015944

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The ability of three age groups to identify pure tones was measured by the method of absolute judgments. Group mean ages were approximately 20, 40, and 60 years, with 25, 20, and 18 subjects per group, respectively. Eight tones in equal logarithmic units from 100 to 8000 Hz were presented monaurally in random order in the better ear at a loudness level of 60 phons. After practice, subjects were required to identify each tone by a designated code number from one to eight (low to high frequency). The correct identification was provided after each judgment. These were 80 judgments per subject (10 trials × 8 tones). Analysis of variance showed a significant difference in the mean number of correct responses among age groups. The means in order of increasing age were 55.52 (69.39%), 51.55 (64.43%), and 48.44 (60.55%) (Fratio 8. 003, 2/120 df,p= 0.001). The last 40 trials yielded significantly better performance than the first 40 trials for the 20 and 60 year‐old groups, but the 40 year‐old group showed no change (Fratio 10.401, 1/120 df,p= 0.002). The age × trials interactions was nonsignificant. It is concluded that the processing of auditory information is adversely affected by normal aging in adults from 20 to 60 years. [Work supported by SUNY Research Foundation Grant No. 023‐7185A.]

ISSN:0001-4966    

DOI:10.1121/1.2015946

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

There has been a recent renewal of interest in the response latency as a psychophysical index of detectability, discriminability, or perceptual magnitude. This response measure depends on a number of variables other than those of the stimulus and thus some care is required in its interpretation. It has been proposed that one of the most powerful determinants of response latency in discrimination tasks should be the distance of the current stimulus from the current criterion, measured along a decision axis. This proposition was demonstrated in nine experimental conditions, in which the tasks were (a) a difficult frequency discrimination, (b) an easy frequency discrimination, and (c) assignment of a two digit number to the correct one of two distributions. Each of these stimulus conditions was tested (1) in a standard statistical decision procedure, (2) with the optimal criterion demonstrated on each trial, and (3) in a “labeling” procedure without real or implied rewards. In all cases the response latencies fall off systematically to either side of the observers' current criterion, suggesting that the perceptual distance between the current criterion and the stimulus, rather than the inherent difficulty of a judgment, must determine the time required to process that stimulus. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2015953

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Texas Instruments controls entry to its corporate computer facility by speaker verification. During two and one half years of operation, 0.4 million verifications have been performed for 300 users. Current performance is 99.9% user acceptance with 99% impostor rejection. Initial user acceptance is not as good (99%), but steady‐state performance is achieved after 50–100 verifications. Careful user orientation is important, and user adaptation and voice consistency continue to improve over a long period of time. The variance of input speech data for those 36 users (24 men, 12 women) who had been verified at least three thousand times was plotted versns session number. Average variance was 108 at 250 sessions, 105 at 500, 101 at 1000, 96 at 2000, and 93 at 3000 sessions. How do you explain this continued improvement?

ISSN:0001-4966    

DOI:10.1121/1.2015959

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Encoder subjects hears, for each item, a disambiguating context such as either “Mac has some cover stories,” or “Max is covering some stories,” followed by the cue “Let's go and see them/him.” Subjects' task was to respond emphatically and negatively in the form “I don't WANT to go and see Mac's/Max cover stories.” These responses were recorded on tape and played to decoder subjects, whose task was to repeat the target phrases in citation form—i.e., with disambiguating accentuation. According to received prosodemic theory, decoders should reliably recover the structures given to encoders, whose responses would,ex hypothesi, carry the same “stress” distinctions, merely realized at weaker “levels.” In fact, however, the patterns given to encoders and those elicited from decoders failed to show significant (above chance) agreement. This finding is interpreted as support for the theory of “binary” suprasegmental features [R. Vanderslice and P. Ladefoged, Language48, 819–838 (1972)], which claims that the feature ACCENT does not occur postnuclearly (i.e., the intonation contour, in this case CADENCE, begins with the last accented syllable of the sense group), and thus predicts exactly the loss of prosodemic contrast observed in these cases. The tune in question, with leftward “shift” of the sentential accent to the emphatic wordWANT, must not be confounded with one also having EMPHASIS (and thus typically highest pitch) onWANT, yet with unshifted sentence accent on eithercoverorstories. The latter, disambiguating, tune is superficially similar but systematically distinct. It should also be noted that the “binary” prosodic features can, mutatis mutandis, be viewed as singularly elements (morphons) in a Cognitive‐Stratificational account of English suprasegmentals.

ISSN:0001-4966    

DOI:10.1121/1.2015970

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP