摘要:

The sound transmission loss (TL) characteristics of panel constructions with thin face sheets and a thicker, lighter core are investigated. Analytical models of TL are developed for constructions with isotropic and orthotropic core materials. The occurrence of acoustic coincidence is described for symmetric and antisymmetric modes of propagation, in the panel. Symmetric propagation involves thickness deformation of the core, while antisymmetric propagation involves a bending deformation of the panel without thickness deformation. For symmetric modes, coincidence occurs near the conventional double wall resonance frequency characterized by the stiffness of the core and the mass of the face sheets, and also at higher frequencies associated with bending wave propagation in the face sheets. Antisymmetric modes account for shear deformation in the core, which results in a softening of the bending rigidity of the panel at higher frequencies. For orthotropic core materials, the acoustic behavior is dependent on the direction of propagation over the surface of the panel. Measured TL results for representative panels show good agreement with predictions. Finally, a procedure for obtaining improved TL performance is described, which involves shifting the double wall resonance to below the frequency band of interest, and limiting the shear stiffness of the core to shift the onset of bending wave coincidence to higher frequencies. Greater than mass law TL, similar to that of conventional double wall constructions, can be achieved over a significant frequency band in the audio range. The mechanical integrity of the panel is provided by the shear stiffness of the core.

ISSN:0001-4966    

DOI:10.1121/1.1894638

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

This paper presents a study on the transmission characteristics of a three‐layered infinite plate excited by a plane acoustic wave. Each layer is described by the two‐dimensional elasticity theory. An expression predicting the sound transmission loss as a function of both the frequency and the incidence angle of the acoustic wave is derived and calculated numerically for various combinations of the facing and the core materials. Further, based on the information thus obtained, a method to fabricate a sandwich plate with high sound interception is presented and applied to the design of a plate consisting of a steel core and foamed concrete facings.

ISSN:0001-4966    

DOI:10.1121/1.1894639

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A planar antenna array, the elements of which are deployed on the boundary of some finite region in the aperture plane, is known as aboundary array. Such a deployment of array elements can produce a point spread function with a narrow mainlobe, but this type of deployment also results in high sidelobes. Because of the potential for high resolution from a small number of array elements inherent in these arays, it is of interest to investigate their use, both in the context of passive (receive‐only) imaging of incoherent source distributions and in the context of active (transmit/receive) imaging of coherent source distributions. In recent years, a technique has been proposed for creating the effect of imaging with afilled circularorellipticalaperture using an aperture consisting only of the boundary of the same circular or elliptical region. This technique consists of the addition of multiple images that are formed with different point spread functions to synthesize an image with the desired point spread function, and it is applicable to both active and passive imaging. In this paper, a technique is presented for creating the effect of imaging with a rectangular aperture using only the boundary of that aperture. This technique is also applicable both for active and passive imaging. Also, simulated images are given of small numbers of point targets from the imaging systems discussed. These are used to motivate a discussion of some of the interesting features of the aperture synthesis scheme.

ISSN:0001-4966    

DOI:10.1121/1.1894640

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

The problem of detecting a sinusoid with drifting phase in the presence of additive white Gaussian noise is considered. A Lorentzian signal model is used, in which the signal to be detected is modeled as a sinusoid whose phase is drifting with Brownian motion. A class of quadratic detectors that trade off coherent and noncoherent averaging of the received waveform is studied. The deflection ratio is used as a performance criterion, and the optimum quadratic detector structure as parametrized by the phase bandwidth is derived. Then, the performance relative to the optimum of a class of suboptical detectors calledm‐order noncoherent detectorsis considered. It is shown that the best detector in this class performs nearly as well as the optimum quadratic detector. This is in sharp contrast with standard envelope detection whose performance is shown to degrade severely in the presence of phase drift. Simulated detection probabilities that verify this performance disparity are also presented.

ISSN:0001-4966    

DOI:10.1121/1.1894641

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

A series of experiments on the detectability of vowels in isolation has been completed. Stimuli consisted of three sets often vowels: one synthetic, one from a male talker, and one from a female talker. Vowel durations ranged from 20–160 ms for each of the sets. Thresholds for detecting the vowels in isolation were obtained from well‐trained, normal‐hearing listeners using an adaptive‐tracking paradigm. For a given duration, detection thresholds for vowels calibrated for equal rms sound pressure at the earphones differed by 22 dB across the 30 vowels. In addition, an orderly decrease in vowel thresholds was obtained for increased duration, as predicted from previous data on temporal integration. Several different analyses were performed in an attempt to explain the differential detectability across the 30 vowels. Analyses accounting for audibility reduced threshold variability significantly, but vowel thresholds still ranged over 15 dB. Vowel spectra were subsequently modeled as excitation patterns, and several detection hypotheses were examined. A simple average of excitation levels across excited critical bands provided the best prediction of the level variations needed to maintain threshold‐level loudness across all vowels.

ISSN:0001-4966    

DOI:10.1121/1.1894642

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Gap detection thresholds were measured by forced‐choice procedure for conditions where the duration of a silent gap was varied adaptively between pairs of sinusoidal markers of the same or different frequency. Frequencies of the first sinusoid in a pair of markers ranged fromF1= 500 to 4000 Hz. Second‐sinusoid marker frequenciesF2includedF1 = F2, and usually frequencies 2%, 5%, 24%, and 50% higher thanF1. In preliminary studies the role of presentation level (E/N0) on gap detection was considered. Preliminary data revealed confounding extraneous factors arising from gating transients and from overall stimulus (i.e., markers + gap) and/or masker duration cues. In the main experiments, the contributions of these extraneous cues were evaluated with experimental designs aimed at identifying and minimizing the confounding roles of these cues in gap detection. For conditions where extraneous gating transient cues were minimized (by presenting the sinusoidal markers in a continuous noise masker with random onset phase for the second sinusoid in every pair of markers) and overall stimulus duration cues were diminished (by randomizing the duration of each marker independently), gap detection thresholds increased from 5 to 90 ms as the frequency separation betweenF1andF2was increased by half an octave. When the gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, the data were closely fit by the roex filter model. On average, the listeners' performances were modeled well by a constant‐percentage (7%) bandwidth filter centered onF1.

ISSN:0001-4966    

DOI:10.1121/1.1894643

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Either an interaural phase shift or level difference was introduced to a narrow section of broadband noise in order to measure the acuity of the binaural system to segregate a narrow‐band from a broadband stimulus. Listeners were asked to indicate whether this dichotic noise or a totally diotic noise was presented in a single‐interval procedure. Thresholds for interaural phase and level differences were estimated from four point psychometric functions. These thresholds were determined for three bandwidths of interaurally altered noise (2, 10, and 100 Hz) centered at four center frequencies (200, 500, 1000, and 1600 Hz). Thresholds were lowest when the interaurally altered band of noise was centered at 500 Hz, and thresholds increased as the bandwidth of the interaurally altered noise decreased. Performance did not exceed 75% correct when either an interaural phase shift (180°) or interaural level difference (50 dB) was introduced to a 100 Hz band of noise centered at frequencies higher than 1600 Hz. In a second set of conditions, performance was measured when both an interaural phase shift and level difference were presented in a 10‐Hz‐wide band of noise centered at 500 Hz. A version of the Durlach E‐C model was able to account for a great deal of the data. The results are discussed in terms of the Huggins dichotic pitch.

ISSN:0001-4966    

DOI:10.1121/1.1894644

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Upper lip, lower lip, and jaw movements were recorded in five adult speakers for repealed sequences of the utterance [bæ] at different speech rates. The results failed to confirm several earlier reports of an invariant upper lip, lower lip, jaw peak velocity sequencing pattern for bilabial closures. While the earlier reported sequence was the most frequent, a wide variety of different sequences was also commonly observed. In addition, significant intersubject differences in sequencing were found. The present results thus do not support the earlier hypothesis that oral closure gestures reflect aspects of a centrally generated pattern of motor output during speech.

ISSN:0001-4966    

DOI:10.1121/1.1894645

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Sibilant groove place and width were initially examined during [s] and [∫]in isolation and in CV and VC syllables. The [s] was found to be produced through a 6‐ to 8‐mm‐wide groove near the front of the alveolar ridge by one talker and near the back of the ridge by the other. [∫]was produced through a 10‐ to 12‐mm groove behind the posterior border of the alveolar ridge by both. In the second experiment three subjects used visual articulatory feedback to vary sibilant groove width and place systematically. One subject was able to do this with comparatively few retrials; one had difficulty with certain targeted grooves; one had difficulty with many targeted grooves. The noises generated were replayed to 14 listeners who labeled them as “s,” “probably s,” “probably sh,” or “sh.” They usually heard the sound as [s] when the grooves were narrow and near the front of the alveolar process, [∫]when the groove was wider and behind the alveolar process. Noise through grooves that matched natural speech places and widths usually produced higher listener recognition scores. Exceptions were found when the subjects had unusual difficulty in achieving stipulated groove widths and places.

ISSN:0001-4966    

DOI:10.1121/1.1894646

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP

摘要:

Postlingually deafened adults reading the Rainbow Passage differed from hearing‐control subjects in producing greater pitch variability and mean pitch on stressed and unstressed vowels, greater fluctuations in pitch within sentences, less correlation of intrinsic pitch with vowel height and slower temporal parameters. When reading the Phonetic Inventory Sentences, they revealed less differentiation of place of articulation in fricative and plosive consonants. The present findings, taken together with those of longitudinal and implant studies, are applied to constraining models of the role of self hearing in the elaboration of speech.

ISSN:0001-4966    

DOI:10.1121/1.1894647

出版商:Acoustical Society of America    

年代:1991

数据来源: AIP