摘要:

An investigation is done on the effects of evanescent modes on the performance of active noise control in waveguides. The effect of the location of the control actuators relative to the location of performance sensing microphones and the waveguide termination is investigated. Both the sound power radiated from the waveguide and potential energy in the controlled section of the waveguide are monitored. In the analysis, the effects of the waveguide termination are modeled using a modal reflection coefficient at the termination. Experimental results for several cases are included to illustrate the predicted effects. [This investigation was supported by Nelson Industries, Stoughton, WI.]

ISSN:0001-4966    

DOI:10.1121/1.2028295

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The objective is to use active control to suppress the acoustic energy that is radiated to the farfield from a structure that has been excited by a short duration pulse. The problem is constrained by the assumption that the farfield pressure cannot be directly measured. Therefore, a method is developed for estimating the total radiated energy from measurements on the structure. Using this estimate as a cost function, a feedback controller is designed using linear quadratic regulator theory to minimize the cost. Computer simulations of a clamped‐clamped beam show that there is appreciable difference in the total radiated energy between a system with a controller designed to suppress vibrations of the structure and a system with a controller that takes into account the coupling of these vibrations to the surrounding fluid. The results of this work provide a framework for a general, model‐based method for actively suppressing acoustic radiation that can also be used to deal with steady, narrow or broadband disturbances. [Supported by DARPA/ONR and AFOSR.]

ISSN:0001-4966    

DOI:10.1121/1.2028300

出版商:Acoustical Society of America    

年代:1990

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 sinusoids of the same or different frequency. Frequencies of the first sinusoid in a pair wereF1= 500, 1000, 2000, and 4000 Hz. Second‐sinusoid frequencies,F2, includedF1=F2, and frequencies 2%, 5%, 24%, and 50% higher thanF1. To minimize the influence of extraneous cues, the onset phase of the second sinusoid in each pair of tones and overall duration of each sinusoid in a pair of tones were randomized. Sinusoids were presented in continuous broadband noise (N0= 30 dB/Hz) at an averageE/N0= 40 dB. Gap detection thresholds increased from 5 to 90 ms as the frequency separation betweenF1andF2was increased. The gap detection thresholds were treated as filter attenuation values by normalizing and converting the data into decibels, and then fitting the roex filter model. On average, the listeners' performances were modeled well by a constant‐percentage (7%) bandwidth filter centered onF1. [Research supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2028303

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Minimum audible movement angles (MAMAs) were measured in the horizontal plane for four adult subjects in a darkened anechoic chamber. On each trial, a single stimulus was presented, and the subject had to say whether it came from a stationary loudspeaker or from a loudspeaker that was moving at a constant angular velocity around him. Thresholds were established by adaptively varying stimulus duration. MAMAs were measured under both monaural and binaural listening conditions as a function of center frequency (500–5000 Hz), bandwidth (pure tone to 1 oct), velocity (10°–180°/s), azimuth (0°–90°), and direction of motion (left versus right). Preliminary data are consistent with previous observations for frequency and source velocity effects [D. R. Perrott and J. Tucker, J. Acoust. Soc. Am.83, 1522–1526 (1988)]. Data will be compared to static measures of auditory spatial resolution (the minimum audible angle) obtained under the same stimulus conditions from the same subjects. Discussion will focus on whether specialized mechanisms in the auditory system are required to account for dynamic spatial resolution. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2028310

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In an earlier paper, it was noted that shorter durations of opening lip/jaw movements in nonfinal syllables compared to final open syllables in French are largely the result of truncated or undershot movements. Final movements are longer because they are not cut short by the onset of a closing gesture belonging to a following syllable. This study looks at the unaccented/accented contrast and the closing phase of motion in the same corpus of reiterant French speech. Unlike the final/nonfinal contrast, the durational difference between accented and unaccented movements is localized in the acceleration phase, i.e., the time from movement onset to the point where maximum velocity is reached. While the magnitude of duration effects in closing movements is much smaller than in opening movements, there is some evidence that the onset of lip/jaw opening in final syllables occurs later in relation to the preceding closing gestures. Thus truncation is occurring in the closing as well as opening phase of syllable production. It also suggests a stress or accent anticipation effect possibly related to pretonic lengthening effects that have been noted in acoustic timing studies of French. [Work supported by the Ohio State University, NSF, and NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2028313

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

This study deals with the analysis of the relationships between stress and duration in French. The duration of stressed and unstressed syllables, taken from 55 read sentences, has been measured. The results have lead to conclude that, while stress is closely correlated to a modification of duration, the nature of this modification is more complex than expected, according to classical theories. The stressed syllable can be lengthened or shortened with regard to the nearest unstressed syllable and also to the other stressed syllable of the sentence. This choice seems to be allowed and motivated according to perception laws and mechanisms of expressivity.

ISSN:0001-4966    

DOI:10.1121/1.2028317

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The aim of this study was to analyze some of the major acoustic‐phonetic changes that occur in French when speech is produced by divers in an air atmosphere at several depths of submersion ranging from sea level to − 50 m (0, − 5, − 10, − 20, − 30, − 40, − 50m). A significant increase in fundamental frequency was found as depth increased. Submersion level seems to have no effect on duration and amplitude. Some significant differences were found in formant amplitude and frequencies. Shifts in the relative energy of formants 2, 3, and 4 were observed on vowels at the deepest conditions. The quantification of the difference in dB between the intensity of the fundamental and the intensity of the largest harmonic in the first formant suggests that phonation varies as a function of depth. At great depths, an increase in vowel effort contributes to speech distortion. These results are mainly discussed in terms of speech production strategies in deep atmosphere.

ISSN:0001-4966    

DOI:10.1121/1.2028322

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

The heart is a three‐dimensional structure that performs its function by undergoing complex deformation. Current clinical evaluation of the heart is limited to silhouettes, outlines, projections, or tomograms, obligating the clinician or investigator to sequentially evaluate a series of two‐dimensional images using mental assimulation of data. To provide more easily understandable three‐dimensional images, techniques have been developed for acquiring data in sequential planes through the heart to display the beating heart in three dimensions. Analysis of such data on a user‐friendly workstation can be accomplished using an extensive set of software tools developed at our institution. Three‐dimensional imaging can be used as an effective means of teaching interrelationships of volume, contents, and function, in addition to the physiologic and anatomic interrelation‐ships. Three‐dimensional images of the beating human heart obtainedin vivousing new data acquisition techniques will be shown. Evaluation of the method using balloons and excised hearts has shown that software and geometry of scanning are appropriate for high‐accuracy measurements of surfaces.

ISSN:0001-4966    

DOI:10.1121/1.2028326

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Albunex® is an ultrasound contrast agent prepared by sonicating 5% human serum albumin to produce stable, air‐filled, albumin microspheres. It is an effective ultrasound contrast agent for use with echocardiography and other ultrasound radiology procedures. The characteristics of Albunex that are responsible for the clinically observed high echogenicity of Albunex are discussed. Albunex is composed of a high concentration of noncoalescing microspheres (400–500 μ/nl) with a mean diameter of ≈4 μm and a shell thickness of 30–50 nm, as determined by particle analysis, light microscopy, and electron microscopy. Attenuation and backscatter measurements as a function of ultrasonic frequency and amplitude are reported for varying concentration and size distributions of Albunex.

ISSN:0001-4966    

DOI:10.1121/1.2028331

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Relatively few studies have dealt with the interaction between linguistic information and talker cues in speech perception and word recognition. The present study examines the effects of talker familiarity on serial recall for spoken word lists. Compared to lists of words produced by a single talker, lists produced by multiple talkers lead to decreased accuracy of serial recall in the primary portion of the recall curve at fast presentation rates. This pattern of recall for multiple‐ and single‐talker stimuli reverses at slow presentation rates. Explanations for these differences in recall for single‐ and multiple‐talker word lists have suggested that processing multiple‐talker stimuli either increases rehearsal demands during transfer to long‐term memory or increases difficulty of perceptual encoding. The present experiment examines these competing explanations for differential serial recall in multiple‐ versus single‐talker word lists using voices that subjects have been trained to identify. As listeners become familiar with a talker's voice, it is possible either that mandatory rehearsal will encompass richer recall cues, including talker‐specific information, or that perceptual normalization will become more automatic. Results provide support for the proposal that rehearsal of enriched cues leads to the differences in recall for multiple‐ and single‐talker lists. Using familiar voices increases serial recall for multiple‐talker lists over single‐talker lists in the primacy portion of the recall curve, but does not appear to facilitate perceptual encoding. [Work supported by NIH Grant DC‐0111‐14 to Indiana Univ.]

ISSN:0001-4966    

DOI:10.1121/1.2028338

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP