• Volume/Page
  • Keyword
  • DOI
  • Citation
  • Advanced
   
 
 
 

Journal of the Acoustical Society of America

BROWSE VOLUMES

Year Range: 
Search Issue | RSS Feeds RSS
Previous Issue

Dec 1989

Volume 86, Issue 6, pp. 2063-2482

Page 1 of 6 Pages Next Page | Jump to Page

Unidirectional, second‐order gradient microphone

Gerhard M. Sessler, James E. West, and R. A. Kubli

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2063-2066 (1989); (4 pages)

Full Text: | Download PDF

Show Abstract
A second‐order gradient microphone with unidirectional characteristics is described. The microphone consists of two commercially available, first‐order gradient electret microphones that are properly baffled and arranged in antiphase with their rotational axes in line. The output of one of these transducers is added to the delayed output of the other transducer. The unidirectional microphone shows a directional characteristic that is relatively frequency independent, has a 3‐dB beamwidth of the main lobe of 76 deg, and exhibits a toroidal sidelobe 10–20 dB below the main lobe. After equalization, the frequency response of the microphone in its direction of maximum sensitivity is within ±3 dB between 0.3 and 3 kHz. The output of the microphone, including equalization and amplification, is −60 dB re: 1 V/Pa at 1 kHz, and the equivalent noise level for the above frequency range amounts to 28 dB linear or an A‐weighted level of 20 dB.
Show PACS
43.38.Ar Transducing principles, materials, and structures: general
43.38.Fx Piezoelectric and ferroelectric transducers
43.38.Kb Microphones and their calibration

Contraction‐related variation in frequency dependence of acoustic properties of canine myocardium

Keith A. Wear, Mark R. Milunski, Samuel A. Wickline, Julio E. Perez, Burton E. Sobel, and James G. Miller

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2067-2072 (1989); (6 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
Results of experiments performed in several laboratories indicate that contracting myocardium exhibits a cyclic variation of the magnitude of ultrasonic backscatter, with maxima occurring at end‐diastole and minima at end‐systole. The mechanisms responsible for this variation are not well understood. The purpose of the present study was to determine whether the frequency dependence of backscatter exhibits systematic variation throughout the cardiac cycle, analysis of which may facilitate improved understanding of biologic factors responsible for the cyclic variation of the magnitude of backscatter. In this study, the myocardial backscatter coefficient, as a function of frequency, was measured throughout the cardiac cycle in nine open‐chest dogs. The frequency dependence of the backscatter coefficient was computed from a least‐squares linear fit to log backscatter coefficient versus log frequency data. A cyclic variation of frequency dependence of backscatter was found with maximum near end‐diastole (f2.6±0.1) and minimum near end‐systole (f2.2±0.1), a significant variation (p<0.01). These results suggest that mechanisms responsible for the cyclic variation of backscatter may include changes in the effective size of the dominant scatterers throughout the cardiac cycle. An alternative explanation for the observed variation is an increase in the myocardial attenuation coefficient during systole followed by a decrease in diastole.
Show PACS
43.80.Cs Acoustical characteristics of biological media: molecular species, cellular level tissues

A sound‐speed sensor for the measurement of total protein concentration in disposable, blood‐perfused tubes

Daniel Schneditz, Thomas Kenner, Helmut Heimel, and Hans Stabinger

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2073-2080 (1989); (8 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
The aim of this investigation was to develop a sensor containing a disposable measuring cell capable of measuring fluid shifts in blood‐perfused circulation systems. Usually, the determination of fluid shifts in such systems is achieved by tracking the concentration of particles or solutes in the perfusate. Since acoustic properties of blood are closely related to the total protein concentration (TPC) of the sample, a new approach for the calculation of fluid shifts is made by the continuous measurement of sound speed. The measuring principle is based upon the evaluation of the propagation time of short acoustic pulses that are repeatedly transduced to the sample. The retransmission is triggered by means of a new type of delay line. The method stands out for its accuracy (better than 0.1 m/s) and for the short acoustic propagation path (5–10 mm). In order to develop the disposable measuring cell, the acoustic properties of porcine blood were determined at different hematocrits and TPC at temperatures ranging from 20–40 °C. The dependence of sound speed on temperature and on TPC is described by a polynomial. The new sensor was tested in vitro simulating mass shifts by adding a mass (Msaline) of isotonic saline solution to the circulating blood mass (M). The acoustic device containing the disposable cell proved capable of sensing mass fractions [Msaline/(M+Msaline)] in the order of 0.5 g/100 g.
Show PACS
43.80.Ev Acoustical measurement methods in biological systems and media
43.80.Vj Acoustical medical instrumentation and measurement techniques

On sentence‐level factors governing segmental duration in Japanese

Kazuya Takeda, Yoshinori Sagisaka, and Hisao Kuwabara

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2081-2087 (1989); (7 pages) | Cited 5 times

Full Text: | Download PDF

Show Abstract
In this paper, the durational characteristics of Japanese are statistically analyzed with the aim of establishing a fine duration setting rule. First, a statistical duration control model is formulated through factor analysis on a large‐scale isolated‐word database (5240 words). Second, using 282 fluently spoken connected speech utterances, segmental durations calculated by this model are compared with measured durations. Error analysis made clear the existence of the following sentence‐level duration effects: (1) Prepausal lengthening is greater than simple word‐final lengthening; and (2) shorter durations are found in sentence‐final position in read sentences than in the other positions. By incorporating these effects into the duration‐setting rules, the prediction error for sentences were reduced to the same level as for isolated words.
Show PACS
43.72.Ar Speech analysis and analysis techniques; parametric representation of speech
43.70.Fq Acoustical correlates of phonetic segments and suprasegmental properties: stress, timing, and intonation

Results for two children using a multiple‐electrode intracochlear implant

P. A. Busby, Y. C. Tong, S. A. Roberts, P. M. Altidis, S. J. Dettman, P. J. Blamey, G. M. Clark, R. K. Watson, R. C. Dowell, F. W. Rickards, and G. H. Nicholls

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2088-2102 (1989); (15 pages)

Full Text: | Download PDF

Show Abstract
Assessments in speech perception, speech production, and language skills were conducted on two children, 5 and 10 years old at the time of surgery, using the Nucleus multiple‐electrode cochlear implant. Data were collected pre‐ and post‐operatively to measure changes in performance over time. For closed‐set speech perception tests in the audition alone condition, post‐operative performance was generally better than pre‐operative performance and performance improved post‐operatively for both patients. In closed‐set vowel and consonant identification and open‐set sentence perception for the older patient, post‐operative improvements from the vision alone to the auditory–visual condition were recorded and performance improved post‐operatively in both conditions. In all measures of speech production for both patients, post‐operative scores were higher than pre‐operative scores and performance improved post‐operatively. In language skills, post‐operative scores were higher than pre‐operative scores and scores improved post‐operatively in all measures for both patients.
Show PACS
43.71.Ky Speech perception by the hearing impaired
43.71.Qr Neurophysiology of speech perception
43.66.Ts Auditory prostheses, hearing aids
43.64.Me Effects of electrical stimulation, cochlear implant

Apparent auditory deprivation effects of late onset: The role of presentation level

Stuart Gatehouse

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2103-2106 (1989); (4 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
Silman and colleagues [J. Acoust. Soc. Am. 76, 1347–1362 (1984)] have reported an apparent effect of late auditory deprivation; this presents as loss of discrimination over time in the unaided ear of individuals using a single hearing aid fitted in middle age. In a replication of the basic effect, the influence of presentation level was examined in 24 monaurally aided subjects. The effect was reversed at presentation levels below about 75 dB SPL. The ear that is normally aided performs better at high presentation levels, while, at lower presentation levels, the converse is true. Thus it appears that a form of selective adjustment takes place in a particular part of the dynamic range, at least in ears with a dynamic range limited by a sensory hearing loss. If this interpretation is correct, there are important implications for research on perceptual learning and for the time course of evaluation in hearing aid provision.
Show PACS
43.71.Ky Speech perception by the hearing impaired
43.71.Qr Neurophysiology of speech perception
43.66.Ts Auditory prostheses, hearing aids

The recognition of vowels differing by a single formant by cochlear‐implant subjects

Richard S. Tyler, Nancy Tye‐Murray, and Steven R. Otto

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2107-2112 (1989); (6 pages) | Cited 1 time

Full Text: | Download PDF

Show Abstract
The ability to recognize synthetic, two‐formant vowels with equal duration and similar loudness was measured in five subjects with the Cochlear and five subjects with the Symbion cochlear implants. In one set of test stimuli, vowel pairs differed only in the first‐formant frequency (F1). In another set, vowel pairs differed only in the second‐formant frequency (F2). When F1 differed, four of five Cochlear subjects and four of five Symbion subjects recognized the vowels significantly above chance. When F2 differed, two of five Cochlear subjects and three of five Symbion subjects scored above chance. These results suggest that implanted subjects can utilize both ‘‘place’’ information across different electrodes and ‘‘rate’’ information on a single electrode to derive information about the spectral content of the stimulus.
Show PACS
43.71.Ky Speech perception by the hearing impaired
43.66.Ts Auditory prostheses, hearing aids
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.64.Me Effects of electrical stimulation, cochlear implant

The speech of a postlingually deafened teenager during the first year of use of a multichannel cochlear implant

Vivien C. Tartter, Patricia M. Chute, and Sharon A. Hellman

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2113-2121 (1989); (9 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The speech of a profoundly postlingually deafened teenager was recorded before, immediately after, 3 months after, and 1 year after electrical stimulation with a Nucleus multichannel cochlear implant. Listener tests of target words revealed significant improvement in overall quality over the year. Spectrograms showed less aspiration and better definition of the lower formants. Acoustic measurements indicated immediate change in F0 and gradual changes in syllable duration and some aspects of voicing and manner of articulation. Vowel space shrank steadily over the year, with both first‐ and second‐formant frequencies dropping. Prestimulation results are discussed relative to the literature on the speech of the congenitally hearing impaired. Effects of multichannel electrical stimulation on speech are compared with studies of single‐electrode stimulation.
Show PACS
43.70.Dn Disordered speech
43.64.Me Effects of electrical stimulation, cochlear implant

Binaural processing of noisy stimuli: Internal/external noise ratios for diotic and dichotic stimuli

Ronald A. Siegel and H. Steven Colburn

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2122-2128 (1989); (7 pages) | Cited 10 times

Full Text: | Download PDF

Show Abstract
A set of ten digitized statistically similar Gaussian maskers was used in one‐internal tone‐in‐noise detection experiments under diotic (NoSo) and dichotic (NoSπ) interaural conditions. Stimulus/response matrices were generated for each masker in the presence or absence of a target 500‐Hz tone. For both NoSo and NoSπ, nonparametric analyses show that response probabilities and sensitivities vary significantly across noise waveforms, indicating a considerable external noise component in subject response variability. A parametric model is developed that maps individual stimulus waveforms onto a decision axis, facilitating evaluation of internal/external noise variance ratios. For both NoSo and NoSπ, internal and external noise variance are of similar magnitude.
Show PACS
43.66.Ba Models and theories of auditory processes
43.66.Dc Masking
43.66.Pn Binaural hearing
43.66.Rq Dichotic listening

Noise and vibration interactions: Effects on hearing

Roger P. Hamernik, William A. Ahroon, Robert I. Davis, and Alf Axelsson

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2129-2137 (1989); (9 pages)

Full Text: | Download PDF

Show Abstract
There is the suggestion in the literature that vibration may potentiate the effects of noise and may thus increase the risk of hearing loss in a variety of exposure situations. However, in human experimental studies, which, by necessity, are limited to low levels of exposure, the effects measured are relatively small. A very limited number of animal studies have also shown an enhanced noise‐induced hearing loss in the presence of vibration, but the scope of these studies is limited. The animal studies (chinchilla) that form the basis of this report were performed using a 30‐Hz, 3g rms and a 20‐Hz, 1.3g rms cage vibration separately and in combination with continuous noise (95‐dB, 0.5‐kHz octave band) and impact noise (113, 119, or 125 dB peak SPL) exposure paradigms. All exposures lasted for 5 days. The impact noise exposures were designed to have approximately equal total energy. Temporary and permanent threshold shifts were measured using evoked potentials, and sensory cell loss was measured using surface preparation histology. The results obtained from some of the noise/vibration paradigms showed that such exposures can alter some of the dependent measures of hearing. This effect was statistically significant only for the stronger vibration exposure conditions and was evident primarily in the extent of the outer hair cell losses and in the shape of the PTS audiogram.
Show PACS
43.66.Ed Auditory fatigue, temporary threshold shift
43.50.Qp Effects of noise on man and society
43.40.Ng Effects of vibration and shock on biological systems, including man
43.66.Wv Vibration and tactile senses

Modulation interference in detection and discrimination of amplitude modulation

William A. Yost, Stanley Sheft, and Janie Opie

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2138-2147 (1989); (10 pages) | Cited 35 times

Full Text: | Download PDF

Show Abstract
Two experiments were conducted to assess the effect of the rate of sinusoidal amplitude modulation (SAM) of a masker tone on detection of SAM of a probe tone (experiment 1) or on SAM‐rate discrimination for the probe tone (experiment 2). When modulated at the same rate as the probe, the masker interfered with both the detection of probe modulation and the discrimination of the rate of probe modulation. The interference was obtained when the masker was either higher or lower in frequency than the probe (the probe and masker were separated by 2 oct). The amount of interference in detecting probe modulation (experiment 1) decreased as the common base rate of modulation was increased from 5 to 200 Hz. For rate discrimination (experiment 2), the amount of interference remained approximately the same for base rates of 2–40 Hz, the range over which rate discrimination was measured. In both experiments, the amount of interference was reduced when the masker was modulated at a different rate than the probe.
Show PACS
43.66.Lj Perceptual effects of sound
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Dc Masking

Segregation of concurrent sounds. I: Effects of frequency modulation coherence

Stephen McAdams

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2148-2159 (1989); (12 pages) | Cited 11 times

Full Text: | Download PDF

Show Abstract
Frequency modulation coherence was investigated as a possible cue for the perceptual segregation of concurrent sound sources. Synthesized chords of 2‐s duration and comprising six permutations of three sung vowels (/a/, /i/, /o/) at three fundamental frequencies (130.8, 174.6, and 233.1 Hz) were constructed. In one condition, no vowels were modulated, and, in a second, all three were modulated coherently such that the ratio relations among all frequency components were maintained. In a third group of conditions, one vowel was modulated, while the other two remained steady. In a fourth group, one vowel was modulated independently of the two other vowels, which were modulated coherently with one another. Subjects were asked to judge the perceived prominence of each of the three vowels in each chord. Judged prominence increased significantly when the target vowel was modulated compared to when it was not, with the greatest increase being found for higher fundamental frequencies. The increase in prominence with modulation was unaffected by whether the target was modulated coherently or not with nontarget vowels. The modulation and pitch position of nontarget vowels had no effect on target vowel prominence. These results are discussed in terms of possible concurrent auditory grouping principles.
Show PACS
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music
43.66.Lj Perceptual effects of sound
43.71.Es Vowel and consonant perception; perception of words, sentences, and fluent speech
43.66.Jh Timbre, timbre in musical acoustics

Within‐ versus cross‐channel mechanisms in detection of envelope phase disparity

Elizabeth A. Strickland, Neal F. Viemeister, Deborah A. Fantini, and Margery A. Garrison

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2160-2166 (1989); (7 pages) | Cited 9 times

Full Text: | Download PDF

Show Abstract
These experiments were designed to examine the mechanism of detection of phase disparity in the envelopes of two sinusoidally amplitude‐modulated (AM) sinusoids. Specifically, they were performed to determine whether detection of envelope phase disparity was consistent with processing within a single channel in which the AM tones were simply added. In the first condition, with an 8‐Hz modulation frequency, phase‐disparity thresholds increased sharply with an initial increase in separation of the carrier frequencies. They then remained approximately constant when the separation was an octave or above. In the second condition, with carrier pairs of 1 and 2 kHz or 1 and 3.2 kHz and a modulation frequency of 8 Hz, thresholds were little affected as the level of one carrier was decreased relative to the other. With a modulation frequency of 128 Hz, for most subjects there was more of an effect of level disparity on thresholds. In the third condition, when the modulation frequency was 8 Hz, subjects showed relatively constant thresholds whether the signals were presented monotically, dichotically, or dichotically with low‐ and high‐ pass noise. Dichotic thresholds were typically higher than monotic when the modulation frequency was 128 Hz. These results suggest that it is not necessary to have information available within a single additive channel to detect envelope phase disparity. In certain circumstances, a comparison across channels may be used to detect such disparities.
Show PACS
43.66.Nm Phase effects
43.66.Mk Temporal and sequential aspects of hearing; auditory grouping in relation to music

Characterization of an EPSP‐like potential recorded remotely from the round window

David F. Dolan, Lin Xi, and Alfred L. Nuttall

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2167-2171 (1989); (5 pages)

Full Text: | Download PDF

Show Abstract
The whole‐nerve cochlear action potential (CAP), to tone burst stimulation, was recorded before and after application of tetrodotoxin (TTX) to the intact round window (RW) membrane. TTX abolished the CAP leaving a residual negative potential without altering the summating potential (SP) or the cochlear microphonic (CM). The residual potential retained its polarity when recorded from scala vestibuli. The peak latency, amplitude, and tuning properties of the residual potential showed features similar to the CAP. Application of kainic acid to the RW membrane eliminated the residual potential, leaving the SP and CM unaltered. It is hypothesized that the sources of the residual potential are the excitatory post‐synaptic potentials from the peripheral processes of afferent dendrites under the inner hair cells.
Show PACS
43.64.Nf Cochlear electrophysiology
43.64.Pg Electrophysiology of the auditory nerve
43.64.Ri Evoked responses to sounds
43.64.Yp Instruments and methods

Statistical and receiver operating characteristic analysis of empirical spike‐count distributions: Quantifying the ability of cochlear nucleus units to signal intensity changes

William P. Shofner and Raymond H. Dye, Jr.

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2172-2184 (1989); (13 pages)

Full Text: | Download PDF

Show Abstract
Analytical methods from signal detection theory were applied in an effort to quantify the ability of cochlear nucleus (CN) units to signal changes in intensity. Of particular interest was the relation between this ability and the different patterns of discharge that characterize auditory neurons. Single‐unit responses to best‐frequency (BF) tone bursts were recorded from neurons in the gerbil cochlear nucleus, and empirical spike‐count distributions were generated. The mean‐to‐variance ratios for regular units were generally larger than those of irregular units. Receiver operating characteristic (ROC) curves were generated from empirical spike‐count distributions. The area under the ROC curve [P(A)] was computed and used to define the performance of an observer detecting whether or not a change in firing rate has occurred, thus signaling a change in intensity. For a given change in mean spike count, units characterized by regular interspike‐interval (ISI) histograms typically gave larger P(A) values than did units characterized by irregular ISI histograms. In addition, onset units gave larger values of P(A) than did irregular units for a given change in mean spike count. These results suggest that regular and onset units are better able to signal intensity changes than are irregular units.
Show PACS
43.64.Qh Electrophysiology of the auditory central nervous system
43.64.Tk Physiology of sound generation and detection by animals
43.64.Bt Models and theories of the auditory system
43.64.Fy Anatomy of the auditory central nervous system

Hazard from an intense midrange impulse

G. Richard Price and Samuel Wansack

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2185-2191 (1989); (7 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
It has been hypothesized that the ear would become increasingly susceptible to impulses (gunfire) as the spectral peak of the impulse approached the frequency region where the ear was tuned best (about 4 kHz for the cat ear) [G. R. Price, J. Acoust. Soc. Am. Suppl. 1 62, S95 (1977)]. This prediction was counter to the predictions of the world’s damage‐risk criteria for impulse noise. It has been supported by experiments using exposures to 100‐Hz and 800‐ to 1000‐Hz impulses; but no test had been run at the point of predicted maximum susceptibility. In the present experiment, three groups of cats were exposed to 50 impulses produced by a primer explosion (spectral peak at 4 kHz) at peak levels of 135, 140, or 145 dB. Auditory thresholds were electrophysiologically measured from the vertex to 2‐, 4‐, 8‐, and 16‐kHz tone pips and losses were determined 30 min after exposure and more than 2 months post‐exposure. Losses were greatest at 4 kHz, began to develop at 134‐dB peak pressure, and the immediate losses grew at a rate of about 7 dB for every dB increase in peak pressure. About half of the loss measured immediately became permanent. The energy required to begin producing a permanent threshold shift was only about 0.07 J/m2 , far lower than that required with continuous noises at lower sound pressures. The data were interpreted as supporting the original hypothesis of greater susceptibility in the midrange.
Show PACS
43.64.Ri Evoked responses to sounds
43.50.Pn Impulse noise and noise due to impact
43.50.Ba Noisiness: rating methods and criteria
43.66.Gf Detection and discrimination of sound by animals

The responses of models of ‘‘high‐spontaneous’’ auditory‐nerve fibers in a damaged cochlea to speech syllables in noise

C. Daniel Geisler

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2192-2205 (1989); (14 pages) | Cited 4 times

Full Text: | Download PDF

Show Abstract
The responses of four high‐spontaneous fibers from a damaged cat cochlea responding to naturally uttered consonant–vowel (CV) syllables [m], [p], and [t], each with [a], [i], and [u] in four different levels of noise were simulated using a two‐stage computer model. At the lowest noise level [+30 dB signal‐to‐noise (S/N) ratio], the responses of the models of the three fibers from a heavily damaged portion of the cochlea [characteristic frequencies (CFs) from 1.6 to 2.14 kHz] showed quite different response patterns from those of fibers in normal cochleas: There was little response to the noise alone, the consonant portions of the syllables evoked small‐amplitude wide‐bandwidth complexes, and the vowel‐segment response synchrony was often masked by low‐frequency components, especially the first formant. At the next level of noise (S/N=20 dB), spectral information regarding the murmur segments of the [m] syllables was essentially lost. At the highest noise levels used (S/N=+10 and 0 dB), the noise was almost totally disruptive of coding of the spectral peaks of the consonant portions of the stop CVs. Possible implications of the results with regard to the understanding of speech by hearing‐impaired listeners are discussed.
Show PACS
43.64.Sj Neural responses to speech
43.64.Pg Electrophysiology of the auditory nerve
43.64.Bt Models and theories of the auditory system
43.71.Qr Neurophysiology of speech perception

A practical method of predicting noise produced by road traffic controlled by traffic signals

Shizuma Yamaguchi and Yuichi Kato

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2206-2214 (1989); (9 pages)

Full Text: | Download PDF

Show Abstract
A new expression of the probability density function for periodic nonstationary noise level fluctuation is first derived in a case where the road traffic flow is controlled by traffic signals. Next, a new practical procedure for estimating and/or predicting the probability distribution form of road traffic noise, on the basis of the simplified time patterns of the statistics on the noise level or number of moving vehicles, is proposed as an application of the above theory. By using the actual road traffic noise data observed in Hiroshima City, it was experimentally confirmed that the theoretical method was valid and effective as a prediction technique.
Show PACS
43.60.Gk Space-time signal processing, other than matched field processing
43.60.Qv Signal processing instrumentation, integrated systems, smart transducers, devices and architectures, displays and interfaces for acoustic systems

Excess sound absorption due to periodically arranged absorptive materials

D. Takahashi

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2215-2222 (1989); (8 pages) | Cited 3 times

Full Text: | Download PDF

Show Abstract
Discontinuities, of any kind, in the surface impedance have a tendency to cause the effect of excess absorption. A well‐known example of this phenomenon is the so‐called ‘‘edge effect,’’ defined as the dependence of sound absorptivity of a test material on its area size. In relation to this problem, the excess sound absorption of periodically arranged flat surfaces composed of different materials is investigated both theoretically and experimentally. The analyses show that excess absorption, having a specific trend of absorption characteristics, clearly occurs over the full frequency range of interest. As a result of parametric survey conducted on the performance of a surface arranged periodically with rigid and porous materials, it is found that flat surfaces with desirable absorption characteristics can be made by adjusting the parameters suitably. The parameters are the period of the surface, width ratio of the two materials, flow resistivity, and thickness of the porous material. Also, it is shown, as an important matter, that the absorptivity is considerably high and smooth over the wide frequency range.
Show PACS
43.55.Ev Sound absorption properties of materials: theory and measurement of sound absorption coefficients; acoustic impedance and admittance

AP threshold elevation in the guinea pig following exposure to a broadband noise

Jan Grenner, Per Nilsson, and Bharti Katbamna

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2223-2228 (1989); (6 pages)

Full Text: | Download PDF

Show Abstract
Sixty guinea pigs were exposed to a steady‐state broadband noise with a falling frequency spectrum. The sound‐pressure level was varied between 96 and 117 dB SPL, and the duration of the exposure was varied from 3 to 12 h. After 4–5 weeks, the auditory thresholds were determined by electrocochleography at 14 frequencies, and the results were compared with a control group. With increasing sound‐pressure level, the thresholds became elevated at all frequencies. The maximum threshold elevation also exhibited a slight shift toward higher frequencies. With increasing exposure time, the threshold elevations increased and shifted into the high‐frequency region, whereas the low‐frequency region was less affected. Linear regression analysis showed that the average threshold elevation between 1 and 20 kHz did not deviate from that predicted by the equal‐energy hypothesis. However, the high‐frequency loss at 5–20 kHz was very dependent on the exposure time, whereas the 1‐ to 4‐kHz loss was not. There was no sign of any critical intensity with sudden increments in threshold elevation.
Show PACS
43.50.Qp Effects of noise on man and society
43.66.Sr Deafness, audiometry, aging effects
43.66.Ed Auditory fatigue, temporary threshold shift
43.80.Lb Sound reception by animals: anatomy, physiology, auditory capacities, processing

Free in‐plane vibrations of a ring–spoke mechanical system

C. P. Filipich, M. B. Rosales, and C. E. Jouglard

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2229-2236 (1989); (8 pages)

Full Text: | Download PDF

Show Abstract
The present paper deals with the analysis of the dynamic behavior of the structures described in the title. It is assumed that the spokes are symmetrically distributed and clamped at the ring center. The circumferential ring response is expressed in terms of a complete set of periodic functions. The elastodynamic behavior of the spokes is taken into account by replacing them with equivalent frequency‐dependent springs. Use is made of Dirac delta, doublet functions, etc. It is demonstrated that taking into account symmetric properties of the structure results in a significant reduction of the order of the system of equations. The free vibration of several cases was studied numerically. Natural frequencies and mode shapes are presented.
Show PACS
43.40.Cw Vibrations of strings, rods, and beams

Free, in‐plane vibrations of circular rings with radial supports taking into account shear and rotatory inertia effects

Raul E. Rossi and Patricio A. A. Laura

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2237-2243 (1989); (7 pages)

Full Text: | Download PDF

Show Abstract
Natural frequency coefficients and modal shapes corresponding to some of the lower modes of vibration of the structural systems described in the title are determined using a finite element algorithmic procedure.
Show PACS
43.40.Cw Vibrations of strings, rods, and beams

Dynamic response of a prestressed, thick strip plate to an impulsive load

N. Nozawa and S. Chonan

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2244-2249 (1989); (6 pages)

Full Text: | Download PDF

Show Abstract
This paper is concerned with the dynamic response of an infinitely long thick strip plate. The plate is simply supported at the edges and subjected to initial in‐plane stresses parallel and perpendicular to the edges. It is excited by an impulsive line force. The solution is obtained on the basis of a thick plate theory that takes into account the effects of shear deformation and rotatory inertia. Governing equations are solved by applying the methods of the Laplace transform with respect to time and the Fourier transform with respect to an axial space variable. Numerical results are presented for plates subjected to a lateral load represented by a time function sin2 ωt. The displacement, bending moment, and dynamic coefficients (maximum dynamic displacement/static displacement, maximum dynamic bending moment/static bending moment) are calculated and shown graphically for several values of the parameters involved.
Show PACS
43.40.Dx Vibrations of membranes and plates

Experimental frequency spectra of ultrasound transmission through two‐dimensional ensembles of trapped microbubbles

Junru Wu and Wesley L. Nyborg

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2250-2256 (1989); (7 pages)

Full Text: | Download PDF

Show Abstract
The frequency spectra of transmission coefficients for ultrasound passing through a sheet of gas‐filled micropores have been measured using incident waves with amplitudes up to 2.4×104 Pa. It is found that as the amplitude of the incident wave is increased, the peak frequency of transmission loss through the two‐dimensional trapped‐bubble ensemble shifts to lower values by as much as 47%. The experiments indicate that the shifting is caused by the net displacements of air–water–membrane triple‐phase lines and the air loss of the trapped bubble, which are due to the radiation force and microbubble production produced by the incident wave. Results of the experiments and possible theoretical explanations are discussed.
Show PACS
43.35.Bf Ultrasonic velocity, dispersion, scattering, diffraction, and attenuation in liquids, liquid crystals, suspensions, and emulsions
43.30.Lz Underwater applications of nonlinear acoustics; explosions

Phase transition and sound velocity measurements in very small solid samples under high pressure by Brillouin scattering

Bernard Bonello, Myriam Fischer, and Alain Polian

J. Acoust. Soc. Am. Volume 86, Issue 6, pp. 2257-2260 (1989); (4 pages) | Cited 2 times

Full Text: | Download PDF

Show Abstract
Brillouin scattering is an ideal tool for accurately determining sound velocities in very small transparent samples (about 20‐μm thickness). In particular, Brillouin scattering in a diamond anvil cell is the only method of measuring sound velocities in small single crystals at high pressure (>10 GPa). In this paper, this technique is used to determine sound velocities in SrTiO3 up to 36 GPa.
Show PACS
43.35.Dh Pretersonics (sound of frequency above 10 GHz); Brillouin scattering
Page 1 of 6 Pages Next Page | Jump to Page
Close

Home Publications Meetings Contact ASA Site Map Back to Top

Copyright © Acoustical Society of America

close