摘要:

Since noise was first recognized as a serious environmental pollutant, a number of social surveys have been conducted in order to assess the magnitude of the problem and to develop suitable noise ratings, such that, from a measurement of certain physical characteristics of community noise, one could reliably predict the community’s subjective response to the noise. Recently, the author has reviewed the data from social surveys concerning the noise of aircraft, street traffic, expressway traffic, and railroads. Going back to the original published data, the various survey noise ratings were translated to day–night average sound level, and an independent judgment was made, where choice was possible, as to which respondents should be counted as ’’highly annoyed.’’ The results of 11 of these surveys show a remarkable consistency. It is proposed that the average of these curves is the best currently available relationship for predicting community annoyance due to transportation noise of all kinds.

ISSN:0001-4966    

DOI:10.1121/1.382013

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Several applications of ultrasonic detectors are suggested for monitoring coal water slurries in coal conversion processes. These include mass flow, particle size, and temperature. Modeling of transmission losses include viscous and thermal transport processes as well as multiscattering effects. Simple monitoring of sound attenuation versus frequency yields a unique dependence from which the value of characteristic parameters may be deduced, all from a single transmitter–receiver pair.

ISSN:0001-4966    

DOI:10.1121/1.382014

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The propagational characteristics of high‐frequency echolocation signals (peak energies above 100 kHz) of the Atlantic bottlenose dolphinTursiopstruncatusin open water were determined by a series of measurements conducted while the animal performed a target‐detection task. The animal was trained to station in a ’’chin‐cup’’ device so that the vertical beam pattern of the projected echolocation signals could be measured with a vertical array of hydrophones and the horizontal beam pattern could be measured with a horizontal array. The projected echolocation signals as a function of distance from the animal out to 2 m were measured with a horizontal array of hydrophones placed directly in front of the animal. These measurements were used to study the relationship of the signals in the near and far fields of the animal sound source. The relationship of the signals measured with a contact hydrophone placed on the animal’s rostrum and on the melon with the signals measured at 1 m and at the target was also studied. It was found that the 3‐dB broadband beamwidth was approximately 10° in both the horizontal and vertical planes. The major axis of the vertical beam was directed at an agnle of 20° above the plane defined by the animal’s teeth. It was also found that the acoustic pressure of the echolocation signals began to satisfy the farfield criterion of decaying inversely with distance at approximately 0.5–0.6 m from the tip of the animal’s rostrum.

ISSN:0001-4966    

DOI:10.1121/1.382015

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A detailed review of the literature on ultrasonic propagation properties of mammalian tissues and organs has revealed 144 papers containing compilable data. Over 1300 lines of parametric data are listed, including the tissue, species, age, specimen preparation, anatomical structure, pathology, temperature, measurement method, frequency, velocity, attenuation, acoustic impedance, and density.

ISSN:0001-4966    

DOI:10.1121/1.382016

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Audiograms were obtained on eight binaural chinchillas trained on a shuttlebox avoidance procedure. Four of the animals were exposed to three successive levels of an octave band of noise centered at 63 Hz: 100 dB SPL (74 dBA), 110 dB SPL (84 dBA), and 120 dB SPL (94 dBA). The other four animals were also exposed to three successive levels of an octave band of noise centered at 1000 Hz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposure durations were 72 h. Little threshold shift (TS) resulted from the lower two exposure levels of the 63‐Hz noise band. At the 120‐dB exposure level, maximum TS of 43 dB occurred at 2000 Hz. Permanent threshold shifts (PTSs) of 16 dB at 2000 Hz and 11 dB at 1400 Hz were found. Exposure to the three levels of the 1000‐Hz noise band produced TSs of 20, 45, and 61 dB at 1400 Hz. The 95‐dB exposure level resulted in PTSs of 6 dB at 1400 Hz and 9 dB at 2000 Hz. The major results were (1) high‐frequency hearing loss to a low‐frequency noise and (2) that noise bands matched within 1 dBAwere not equally hazardous as dictated by damage‐risk criteria. The 63‐Hz noise band produced nearly twice as much PTS as the 1000‐Hz noise band.

ISSN:0001-4966    

DOI:10.1121/1.382017

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Most research on timbre perception has studied isolated tones. This study compares timbre discrimination of isolated tones with discrimination in various musical contexts, both single‐voiced and multivoiced. Twelve different contexts were used (four isolated tonal comparisons, four single‐voice musical patterns, and four multivoice patterns). Listeners judged whether the timbre remained the same or changed during the trial. Two possible versions of any instrumental timbre differed in the physical information used in thier synthesis. Three instrumental timbres were tested in all contexts: clarinet, trumpet, and bassoon. The effects of context upon discrimination varied across instruments. The clarinet and trumpet versions were best discriminated in isolated contexts, with discrimination progressively worse in single‐voice and multivoice patterns. The bassoon versions were best discriminated in the single‐voice patterns, with equal discrimination in the isolated and multivoice cases. It is suggested that these results were due to pronounced physical differences observed between the spectra of the two versions of the bassoon that were not apparent between the versions of the clarinet or trumpet.

ISSN:0001-4966    

DOI:10.1121/1.382018

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Zwicker has demonstrated that the threshold for a high‐frequency test‐tone burst in the presence of a continuous low‐frequency masking tone is a complicated function of the frequency and intensity of the masker and the phase of the masker at which the test tone is presented. ’’Masking period patterns’’ measured for these stimuli show nonlinear effects in that at high masker levels the threshold of test‐tone bursts reaches local maxima at two different phases of the masker. We have investigated the implications of these psychophysical data on a computational model for motion of the basilar membrane. The model consists of a nonlinear mechanical system followed by an additional stage of frequency selectivity (’’second filter’’). The output of the model is applied as input to a threshold‐level detector. With this model it is possible to reproduce the effects Zwicker observed. Masking period patterns are interpreted as a mnifestation of two‐tone suppression. On the basis of our computer simulation of Zwicker’s psychophysical data, we make the following specific predictions concerning the nature of mechanical to neural transduction at the auditory periphery: (1) Membrane motion in one direction produces a nonlinear increase in the loss term, while membrane motion in the other direction does not. (2) The direction of membrane motion that produces increased loss is also the direction of motion that produces neural excitation. (3) There is a stage of sharpening, a ’’second filter,’’ between membrane motion and the neural excitatory signal.

ISSN:0001-4966    

DOI:10.1121/1.382019

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Five squirrel monkeys were exposed for 1, 2, 4, 8, 16, 24, and 48 h to a 375–750‐Hz band noise at an overall SPL of 95 dB. The TTS4.5growth pattern for the 750‐Hz test frequency was biphasic and did not reach an asymptote after 48 h of exposure. For all exposures, the mean thresholds of the five monkeys returned to within 5 dB of the preexposure mean 20 h after exposure. Recovery curves from all exposures at the 750‐Hz test frequency appeared biphasic. Increasing SPL from 95 to 105 dB increased TTS4.5by 4 dB at 750 Hz for a 1‐h exposure. Recovery from the 105‐dB exposure followed the same pattern as recovery from the 95‐dB exposure. When compared with data collected from human subjects under similar conditions, these experiments indicate that the growth and recovery of TTS in squirrel monkeys are sufficiently similar to growth and recovery in man to justify further comparative investigation.

ISSN:0001-4966    

DOI:10.1121/1.382020

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A discrimination procedure was used to measure the pitch strength of the repetition pitches associated with comb‐filtered or ripple noise. Pitch strength was measured as a function of overall ripple noise level, the repetition pitch of the noise, and as a function of the center frequency of 1/3‐octave bandpass filtered noise. In addition, other experiments were conducted to help determine which parameters should be used in measuring pitch strength when the discrimination procedure is employed. Pitch strength was strongest for pitches of approximately 500 Hz. The stimuli had essentially no pitch strength for pitches below 50 and above 2000 Hz. The strongest pitches were obtained when 1/3‐octave filters were placed in a frequency region cented at four times the repetition pitch. Filtering at other center frequencies resulted in a large decrease in pitch strength. These results are consistent with assumptions concerning the dominant region for pitch perception of complex stimuli. The results are also discussed in terms of processing information from reflected sound sources.

ISSN:0001-4966    

DOI:10.1121/1.382021

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The synchrony of neural impulses in response to low‐frequency sinusoids is described for auditory medullary neurons. The results are summarized as follows: (1) In general, neural synchrony is found to improve with increases in intensity and frequency of stimulation for both monaural and binaural neurons when measurements are made in absolute time. (2) An analysis of our population of neurons implies that two separate mechanisms are responsible for the decrease in synchrony found in many neurons as compared to primary‐like neurons with high‐locking ability. The two mechanisms are convergence of mistimed impulses and electrontonic changes which occur in dendrites. (3) An analysis of binaural vector strength data provides an explanation for physiological differences between cyclic and noncyclic vector strengths as a function of interaural time and reveals the effects of mistimed convergence upon neural synchrony. (4) In contrast to the inferior colliculus, where the neurons discharge best with contralateral leads in time, superior olivary neurons exhibited no such preference. Some discharge best to ipsilateral while others to contralateral leads. This comparison reveals a striking difference in the coding characteristics of medullary and inferior colliculus neurons. (5) Finally, the results are compared with the psychophysically determined difference limens.

ISSN:0001-4966    

DOI:10.1121/1.381999

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP