摘要:

In this paper a method is described for calculating the effect of the finite‐amplitude propagation on the travel times of pressure waves from explosions at high altitudes to the ground. Numerical results are presented for explosions of 2‐lb and 4‐lb H. E. charges at altitudes ranging from 15 to 95 km. Vertical propagation is assumed in the calculations. This work has been carried out in order to improve the systematic accuracy of the rocket grenade experiment for upper atmosphere temperature and winds. The significance of the finite‐amplitude propagation in this experiment is discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907737

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

An analysis is given of a solion acoustic pressure detector which has a direct current output proportional to the logarithm of the pressure input. An approximate method is used which avoids solving the Navier‐Stokes equation describing the fluid flow and the convection diffusion equation for calculating the current.The calculation consists of (1) solving the zero flow “transient” diffusion equation for the reducible component in the electrochemical redox system, (2) using this transient solution to calculate the output current, with the time spent inside the detector orifice as the independent variable, and (3) relating this time to the pressure by using the known acoustic impedance of the detector orifice.The calculated results show that the logarithmic response is obtained through a combination of diffusion and hydrodynamic effects. For the ideal case of constant impedance as a function of volume flow, the logarithmic response is degraded.

ISSN:0001-4966    

DOI:10.1121/1.1907738

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The latency of the well‐synchronized whole‐nerve action potential (AP) in the cochlea of the guinea pig includes both neural and traveling‐wave delays. The latency varies with the intensity and with the frequency of the acoustic stimulus. Selective local interference with the response was produced by (1) selective masking, (2) local fatigue of sensory elements, and (3) local injection of drugs. Such interference the basal turn prolonged the latency of the AP response. Low‐frequency tones can reduce theN1response to click stimuli without changing the modal latency. Apparently nearly all of the well‐synchronized AP is due to neurons that arise in the first turn of the cochlea, regardless of the frequency of stimulation. The traveling‐wave delay appears as a significant component of latency only in the smaller AP responses that remain after the impulses arising in the first turn are suppressed. Information about the time of onset of an acoustic signal can be delivered to the central nervous system primarily by the best‐synchronized or modal portion of the AP response.

ISSN:0001-4966    

DOI:10.1121/1.1907739

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Previous investigations on the auditory localization of sounds have established that interaural differences in time and in intensity are both important. There have also been attempts to set temporal and intensive differences against each other, so that a lead in time at one ear accompanied by an increase in intensity at the other ear would cause a sound to be localized in the midline. On the basis of hypotheses suggested by physiological observations, two experiments were carried out. The first showed that the intensive difference required to offset a difference in time at the two ears depends upon the level of the sounds. Clicks at low level require smaller differences in intensity to offset a given temporal difference than do clicks at a high level. The relation between intensive differences (decibels) and temporal differences (microseconds) is not linear at any of the levels studied. In the second experiment, high‐frequency masking noise interfered with reception in the basal turn of the cochlea. Although this noise did not mask the clicks, it produced a temporal lag that required compensation by a time delay at the opposite ear. The relations between these psychophysical results and physiological findings are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1907740

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

Twenty passive sonar recordings were ranked by 50 subjects in terms of their aurally perceived (psychological) characteristics on seven different dimensions. Correlations were run between octave band sound pressure level measurements of the sounds and their rank orders on the seven psychological dimensions. Meaningful relationships were found between ranks on certain psychological dimensions and energy concentration within certain octave bands.Also, an analysis was made of the manner in which the twenty sounds clustered within the space defined by the seven psychological dimensions. Analyses of these sound clusters revealed that the rhythmic beat pattern of the stimulus is a principal attribute upon which sonar men base their judgments of “similarity.”

ISSN:0001-4966    

DOI:10.1121/1.1907741

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

In recent years there has been an increased emphasis on medicolegal problems involving the assessment of hearing loss due to noise exposure. One of the attendant difficulties, however, has been the problem of separating the factors of noise exposure and of age as contributors to hearing disabilities. The present study was performed to determine the normal thresholds of hearing for pure tones for an age‐stratified sample of subjects drawn from a population exposed to minimal levels of industrial noise. Audiometric measurements from 250 to 8000 cps were made on a total of 500 subjects divided into four age groups: 18 to 24, 26 to 32, 34 to 40, and 43 to 49 years, inclusive. The results of this study indicate that, in general, only minor differences (less than 5 db) exist between the average thresholds of right and left ears, but that women have more sensitive hearing than men and show less intersubject variability. This sex difference is independent of age and is more marked at the higher frequencies. For both men and women, there is a decrease in hearing sensitivity with increasing age and a progressive spreading of the loss from the higher to the lower frequencies. Men are more affected than women, with the hearing loss occurring at an earlier age and producing a greater degree of auditory impairment. The threshold curves of the present study are considered to yield a more valid estimate of the “pure” effects of age on hearing than previously available. It is recommended that future audiometric standards be specified independently for men and for women according to particular age levels.

ISSN:0001-4966    

DOI:10.1121/1.1907742

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

This study investigated the effects of 4 band widths of noise of different center frequencies presented at three sensation levels on the size of the differential threshold (ΔI) for intensity. Eleven untrained subjects and three trained subjects served in a study employing the method of limits. Analysis of the data showed that ΔI's for a low octave band (127–225 cps) of noise were larger than those for a middle octave band (1040–2080 cps) and high octave band (4080–8160 cps) of noise. The middle and high bands in turn yielded ΔI's that were larger than those for a wide‐band noise. The magnitude of the ΔI's for the octave noise bands were tentatively related to the average ΔIfor those frequencies contained in the band. Comparison of the ΔI's for wide‐band noise to those obtained by other experimenters showed close agreement.

ISSN:0001-4966    

DOI:10.1121/1.1907743

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The index of detectabilityd′ was estimated from data collected with various psychophysical procedures, specifically, the forced‐choice method with different numbers of alternatives, and the yes‐no method. The estimates were, in all instances, quite comparable. This result is comforting in view of the fact that none of the other indices extant provide a unification of data collected with different procedures. This result is also somewhat surprising view of the fact that the calculation ofd′ assumes perfect memory, and forced‐choice experiments were conducted with as many as eight temporal alternatives.

ISSN:0001-4966    

DOI:10.1121/1.1907744

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The use of repeated presentations of a given signal event as an experimental technique in psychoacoustic studies provides information about several general properties of the hearing process. From the relationship between the gain in detectability that results from additional observations and the type of signal and noise employed, inferences can be made about: (1) the observer's ability to integrate over time, (2) the amount of noise generated by the auditory system, (3) the nature of the process of frequency analysis, and (4) the observer's mode of dealing with uncertainty as to signal frequency. The first set of experiments permitted five observations of each signal where the signal consisted of a pulsed tone, of known frequency, in noise. Both variable noise, i.e., noise that is statistically independent from one presentation to another, and constant noise, i.e., noise that is exactly the same on each of the five presentations, were used. With variable noise, the detectability indexd′ improves, as predicted, as the square root of the number of observations. The use of constant noise, which results in less improvement, provides an estimate of the portion of the total noise affecting detection that is of internal origin. The results under different levels of external noise indicate that internal noise is proportional to external noise. A second set of experiments employed signals whose frequencies were unknown to the observers, and signals comprised of several widely spaced frequencies. Their results are discussed in relation to three alternative models of the process of frequency analysis.

ISSN:0001-4966    

DOI:10.1121/1.1907745

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP

摘要:

The growth and recovery of TTS in normal observers following exposure to octave‐band noise is shown to follow the same course as that after broad‐band noise: both are linear in log time. Rate of growth varies with frequency of exposure band and test frequency, being greatest at 4 kc following exposure to 2400–4800 cps or 1200–2400 cps, less at lower test frequencies and octave bands. The time for total recovery apparently is a function of the initial TTS. The results support present damage‐risk criteria for continuous noise, which (1) suggest ear protection when octave‐band levels exceed 85 db SPL and (2) require it in levels above 95 db SPL.

ISSN:0001-4966    

DOI:10.1121/1.1907746

出版商:Acoustical Society of America    

年代:1959

数据来源: AIP