摘要:

Five experiments were conducted to determine those aspects of a masking noise for which remote masking is invariant. The relative contributions of spectrum level and band width to remote masking can be described by the general equationLR = 2Ls+Lf+C, whereLRis remote masking in db;Lsis spectrum level in db, the SPL of a 1‐cps band width; andLfis band‐width level in dbrea 1‐cps band width. The constant is specific to each group of subjects. For remote masking less than 30 db, the formula does not predict remote masking, but does enable us to equate different conditions of spectrum level and band width. This equation does not hold as well when frequencies above 4000 cps are included in the masking noise. The possible causes of this inconsistency are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1909777

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Three groups of Naval Ratings worked for two sessions each at a subtraction task involving a considerable immediate memory load. One group had both sessions in relative quiet (70 db), a second had the first session in 100 db noise and the second in quiet, and the third group had noise and quiet in the reverse order.In the first session the noise group slowed down at solving the subtractions as time went on, relative to the groups working in quiet. A similar difference appeared in the second session, but, in addition, there was an aftereffect of noise such that the subjects who had had noise previously slowed down relative to those who had not.Slowing down of performance with time was in all groups most marked in extroverts.These results suggest firstly that intellectual work as well as simple sensory tasks must be regarded as endangered by noise. Secondly, there may be harmful aftereffects from noise, but it is not clear whether these will appear in any situation or only in one similar to that in which the noise was experienced.

ISSN:0001-4966    

DOI:10.1121/1.1909779

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The dependence of binaural masked thresholds on the interaural phase relations of both the signal tone and the noise has been demonstrated in previous studies, and has been repeated here for a wide band of noise (200–4000 cps). A second experiment was carried out to test whether this dependence extended to the remote masking of low‐frequency tones by a high‐frequency band of noise (2000–4000 cps). The results indicate that a phase reversal of the tone at the two ears has the same effect in remote masking as in ordinary masking; but a phase reversal of the high‐frequency band at the two ears produces changes in the masked threshold midway between those encountered in ordinary masking and no change at all. The results are interpreted as indicating that the interaural time relations between the remote‐masking sources that result from a phase reversal of the high‐frequency band involve a time shift of about one half‐period of the band midfrequency and a decrease in the interaural correlation.

ISSN:0001-4966    

DOI:10.1121/1.1909781

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Recently Kerka, and earlier Beranek, Reynolds, and Wilson, discussed the measurement of sound power radiated by a fan in a straight duct, by measurements of the sound pressure inside the duct. A difficulty associated with this technique is that above a certain frequency the sound pressure varies markedly across transverse section of the duct and the relation between mean square pressure and power is not simple. The transverse variation can be understood by application of mode theory to propagation of noise in the duct. In the theory it is assumed that the noise source is purely random and of low internal impedance. Propagation in the various duet modes is shown to be statistically independent, and to give rise to equipartition of energy in the limit of high frequencies. The theory agrees well with measurements reported by Kerka. With the use of the theory, it is possible to select measurement positions inside the duct such that the mean square pressure is related to the power flow by the simple plane‐wave equation.

ISSN:0001-4966    

DOI:10.1121/1.1909783

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A portable direction finder utilizing correlation techniques was developed for locating noise sources in mechanical equipment. A description of this instrument and some test results are given. The test results include studies of the direction finding characteristics of the apparatus and a simple method of determining wave fronts.

ISSN:0001-4966    

DOI:10.1121/1.1909785

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A receiver may be required to decide whether the message he has recorded is or is not the message actually received. The degree of certainty needed for confirmation (the criterion) may be controlled by instructions. A sequence of decisions is generated by repeatedly sending each of a set of messages until the set is confirmed. A simple stochastic model assumes that the probability of confirmation,py, is constant over such a sequence. IfNmessages are sent, the expected number confirmed after the firstnpresentations isE(n) = N[1 − (1 − py)n].Two experimental tests were (1) of the constancy ofpyby noting whether the equation forE(n) holds, and (2) of the constancy ofpy's three component probabilities: the probabilities of correct reception, correct confirmation, and incorrect confirmation. Receivers listened under two noise conditions to sets of several hundred messages each. Each message was immediately repeated until confirmed. Estimates ofpyand of the component probabilities were made from proportions of correct and incorrect responses. The data show that the assumption of constantpyyields a very accurate description of the process, and justify the more basic assumption thatpy's three components are constant over repeated trials. Further, the data are in excellent agreement with predictions from the theory of the total number of communication events required before the entire set ofNmessages is confirmed, and of the total numbers of correct and incorrect confirmations.

ISSN:0001-4966    

DOI:10.1121/1.1909787

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Ultrasonic measurements in two associated liquids, glycerol and Arochlor, show that the temperature coefficient of sound velocity in the glassy state is less than in the liquid. No discontinuity in the velocity data is observed at the “transition temperature.” Using ultrasonic waves a “pseudo transition” occurs at temperatures higher than the normal glass transition temperature.

ISSN:0001-4966    

DOI:10.1121/1.1909789

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

An instrumentation system has been developed to allow continuous determination of the relevant micrometeorological parameters of the atmosphere near the ground in order to relate them to the measured attenuation of an acoustic signal propagated along the ground. Arrays of precision cup anemometers and shielded thermocouples mounted on a 30‐ft tower were used to obtain the mean wind and temperature gradients above the ground. To obtain a measure of the atmospheric turbulence, a high‐speed wind vane and a bead thermistor were used. The electrical signals obtained from scanning these transducer arrays were fed into a mobile central recording and control facility. Simultaneously, the information provided by the acoustic signal was recorded there by scanning the output of several microphones placed along two test courses each approximately one mile long. The mobile laboratory also contained the necessary equipment for energizing two loudspeakers, one for each test course. This paper discusses the micrometeorological instrumentation in some detail, together with the calibration techniques used. Typical mean wind and temperature profiles as well as turbulence spectra are presented. The relation of the micrometeorological data to the propagation of sound along the ground is discussed elsewhere.

ISSN:0001-4966    

DOI:10.1121/1.1909791

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

This paper describes measurement of vibration amplitude with a Fizeau type interferometer using pulses of monochromatic light of adjustable phase. The interferometer is used to calibrate vibration pickups over the frequency range from 100 to 20 000 cps.

ISSN:0001-4966    

DOI:10.1121/1.1909793

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The absorption coefficient of sound in sea water has been obtained by a series of direct transmission measurements at several moderately high frequencies in a sheltered deep water bay in Puget Sound. Advantage was taken of the isothermal and isosaline properties existing during certain seasons of the year in this location. The fluctuations normally encountered in such a measurement were minimized by the utilization of fixed buoys, a radio link for range determination by acoustic travel time, and a method of space averaging. Values obtained, in decibels per kiloyard at a temperature of 10°C and a salinity of 30 parts per thousand, are: 14.4±0.3 at 60 kc, 35.7±0.7 at 142 kc, 57±3 at 272 kc, and 101±3 at 467 kc. Although the frequency dependence of the absorption coefficient given by these measurements follows the normal relaxation law, the magnitudes are lower than those given by Del Grosso by 4 to 10 db/kyd.

ISSN:0001-4966    

DOI:10.1121/1.1909795

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP