摘要:

Field studies have been performed to provide experimental data on noise intrusion into community areas from aircraft flight operations. Air traffic activity over selected community areas in the vicinity of two air bases was determined from analysis of air base flight movements and from field observations. Flight paths, pattern altitudes, climb profiles, and engine power changes were determined from aircraft tracking observations, from interrogation of flight and operations personnel, and from special logs prepared by crew members on aircraft in flight. Noise from flyovers observed at ground locations was recorded in synchronization with position data. Simplified prediction models were formulated from the experimental data, and these were used, together with previously developed procedures, to describe the noise intrusion. This paper describes the types of data obtained and discusses significant experimental findings on flight activity variations, flight path variations, and time patterns of sound pressure level observed on the ground for aircraft flyovers. Conclusions drawn from the experimental data on sound propagation from aircraft to ground and on the effects of jet aircraft speed on noise generation are also discussed. Several indices used in the description of aircraft noise intrusion are defined. [This work was supported in part by the U. S. Air Force under Contract Nos. AF 33(616)‐3335 and AF 33(616)‐3938.]

ISSN:0001-4966    

DOI:10.1121/1.1930061

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

This paper presents noise data obtained during recent tests of the prototype of the British Comet 4 airliner in take‐offs from the De Havilland plant at Hatfield, England. The data are analyzed in terms of noise levels, spectrum distribution, and noise duration and are compared with related data obtained from tests with several propeller‐driven airliners. Measurement positions were located at points under the take‐off path corresponding to residential areas near present‐day airports. This work was sponsored by the Port of New York Authority.

ISSN:0001-4966    

DOI:10.1121/1.1930063

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Far‐field noise measurements from model tests of a shielding‐flap‐type jet noise suppressor are presented in the form of radiation patterns and frequency spectra. The tests were conducted using a cold air jet issuing from the nozzle in such a manner as to attach to and flow along the surface of a shielding flap. Whereas other proposed noise suppressors provide generally symmetrical noise radiation patterns, the present device skews the pattern in a beneficial way such that large noise reductions are obtained in the downward direction. These large noise reductions are thought to result from both the acoustic shielding of the flap and the benefits of flow attachment.

ISSN:0001-4966    

DOI:10.1121/1.1930071

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Reasonable extrapolation of existing experimental data suggests that, while there may be no measurable change in the temporary threshold shift (TTS) following exposure to low noise levels, such exposure may have a sensitizing effect upon the hearing system. The present study measures the TTS following high‐level noise exposure under two conditions: (1) a control condition where the high‐level noise is preceded by a period of silence; (2) an experimental condition where the high‐level noise is preceded by noise levels which alone are not associated with a measurable TTS. Four listeners were exposed to a series of noise conditions for 18 min per condition. The control condition consisted of 15 min of silence followed by a 3 min exposure to a noise level of 118 db SPL. The experimental condition consisted of a 15‐min exposure to sensitizing noise levels ranging from 18 to 88 db followed by a 3‐min exposure to 118 db. Threshold measurements were obtained at 4000 and 6000 cps for 5 min preceding the sensitizing exposure, and continuously for 10 min after cessation of the 18‐min exposure duration. In general, when the sensitizing noise preceded the high‐level noise, a significantly greater TTS resulted than when silence preceded the high‐level noise. That is, a “sleeper effect” was generated by the sensitizing, low noise levels. This held for most of the listeners, and for most of the sensitizing levels employed. It is concluded, then, that (1) noise exposure levels which in themselves produce no TTS may have a sensitizing, or residual effect upon the hearing system and (2) that zero db of hearing loss following noise exposure does not necessarily constitute complete recovery of the auditory system.

ISSN:0001-4966    

DOI:10.1121/1.1930077

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A first experiment has confirmed the findings of Hirsh and of Jeffress with respect to the effects of changes in the interaural phase difference for both noise and tone on the masked binaural threshold. The threshold for a low‐frequency tone is some 12 db higher when both tone and noise are in phase at the two ears, than when either one is 180°. A second experiment utilized a high‐frequency band of noise at a high level to produce “remote masking” for the same low tones in order to determine whether or not this other kind of masking would be similarly affected by changes in interaural phase. With the noise band in phase, a 180° change in the phase of the low‐frequency tone produces a change in threshold of only slightly less than 12 db. But a similar change in the phase of the noise band produces no change in masking, except for a slight shift that can be predicted from the time shift at low frequency that would correspond to a half‐wave in the high‐frequency band.

ISSN:0001-4966    

DOI:10.1121/1.1930084

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A new method has been used for the study of noise arising from the collapse of cavitation bubbles. Isolated vapor bubbles were formed in de‐aerated water undergoing vertical vibrations of about 1/30 sec period, whose amplitude was sufficiently large for the water to be in tension for part of the cycle. The bubbles were initiated from minute gas nuclei released by electrolysis at a certain instant each cycle; consequently, a long succession of identical bubbles was produced, each of which repeated the same sequence of growth, collapse, and several rebounds, and then disappeared before its successor became due. The noise pulse could conveniently be examined by displaying a hydrophone signal on an oscilloscope adjusted for fast single‐sweep operation but triggered repetitively (by the signal from a second hydrophone placed nearer the noise source) at the frequency of bubble formation. The pulse was found typically to have a duration of about 10 μsec, and under certain conditions to undergo steepening such as to develop a shock front of duration considerably less than 1 μsec.

ISSN:0001-4966    

DOI:10.1121/1.1930087

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A recent innovation in the musical field has been the introduction of drum heads made of sheet Mylar plastic. This investigation reports the acoustical differences found in heads made of the two materials. Two types of drums were chosen, the bass drum and the field drum. Two identical drums of each type were fitted with heads, and investigations were made for several tension adjustments. A professional drummer was engaged to adjust and play these drums and a professional quality tape recording was made of their sounds, including single impact beats and steady rolls. These tape recordings were then analyzed in the laboratory. The average acoustical spectra of the drums were determined in half octave bands (similar to the method of Sivian, Dunn, and White), using the quasi‐steady‐state sound of the roll. The peak sound level spectra were also obtained using the General Radio impact sound analyzer. A further analysis was made of the buildup and decay of the drum sounds in chosen frequency bands using a high speed graphic level recorder. The analysis of the test results shows that under certain operating conditions there are considerable differences in the performance of the two kinds of heads. These differences correlate with subjective reactions. The chief physical differences are: (1) the calfskin drum head is capable of a much larger range of tension adjustment, and (2) under certain conditions it has more damping. When the bass drum is tuned to concert tightness, there is a significant difference in the two spectra and in the time variation of intensity. In the field drum there is little spectral difference, but the calfskin gives a more staccato beat with less “metallic” ringing.

ISSN:0001-4966    

DOI:10.1121/1.1930097

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP