Correction Procedures for Aircraft Noise Data: Tone perception PDF Download

Author:
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ISBN:
Category : Acoustical engineering
Languages : en
Pages : 80

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Author: D. N. May
Publisher:
ISBN:
Category :
Languages : en
Pages : 67

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Book Description

Author:
Publisher:
ISBN:
Category : Acoustical engineering
Languages : en
Pages : 64

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Book Description

Author: D. N. May
Publisher:
ISBN:
Category :
Languages : en
Pages : 75

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Book Description
The existing tone correction procedure in the Effective Perceived Noise Level (EPNL) calculation procedure required for aircraft certification under Part 36 of the Federal Aviation Regulations was compared with other tone correction procedures, including the SAE Aerospace Recommended Practice 1071 and a multitone procedure due to Kryter and Pearsons. Different amounts of tone correction (level-weightings) and varying degrees of tone correction at different times in the flyover (time-weightings) were also explored. Also studied was a measure of spectral fluctuation, developed by NASA and known as spectral change. The research was limited to considering revisions within the framework of one-third octave, 0.5 second interval analysis, since such revisions can be quite easily implemented. The various tone correction noise metrics were tested against subjective judgements furnished by NASA of the noise from a range of propjet, turbojet, low and high bypass ratio turbofan, and supersonic commercial aircraft. It was found that a revision based on spectral change could, after further development, be a means to improve the accuracy of the EPNL metric. However, the success of the various other potential revisions depended on the characteristics of the data base tested. It was shown that research into improved metrics should be based on experimental plans which account for the correlations among the noise variables and the presence of any interactions. A separate, psychoacoustical pilot experiment was also performed into the effects of pseudotones on judged noisiness. (Pseudotones are low frequency tones introduced into a measured spectrum by ground reflections near the microphone).

Author: R. Rackl
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ISBN:
Category :
Languages : en
Pages : 210

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Pseudotones are spectral irregularities due to ground reflections which can cause tone corrections in the calculation of Effective Perceived Noise Level which are not generated by the aircraft itself. Several analytical (reflection theory, lower cutoff frequency for tone corrections) and instrumentation (ground and pole microphones) methods were investigated which remove the pseudotones. In support of this study, a substantial number of aircraft noise measurements were obtained and analyzed in detail; these data are also summarized in the report. (Author).

Author: David Brown
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ISBN:
Category : Airplanes
Languages : en
Pages : 58

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Author:
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ISBN:
Category : Acoustical engineering
Languages : en
Pages : 102

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Author: Louis C. Sutherland
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ISBN:
Category :
Languages : en
Pages : 93

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A method has been developed to quantify errors in measurement, correction and extrapolation of aircraft noise data which are attributable to spectrum slope and nonideal filter transmission characteristics. The method's fundamental basis is an iterative calculation scheme which recovers an estimate of the true spectrum shape of a signal from its measured band levels. This 'true' spectrum can then be extrapolated to other distances or have frequency dependent corrections made to it on an exact basis without need for worry about filter or slope errors. The new spectrum may then be re-integrated to produce band levels suitable for input to EPNdB or PNL calculations. Applying this procedure to real flyover data and comparing the resultant values of EPNL with those using FAR Part 36 procedures showed only small differences usually. However, the technique provides a consistent method for the analysis of errors due to these sources and should be useful for estimating their magnitude in the future. (Author).

Author: L. Sutherland
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Category :
Languages : en
Pages : 114

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The impact of background noise on the value of PNL, PNLT, and the resulting EPNL noise metric in aircraft certification to FAR Part 36 is examined in this report, the second in a series of reports on aircraft noise measurement correction procedures. Procedures to remove background noise effects from data measured in the form of one-third octave band sound pressure levels for jet and large propeller aircraft, or data in the form of A-weighted noise levels for light propeller driven aircraft, are defined. After evaluating various techniques for different ratios of signal-to-background noise, one simple correction method for turbojet/turbofan aircraft noise is proposed. The recommended method consists of applying an energy correction, up to a maximum of -10 dB, for that portion of the background noise spectra dominated by energy-adding or predetection background noise. For the remaining portion of the background noise spectra, the non-additive postdetection background noise floor tends to mask out bands very close to or below this noise floor. A simple spectrum extrapolation procedure is recommended in ths case. Another background noise correction method for light propeller aircraft noise is also proposed. This procedure simply involves application of an energy correction to the 'as measured' A-weighted aircraft signal using the A-weighted background noise level. Procedures are also suggested for measuring the background noise level in order to account for the randomness of the fluctuating background noise level. (Author).

Author: David Brown
Publisher:
ISBN:
Category :
Languages : en
Pages : 59

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This report examines three particular problem areas associated with the measurement of noise levels of propeller-driven small airplanes required to comply with FAR Part 36, Appendix F. These problems are directly related to effects of atmospheric conditions on (1) the performance capabilities of an airplane when tested at various barometric pressures and altitude densities; (2) the noise signature generated at such conditions; and (3) the propagation of sound from the airplane to the measuring station. The first two of these have been addressed by deriving potential correction procedures which could be applied to noise levels obtained by tests not in strict compliance with Appendix F. These corrections are based on aircraft operations conducted within a specific margin of power setting. The corresponding measured noise levels are subsequently corrected for variation of propeller tip speed, forward velocity and barometric pressure relative to predetermined reference conditions. The third effect, that of sound propagation, si examined by applying SAE ARP 866A to a typical propeller airplane noise spectrum and demonstrating the range of A-weight noise levels that would result within a range of ambient conditions. (Author).