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In the following work, the relationship between the perceived level of sound (loudness or noisiness) (PLdB) is shown to be a function of the sound pressure (p) squared and the sound frequency (f) squared; that is, PLdB = 10 log (25 p2 f2) in the psychoacoustically important low frequency range up to 4000 Hz. The perceived level of an aircraft takeoff or landing is demonstrated to be equal to the logarithmic sum of the peak perceived levels calculated for each one-third octave band. Effective perceived level (EPLdB) may be calculated by using the procedures contained in the Federal Air Regulations (FAR), Part 36, to correct for the duration of the sound 10 dB below peak level. PLdB and EPLdB show the highest relationship between subject ratings and the physical characteristics of the flyover sounds accounted for by any calculation procedure.
The average rate of growth of annoyance (loudness or noisiness) for a diverse mix of aircraft operations ranging from low to high power levels is shown to be a function of log (k pf)½ for the low frequencies which propagate over long distances with relatively small power loss.
The results are found to be accurate in the useful range of sound pressure levels and frequencies associated with operational aircraft including helicopters, turbofan, turboprop and turbojet powered aircraft. This work, therefore, provides the systems engineer with an easily understood and useful design and evaluation method. The formula developed clearly shows the design engineer and management personnel the relationship between the physical characteristics of an evolving system and its potential impact on human and community response.
sound theory, perceived level (PLdB) equations, growth of annoyance/loudness/noisiness, psychophysical method, sound weighting network, human/community criteria and response
Program manager, Research and Development, Federal Aviation Administration, Washington, D.C.