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In exploring the possibility that people can ascribe an absolute scale of acceptability for aircraft noise, subjects from airport neighborhoods judged, in separate tests, the relative and the absolute acceptability of noise produced by actual aircraft flyovers and by recorded flyover signals. The flyover noise judgments were made indoors and outdoors at two locations near the Los Angeles International Airport. Most subjects judged both approach noise and takeoff noise (produced mainly by jet aircraft). Judgments were compared with the maximum perceived noise level occurring during the flyovers. Little difference was observed in acceptability rating scores for approach and takeoff noise or for actual and recorded noise signals. However, a shift in ratings between outdoor and indoor judgments occurred similar in magnitude to that observed in earlier British tests. The relative judgment tests also showed little difference between ratings of takeoff and approach noise or live and recorded signals. However, the results indicated that a larger change in perceived noise level was required for a doubling (or halving) of the acceptability rating than originally assumed in developing the perceived noise level scale. [Work supported by the Systems Research and Development Service, Federal Aviation Agency.]

Field noise reduction measurements in 21 school, motel, and residential rooms during flyovers of jet and propeller aircraft are described. The measured noise reduction for most rooms was found to lie within or near the range of moderate noise-reduction values observed in previous measurements of houses and wood-frame air-base buildings. Sizeable differences in room noise reduction values were observed during successive aircraft flyovers. For jet-aircraft flyovers, the root-mean-square value of the standard deviations for noise-reduction measurements in school and motel rooms was 2.7 PNdB. For the four residential rooms studied, a root mean-square value for the standard deviations of 3.4 PNdB was observed.

Construction of a model reverberation chamber, patterned after the Riverbank reverberation chamber on a scale of ten to one, allows measurement of the sound absorption coefficient of materials over the frequency range from 4 kc to over 30 kc. Knowledge of the absorption coefficients of materials at high frequencies is important in acoustic model studies of large silencing structures and of auditoriums. The model is also intended for study of the effect of changes in room configuration which might be considered for the full size reverberation chamber. Sound sources used in the model include a WE 633 dynamic microphone and an electrostatic tweeter. Instrumentation, measurement techniques, and limitations of reverberation time measurements at high frequencies are discussed. The absorption coefficients of a few materials useful in model work are presented.