SOME FACTORS INFLUENCING HUMAN RESPONSE TO AIRCRAFT NOISE: MASKING OF SPEECH AND VARIABILITY OF SUBJECTIVE JUDGMENTS.

Abstract : Statistics of the variability of subjective judgments of the loudness and noisiness of pure tones and complex sounds as studied in the laboratory and in the field are presented. An analysis of possible sources or causes of this variability is made in terms of test-retest reliability, differences among subjects, type of sounds judged and experimental method used in obtaining judgments. Possible contributions to variability of judgments due to differences in the size of the external ear and the thresholds of auditory sensitivity at different sound frequencies for different age groups are discussed. Word intelligibility tests at various intensity levels were administered to a crew of trained listeners in the presence of recorded noise from jet and propeller-driven aircraft. The noise was that which would be present outdoors and in a house as the result of engine run-up operations and when the aircraft were flying overhead shortly after take-off and prior to landing. Methods of measuring or evaluating aircraft noise predict the results of the speech tests in the following order of merit, from best to worse: (1) Articulation Index (AI); (2) and (3) perceived noise level in PNdB and Speech Interference Level (SIL) (SIL and PNdB appear to predict the masking of speech about equally well); (4) Noise Criteria (NC); (5) overall SPL, A scale; and (6) overall sound pressure level, C scale. (Author)