Human Response to Helicopter Noise: A Test of A-Weighting

Department of Defense and U.S. Army police has long been to adjust measured helicopter noise levels upwards to account for the special character of helicopter noise in terms of human and community annoyance. In the United States, the A-weighted Day/Night Average Sound Level (DNL) descriptor is used most often for this purpose, but research has shown that it is not completely adequate. Also, many questions remain about human perception of, and response to, helicopter noise. This study is an extension of earlier research that tested human response to the noise of an Army UH-1H (Huey) helicopter flown over various indoor environments. This report documents a follow-up test using six different helicopters to replicate and expand on the earlier study. The data generally indicate that the A-weighted DNL is inadequate for assessing helicopter noise. The C-weighted scale was also tried and found inadequate. Helicopter noise measurement by either scale must be corrected to accurately correspond to human perceptions. Measuring indoors, the use of A-weighting to assess helicopter noise requires an offset that varies with helicopter A- weighted sound exposure level (ASEL), and this offset varies for different helicopters.