Testing instruments that measure transient sounds

Abstract

An unattended instrument for audible environmental noise must measure and report whatever and whenever sounds occur at the monitoring location. Test signals for steady sounds are here voltage-equivalents of sound pressure levels; the signals are sine waves at one-third octave intervals, 10 Hz to 20 kHz. Test signals for responses to transient sounds are sound exposure levels of single-cycle sinebursts, 10 Hz to 20 kHz. For a wide-band system and 1 kHz, the sound exposure level of a single cycle relative to steady sound pressure level is theoretically −10 log(1000)=−30.0 dB. With A-weighting, the relative sound exposure level is theoretically −30.7 dB; with CEL-493 integrating sound level meter No. 198107 the relative level was also −30.7 dB. At 32 Hz (more precisely 31.6228 Hz), the theoretical relative A-weighted sound exposure level is −10.6 dB [not −10 log 31.6228=−15.0]; with the CEL-493 the relative level was −10.8 dB. For a conventional sound level meter, at 1 kHz the theoretical fast A-weighted sound level of a single cycle, minus steady sound pressure level, is −21.8 dB; for CEL-493 the difference was −21.7 dB. At 32 Hz the theoretical fast A-weighted sound level of the single cycle, minus steady level, is −2.2 dB; for CEL-493 the difference was also −2.2 dB.