Loudness, Annoyance and dBA in Evaluating Low Frequency Sounds

The study reported here was undertaken to evaluate annoyance and loudness of low frequency sounds, to establish a reason for the discrepancy between the dB(A) unit and annoyance after exposure to low frequency sounds. Annoyance was evaluated by 98 test subjects who were exposed for 4 × 30 minute periods while studying. Four continuous fan noises centred at 80, 250, 500 and 1000 Hz were used as exposure noises. The relative annoyance of a low frequency noise and reference, noises were evaluated at the same dB(A) level using category scales. Noise levels betwen 40 and 70 dB(A) were included. Loudness estimates for pure tones at 63, 80, 250 and 1000 Hz were made by 12 subjects using magnitude estimation. Equal loudness contours were obtained at 45, 60 and 75 dB SPL. The loudness functions and contours derived were largely in agreement with ISO R/226, 1961. The estimations of loudness were higher than the degree of annoyance for these exposure noises. This effect became less pronounced towards the lower frequencies. The relation of the annoyance contours and the dB(A) demonstrates that the dB(A) weighting underestimates annoyance for frequencies below about 200 Hz.