A factory workshop with hard uniform surfaces has dimensions 13 m by 25 m by 3.5 m high and a reverberation time of 2.2 seconds at 500 Hz.

A factory workshop with hard uniform surfaces has dimensions 13 m by 25 m by 3.5 m high and a reverberation time of 2.2 seconds at 500 Hz. The noise level at this octave band in the workshop is 102 dB (re 20μPa). Predict the new noise level if the ceiling is covered with an acoustically absorbent material which has an absorption coefficient α500 = 0.84.