Effects of air conditioning on sound propagation in a large space

Sound-pressure level (SPL) fluctuation caused by air conditioners was measured by use of pure tones as the sound source in a gymnasium. When the air conditioner was turned on, the fluctuation of the SPL was more than 2 dB at 2 kHz, 5 dB at 4 kHz, 6 dB at 8 kHz, and 10 dB at 16 kHz. The cumulative density of mean-squared amplitude corresponds well with the gamma distribution. From this statistical analysis, it is considered that the SPL change is caused by the impulse response which is represented by the direct sound (regular) and changing delay time of reflection sound (irregular). The cumulative density of mean-squared amplitude for this model by using the pure tone also indicated the gamma distribution. It is found that the frequency characteristic and the cumulative density of the SPL change have the same tendencies as the method of modulation for the delay time of reflection sound.