The effects of the aircraft noise and multiple echoes on speech intelligibility of outdoor public address system

This study investigates how multiple echoes reflected from adjacent buildings influence the speech intelligibility of outdoor public address systems when aircraft noise is added. To accomplish this, the sound of an aircraft flying over industrial areas was recorded from the vicinity of an airport in Tokyo and then added to speech sounds at a signal-to-noise ratio (SNR) of -5 dB. Then, the speech signals, with or without artificial multiple echoes, were presented to 18 young adults at sound pressure levels (SPLs) of 60, 70, and 80 dB. The results of the listening test showed that aircraft noise and multiple echoes separately decreased speech intelligibility, but that speech with the multiple echoes present had significantly lower word identification scores than speech without multiple echoes. The results also showed that speech intelligibility increased when the SPLs was increased from 60 to 70 dB, but no further increase was observed when the SPLs rose from 70 to 80 dB, with or without multiple echoes. Taken together, the results indicate that both aircraft noise and multiple echoes decrease the speech intelligibility of outdoor public address systems, and to ensure sufficient information is transmitted when multiple echoes and aircraft noise are present, SPLs should not be lower than 70 dB.