Varying the spectral envelope of air-conditioning sounds to enhance indoor acoustic comfort

Sounds of ceiling mounted air-conditioners were recorded at various conditions of classrooms, offices, and libraries. Sound quality was manipulated by varying spectral envelope of the sounds to investigate its effects on acoustic comfort. Tonal components of the sounds were removed, and the sound pressure levels at 250–630 Hz frequency band were varied to generate experimental sounds using original recordings. Subjective auditory tests were conducted by using paired comparison and semantic differential tests. The results showed that sounds without tonal components were preferred over sounds with tonal components. The subjects had a more favorable impression of the sounds which had a larger energy at 250–630 Hz in cases both with and without tonal components. Statistical analysis showed that both tonality and fluctuation strength play major roles as the sound quality metrics which describe the acoustic comfort from the subjects.