Effects of Sound Absorption on Acoustics Quality in Classrooms
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Abstract
The objective of this study is to investigate the relationships between the percentage of absorbing surface area to the total surface area of a classroom and three different acoustical indexes of the room. This paper is the experimental research that investigated six large classrooms of a public university in Thailand that were as large as 288–566 cubic meters. These lecture rooms, each belonged to the faculty of engineering, architecture, agriculture, science, industrial education and information technology of KMITL, were investigated in the following manners: the width, depth, and height of each room, as well as the dimensions of the curtains and blinds. Measurements of the Background Noise Level (BNL), Reverberation Time (RT) and Speech Transmission Index (STI) followed ANSI S12.60 standard. These measurements yielded the percentage of the absorbing surface areas to the total surface areas (PAS). Then, the BNL, RT, and STI were obtained by generating test sounds with a sound generator. The results show the relationship between PAS and STI, RT, BN. STI increased by 6.12–20.39%, but RT and BNL decreased by 1.45–16.54% and 1.5–3.0%, respectively, as PAS increased. Moreover, Pearson correlation analysis determined the relationships between PAS and the three indexes at 99% confidence level. The relationship between PAS and STI was significant at r = 0.617 as well as PAS and RT was significant at r = –0.557 but the correlation between PAS and BNL was insignificant at this confidence level.
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