Malaysian enclosed room acoustics design criteria for good speech intelligibility: the way forward from acousticians perspective

Abstract

Generally, in terms of functionality, the enclosed room can be categorized for speech, multipurpose or music. There shall be different acoustics requirements that need to be achieved in order for the respective room to function effectively. For a room that the main function is related to speech such as lecture hall, mosque and classroom, optimum speech intelligibility need to be achieved else the effectiveness of the enclosed room might be compromised. For the enclosed room to have good speech intelligibility, the primary acoustics design criteria that need to be achieved are reverberation time (RT60), sound field behavior inside the enclosed room as represented by the Energy Time Curve (ETC), speech intelligibility indicator, mainly Speech Transmission Index (STI) and its simplified version of STI which is Rapid Speech Transmission Index (RASTI) , ambience noise level, through Noise Criteria (NC) and its wall noise insulation through Sound Transmission Class (STC). The case studies discussed in this paper are 2 lecture halls which are in Electrical Engineering Faculty, UTM, Skudai, Johor and a multipurpose hall, located in JKR Headquarter, Kuala Lumpur. In this paper, the suggested acoustics design criteria are the RT60 which is maximum RT60 of 1.0 second, ETC where the direct sound and early reflections shall occur within 35 ms, STI or RASTI shall be with a minimum of 0.6, NC shall be around NC 40 and STC shall be in the range of STC 40 for enclosed room to have good speech intelligibility and with pleasant acoustics. Thorough discussion on the suggested acoustics design criteria to have good speech intelligibility in an enclosed room is the main issues discussed in this paper.