Experimental Study of Evaluation of Acoustical Characteristics for a Speaker in Lecture Room

Abstract

Primary communication in lecture rooms comes in the form of speech and listening. A large number of studies examining room acoustics of lecture room for the listener as they affect speech intelligibility have been conducted. However, studies focusing on the point of view of the speaker are lacking. The purpose of this study was to propose a subjective measurement of “speaking difficulty” for a speaker and investigate the relationship between the reflected sound parameters of the rooms and the evaluation of the speaker’s “speaking difficulty”. Subjective judgement tests were conducted in simulated stage sound fields and in several actual lecture rooms. Results of the tests on the degree of speaking difficulty in simulated stage sound fields suggested that reflected sound involving a single echo with more than 50-75 ms delay can cause an echo disturbance for a speaker. The same judgement tests in actual lecture rooms indicated that speakers automatically adjust their voice levels and rates of speech for verbal communication when hearing reflected sounds of self-feedback speech. However, within a certain range of vocal levels, the degree of speaking difficulty tends to be strongly affected by reflected sound. Both the placement of acoustic absorption materials in the room and the spatial balance of reflected sound influence the speaker’s evaluation of speaking difficulty.