From Handbook For Sound Engineers, Third Edition
by Peter Mapp
36.1 Introduction
The fundamental purpose of a paging, announcement, voice alarm, or speech reinforcement system is to deliver intelligible speech to the listener. A surprising number of systems however fail to achieve this basic goal. There can be many reasons for this, ranging from inadequate signal to noise ratio to poor room acoustics or inappropriate choice or location of loudspeaker. It is the job of the sound system designer to be aware of these factors and take them into account when designing a sound system and selecting devices to provide the degree of intelligibility required. In order to do this however, an understanding of the basic factors that affect speech intelligibility and the way we hear speech are required. This chapter therefore begins by taking a look at the nature of the speech signal and how we hear it before discussing design strategies and ways of optimizing system design and performance. Current methods of assessing and measuring intelligibility are then also discussed together with comments on their practical limitations.
36.2 Parameters Affecting Speech Intelligibility
Although sound quality and speech intelligibility are inextricably linked, they are not the same thing. For example it is quite possible to have a poor sounding system that it highly intelligible (e.g., the frequency response limited and resonant re-entrant horn) or alternatively a high quality system that is virtually unintelligible (e.g., hi-fi loudspeaker in an aircraft hangar). Similarly a common mistake, often made when discussing intelligibility, is to confuse audibility with clarity. Just...
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