Speech intelligibility improvement for multiple loudspeakers by increasing loudspeaker directionality architecturally

The objective of the research described in this paper is to improve the speech intelligibilty of multiple loudspeaker public address systems in long and flat enclosures, such as underground stations and supermarkets. It was theoretically demonstrated that strong directional loudspeakers are effective for increasing the speech transmission index (STI), and thus, a series of experiments were carried out to increase the loudspeaker directionality by an architectural method. It was found that a significant increase can be obtained by putting the loudspeaker inside a box, both with and without absorbers on the inner surfaces. The corresponding frequency spectrum change is very small and acceptable.