SPEECH-INTELLIGIBILITY ENHANCEMENT BY A LINEAR LOUDSPEAKER ARRAY IN A REVERBERANT FIELD

In a reverberant space, speech intelligibility increases as the ratio of direct to reverberant sound energy (D/R) increases. This paper describes how the D/R is increased using a linear loudspeaker array, in which five loudspeakers are arranged vertically with appropriate delay and level corrections. The theoretical increase in DIR caused by the linear loudspeaker array is confirmed by measuring the Rapid Speech Transmission Index (RASTI) under highly reverberant conditions. The maximum D/R (or RASTI) is obtained on a circle around the array, where all direct sounds are added completely in phase. Moreover, the D/R (or RASTI) is improved over a region extending to several times the critical distance, in the reverberant field. Speech intelligibility tests are performed in a reverberation room to confirm the increase in speech intelligibility scores. The results show that the intelligibility of speech in auditoria or teleconferencing systems can be improved significantly using this type of array.