STI Measurement in The Car

Abstract

In modern car industries, the intelligibility of sound inside the cabin of vehicles has been known as a factor of comfort [6]. One of the known objective methods for evaluating speech intelligibility inside cars is the speech transmission index STI which is the main subject of this report. The measurement aim is to predict the STI in a running car as a factor of speed (background noise). For this purpose, a series of audio- acoustical measurements have been conducted inside a five-door car (Mazda) based on the European standard IEC 60268-16 [4]. As the harshness of background noise in different speeds, compartment reverberation time and speech level are accounted for in the STI calculation, the resulting data can be interoperated as the quality of sound in the car [6]. Further investigations have been done for better understanding the effect of source spectrum and direction on the transmission index and finally the direct measurement method in aarae has been compared with a similar method in Arta (Audio Measurement and Analysis Software) in the room space.