Measurement of the Speech Intelligibility Inside Cars

One of the most used intelligibility’s parameters is the Speech Transmission Index: the techniques for determining it employs artificial speaker and listener. Inside cars, where signal to noise ratio is particularly low, the value of STI is mainly influenced by this ratio and determining the sound power of real speakers is the only way for piloting correctly the artificial mouth. We have implemented a technique that is based on throat-activated microphone and it is able to find the level of real speaker’s voice inside noisy spaces in the effective conditions. Especially, we have studied the speech inside cars and we have discovered how the value defined by typical configuration may be extremely different from real one and, in this way, we have been able to produce more reliable excitation signals. Using this “raised” signal we have tested one car and we have tried to find a good correlation between drivers’ impression and objective values.