Directivity Balloons of Real and Artificial Mouth Simulators for Measurement of the Speech Transmission Index

One of the most used intelligibility’s parameters is Speech Transmission Index: the technique for determining it employs an artificial speaker and listener. In many cases (i.e. big rooms or system of telecommunications) the precision of directivity of the artificial mouth doesn’t influence too much the result; on the contrary inside cars, but also in other cases, the shape of the whole balloon of directivity is important for determining correct and comparable values, and different mouths give really different results in the same situation. Moreover there isn’t a current standard that fixes the whole balloon of directivity of artificial mouths, but it defines only limits for some frontal position. For this reasons we have measured, in an anechoic room, the directivities of a real speaker and some artificial mouths and finally we have compared them for underlying the need of a more precise standard in this field.