Calculation of Speech Transmission Index in Rooms


Sufficient acoustic quality of speech communication is very important in many different situations and places. The most known available objective method for measurement and prediction of speech intelligibility is the Speech Transmission Index (STI), described in the international standards IEC 60268-16 and ISO 9921. A new application note on how to perform correct predictions in ODEON is available on the Application Notes page.

Two cases of speech transmission index are discussed: Direct communication between two people in the same environment and public address (PA) systems where an electro-acoustic system is used to address a group of people.

A high signal to noise ratio (SNR) improves STI but the obtainable value may be limited by Sound Pressure Level design criteria. An example of calculation is shown below where the STI from a PA voice alarm system is simulated . In this case the STI should be at least 0.35 in the area where people have access, but at the same time a 1 KHz alarm tone should remain below 115 dB.

Read the whole application note here.