Application of the Speech Transmission Index (STI) for planning communication areas

The STI (Speech Transmission Index) quantifies the transmission of a speech signal between a speaker and a listener. It takes into account the remaining signal strength of the speech-relevant frequency bands, the detailed energetic impulse response of the room - or generally speaking the surrounding of the source and receiver position - as well as the reduced modulation depth due to background noise. Therefore it is an excellent parameter to identify problems occurring in open plan offices, restaurants or any other communication area and assess alternative planning scenarios. The workflow of such a planning is demonstrated using a restaurant or an open plan office as an example. The general idea is to use the persons as sources for the background noise as well as the desired speech signal. Although standards often set upper limits for the reverberation time taking into account the STI would be a major improvement for acoustic planning.