Speech intelligibility measures how much spoken information can be understood in a particular environment. It is affected by reverberation time, background noise level or rather the signal to noise ratio (S/N), room volume and geometry together with the placing of sound absorbing, sound reflecting and sound scattering surfaces.
The shorter the reverberation time, the better the intelligibility of speech, until the background noise begins to dominate.
In a room with a long reverberation time, one word does not have time to decay before the next reaches the listener, so the intelligibility of speech is poor.
METHODS AND VALUES
There are several methods to measure and evaluate speech intelligibility in a room. Of all the objective methods, three will be mentioned here: STI, RASTI
. These methods can be used to evaluate the intelligibility between two points in a simple and objective way. The results point to how intelligible the speech is actually perceived to be. Suitable values for speech intelligibility tend to be based on the experience of young adults with average hearing. It is worth remembering that around 5 % of the population use hearing aids or other technical aids. Many more have a less serious hearing loss that causes problems when trying to understand speech in noisy situations. Even a common cold can give temporary hearing loss. Old people and children are particularly dependent on good speech intelligibility, because they have different requirements to young adults for assimilating information. It has also been proved that people listening to a language that is different to their mother tongue require particularly good acoustic conditions.