Speech intelligibility is the ability of a listener to understand a sound or an entire conversation.
The STI (Speech Transmission Index) is the most used method to quantify the speech intelligibility in a specific location in the environment.
The scale ranges from 0 to 1: 0 is the worst result, where the message is not understood at all, while 1 is the maximum level, with a 100% understanding of the message.
Speech intelligibility can be simulated (a very useful process for newly built environments) or measured.
There are several factors that can affect speech intelligibility in an indoor environment: distortion of an audio system (for example a meeting room with an amplification system), ambient noise (for example fans, background hum) and environmental acoustics.
In most cases, it is environmental acoustics that mostly compromises speech intelligibility.
Try to imagine a presentation of products or services in an environment with poor intelligibility and where only 50% of the information told by the speaker reaches the listener.
What is the point of attending such a meeting if so much information is lost?
It is extremely important to design the acoustics of the rooms, but unfortunately still few take care of it, and many intervene only later, when the problem comes to their attention. This is why we speak of acoustic “correction”.