Speech intelligibility in public spaces is a regulated engineering requirement

Evidence

The understandability of speech is of crucial importance in public announcement systems, in telephones, and also in auditoria with or without sound reinforcement. The intelligibility can be estimated by computing the speech transmission index (STI), which is based on the concept of the modulation transfer function. STI methods are well established, and in some countries the STI values for sound systems in public spaces are regulated. Furthermore, the standard that describes sound systems for emergency purposes ISO 7240-19 (2007) defines the minimum STI value to be 0.5. Public announcement systems for public spaces are costly, and if the STI of a new building is measured to be lower than that targeted in the design process, the acoustic and electrical changes that must be made may be expensive. This is one reason why STI simulations and measurement systems are of great importance. — Ville Pulkki, Matti Karjalainen, Communication Acoustics- An…, 2393

Categorization

• ADDENDUM: Directly supports the infrastructure/human-built-environment theme in ‘Grafting and Growth’ at the acoustic-application level; a concrete regulatory fact about how sound systems for emergency purposes are benchmarked.
• CANDY: The specific ISO 7240-19 minimum STI of 0.5 for emergency sound systems is a light, concrete fact easy to drop into conversation.