NTi Audio Acoustilyzer AL1 - Manual (Page 89)

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9. Appendix: Introduction to STI-PA
Application:
In case of emergency, public address systems in buildings like airports,
railway stations, shopping centers or concert halls have to (clearly)
inform persons in danger about escape information and directions.
However if such announcements are misunderstood due to poor system
quality, tragic consequences may result. Therefore, it is essential
to design, install and verify sound reinforcement systems properly
for intelligibility. In addition, a variety of other applications such as
legal and medical applications may require intelligibility verification.
Standard:
The IEC 60849 standard (national standards - see next section) requires the
verification of electro-acoustic sound systems for emergency purposes to
ascertain a minimum level of speech intelligibility in case of an emergency
under realistic circumstances. Therefore, speech intelligibility from a
regulatory view is not a subjective measurement, but can be verified with
several, more or less complex methods that have been standardized in IEC
60268-16.
National standards:
• IEC 60849 Sound systems for emergency purposes (also VDE 0828
part 1 and DIN-EN, BS-EN, SN-EN, OEVE-EN, …)
• NFPA 72 National Fire Alarm Code 2002 (2002 edition, section 7.4.1.4)
• BS 5839-8 Fire detection and alarm systems for buildings. Code
of practice for the design, installation and servicing of voice alarm
systems
Subjective Testing Methods:
Although frequency response, distortion and loudness are important
to intelligibility, conventional measurements of these parameters alone
only marginally relate to intelligibility. When additional issues such as
directionality of drivers and the environment are taken into consideration,
the question then is how well a spoken message can be understood at
different locations, and particularly at the “worst” location.
One approach is to let a trained human speaker read a number of
existing or synthetic words, while a representative number of listeners