{"id":1937,"date":"2026-04-01T09:35:56","date_gmt":"2026-04-01T13:35:56","guid":{"rendered":"https:\/\/groupecsx.ca\/?p=1937"},"modified":"2026-04-22T09:37:35","modified_gmt":"2026-04-22T13:37:35","slug":"the-intelligibility-of-an-emergency-communication-system-is-not-validated-at-the-end-of-the-project-it-is-designed-from-the-outset","status":"publish","type":"post","link":"https:\/\/groupecsx.ca\/en\/lintelligibilite-dun-systeme-de-communication-durgence-ne-se-valide-pas-en-fin-de-projet-%e2%80%92-elle-se-concoit-des-le-depart\/","title":{"rendered":"The intelligibility of an emergency communication system is not validated at the end of the project - it is conceived from the outset."},"content":{"rendered":"

<\/a><\/p>\n\n\n\n

It's a common structural error in the management of these projects: treating intelligibility as a compliance criterion to be achieved at provisional acceptance of work, in the same way as a cabling check or a bump test. An STI (Speech Transmission Index) measurement is ordered, a report indicating 0.62 or 0.65 is obtained, depending on the zone, and the deliverable is accepted.<\/p>\n\n\n\n

This reasoning is technically defensible. It is operationally insufficient.<\/p>\n\n\n\n

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Modelling, measurement and ITS objectives have their place - but not as sole criteria.<\/h5>\n\n\n\n

STI is a standardized index (IEC 60268-16) that quantifies the degradation of a speech signal between the source and the point of reception, taking reverberation and background noise into account. Its value is real, useful and necessary for all serious system documentation. Current codes - including NFPA 72 - legitimately allow and support its use as a measurable objective.<\/p>\n\n\n\n

But an STI result, whether simulated or measured, cannot be interpreted in isolation. An insufficient index may reflect poor acoustic design, but it may also result from unrepresentative measurement conditions, abnormally high background noise at the time of testing, or inadequate positioning of the reference source. Conversely, a compliant ITS does not guarantee intelligibility in real-life conditions if the parameters influencing it outside the model are not controlled.<\/p>\n\n\n\n

The most robust approach combines clear ITS objectives, planned in-situ measurements, usage scenarios tested under representative conditions, and subjective listening assessment - the latter being recognized and permitted by several standards. None of these methods is sufficient on its own. It is their convergence that produces a reliable conclusion about the system's actual performance.<\/p>\n\n\n\n

What the models don't capture<\/h5>\n\n\n\n

An STI measurement is taken under defined conditions: a calibrated reference source, a background noise level measured at a given time, a fixed geometry. It produces a punctual result under conditions that never correspond exactly to those in operation.<\/p>\n\n\n\n

What acoustic models don't take into account:<\/p>\n\n\n\n