Achieving Maximum Intelligibility in Mass Notification Systems

July, 2023

Written By: Ray Bassiouni and Tom Hinchliffe


Intelligibility is a measure of how easy it is to understand a voice message such as live public address (PA) or a pre-recorded message delivered from an MNS.  It is affected by the quality of the original message transmitted, the level of background noise, reverberation and, for messages transmitted over an MNS, the properties of the communication system. The original message must be spoken clearly and more slowly than the typical person to person speech. Background noise can mask an emergency message in what is known as the signal to noise ratio, and reverberation can blur the speech over time by lengthening vowels and shortening pauses. All of these factors must be considered in MNS design to create the most effective Giant Voice or PA system.

Outdoor Acoustic Coverage

Designing outdoor systems requires taking into consideration all factors that affect outdoor acoustics including: wind effects, ground cover absorption, and barrier attenuation effects (such as those posed by buildings and above-ground structures).

Indoor Acoustic Coverage

Indoor areas have different acoustic considerations. Factors to be considered include the square footage of the building and layout, the shape of the space and the existing background noise level.

“During major emergencies and disasters, accurate and timely voice warnings to all affected people are among the most important factors to successfully protect lives, contain property damage and minimize community impact.”