Tuesday, Feb. 27th 2018

Speech Intelligibility

If you have ever heard a speaker, teacher, or public announcement that sounded like Charlie Brown’s teacher, you know the importance of speech intelligibility. It is essential for a speaker’s message to reach its audience, for a teacher’s class to understand her lesson, for a passenger listening for announcements regarding his train or her flight, and for people to understand instructions from a mass notification system during an emergency. So, what goes into designing for high speech intelligibility?



When reverberation time in a space goes up, then speech intelligibility goes down. Even the best sound reinforcement systems cannot overcome an overly reverberant space. If involved early in the design, then AVANT can recommend appropriate room volume and shaping, as well as adequate sound absorption. This keeps reverberation in check.


Speech intelligibility

The higher the wanted signal is above the noise, the better the signal-to-noise ratio.


Signal-to-noise ratio helps to determine speech intelligibility. You can’t hear clearly with too much background noise. And just turning up the volume does not necessarily make it better.

AVANT ACOUSTICS can help you control noise sources, such as mechanical and electrical equipment, or exterior noise from rainstorms, or nearby traffic or airports. Our paging and mass notification systems can even include ambient noise sensing to appropriately adjust announcement sound levels in places where crowd size changes throughout the day.



All sound reinforcement system components are not created equal. Telephone microphones simply cannot deliver crisp paging announcements. Furthermore, loudspeakers have different characteristics for different ceiling heights or venue types. How to choose? AVANT prefers not to specify a product until we’ve had the chance to test it in our lab or hear it in action. We always ensure we fully understand its strengths and weaknesses. This enables us to make the right recommendations for any application.



We’ve said it before and we’ll say it again – we can make your system sound better, and more intelligible, just by making sure that everything is properly installed and that all parameters – from hardware to software – are correct.



Speech Transmission Index (STI) and STI for Public Address systems (STIPA) are international standards for measuring and predicting speech intelligibility. STI and STIPA scales range from 0.0 (bad) to 1.0 (excellent). In addition, codes may require that a paging or mass notification system have a minimum STI or STIPA rating. This is especially true in large-volume venues requiring paging or mass notification for life safety.

Using our measurement devices, we can evaluate STIPA in an existing space. For an unbuilt space, we can predict STI or STIPA using acoustic modeling. These measurements allow us to recommend improvements, or to adjust our design to ensure compliance with various standards.

Now that you understand a bit more about designing for high speech intelligibility, let AVANT ACOUSTICS help make your new or existing space one that allows for crystal clear communication in every situation.


This post was authored by AVANT ACOUSTICS Senior Associate, Emily Jaumard.



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