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Speech Intelligibility: Gathering Additional Pieces Of The Audio Puzzle
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Figure 1 - For speech to be intelligible, the direct sound field level must exceed the level of the reverberation and/or noise at the listener location.
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  Acoustic Measurement, Pat Brown

Path To Competence
SI in sound reinforcement systems lends itself to scientific investigation. There is science behind the sound. I outlined the required skill set earlier in this article. How do you get there?

Fortunately you have more options that I did nearly 30 years ago. Trying to glean this stuff out of textbooks is challenging, to say the least. Synergetic Audio Concepts offers some resources to shorten the learning curve. These include:

Web-based Training Programs
Our “Sound Reinforcement for Designers” web-based training was developed with the speech intelligibility professional in mind. It covers basic room acoustics, loudspeaker directivity, and how to measure and predict SI.

It doesn’t replace product-specific training, such as for a room modeling program or measurement system. What it will do is help you use these tools more effectively. You can find a complete description at

In-Person Training
SynAudCon will hold the Emergency Communication System Speech Intelligibility Workshop on January 3-5, 2013. This event brings together leaders from the various fields that comprise SI, including measurement, prediction and code compliance.

Figure 3 - Speech intelligibility can be measured with instrumentation. This app measures the Speech Transmission Index for PA Systems (STI-PA). Credit: Embedded Acoustics (click to enlarge)

It will also include active demonstrations, panel discussions and presentation of the results of a number of SI studies of loudspeaker types, rooms and measurement systems done specifically for this workshop. It is a one-time event and space is limited.

Universal Principles
Knowledge gained about SI will apply to every sound system that you design or modify, not just those that might be used as an emergency communication system (ECS). My approach to a sound system design is to first design for SI. This necessitates loudspeaker selection and placement that assures a dominant direct field level in the speech octave bands at all listeners. If the system will also be used for music, its bandwidth can be extended accordingly.

The natural law of the universe dictates a progression from order to disorder. You can’t unscramble eggs. Design for speech first, since speech systems have more stringent sound energy ratio requirements than music systems.

My sound system design disaster from the 1980s may have been the best thing that ever happened to my audio career. It made me aware of viewing sound system design as a science rather than as an art. This, in turn led me into the world of acoustical measurement instrumentation.

While our tools of yesteryear pale in capability when compared to those available today, the principles governing their use have not changed at all. Direct your training endeavors toward concepts that are timeless. These will be around long after today’s latest, greatest mixer finds a permanent home in a museum.

Pat & Brenda Brown lead SynAudCon, conducting audio seminars and workshops around the world. For more information go to

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