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Pop Quiz: August 2006

Test Your Knowledge of Speech Intelligibility


  1. Speech intelligibility and sound masking are related issues.
  2. The higher the %ALcons score, the better the speech intelligibility.
  3. The most effective way to increase speech intelligibility in a room is to increase the playback level of the sound system.
  4. Because most speech consonant sounds occur above 2 kHz, a sound system doesn't need to reproduce the full frequency range to provide good speech intelligibility.


1. TRUE. In a highly reverberant space (such as a large, old church), excessive reverberation causes late arrivals of sound energy, which essentially masks early arriving sound, and causes speech to be rendered unintelligible. As the energy in the reverberant field approaches the energy of the direct field, intelligibility will suffer.

2. FALSE. A higher %ALcons score literally means that a higher percentage of speech consonant sounds will be lost. Consonants are thought to play a larger role than vowels do in our ability to discern speech content.

3. FALSE. Increasing the amount of energy in the reverberant field can degrade speech intelligibility. In most cases, it's more effective to take steps to minimize or reduce reverberation by using acoustic treatment materials in a room. Increasing the directivity of the loudspeaker system can also help, thereby directing more energy to the listener and less energy to the reverberant field.

4. FALSE. Only one type of consonant sound — the “fricatives,” such as “f,” “s,” “h,” and “th” — has significant energy above 2 kHz. Severely band-limited systems, such as a typical telephone, deliver speech poorly.

Sources: Meyer Sound, McSquared System Design Group

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