Friday, June 11, 2010

The sound just goes round and round

One important constraint for a speaker is room acoustics - how sound behaves in the space where you speak. Some spaces are excellent, like Symphony Hall in Boston. Other spaces, like sports arenas or stadiums, are notoriously poor - about like speaking in a fishbowl. Most of us are more likely to speak in a local church or high school gym, but we still need to consider the space when planning a speech.

Reverberation time is an important factor which describes how sound behaves. It measures how long it takes for a sound to die away completely, and depends both on the room volume and how sound is absorbed.
Speech is more intelligible when the reverberation time is short, somewhere around a second. Music sounds better when the reverberation time is around two seconds. Before it was fixed the San Diego Sports Arena had a reverberation time of around seven seconds.

Sound travels much more slowly than light. The speed of sound is about 1125 feet per second. You can estimate how far away a lightning strike is by listening for the thunder, and counting five seconds per mile. A concert hall is much smaller than 2250 feet, so the two second reverberation time represents many reflections of sound from different surfaces. The sound bounces round and round before it dies away.

For two years Marisa Minor was a keynote speaker in the Miss Ohio program, and learned to deal with crowds of several thousand people. Some of her advice for large audiences is that:

“The actual words of the speech must be altered to suit a larger audience, as well. Short sentences are better for larger crowds. Longer pauses are more effective. The use of powerful verbs and strong statements is amplified in the presence of several thousand people. They can sense each other’s excitement, which triggers the memory to recall that feeling long after the speech is over. The manner of speech is also important in delivering to large audiences. Projecting the voice, enunciating up to 5x more than you would in normal speech (which will come across as “normal” to the audience after reverberation has taken its toll), and using more exaggerated inflection (the rising and falling of pitch) all lend to a professional-sounding speech.”

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