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Reverberation: Good or Evil?
Recently, two different people called me about the acoustics in their church. "The acoustics are terrible!" both said. Whenever someone says the acoustics are terrible, I ask for a description, since this can mean almost anything. Usually, it means the room is too "live" (too much reverberation). In both cases, however, the caller was an organist. To an organist, terrible acoustics means a "dead" room. For an organist, there is no such thing as too much reverberation.
Reverberation is the persistence of sound in a room after the source has ceased. It is easily heard if you clap your hands in a "live" room. Try this in a typical Catholic Church. Come back after lunch, and you will still hear sound reverberating from your clap.
Organists (and violinists, such as myself) love reverberation because it adds a halo to our sound. It helps blend the disparate voices of a choir or ensemble, and gives support to players and singers.
More reverberation (a "live" room) is usually better for music. But reverberation can interfere with understanding speech, especially in a room with background noise. People with impaired hearing are particularly intolerant of reverberation. As a general rule, then, less reverberation (a "dry" room) is better for speech.
Curtains can be used for adjusting the reverberation of multi-purpose theatres. They are brought into the room to "dry" up the room for speech, and retracted to "liven" the room for music.
Retractable curtains are just not practical for churches. They need to support music and speech in the same event. Reverberation is particularly important for church music, but the Word is fundamental. How does one reconcile these conflicting demands?
- It is always easier to reconcile speech and music in a smaller room (though a smaller room may not be optimal for organ).
- Reverberation amplifies noise, so lower background noise allows more reverberation without interfering with speech.
- Proper room shaping can help. I have been in highly reverberant concert halls and been surprised by how easy it was to understand speech.
- In a very reverberant room, a properly designed sound system can provide good speech intelligibility without exciting the reverberance of the space.
Reverberation is a wonderful thing-with a price.
Good speech intelligibility in a reverberant room with a sound system is achieved by two means:
- Bring loudspeakers closer to people.
- Use more directional loudspeakers.
You can hear this for your self. In a very reverberant room, you can make yourself understood if you stand close enough to your listener. You can make yourself understood farther away if you increase the directivity of your voice by cupping your hands into a megaphone.
In a reverberant room with mechanical ventilation or air-conditioning, listen to how much improvement you get by simply switching off the ventilation .
The proper amount of reverberation is a matter of judgement. The client should clearly understand the benefits and costs.
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