How To Create an Echo
Foyer Speaker Systems
Have you ever been sitting near the back of a church and heard and echo? Did it appear to come from the back of the church? Would your first reaction be to think that the echo was from the back wall? What would you say if it was really coming from the Foyer Speaker System?
Science Lesson 102
If you have an interest in science and you like to see God's beautiful laws of physics at work, then the church sound system provides many examples. In nature, until recently, everyone thought that a bolt of lightening traveled from the clouds down. The fact is, the flash of light travels from the ground up to the clouds. It has been the invention of high speed photography that has captured the event to help scientist to better understand lightening. Likewise, church sound has many myths and events that appear to happen one way but actually happen by other means.
In terms of church sound, there are some constants that can not be changed. Here are some of the basics.
Sound travels faster in water - 4921 feet per second
Sound travels faster as temperature and humidity increases. Usually about 5% for the first 20 degrees.
Sound travels at the speed of light when transmitted through electrical wiring.
With these fact at hand, we can now study the echo. An echo is a reflection of sound energy from a surface that is larger than ¼ the wave length and having a signal path that is 140 feet or further. Therefore a wall that is 70 feet away from where the sound starts can produce an echo. At this distance, the echo may return soon enough that it doesn't interfere with the program. As you get further away, the echo becomes more apparent.
HOW DOES A FOYER SPEAKER CREATE ECHO'S.
Most churches have foyer's at the back of the church. The foyer will have either doors or a direct path into the worship area of the church. It is common to have speakers on a volume control to allow people to know when to enter the worship area and they often work as overflow speakers when the sanctuary is packed.
When standing near the foyer speakers, the foyer speakers will get the sound first to the foyer. The sound from the main sanctuary speaker system has to travel though the air which is a slower medium for sound transmission. As a result, people sitting near the back of the church who can hear both the foyer speakers and the live sound at the same time will hear an echo.
There are several solutions.
1. IF your foyer has doors, keep them closed at all times. Oh! You don't like that idea?
2. Turn the volume lower. Oh! You don't like that idea either???
3. Add a digital delay to the distributed sound system signal and set the delay for one millisecond for each foot from the speaker cluster system to the first foyer speaker and add about 7 to 15 millisecond to give the foyer section the impression that the sound is coming only from the sanctuary. (This is usually referred to as the HASS Effect.)
Option 3 is the only real solution to the problem. If you have already an under balcony system on a proper delay setup, you should use another delay circuit just for the foyer system. TOA and a few other manufacturers offer delay systems that have one signal line in and three delays outs.
Church Sound System Delay Rules
As stated in another article, there are rules to church sound that are based on mathematical equation. Although many people know the math, they don't always know how it applies or it is applied wrong.
As a sound system rule, it would be better to say that a delay circuit is needed for every 20 feet of distributed sound from the original sound source. Therefore, if your church had a large foyer and you had four rows of speakers that were 10 feet apart then there should be two delays. This unfortunately drives up the cost of church sound since a separate amplifier is needed for each delay circuit.
By Joe The Soundman
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Most recent revision Monday, February 19, 1996