How To Create an Echo with Foyer Speakers
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 or Narthex 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 as well as from the clouds down. It also goes side to side. 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 this is about 5% for the first 20 degrees.
Sound travels almost at the speed of light when transmitted through electrical wiring.
With these fact at hand, we can now study the echo problem. 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 or Narthex 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 two sounds. The sound from the foyer speaker first and the live sound second.
When your in the foyer and the doors are open, you hear both sounds as well, however, the delayed live sound will smear the amplified sound. The live sound will interfere with the amplified foyer speakers and reduce the volume 3 to 6dB. The tendance in the raise the volume of the foyer speakers and this creates a bigger echo problem in the sancutary.
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 about 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.
Update 2009; Newer digital processor and digital delays can give you the distance in feet from the main central speaker system to the first speaker and convert the distance from feet into time. So you don't have to do any conversion. However, you will need to know your trigonometry. You can't just get a tape measure on the ground and measure the distance. You have to include the height too.
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 or it isn't even applied in the first place.
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. This unfortunately drives up the cost of church sound since a separate amplifier is needed for each delay circuit.
For under a balcony this rule has to be adjusted for ceiling height. The lower the ceiling, the more rows of speakers needed and the more speakers are needed on each row.
By Joseph De Buglio
Some statements and Specs have been left out under the understanding that it is part of the "intellectual Knowledge" guidelines and is exclusive to the author.
Back to THE LEARNING CENTER
JdB Sound Acoustics
63 Lockerbie Avenue, Toronto, Ontario Canada M9N 3A3
For questions or comments, our e-mail address is - firstname.lastname@example.org
Copyright (c) 1996 JdB Sound, Acoustic
Copyright © 1995-2011 JdB Sound Acoustics & Joseph De Buglio