Many times we are asked to look at a Church and figure out what is wrong with a perfectly good sound system. Most times the problem is the acoustics in the room. If you took your sound system outside and ran everything flat it would probably sound great. So throwing more money at Speakers, Amps & DSP may not be the fix.
Acoustics in the room can cause a few audible issues which we will cover today.
Standing Waves
A standing wave is the result of a sound wave that bounces between two or more surfaces and emphasizes one specific frequency that you hear as the waves reinforce each other.
When the wave bounces off the surface, it cha
nges phase. In the case of waves that create a standing wave, the reflected wave is a mirror image of the original. The waves then combine.
If the amplitudes of the two waves have the same sign (both positive / both negative), they will add together to form a wave with a larger amplitude. This adding together is called constructive interference. This added wave doesn't appear to move, thus it's called a standing wave. Standing waves are usually low frequency waves below 300 Hz. Above 300hz, the waves tend not to reflect directly back and the sound is greatly influenced
by the objects in t
he room and the composite of the room's walls, floor, and ceiling.
Here's a chart to give you an idea of the size of wavelengths based on the frequency. As you can see, the lower the frequency, the larger the wavelength such as a 20 foot distance from crest to crest.
What Causes Standing Waves?
Standing waves are created when the distance between the walls is a multiple of a sound's wavelength.
Walls that are 20 feet apart, with a wavelength that is 19 feet long, won't produce the conditions for the wave reinforcement. However, if the walls are 20 feet apart and the wavelength is 10 feet or 20 feet, then a standing wave will be produced because of the reinforcement.
Standing waves can be caused when waves bounce between;
- Opposite walls
- Four sides of the room
- All six sides of the room (given most rooms have four walls, a floor, and a ceiling!)
This image shows the blue and red waves moving back and forth with the resulting black standing wave being produced.
Echo - Reverb
A Echo is a single reflection of a sound source. If so many reflections arrive at a listener that they are unable to distinguish between them, the proper term is reverberation. When dealing with audible frequencies, the human ear cannot distinguish an echo from the original sound if the delay is less than 1/10 of a second.
When your dealing with your congregation, not distinguishing the message could be the difference in changing someones life.
Comb Filtering
Simply stated, comb filtering is two signals arriving at the same location at different times. Because of the differences in the arrival times, the sound waves will have additions when they perfectly overlap and reinforce each other, and also have cancellations or nulls where they cancel each other out (the latter is called destructive interference). This occurs in virtually all Speaker Systems whose musical ranges overlap, where both drivers are reproducing the same sounds, as in stereo or surround sound, and because of multiple drivers with different physical locations used to cover the same frequency range.
How do we fix our room and make the sound better?
You can fix your room with an assortment of sound absorption & deflection panels, padded seats, carpet, and the proper sound system. Try to stay away from too many hard surfaces, square walls if your building.
Grace United Methodist fixed their sound issues by simply adding sound absorption panels.
For more help you can call our office at 239-458-3408 or email info@creativesoundsolution.com
Tony
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