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In Reply to: RE: David Aiken posted by Jolida on June 28, 2009 at 23:34:58
Room modes are mostly caused by sound reflecting and resonating between 2 opposite surfaces like the front and back walls, left and right walls, and floor and ceiling. They are at their strongest wherever 2 surfaces intersect which is why it's recommended that you put bass trapping in the corners of the room—that's where the walls intersect and by treating the corner from floor to ceiling you also treat the places where 3 surfaces intersect, the 2 walls and either the floor or the ceiling.
800 Hz is probably too high to be a room mode. Room modes are usually only a problem up to 300 or 400 Hz or so and if you've got a 7 dB room mode at 800 Hz then I'd expect there to be stronger resonances at other frequencies such as 400, 200, 100, 50 and 25 Hz which are in octave relationships to 800 Hz.
Another reason why I doubt it's a room mode is because the wavelength of an 800 Hz tone is only 1.4', around 17", which is far too small to be a normal room dimension. If you've got 2 parallel surfaces that far apart—say a cupboard that far from a wall—you may be triggering a resonance between them, especially if one of the surfaces is prone to vibration, in which case moving one of the surfaces should solve the problem but you won't have 2 actual room surfaces that far apart. You may have a cupboard that deep or wide in which case either sealing it so sound can't get in, leaving it open, or filling it with some kind of absorbent material like cushions or clothes, may solve the problem.
Alternatively the cause could be some object in the room which resonates at 800 Hz. If you can find an 800 Hz test tone you can try walking the room and listening for the point where the sound is loudest and see what objects are there and removing them from the room one at a time. The resonance should disappear when the object causing it is removed. Once you know what it is you may be able to find some way to damp its resonance and return it to the room if you want it there, otherwise simply place it somewhere else in the house.
On the other hand it could be a fault somewhere in your system. If you have a portable music system of some sort, I'd put that in your room and try playing your test signal on it. If you still get the problem when the tone is being played on a completely different system and speakers then it's something in the room. If the problem goes away then it's something in your system.
David Aiken
I cant thank u enough. You have always been of great help to all of us. I will surely follow your procedure tonoght when i return home & post a follow-up. So u mean i must play the offending tone on 'repeat' & walk around the room to see where it is the loudest?
Thaks a million for the time you take to help us..
God Bless
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