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In Reply to: RE: Combined Bass Traps on Ceiling? posted by Ferrstein on January 18, 2009 at 16:56:54
Ethan can help you more on the testing front than I can. I've got no measurement software and the RS meter doesn't cut it.
Basic recommendations:
Bass traps will help in almost any room. Placement at corners is best and going floor to ceiling if you can, or from one end of the room to the other if you're doing them along the ceiling. It's hard to do too much bass trapping, especially in corners.
If you want an expansive sound then some diffusion on the front wall between the speakers and absorption on the back wall seems to be the recommendation from Rives.
If you're interested more in soundstage and imaging, then absorption on the front wall at the first reflection points and either absorption or diffusion on the rear walls at the first reflection points.
Absorption at the side wall first reflection points tends to control the width of the soundstage and add a little to the precision of the imaging. Floyd Toole recommends leaving these points untreated but says that some people, especially musicians, are sensitive to these reflections. In my room I treat them. The soundstage isn't quite as wide but it is more precise and the imaging is definitely more precise in my room.
First reflection points on the ceiling: I can't comment personally on this one because I've never tried attaching anything to my ceiling apart from some thin foam tiles which kept falling down and didn't seem to do much anyway, but then thin foam won't do much anyway.
Some people argue for diffusion over absorption at first reflection points. The closer you are to a diffuser, the less effective it will be. Diffusion takes distance and space in which to develop and first reflection points tend to be relatively close to you unless you've got a sizeable room. With the exception on diffusion on the back wall I'd tend to side with absorption at first reflection points unless you're going with the Rives style approach of a live end of the room in front of you, in which case I think you should use absorption rather than diffusion on the back wall. In general if you want to add diffusion I'd tend to place it towards the rear of the room and further away from you than the first reflection points on whichever surface you place them on.
You want carpeting on the floor between you and the speakers, and drapes covering windows if you have a lot of window area and you find the sound getting bright. If you've got windows at first reflection points, I'd definitely recommend curtains, especially if it's on a side wall and you're thinking of leaving the first reflection points untreated.
Some people talk about deadening the room too much and turning it into an anechoic chamber. You couldn't turn a room into an anechoic chamber without covering all of each room surface with very thick, very effective absorption. The approaches I outlined above leave most of the room's reflective surfaces untreated and you're not going to get anywhere near an anechoic chamber with that sort of treatment approach. Still, some people like much liver rooms than others and I have no doubt some people would object to even the basic treatment approach I've outlined. Individual tastes do vary. Some people would like the room even more absorbent than the approaches outlined above.
One thing is important, however. If you're going to use absorption apart from bass traps in corners, make that absorption as broad band as possible. It seems many people have a tendency to use relatively thin absorption which is only effective at high frequencies so what that does is to dramatically alter the tonal character of the reflected sound, absorbing the highs and making it sound dull. The reflected sound contributes a lot to what you hear and that will end up making things sound dull or dead but the problem isn't too much absorption, it's the use of narrow band absorption. If you use broad band absorption the tonal character of the reflected sound isn't changed very much, only the level of the reflected sound from that area is reduced. That's what you want to achieve—a reduction in level with minimal change in tonal character.
David Aiken
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