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Originally Posted by Ethan Winer Steve,
> if you have an inch or two of gap behind the fiberglass built INTO the frame, you only have to have the trap another two inches off the wall via spacers <
I think you're missing Glenn's point about mid and high frequency absorption. Most panels based on rigid fiberglass can absorb through the rear surface as well as the front. But in order for sound to get to the rear the edges must not be blocked. That is, more total sound is absorbed with a panel spaced 4 inches off the wall, when compared to a panel having sides 2 inches deeper than the panel thickness and spaced 2 inches.
I also agree with Glenn that it's not possible to have too much absorption at bass frequencies. No matter how many bass traps you have, the room will still not be flat and there will still be low frequency ringing. So the best you can aim for is as much bass trapping as possible, then you accept the results. I do agree with you about listening, but more to "tune" the appropriate amount of mid/high frequency absorption.
--Ethan |
I think you are missing my point. Given there is already space behind the fiberglass, you can put it two inches off the wall and air CAN and WILL get to the fiberglass because there is nothing blocking the back of the traps. It is more aesthetically pleasing to me to have a trap 2 inches off the wall rather then 4 inches, especially if the traps are doing equal absorption.
Now about too much bass absorption, it is very real and I've heard it and measured it in more then a few rooms. A few calls to some of the top guys in LA and you'll hear them say the same thing and they are very right. You have to be very careful when piling in the absorption to carefully monitor the 100 to 300Hz area. Sometimes you're sucking too much out of this area. It really all depends, but simply throwing in a zillion fiberglass or mineral wool bass traps all over the place does not insure a flat room and not just because the dampening of the high end. Its very difficult to get an even ratio of absorption at say 80Hz and absorption at 250Hz, especially in room not built to be a studio room. Depending on many factors, its easier to suck out a lot of 250Hz and not as much 80Hz. Hence the reason why tuned absorbers are such a presence in high end studios.
Case in point, a room Teale just did had a huge 80Hz resonance due to its room dimensions. The owner of the room had made his own OC 705 traps, piling them up in each corner and stuffing behind them with more OC 703 pieces. The 80Hz resonance was down a bit, but it sucked the hell out of 200Hz a lot MORE. So we tuned a trap to 80Hz to relieve that peak FIRST, then proceeded to appropriately bass trap the rest of the room resulting in a beautiful sounding space.