Posted by Duke on May 02, 2004 at 22:08:27:
In Reply to: Acoustic absorption panels behind Soundlab ? posted by Kenny on May 02, 2004 at 11:14:01:
Your speakers will work with that 3-foot spacing. One of the questions to consider is whether diffusion or absorption of the backwave makes the most sense. Of course there's no substitute for a little trial and error, but a little rambling here probably won't hurt.
I recommend treating the backwave if your speakers are less than 5 or 6 feet from the wall, as they are in your situation. The reason is this: you don't want a strong, coherent reflection off that back wall because that will degrade the depth of image. Instead, you want to either diffuse or absorb the energy that would otherwise be reflected.
Note that when you place a dipole close to the backwall, the bass is actually decreased because it's the out-of-phase backwave that's getting the boundary reinforcement. The reason I mention this is that if you want to restore the normal, out-in-the-room tonal balance, then absoprtion of the backwave might make the most sense (since the absportive material will be most effective in the midrange and highs, which will help balance out the somewhat decreased bass).
On the other hand, if your room is already well damped, then additional sound absorptive material behind the speakers can suuck [monitoring program objects to correct spelling] the life out of the sound. So in many rooms diffusion gives the best results.
In either case, it's a good idea to play around with the location of the sound treatment. For example, a Sallie placed right behind each speaker at the focal point is extremely effective, but might be too much - you can move them back or off to the side to reduce their net effect. Just be sure you're still intercepting that first reflection energy that would be bouncing off the rear wall behind both speakers and thence straight at the listening position, in a more or less W-shaped pattern.
You can probably experiment a bit using items on hand (blankets draped over chairs to simulate Sallies, for example) to see which direction you want to go in - diffusion or absorption.
The best imaging I ever heard from a pair of Sound Labs was a pair that Roger West set up in a living room adjacent to the old factory in Park City. The U-1's they had were only about 3 feet out from the walls, with Sallies right smack behind them. There were no other treatments in that otherwise slightly bright-sounding room, so the Sallies were killing two birds with one stone. The soundstage extended well beyond the walls, like what you get with a really good pair of mini-monitor. I use fake ficus trees in my room because with absorbent treatments the sound is overdamped, but I still don't get imaging like Roger did in his room (but then, I don't have U-1's either).
Best of luck to you!
Duke