AVS Addicted Member
Join Date: Dec 2000
Location: Venice, Florida, USA
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Once again, I agree with Dennis. Every room is different and that is why, if one is going to do it right, you need the services of an expert acoustician, I am not one! I do know where to go to get one or more, though my favorite is Norman Varney (I am biased, he is an old friend, too).
No, we haven't solved anything, Ethan, Every HT room to be optimized requires some strong absorption. Very broadband. This is required on the front wall, the front corners, and on the side walls (to kill the reflections between the LCR speakers and the listeners). That is every listener should hear these three speakers only directly and not also bounced off both side walls. That is very very clear.
HOWEVER, and note well, the side wall absorption need not go deep into the bass region. The 3db down point of the front speakers should be sufficient for this absorption. Elsewhere along the sides we do not want much if any absorption above 1000 HZ or so. Below 1000 hz we indeed want broadband absorption. You can go as low as you want here but there are practical reasons as to how low you can go. There are limits as to how much absorption you have room for in wall or on wall.
To deal with very low bass absorption by side wall treatment is generally not praticable. Dedicated broad band bass absorbers (say from 300 cycles down (upper mid bass and below). We need to depressurize the bass waves so they do not inhibit the ability of the front speakers to work optimumly. High bass back pressure will really screw the midrange up. Fact. Most rooms will have a bass resonance peak, A flat broadband absorper will tame this but the peak will still be there because of the other bass frequencies attenuation. So measure where the peak is is, or you can easily calculate what it will be from the room dimensions, and then treat it if is severe. Nothing really wrong with broad band bass absorption but it is not the end all.
By no means do we want rhe rear wall to be highly absorptive. That would be a very big mistake. The room will sound overly dead, decay times will go to hell and a handbasket. We want the wall to sound like it is relatively far away but seill there, and not like the listener is in an open field or an anachoic chamber. Diffusion (and many diffusors will absorb as well) is what is called for.
And not that I waqt to give everything away, but on the rear wall my mild diffusion goes on the upper half of the wall and below that I generally treat with broadband diffusion (below 1000 HZ). No reason this broad band can't be as low as you want. The lower rear wall is generally hidden acoustically by the seats so you can make it as dead as you want, Hide you deep bass absorption there if you want. Just do not make the wall above halfway up absorptive. OK you can have some absorption but mostly diffusion