Originally Posted by dgkula
I'm finally building my first small dedicated room as part of a post-pipe-burst basement remodel. The room is 12 x 14 with 7.5' ceilings. I need to orient the room with the projector/screen along the 12' length owing to requirements to have a door to a mechanical area. I will have 4 seats and a 92 inch screen (accommodating for another door on the front wall). Not ideal given the limited space and access requirements but I will be moving from a mixed use space with windows to a dedicated space with no windows and openings.
I have wired the room for 7.2.9 with in-walls for SL, SR, RL, RR and 4 Atmos speakers in the ceiling. My L/C/R/SW will be cabinets placed around the screen; I don't have room for a false wall and so am not doing an AT screen with false wall. I have a regular Elite fixed screen from my prior multi-use space. I plan to run dual subs to balance room modes. The walls are up and painted dark blue with a black solid ceiling (i.e. sheetrock not drop). The projector is ceiling mounted with 10.5' throw.
My question is about acoustic treatments. I have tried to read as much as possible but this thread is really hard to get through. Here are my questions:
1. Since I don't have an AT screen, is there any point in treating the front wall? Presently I am not planning to treat the front wall. Most posters do 1" linacoustic but that seems to go with AT screens.
2. For side walls I am torn between 1" linacoustic to 48" height versus four 3" 2 x 4 acoustic panels on each side wall (for a total of 8 panels). Cost is close - with the raw materials from Fabricmate coming in at $200 more than eight completed GIK 3" panels. Other than the aesthetics, is there any reason to go one way over the other? The panels are thicker and would provide 70% of the surface area coverage of the Linacoustic so I'm not sure what would be "better." I need to determine is aesthetics is the only basis for making this decision or if there is another factor to consider.
3. Should I do anything with the rear wall? Many threads discuss diffusion, but my seats are 1" from rear wall which seems too close for diffusion. Some threads talk about not treating the rear wall to have reflections to minimize localization of surrounds. I haven't come to a conclusion yet and would appreciate some guidance.
4. Since I will be running dual subs, is it fair to assume that with DSP/Audyssey will minimize the need for bass trapping?
Thanks very much! Should be up and running in the next 90 days and I will post pics?
1) It is good to treat the front wall for SBIR. However 1" won't have any impact on that. The 1" is used because Dennis Erksine has been suggesting two layers of it with a plastic layer in-between. He does this because he finds 2" tends to over-absorb in the 200-500hz range (if I recall his old post on this). I've found he is right and have a measurement of my sparsely treated room that is consistent with his finding, too much absorption in that range. This recommendation is to absorb sound that radiates behind the speaker. as well as any sound that is reflecting off other surfaces onto that back wall and toward the listener. These are mostly later reflections but still bad.
2)1" is going to only absorb down to around 500hz or so. It won't provide a lot of absorption below that. In a later point you make a false assumption that leads to this. You want 4" panels here, not 1". You also don't need to treat the entire wall necessary and that decision should be dictated by your rooms RT60 response. Most small rooms that are nearly completely untreated still have RT60 values of like .3-.4ms, which is low enough that if you start covering all the surfaces with 1" absorption, would be too much. It would likely drop below .2. I would 2x4 panels, but you may consider two of these for a 4x4 area at 4" thick.
3) You should not use diffusion if you are sitting 1" from the rear wall. You want to make the wall disappear in this case, you want absorption and lots of it. you are so close to the rear wall you won't have room for thick, but I would still go with 2" on the entire area around your head, including the side walls there. It will make the room appear larger.
4) While it is true that multiple subs and Audyssey can reduce the problems, it is not true that you don't need bass traps. You can reduce the modal ringing somewhat by reducing the modal peaks, but you can't reduce the overall decay of the bass in the room. Most rooms have far too little LF absorption. You should think about bass traps on top of the rest of this. Also remember that 2 subs doesn't automatically equal improved LF response. You have to place them precisely. You can place them in the 1/4 points of the front wall, which is symmetric and possibly between your mains, but...while that might cancel the side to side modes, it might not and it very well may not do much good at your listening position. There is a power point floating around that talks about this, but my experience is the same, this isn't a great location. There really needs to be either two subs placed in very different parts of the room (front and back for example) or really, 3-4 at key points. I've also found that Geddes approach netted smoother bass than Welti's, that using non-symmetric locations seems to work better.
You don't mention this, but consider treating the ceiling. It helps make the ceiling appear to disappear too.