I am looking to add simple, low cost DIY bass trapping in my basement home theater. I've been reading up on bass traps and watching Ethan's excellent YouTube videos. One thing I've seen time and again is that sound aborbing material is much more effective at bass trapping if it is positioned some distance from the corner boundaries. I realize the unused space behind a false screen wall is the perfect place to "load up" on bass trapping at a low cost because you don't need to make it look good and there is lots of room. I have put no acoustic treatments at all behind my screen wall. I have 8' of vertical height and about 2' of depth.

I have two ideas about how to use this space. (screen wall above and below screen is framed and covered in GOM)
1) Stack bags of fluffy fiberglass from floor to ceiling in both corners
2) Stuff R19 or thicker fiberglass batts between the framing above and below the screen wall. This would be a ceiling/wall and floor/wall boundary corner trap. My thinking is that instead of putting bass trap panels angled against the ceiling/wall or floor/wall corner that would have about a 16" max triangular shaped airgap, placement here would be like standing a small 6'x2'x6" bass trap 24" away from a wall.

What do this forum's members think about these two ideas, especially about the second one ? Did I come up with some sound(pun intended) conclusions from info posted here and elsewhere on the web ? If the second idea is a good one, I have two little detail questions about it:
1) Do I use faced (to make it a thin membrame trap) or unfaced fluffy fiberglass
2) If I use unfaced (this would add some mid and high freq absorption), will the fiberglass come through the GOM ? Should I fix that by placing some polyester batting between the fiberglass and the GOM fabric ?

This would just a starting place. I realize more should be done - some aborption panels at the 1st reflection points on the ceiling, side walls, and rear wall. Perhaps I could even convert my existing soffits, which are stuffed with blow-in cellulose insulation and covered with 5/8" sheetrock, into a bass trap by cutting vent holes into it, a la DE's seat riser bass trap plans.

Thanks much,
Bill

I am interested as well as to what people think, so I am bumping this this thread.

From most theaters that I have seen on here they generally line the back wall behind the AT screen and in the corners they cut the insulation at a 45 degree angle and stack it to the ceiling. Faced or unfaced doesn't matter. That's about all my knowledge on your questions at the moment :)

Thanks Vili. Yes, I've seen many pictures where the walls behind the proscenium were lined with absorbent material. I was getting my idea to place the absorbent material on the backside of the proscenium from the tables on Bobgold's site. For fluffy pink R19 fiberglass positioned 16" away from the wall, the absorption coefficients are nearly > 0.90 at all frequencies. There is generally 16" to 24" between the solid front wall and the proscenium wall, so I figure the same depth of fiberglass placed on the proscenium wall will be more effective at absorbing or trapping bass frequencies than if placed/mounted directly to the solid wall. (greater velocity here than against the solid wall)

Bill

From most theaters that I have seen on here they generally line the back wall behind the AT screen and in the corners they cut the insulation at a 45 degree angle and stack it to the ceiling. Faced or unfaced doesn't matter. That's about all my knowledge on your questions at the moment :)

That doesn't mean its the right thing to do though :) Isn't it more dependent on the room size/shape? What might work for one room might not work for yours and visa versa. I was always under the impression that just treating a room without testing it first could be as bad as not treating it at all.

I would be interested to see if it is a good way to go though as I'll be looking at the same thing (DIY treatments) in a few months and don't want to get it wrong.

storman, I came to the same conclusions as you, the dead space behind a false front wall is a good spot for bass traps. In my case, I took my left-over linacustic roll, cut in in half and put the two resulting cylinders in the front corners behind the wall. This tightened up the bass. I don't have a RTA so I can't say what the real results were, but it sounds better to me :) I do agree to some degree with masterleet - without measuring devices, you are kind of winging it, so what trap design will work best is just a guessing game. The other side of that, is that insulation is cheap and very easy to do because looks are not an issue - so do anything. However, if your room is untreated, I think I would concentrate on treating the room before I worried about bass traps. My 2 cents.

One of the experts on here claims that you can never have too much bass trapping. It's the midrange and above that you have to worry about over-doing. I used rolled up insulation, still in its packaging, for bass trapping behind my screen wall.

CJ

Thanks CJ. Yes, I've heard that and plan to stack rolls/bags of insulation in the two front corners. I have my center channel behind the proscenium wall, below the screen and tucked between two of the framing members. I plan to get some insulation around it so that it doesn't suffer from edge diffraction. This would be a loose adaption of the "baffle wall" I've heard about recently. THX is promoting this idea, that is when the LCR are positioned behind an AT screen, they should be flushmounted and surrounded by sound absorbing material.

OBTW, love your Dark Knight theater, especially as applied to your remote control device. :cool::cool:

Bill