Flat Bass Trap for stairway?

Tweakers' Asylum

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I have treated my basement listening room with a couple Jumbo JR cylindrical traps in the corners, with great improvement in the sound. The layout of the room doesn't permit doing all 4 corners. I then noticed that there was a single resonant peak left which corresponded to the length of the room. There is a clear (of furniture) path about 4 feet wide running from my subwoofer on the front wall, across 20+ feet to the back wall. I built an original design trap to sit on the back wall opposite from the sub. It's essentially a box 2 feet high and wide and 14 inches deep, open on the front. It's the bottom half of a home built bookcase. I fixed 3 layers of semi-rigid fiberglass (ceiling panels) into the open front. This seems to work well to dampen the previously audible resonance, and with a layer of attractive fabric over the panels, it has a high WAF.
Now I've noticed one remaining resonance which is not really in the room, but rather in the stairs that lead down into the room. The sub is almost at the foot of the stairs. The only other place I could put it would be in a corner, and I expect that would cause more resonance problems. The resonance in the stairway causes a boom that is rather annoying on the next floor up, although it's less prominent in the listening room. I think this could be eliminated by a trap at the top of the stairs. There's a 3 foot square landing, and a right angle turn to the doorway. This leaves the wall at the top of the stairs (3 feet wide x 8 feet high) open for an absorber of some sort. Clearly there's not at lot of depth to play with. A standing panel absorber of the sort JR describes would intrude too much on the landing, especially if spaced from the wall to optimize low frequency absorbtion. I've been thinking of building another box style absorber that's actually flat against the wall. I'm considering building it 3x8 feet to cover essentially all of the available wall, and 4 inches deep. Plywood back, probably with a carpet pad between the box & wall to prevent buzzing and reduce transmission to the wall, and 1x4 sides. Then an inner 2x2 around the perimeter. This would create a 2 inch step all the way around. I then could glue 2 layer of fiberglass ceiling tile on top of this step to form the front of the box. I'll cut down 2x4 foot tiles to 3 feet, then duct tape 4 of them together edge to edge to create a 3x8 sheet with no leak. Two layers like this gives 2 inches of fiberglass over a 2 inch air space.
Questions for any and all before I go through with this-
Am I right to leave an enclosed air space behind the panel for "capacitance?" Or should I fill it up with soft fiberglass batting, of which I have plenty? Should the air space be deeper? I could manage 4 inches, for a total depth of 6, but it'll start getting awkward. Or am I really wasting time and effort trying to soak up about 60 Hz sound in a space this shallow, even if the panel covers the whole wall?

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The Cable Cooker

Topic - Flat Bass Trap for stairway? - GCNewsom 22:38:16 01/01/05 (2)

Re: Flat Bass Trap for stairway? - Jon Risch 20:48:51 01/04/05 (1)

Unconcious influence? - GCNewsom 20:36:45 01/05/05 (0)

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