sealing gaps/bass traps?

[creeping justin]

question for yinz.

my band has studio in the basement of a commercial building. it consists of a fairly large area where we practice, a tracking room, a control room and an iso booth. basically, it was one large concrete and stone room and someone before us built four small, connected rooms using sheet rock and steel studs. we have since torn down the wall between two of the rooms to create a roughly 20"x12" tracking room.

so, the tracking room is actually acoustically decent (at least to my ears)... i think because of the weirdness of it. half of it is carpeted, half has hardwood flooring. half of it has a 9" ceiling and the other half is 7". also, one wall is stone, one wall is covered in what looks like indoor/outdoor carpet and the rest are drywall.

while the room sounds decent, it definitely could use some help. so, this morning I picked up two cases of 2" Johns Manville 817 (sames as OC 705). my plan is to use it to make floor to ceiling bass traps in three of the corners (one corner is the door to the control room - so no room for a bass trap). the rest of the 817 will be used for wall panels.

wow, this post is getting long for a simple question. Here it goes... in one corner where the sheet rock meet the stone, there is a gap in wall that leads into to practice room. it's due to the fact that stone juts out randomly, so the two walls can't be flush. the gap varies in width from about 1/4" to 1". before I mount the fiberglass in this corner, does it make sense to seal the gap with that spray sealant for windows/door (it's sold at Home Depot and dries flexible)? I don't have any real need to keep sound out of the practice room, just didn't know if there would be some reason why this gap would impact the tracking room sound in someway either positive or negative.

anyone have any thoughts on this?
also, do you think it makes sense to mount some wall panels on the one stone wall? I like to think of it as a big diffusor because of the variations in the stone, but maybe it should get some trapping? just want to get your thoughts before I attempt to drill into it.

thanks!

[Phiz]

The only reason to fill the gap is if you care about bleed between the rooms. Leaving the gap there will let a (tiny) bit of low frequency energy out of the room and should help dampen your room modes a very small amount.

[JWL]

I agree, if you don't care about bleed there's not much reason to seal it up.

However, if there is a gap, then this corner may not be a "corner" in terms of acoustics. Bass tends to collect in corners, so if sound energy can get through the gap it may not behave in this way. There's a simple test though; put something on the speakers with some slamming bass and walk around the room. Go in the corner and see if you notice a bass boost. If so, it's a good spot for a bass trap. If you don't notice such a boost, I'd put the 3rd corner bass trap somewhere else, most likely in one of the wall/ceiling corners.

Good luck!

[creeping justin]

interesting. thanks!

i actually haven't noticed if bass builds up in that corner... definitely does in the others. I hadn't considered hanging the panels as wall/ceiling traps. I guess the main reason is I have a drop ceiling in that room. so, the ceiling isn't a "true" ceiling. i was thinking about laying some thick fiberglass (R38) above the ceiling tiles based on info I got from Ethan Winer's site. although I was also thinking about removing part of the drop ceiling. I could get about 3'-4' extra feet of height, but expose a lot of pipes, etc. that would probably resonate pretty badly. They kinda do already...

[JWL]

Yeah, putting thick fluffy insulation above the ceiling tiles should definitely help with bass absorption. Another option might be Ultratouch cotton insulation batts; these are 2'x8' batts, 5.5" thick, that you could put up there. I mention this in the event that you leave, it'd be a lot easier to pull these back down and take them with you to your new space. TONS easier to work with than fiberglass. You could stack as many as you want above you in that space....

Depending on what you have for ceiling tiles, specifically on how reflective they are of high frequencies, you may want to remove some of them in strategic spots and replace them with cloth, so that those spots absorb at all frequencies. Above the mix position, and above where you set up the drum kit are good candidates for this kind of treatment. If your ceiling panels are absorptive, then you're already all set, and this would be unnecessary.