Flanking around soundwall in basement

[motmclergy]

Another question...

I'll try to describe this as best I can, as I don't have a spiffy drawing program with which to attach a nice diagram.

I'm building a studio in my basement. The basement is a rectangle, and I'm using half of it for the studio - so I have a double stud wall down the center lengthwise. (the studio dimensions are roughly 11' x 35', and the sound wall is the 35' one) This wall is perpendicular to the joists, so above the top plate there is about 12" of space. I.e., the joists are about 12" deep, and the subfloor is on top of them and the top plate of my wall is underneath. What would you recommend I do to seal out these squares of space? The ceiling of the studio room will be drywalled - screwed to the joists probly. I will insulate between the joists above the ceiling too. The other side (the non-studio part of the basment) will remain unfinished for the present (open joists).

I don't want to waste a double stud wall that i'm hoping to get high STC with, by having bad flanking via the ceiling. I've thought of putting some 1x2" framing in these squares and drywalling both sides - maybe double sheating both sides - but I wonder if this is good enough - and frankly it looks like a lot of painstaking work as each opening varies slightly in size. Also, I'm concerned about the joists transmitting sound even if i do seal up the openings. As far as transmission to the rest of the house, i fear my basement ceiling may be my limiting factor - just don't know how bad it is. ( I will have only one door - double doors actually) I read a thread here about basement ceiling TL that suggested a search - which i did using several different keywords and couldn't find anything directly addressing this.

Thanks again,
Larry

[Aaronw]

Larry,

Click here to download a free trial of the Smart Draw program that everyone here uses... http://www.smartdraw.com/

For the ceiling joist flanking, you can use RC. For an example, click here: http://www.johnlsayers.com/phpBB2/viewt ... &start=258

[knightfly]

Larry, do you need isolation between studio and the other half of the basement, or just to the upstairs? Is the upstairs subfloor visible between the joists from downstairs, or is it already insulated?

Without knowing, I made some assumptions for the sake of discussion - if your subfloor is 3/4 plywood, your joists are 2x8, and you fill the cavities with insulation and add two layers of 5/8" gypsum, the approximate STC withOUT using Resilient channel would be around STC 45, with the TL at 50 hZ running somewhere around 23 dB - adding RC to this would raise STC to around 58, but the low end would only improve by maybe 1 dB, if that. For more isolation at low end, you would need either more mass in either leaf (subfloor, or extra layers of gypsum), or a wider air gap. IF space is tight for ceiling height, you can get maybe 3-4 dB more by adding an additional layer of 5/8 gypsum in between each pair of ceiing joists, gluing and caulking at ONLY the edges, and THEN filling with insulation and doing the RC and double gypsum. This would impact head height by about 1-3/4" total as compared to the raw joists.

Here's a dwg of the basic idea, not showing the insulation -

http://www.johnlsayers.com/phpBB2/viewt ... =7948#7948

It's the last dwg on that page - what is labeled "outer ceiling leaf" would be your subfloor. Note the resilient channel isolates the wallboard from frame in each case, minimising flanking noise through the frame and into the rest of the house - packing the cavities with fiberglass insulation improves isolation by several dB... Steve

[motmclergy]

Thanks for the help. Here's some answers:

- i don't need isolation between the studio and the rest of the basement per se, but the rest of the basement is in no way isoloated from the rest of the house - so i assume any sound that gets into it, will get into the upstairs pretty easily. and it's the upstairs (and the outside/neighbors) that i really want isolation from.

- the ceiling of the studio area is not now insulated - yes i can see the subfloor from below - and it is not plywood; it's diagonal tongue and groove (loosely arranged) boards, with oak hardwood flooring on top; and the joists are nominal 10" i think (9 and 1/4 actually - i was wrong when i said they were 12")

One important note: this is a total "budget studio" construction project. $$$ is by far my limiting factor in the design (as it is for most if not all of the people here, but my limit is looooow ). i have no illusions about building a super-quality room for next to nothing, but i want to make the most of what i have.

Ok, now some follow-up questions:

- from the helpful posts so far, it seems that if the ceiling is decoupled from the wall framing (and the joists too i guess), then flanking around the wall won't be a problem. and the way to do that is with resiliant channel. BUT; i'll only get a db or so TL improvement on the low end - where it's hardest to get, from what i understand. sooo, considering i'm on a peanut budget, how terrible would it be if i didn't use RC on the ceiling? it sounds like if i use lots of insulation, and as much mass as i can get up there, i might be able to get away without RC. this is all assuming RC is expensive - i haven't looked it up recently but i did once and remember it being a lot more expensive per area than an extra layer of drywall.

- are recessed lights in this basement studio ceiling totally out of question? i was going to use track lighting but have two big reasons not to: 1. my ceiling is 78 to 81" to the joists before any drywall or flooring; track lights hang down at least a few inches - i'm only 5'8", but i think i might be pushing it 2. $$$ recessed lighting costs about 1/4 as much as equivalent track lighting, maybe less. the concern of course is puncturing the ceiling - the tracks run on the ceiling surface (except for one small junction box connection). the recessed cans are 6" in diameter, and i would need at least 4 of them. i thought of framing heavy boxes around them in the joist spaces and filling them in with plywood/drywall layers - 5 or 6 layers if needed - does this sound feasible?

Finally- thanks for the link to the drawing program. alas, i am one of those Mac-using music guys and it is a windows program.

Thanks again-
ld

[knightfly]

Here's some other possibilities for drawing pgms for mac -

http://www.download.com/3150-2187-0.html?tag=stbc.gp

http://www.download.com/3000-2187-63952 ... egacy=cnet

It's starting to sound like one thing you could do for your ceiling is buy a 5 gallon pail of gypsum "mud" and a 6" taping knife, and "butter" the entire underside of your subfloor to fill those cracks - then you could screw on a layer of sheet rock under the subfloor, up between the joists - caulk and cleat this layer, fill with fiberglass insulation, and add two layers of 5/8" sheet rock on the joists, preferably mounted on resilient channel. That should handle the ceiling reasonably well - as to your questions of effectiveness - this construction WITHOUT the RC, should run around 28 dB TL @ 50 hZ, with an STC of around 48 - adding the RC with no other changes, improves the bottom by a dB or so, but brings overall STC up to closer to 60 dB.

Resilient Channel from drywall/insulation supplies in my local area, was around $2.20 per 12 foot length a few months ago - with steel prices going insane, it could be easily twice that or more (haven't priced it lately)

Considering that the human ear requires about 54 dB SPL to hear really low frequencies, like around 50 hZ, this means that another 30 dB of isolation lets you mix with bass up around 85 dB, and be nearly inaudible. Not so with live bass or drums, these are more like 110-120 dB.

Keep in mind that the ENTIRE studio would need to be as effectively sound proofed before it would REALLY be this quiet.

What is the layout going from downstairs to the living space? hallways, stairs, open or closed stairwells, doors, etc - we need to know what other things will keep you from getting a quiet space... Steve