John Sayers' Recording Studio Design Forum Archive

Here's a short, but possibly complex question. "Is there anything to gain by building walls to a greater STC than the weakest wall/link in your room?"

More specifically for my case:

In my situation, I'm building a 1 room (plus amp closet) studio/rehearsal space in the basement of my freehold house. I'd like build to a reasonable STC between the studio room, and the bedrooms two stories up (wood framed typical residential construction on main and 2nd floor, concrete foundation walls).

I figure that the ceiling of my room will be the primary transmission path as it is the largest shared surface. Since I'm not independantly wealthy, and don't have too much ceiling height to spare (8'10") I'm likely looking at a RC + insulation + double drywall type of construction for the ceiling. I don't have the numbers in front of me, but lets say that the STC of this ceiling construction is 49. Now, for the design of my walls is there really any point in using a type of construction that has a higher STC than 49?

Double wall construction is possible and offers higher STC's, but if my ceiling is only STC 49, what difference does this really make to people on the main and second floor? I suppose that the total sound on the main and second floor will be the sum of the sound leaking from around the walls and up the stairs plus that which gets through the ceiling (plus again the stuff that gets transmitted through the structure and HVAC). Is it a big difference?

So, in a nutshell, once you've decided on the weakest link in your construction, how do you tailor the other walls so as not to waste too much time/money/effort on dimenshing returns?

Thanks,

Kris

Forget STC. The TL at low frequencies is the most important thing for music, especially going up two floors!

Figure out how much isolation you want, and look at flanking paths also. Flanking paths are hallways with thin doors, stairwells, heating ducts etc.

Good luck!
Andre

{edit}put it into english.

Okay, same question then, but with low frequency TL in mind. Assuming my joists can support the dead load, my construction will be:

1. 3/4" Hardwood
2. 1/2" subfloor
3. 1/2" drywall run between joists
4. 9.5" Joist filled with insulation to a depth of 6"
5. RC
6. 5/8" drywall
7. 1/2" drywall

In places though, due to the HVAC there will be no insulation. I guess I need to determine the TL at around say 80 Hz and match my wall construction to what I can expect from this ceiling arrangement. Doors shouldn't be a problem as I will make double studio doors (that is if I can't get my hands on a couple surplus Overly doors).

Cheers,

Kris

1. 3/4" Hardwood
2. 1/2" subfloor
3. 1/2" drywall run between joists
4. 9.5" Joist filled with insulation to a depth of 6"
5. RC
6. 5/8" drywall
7. 1/2" drywall

Kris, what's your longest un-supported span on those joists, what is their exact thickness, and (if possible) what species of wood are they? Given those, I can tell you whether you're OK on loading.

Also, if you're after LF TL (and you probably should be) I would use 5/8 drywall in both places.

Yes, your HVAC will weaken things where the ducts are; can't be helped in most cases. All you can do is make sure you don't FURTHER weaken isolation by using short, straight runs or drops to more than one room from the same trunk line... Steve

Thanks for the response,

My basement has joists on approximately 20" centers for span of 12 feet across two metal I-beams. There is a longer section where the beams span about 16 feet but they are on 12" centers there. The joists themselves are of the engineered variety. They look like little wooden I beams, with top and bottom plates of solid wood, and a vertical run of chip-board. They are about 9" tall. The josits are 1.5" wide (at the top and bottom flange, each of which have a depth of about 2.5 ")..

I hope it can take the load, as I'd really like to make it work.

Cheers,

Kris

Engineered joists have their own separate span specs, which are generally better than standard wood joists; and 2x10 standard joists would have a span of at least 14 feet placed on 19.2" centers, even for a load rating of 60 psf live/20 psf dead load.

The total weight of what you propose would result in a dead load of about 17-18 PSF, so 20 dead load is fine; and, as I said the "trusjoist" type materials normally exceed regular framing members... Steve

BTW, you're still good for 20 dead load on the 12" centers, for up to 16'8" using standard 2x10's (select grade) - with engineered joists that's probably another foot or two...