I noticed you'd been away for a while, and I'm glad to have you back. Hope all is well, my friend
Thanks for noticing! Yup, just got a lot going on right now...
but having a 2 leaf system doesn't seem practical in my situation in regards to the new walls.
Well you CAN go 4-leaf if you want, but the extra mass and large loss of space seem to be things that you could avoid. Higher expense, greater complexity, and a smaller room to show for it, doesn't make a lot of sense in my book. But I guess if you have a big enough budget, a long enough time, and lots of extra space to play with then that could be an option. Personally, I try to minimize expense and maximize space, but I do realize that not everyone is a perfectionist, like me.
Using the existing left and bottom walls of my existing garage would be a 2 leaf system. In order to improve isolation on those walls I propose using green glue and adding a layer of 5/8" drywall to increase TL.
The way I would improve the isolation of those walls is to take the drywall off! Not put more on. Take the drywall off to expose the studs, and if necessary use the stuff you took off to "beef up" the wall from within, between the studs. That's a very common method for improving isolation. That leaves you with a single.leaf wall. Then all you need to do is to put up your new framing about an inch away from that, and put drywall on only ONE side of that. Then you'd have a classic two-leaf wall: high isolation, low cost.
This should give me a STC of around 52
Forget STC. It is useless as a measure of isolation for a studio. STC does not take into account the bottom two and a half octaves of the musical scale, and it does not take into account the bottom two and a half octaves of the musical scale. It only takes into account a narrow section in the middle, which is basically the area where normal speech occurs. If you only plan to isolate talking voices, then by all means use STC, but if you need to isolate full-spectrum music, forget it. Just look at the full TL data. I can build you two walls, one rated at STC-50 that is really lousy at isolating rock music, and one rated at STC-40 that is much, much better at isolating rock music...
Adding green glue and a layer of 5/8" drywall to the ceiling and adding insulation would be a 2 leaf system as well, but I'm not clear on what kind of isolation I will achieve here given that the attic space is ventilated.
With a ventilated attic, normally the easiest thing to do is to just go with a 3-leaf ceiling. However, if the joists are already very low, and you have a decent budget, then it's much better to modify the trusses to collar-tie first, so you can gain some height inside, and also get better isolation. I've done that on a few projects, and it works rather well.
but wouldn't the existing 15'x7' garage door being lightweight steel and the fact that it is unsealed be a big problem in terms of isolation?
Yep. There too the common solution is to build a wall across the room in front of that, to create your actual leaf. Yes, technically the garage door is a third-leaf like that, but in practice it is not an issue for the very reasons you mentioned.
Closing off and sealing this existing 15' x 7' garage door is not an option I am willing to entertain. I still want access to the remaining garage space from the outside.
Then you have a problem. You can't eat your cake and have it too! If you want the garage door to open, the you'll have to sacrifice several feet of space above the studio for it to open into.... you'll end up with a studio that has a very, very low ceiling.
Go out and open your garage door right now, so that it is fully open and horizontal to the floor. Now measure the distance from the under surface of that door down to the slab. Subtract one foot. That's the
maximum ceiling height you could expect for your studio, realistically.
If I achieve around -30db to -40db of TL I would be a happy guy
30 dB is about what a typical house wall gets you, which is not very much at all...
I have read that ...
as Rod says on one of the threads you mentioned: "
From my perspective it's a no brainer if all I have to do is lose the drywall face on the inside of an existing wall." Yup. Agreed.... And another highly regarded acoustician (Andre) responded to Rod with: "+1". In fact, that entire thread says the opposite of what you think it says. The experts there (Rod, Andre and John) all agree that the 2-leaf wall is a much better option than the 4-leaf.
On the other thread, where someone mentions doing a three-leaf window, Rod replies: "
Not the approach I would take. Why not simply 2 glass panels with enough mass to get the job done at each wall face?" Yup!
Your third link doesn't seem to work at all!
Am I missing the plot all together or can I reasonably expect my desired TL using a 4 leaf system?
With large air gaps and plenty of mass, yes, you can get there. But the very low ceiling height, the smaller room, and the higher costs and complexity don't seem to be justifiable to me. Of course, like I said before, if you have plenty of money and don't mind the small room with the low ceiling and poor acoustics, then it probably is an option.
- Stuart -
that would be a 4-leaf wall! terrible isolation in low frequencies. Study this diagram carefully:
