Basement Iso Booth - Ceiling question

[Onder]

Hello all,

I've been a long-time lurker here, and have been studying up on Rod Gervais's book - now I'm working on planning a Iso booth/amp room that will go in my basement. The main purpose of this room will be to isolate and record vocalists, and loud guitar/bass amps. The booth will back to the outside foundation on two sides and the other two sides will back to the control room.

Construction Details

The footprint of the room will be about 7'x10'. The walls will be a single stud construction with clips and hat channel, (1) layer of 5/8" drywall on the outside and (2) layers of 5/8" on the inside, with Safe n Sound in between the studs. The Green Glue website suggests this assembly will yield about 61 STC (IIRC). The height from the floor to the bottom of the joists is approx 8'4". The floor joists are 2x10" with (what appears to be) Green Glue, then subfloor, then hardwood upstairs.

Now being in the basement, I'd naturally like to minimize the sound transmitted to the living room upstairs, as well as foot fall and other noises from coming down into the booth. The two options I'm weighing are:
1.) connecting clips and hat channel directly to joists above, then (2) layers of 5/8". I'm not sure if I'll be able to use the normal clips or if I'll have to use the ones on extenders, since there are some pipes/wires/air ducts running between the joists, and I'll want room to stuff Safe n Sound. But here's a rough diagram:

ConstructionDetail2.png

2.) or, building independently framed ceiling, attached to the wall plates, then clips, hat channel, (2) x 5/8", insulation.

ConstructionDetail1.png

So here's my question:

What difference in isolation could I expect between the two assembly options?

I've read option 1 should result in about 54 STC. It seems option 2 should give better isolation, and I know people have had good results, but I'd like to know how much the difference is and if it's worth the loss in headroom plus additional cost. It's possible the difference in TL is mostly in a lower range that's less problematic in vox/guitar amps?

I've been advised that a room that small needs a lot of thick trapping, and it seems the ceiling would be a natural place to get some traps, but I also don't need vocalists bumping their head or being uncomfortable.


Thanks,
Tim

[Soundman2020]

Hi Tim, and welcome!

[quote]The Green Glue website suggests this assembly will yield about 61 STC ... I've read option 1 should result in about 54 STC/quote]When you are talking about high levels of isolation like this, your weakest point is not going to be the walls or the ceiling, but rather the doors, electrical, and HVAC system. Those are all compromises, since they involve cutting large holes in your otherwise great isolation system. And at STC-61 (which I'd take with a grain of salt anyway!), you are also very likely closing in on the flanking limit of your structure anyway.

But to answer your question, there really isn't much to choose between your two proposals, since both have the same deficiencies.

First, you are limited by the clips themselves, and I remain unconvinced that you'd get STC-61 with clips. Are you sure you got that right? The clips do decouple quite well, but not as completely as air.

Second, you seem to be combining separate frames with clips, which is a bit pointless. The wall on the right seems to be a totally separate frame, with the outer leaf being the grey wall and the inner leaf being the studs plus drywall. In that case, you do not also need clips: the simple fact of having a separate frame means that the leaves area already decoupled, so there is no point to decoupling again.

However, the wall on the left does need clips, since it has the outer leaf on the studs and the inner leaf also on the studs, so you do need the clips there. But what you didn't show is how those two walls are joined: If we call those two "east" and "west", then the question is: how are the "north" and "south" walls done? Since those will somehow join the fully decoupled frame on the "east" with the clip-decoupled frame on the west, there are two competing concepts that are somehow joined in the middle, and how they are joined is the big question.

So, independent of which way you go with the ceiling, I'd suggest that you first need to get your walls sorted out, and stick to just one system all around the room, rather than trying to combine two systems.

Sorry to not be able to answer your question simply, but there is no simple answer when you have a complex system and don't show all the details.

- Stuart -