Interior Wall Build - Insulate?

[Birky]

Hi There! First time poster here.. I'm very glad this forum exists!

I'm sorry if this is covered in the forum already (I couldn't find it), but I have a small question about my studio build.

I'm in the process of converting a detached 20'x20' garage into a "mastering room" (a budget version.. just something that works as well possible given budget constraints). Construction is in early stage process.

I live in a rural area and sound leakage isn't an issue. However, it gets real cold here so we're building decoupled walls. We're insulating the existing 2x4 framing with R14, adding a 1/2" air gap and building another interior 2x4 insulated wall inside.

I've done some research on dimensions and am aware that square rooms are a sonic nightmare. So the plan is to build in a storage closet the length of one wall so that the main room becomes 8.5' h x 14.5' w x 18.5' l.. not one of the optimal ratios, but it does fall in the Bolt Area.

My question is this: Should the closet wall connecting to the mastering room be insulated? Not for soundproofing purposes, but to match the rest of the interior walls (2x4 with R14 insulation and drywall finish)? Will not insulating it affect sound absorption/reflection properties differently enough from the other walls that I should add that insulation for consistency? I will definitely be treating all the walls with external treatment (hanging absorbers/diffusers) as well.

If anyone could help me out on this one I would really appreciate it!!

Cheers!

[John Steel]

Hello & howdo' Birky?
I'm not 100% sure I've understood what you want to achieve - a diagram would be helpful in this regard but a couple of thoughts / questions have occurred to me.

I'm in the process of converting a detached 20'x20' garage into a "mastering room"

How is the building constructed and what materials is it made from?

I live in a rural area and sound leakage isn't an issue.

Remember sound leakage is a two way and you will want to avoid unwanted noise getting in. Have you measured the noise level in the immediate outside environment? Do planes fly overhead - does traffic pass by? These and other sound sources could be more of a problem than you think. I live in the woods and when it's windy the trees rustling can measure over 60dB!

. . . it gets real cold here . . .

I'm sure you know this already but you will almost certainly need a correctly placed vapour barrier. Looking forward to hearing more about your project.
Best wishes, John.

[Birky]

Thanks for the reply John!

The building is a slab on grade detached garage. 2x4 construction. We've insulated the existing wall with R14 rockwool, and have built an interior decoupled wall which will also have R14. We've built up the floor with 6x2 and insulated that with rockwool as well. The whole thing will be airtight with vapour barrier. The floor will remain finished plywood. The ceiling will be flat, 8.5' with shiplap, and we'll be blowing insulation into the rafters. There are 2 windows and patio doors, so there will be some sound leakage in/out, but we're hoping it will be minimal considering the decoupled interior walls. There are occasional planes overhead, and some passing traffic, (and bull bellows!), but it's all pretty minimal. I won't be doing much recording in there, so it should okay for mastering (I hope!). I'll be making (more) external bass traps for corners, diffusers for back wall, and cloud/wall absorbers at first reflection points.

I dont' have a proper diagram of the construction, we're just working from a rough hand sketch I've made. The closet is the length of one wall. The storage space will be useful, so I'm happy to have it. I'm just not sure whether to insulate the interior closet wall, connecting to the main mastering room, with R14 to match the other 3 walls. I feel like it's simple enough to just do it.. but I'm curious how much room acoustics can be affected with one wall slightly different from the others?

Thanks!

[John Steel]

Hello again Birky,
I find described projects difficult to understand without being able to see a drawing, so I still can't speak with confidence, I'm afraid:

There are 2 windows and patio doors, so there will be some sound leakage in/out, but we're hoping it will be minimal considering the decoupled interior walls.

I haven't noticed any mention of adding mass to your walls or ceiling but sliding doors and conventional windows will definitely not help. I remember reading here some time ago that an opening window, no matter how well sealed, limits transmission loss to around 50dB or so. I know you are unconcerned about this, but I would recommend measuring both the environmental noise you want to exclude and the level of sound you generate. Then you can calculate exactly how much isolation you need and you won't have to hope that it'll be OK.

There are occasional planes overhead, and some passing traffic, (and bull bellows!), but it's all pretty minimal.

How minimal - in dB? Buy a good quality sound level meter (it's a handy thing to keep in a studio in any case).

I feel like it's simple enough to just do it..

You may be surprised! Again, I'd recommend drawing up an accurate plan (sketchup is great for this as it enables you to digitally 'build' your project and solve problems you may not have anticipated before you have spent a penny). My experience is that building a studio is rarely as simple as it first appears.
I'm certainly not trying to discourage you or dampen your enthusiasm - I just want to point out that it's impossible to know too much about acoustics and the more you know, the better you can plan. I started building a couple of months ago but I've been planning my studio for 3 years. You may well feel that you are sufficiently prepared and I'm not suggesting that you are necessarily mistaken, but what harm would it do to check what you think you know? Best wishes & good luck! John.