Strange sound proofing question

[zandurian]

I have built a few small studios in my day, my present one is pretty cool - I actually have two layers of 1/2" sheathing sandwiched inbetween 3 layers of 5/8" sheetrock on the 'outside' walls, and 'floating' rooms inside of those rooms with the same (!), so jets, garbage trucks etc. have no effect on what I'm doing
BUT I'm wanting to enlarge the studio so I'm finishing out a connected 8 x 40 storerooom (only studs and siding right now) that has LOW ceilings so I want to do the layering without lowering the ceiling (will have no floating inside rooms) and without reducing the small 8' width. I'm thinking of putting 2 layers of sheathing and three layers of 5/8 rock in between the studs (directly against the siding) but that would give me only the 3 1/2 " of wood (plus siding) to the outside world wherever the studs are. Since wood isn't nearly as dense as the rock/sheathing I'm wondering if it will defeat my purpose? Or would the 3 1/2 inches worth compensate for the lack of density?
I'm not so worried about outside noise coming in as much as the sound going out to my sweet wife who will be trying to sleep in our bedroom (separate building) 25 feet away

- byron

[jayfrigo]

There's no cheating when it comes to mass. You definitely need some. Airspace is the next big thing. Unfortunately, your condition is that space is at a premium, so that too is hard to come by. You are left with split construction, or decoupling. Since space is an issue, springs aren't possible, but a hat channel is (not simply the old R1 Z-channel). Check out some of the options from kinetics and you'll only need to sacrifice a few inches. And get serious about flanking paths. Seal it up like a submarine.

edit: re-reading - I get it - you want to just put it inbetween the joists. Double what I said about flanking paths. You need to seal the living daylights out of this, and with something that won't harden and pull away as it sets. That wood is going to be a structure bourne path, and it does lack desity, and you'll also be exciting it not only from the bottom, but both sides as your rock won't start until the top. Don't count on the extra depth of the joists where they protrude. You may still do OK, but there are some practical limits here.

[zandurian]

Originally Posted by jayfrigo

Seal it up like a submarine.

Thanks for your input and, yeah, I definitely have the submarine thing down. I overheard the construction crew on my present studio saying "this guy is not all there" because of my caulking every layer to the hilt. I must have used 1000 tubes!

- byron

[avare]

This is in addition to the excellent advice Jay has posted.

You have my sympathies with the restrictions you have. The first thing that came to my mind is can your roof construction support the weight of the additional material? A collapsing roof can significantly interrupt the groove of a session. Do you have option of building a second isolated layer above the current roof if the current roof can not support the added weight?

As far as putting the additional layers in between the studs, that in itself can be done. It is just very expensive in terms of labour. Instead of putting the additional layers right against the outside leaf, I would use strapping and flush the material to the inside. This would create the needed spring in a mass-spring-mass system. Not mentioned, and maybe already there, put fiberglass/mineral wool insulation in the cavities.

The key component is mass. If I follow it correctly, the leaf that you are proposing to add is:

drywall
fiberboard
drywall
fiberboard
drywall

This is fairly thick, reducing the gap (spring). I would investigate the most dense (heaviest for thickness) material that I could get and afford. MDF, HDF, various "moistureproof" made from concrete like materials for bathrooms, for examples. I would then use TWO layers with Green Glue in between. In other words the added leaf would be:

dense board
Green Glue
dense board

The biggest weakness compared to your original construction will be the solid connection of the studs. This will limit the low frequency isolation achieved. Unfortunately this is the frequency range most difficult to control to begin with.

I am loathe to make blanket statements about lab untested designs, but all my suggestions are based on collective knowledge of past experience, and extensive research.

Keep asking questions! Posting is cheap. Building and having to tear down and redo is not.

Wanting isolation,
Andre

ps. Where are you? There are differences around the world in materials cheaply available.

[Eric Desart]

Andre, Jay

Take into account that the MSM, will be defined by the lightest of both sides if you construct a double leaf system with 1 cavity.
At a certain moment adding mass one-sided will hardly influence MSM anymore.

Hence this siding (not described in Byron's post) can become deciding and limiting.
The best MSM is when both sides are equal. You can divert somewhat from that within reason.

Be careful not to create a resilient skin in front of a heavy wall principle, where the resilient skin here is the outside siding in this situation.
If you create an air gap it can be good somehow to make that outside leaf heavier, or prevent a cavity from existing.

And Byron should better describe that roof and siding.

Leave it further up to you.

[avare]

Originally Posted by Eric Desart

Hence this siding (not described in Byron's post) can become deciding and limiting.
The best MSM is when both sides are equal. You can divert somewhat from that within reason.

And Byron should better describe that roof and siding.

Thank you Eric! I had mistakenly thought the outside was the same leaf Byron described earlier.

Only one misatke today,
Andre

[zandurian]

I have definitely put aside the idea of going inbetween the studs for layering, so will put insulation in the cavities. As far as the extra weight on the ceiling, I am doubling each 2x4 which supports the 1/2" plywood decking which supports a v-crimp tin roof.
The outside siding is I guess what you would call 'standard' 1/2 wood siding.

So Eric, you're saying the siding would be the resilient skin which would need to become more dense, so maybe putting one layer of dense rock inbetween the studs glued to the siding from the inside before adding insulation and then the other layers would solve this?
- byron

[Eric Desart]

Originally Posted by zandurian

So Eric, you're saying the siding would be the resilient skin which would need to become more dense, so maybe putting one layer of dense rock inbetween the studs glued to the siding from the inside before adding insulation and then the other layers would solve this?
- byron

byron,

I'm not sure how to handle this mechanically the best. I hope others jump back in.

I just explained the principle.

Is this siding from this overlapping wood or tongue and groove?
You also must take care of moisture to prevent hygrothermal problems (vapor barrier on the warm site, if applicable where you live).

At a first glance this looks OK, if you could fix sheetrock (moist resistant) to the outer siding. Doing it with Green Glue should be better (but that needs additional mechanical fixing).

The idea of a double leaf system:
Masses as heavy as possible.
Internal damping as high as possible.
Cavity as large as possible.

The mass and cavity + wool filling defines the MSM (mass-spring-mass) which is a defining factor for insulation.

Symmetry in masses gives you the lowest MSM, but relative small differences don't matter that much.