Two layers to close off windows - MLV in between?

[riffwraith]

I am thinking of closing off the windows in my studio - don't need them, and I can hopefully get rid of some road noise, such as trucks and motorcycles. I am thinking of a layer of Homasote, and a layer of sheetrock. Since there is some depth to the frame, I was going to add two studs, and nail the Homasote/sheetrock combo to the studs, and then caulk the perimeter. This would create an air gap, which I assume would work well. Should I put a layer of MLV in between the Homasote and sheetrock?

Thanks in advance.

[Soundman2020]

I maybe didn't fully get what you are proposing, but a couple of key things in closing off that window:

First, seal everything around that window with abundant caulk... all gaps, cracks, joints.. everything. If you can replace the glass with something thicker, that also might be worthwhile, depending on how bad the problem is. if it is really bad, consider replacing the glass with a thick pane of acoustic laminated glass. On the other hand if the problem isn't too bad, and you just need a few extra dB of isolation, the just sealing it should be enough.

Gor the second leaf you propose (facing the room, I imagine), it I understand you correctly you plan to put some studs in the gap to get a nailing surface all around the perimeter, then nail a layer of homasote to that, followed by also nailing a layer of drywall (sheetrock) on top of the homasote. Is that the idea? If so, don't forget to first fill the cavity with suitable insulation of suitable density, as that will greatly increase the isolation of the system. In this case, mass is your friend, so two layers of drywall would be better, and get the thickest stuff you can find. 2 layers of 19mm would be great. Here too, seal up the edges of each layer right as you put it on.

MLV is mass, yes, but it is very, very expensive mass. Sound waves don't care how much you pay for your mass: they only react to the mass itself. So get the cheapest, most dense mass you can find. Usually that is sheetrock. Yes MLV is also flexible, and that can be useful in some places in acoustics, but not between layers of drywall. -if you really wanted to get the absolute best isolation there, you could consider using something called "Green Glue" in between the layers. NOt cheap, but very effective. Despite the name, it is NOT glue, and cannot be used as an adhesive. Nor can any normal adhesive be used instead. Green Glue Compound is a very special formulation. It is a viscoelastic polymer that does wonders to damp vibration in sandwiches of drywall, and does a real good job. But it isn't cheap, and you'd only need it if you really want the best possible increase in isolation from the outside world.

So, to summarize: seal everything absolutely airtight, put as much mass on each leaf as you can, use Green Glue if necessary between your layers of drywall, and fill the cavity with suitable insulation (mineral wool or fiberglass). That will maximize isolation.


- Stuart -

[riffwraith]

Thanks Stuart.

seal everything around that window with abundant caulk... all gaps, cracks, joints.. everything

Yep, did that.

depending on how bad the problem is

It's not bad, but there is some room for improvement.

facing the room, I imagine

Yes.

studs in the gap to get a nailing surface all around the perimeter, then nail a layer of homasote to that, followed by also nailing a layer of drywall (sheetrock) on top of the homasote. Is that the idea?

Yep.

don't forget to first fill the cavity with suitable insulation of suitable density, as that will greatly increase the isolation of the system

That's interesting. I thought the air gap with nothing there (but air!) would be the way to go. I guess that's wrong?

Sound waves don't care how much you pay for your mass

Bastards!

Green glue - was considering that, but thought MLV might be better. This is why I ask! So, GG inbetween the H. and SR. layers is better?

But it isn't cheap

I am only doing two windows, 32 x 46, that's 21 sq ft. Based on what I see, two tubes covers 32 sq ft, which is more then enough here. That's $56 - you are right, that ain't cheap, but it's relativeley nothign.

Thanks!