Will a 2nd layer of drywall really help?

O

oldsneakers

New member
Hey All. I'm converting an 8'x12' shed into a music room for recording and mixing. I installed resilient channel and one layer of 5/8" drywall on all the walls and ceilings. I was very careful not to short out any of the drywall screws. I put the wall drywall on rubber pads. I used silicone caulk on all the joints. I put a layer of 3/4" plywood on the existing 3/4" plywood floor and used silicon caulk to glue it down. I made window plugs with three layers of 3/4" MDF and sealed them with closed cell weather stripping. I added two layers of 3/4" MDF to the two doors and sealed them up with a combo of vinyl tube weather stripping and some closed cell foam.

I thought at this point I would have seen an almost useable reduction in noise. I'm about 30 yards from a fairly busy street. I can still hear every car that goes by. It's quieter, but not as much as I expected. I can't really pin point where the sound is coming from. It seems like from everywhere.

I was next planning on buying green glue and adding a 2nd layer of 5/8" drywall everwhere. And also green glue down a layer of 3/4" OSB on the floor.

My question is, is anyone here familiar with the improvement I can expect that a green glued 2nd layer of drywall gives in noise reduction? I've read green glue's site and I'm not sure what to make of it all. I really don't want to spend another $600 if it's not going to stop the noise of most of the vehicles that go by.

Thanks
 
The problems you're running into are all low frequency issues, and if they're traffic-related chances are that much of the problem is due to transmission rather than airborne propagation. To deal with that you're going to need not only more mass, but better, more comprehensive decoupling...everything from the floor to the rafters has to be addressed. That's the deal with soundproofing: the reason why we're always banging the "it's not cheap" gong is that you have to address absolutely every single thing because the result is only going to be as good as the weakest link.

So...you have low frequency stuff being transmitted into the space somehow. How did you build the rest of the room?

Frank
 
I haven't looked at these sorts of things in quite a while, but got yee a starting point -searched S T L (sound tranmission loss) of construction materials-
http://www.stcratings.com/assemblies.html
(My recolection is you don't get a lot of bang for the buck for a second 'attached layer, but that's a lot of worthless.. :)
 
If I had to guess, the sound is lower frequencies. I don't think I have the space for extensive decoupling. It's a 8'x12' shed. I wouldn't have much left of the room by the time that was done. The walls are 2x4 16" OC with R-13 insulation. Outside wall is vinyl siding on 1/2" plywood. Oh well, I guess I can go back to keeping my lawn mower in it. :)
 
Before you bail completely, considering you've invested in this thing already, see if you and seven other really big guys can lift the shed and turn it say, 35 or 45 degrees. Most sheds usually have a flat side facing the street, and often times you can significantly reduce noise just by turning it sideways, encouraging the incoming traffic noises to hit the outside at an angle, and reflect more than remains to vibrate the walls.

It's almost a free solution as I'm sure your friends will work for beer and pizza, beer and burgers, or whatever. So it's not completely free :)
 
How do you breathe in there?

What about HVAC...do you have any (though I don't think heating will be as much an issue as AC)?
 
Frederic may be on the right track here.
I don't see how adding more drywall is going to help but I do think that the sound can be absorbed outside with hedges, trellises etc.
Some food for thought.
 
Hedges and trellises with pretty flowers will help a little, but I don't think enough to allow a truly quite space to record in.

Turning it is a free solution, I'd give it a try.

If that doesn't help, a shed that size is about $2500 worth of materials at Home Depot, so one could maybe sell it and build another one, a foot larger in all directions to give the space inside to build a full floating room. Of course that will cost more than $2500...
 
I appreciate all the advice. You all are very nice. Unfortunately I can't move the shed. The land is not level. Also, I already had electricity run to it. I haven't dealt with the air side of it yet. I know it's not going to be easy.

How about fencing of some kind?
 
Fencing of some kind will help but in all honesty, the low rumble of traffic goes through walls and floors.
Is there a quiet time of day?
 
Maybe building a concrete block wall between the shed and the road would help...and fill the block cavities with sand as you build for added sound deflection...???

Of course, sound goes out in all directions, so how much would get in through the roof...???
 
I totally get you don't want to move the shed, fair enough. I was just looking for a low-buck idea that could help.

That's actually a very good idea Miro... as concrete blocks filled with sand certainly constitutes "mass".

Unfortunately, he'd have to do the same on other sides of the shed depending on the landscape and neighboring properties, as vehicle sounds can reflect off other houses, other sheds, ledges and cliffs, and so on.
 
So to sum it up, don't try to convert a shed for a recording room if it's near a busy street! That's ok, I can still use it for mixing and recording direct instruments. Thanks everyone for the help. This site sure has a nice bunch of people involved.
 
Ah yes, the home recording- Where the potential runs the gamut from totally pro results thank you very much,
.. to being shut down by the neighbor's leaf blower..
 
I'm going to disagree with Frederic a little bit here and say that, while turning the shed might help some in other ways, it won't cut down on low frequency transmission through the structural members. I'd say, based on what you're telling me, mechanical transmission is the biggest problem so even adding lots of mass probably wouldn't *solve* the problem, just mitigate it.

These kinds of problems really have to be addressed using a bottom-up solution and not a this-or-that approach. It takes mass AND decoupling not mass OR decoupling.

Frank
 
Folks,

Finding out whether the sound is really being transmitted through the ground to structure is not that hard....... if the shed is on a slab (which I would assume it is) then simply pick up a decent mechanic's stethoscope and listen to the slam when some trucks drive by......... if you have a strong signal then it's a pretty good bet - if not then it's airborne for certain....... check the walls as well......

Next - every doubling of mass doubles your isolation (all other things being equal.....)

So although the law of diminishing returns comes into play here (would it be worth it to install 2 layers of drywall to cut airborne transmissions in 1/2 - hell yeah - would it be worth it to install 16 additional layers when you already have 8 for the same increase in isolation - hell no.........) I would not be so inclined to instantly assume that the problem has to be structural borne........ more often than not in a residential area it is not.........

You do not say if you did anything to the outside wall before closing the wall in - if not that would have been a big increase for a small investment - BUT - assuming you really did put the RC on correctly (leg down not up) you can support another 2 layers on the inside - which will basically double you isolation - a layer of green glue between those layers will do it again all of this supposing that the majority of transmission are not coming through the earth....... you won't know that until you check........

The suggestions of screens just don't make sense on the face of it - he says he is almost there - just a little more isolation would get it done - people start taking about structural borne sounds from the truck - which would mean ground transfer not air borne - which would also mean screens are not going to help in the least - the ground still runs under them - and when we speak of reflections from trees and neighboring properties and developing screens to handle the possibility of them as well - again we are talking airborne and not structurally drive transmissions -

IF they are indeed air borne and not structural - then adding mass to the inside of the structure is by FAR the cheapest way to increase isolation - all he has to do is double it to cut it in half - which would be just adding those 2 more sheets I mentioned above......

Sir - get the stethoscope and find out where it's coming from - if structural then the floor should show it a lot and the walls little (after all they are pretty much decoupled from the structure) if the walls have it loud then the mass gets the job done........ buy the scope - stop guessing........

Sincerely,

Rod
 
Wow what an awesome response. Thanks for taking the time Rod. I'll pick me up a stethoscope. What an great idea. That would have never occurred to me. I did buy your book btw. Thanks!
 
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