Stopping sound transmission: Air only or air and insulation?

[badboymusic]

I have a guitar isolation room almost finished, but cannot find a definitive answer on any existing threads concerning insulating the inside wall. The outside wall is 4 inches thick filled WITH pink insulation, covered with a layer of 1/2" particle board, 1/2" Celotex sound board and 5/8" drywall. Then there is a 1/2" air space between the outside wall and the inside wall. I will be putting another sandwiched layer of particle board. sound board and drywall on the inside of this wall too.

I am wondering; is it best to fill the inside wall cavity with pink insulation too (which would leave a 1/2" air space between walls) or leave the insulation out of the inside wall so I would have 4" of air space between the sandwiched layer and the outside wall?

Which is going to stop sound better; 4 inches of air or 1/2 inch air and 3 1/2 inches pink insulation?

Thanks!

[DanDan]

I do hope that your stud frames are floating and isolated from each other and the floor and ceiling as much as possible. i.e. separate stud systems floating on neoprene. If his is not the case, please read up on Resilient Channel which you might be able to include. One or the other technique is necessary.
Regarding your question. I guess insulation would probably improve performance. Hopefully you are not referring to pink loose fill attic insulation. Semi Rigid Batts or a 'blanket' are normally used in stud walls. They sort of hang out in there loosely damping the void. They touch the wall panels only lightly. A tightly stuffed fill of pink would actually start to connect the two walls at very low frequencies, diminishing isolation.
Best Regards, Dan FitzGerald
Sound Sound - Homepage

[badboymusic]

Yes, the inside room is completely isolated and floating, sitting on Auralex U-Boats. My concern is if the sound transmission would be less with 4 inches of air or 1/2 inch air and 3 1/2 inches of batt insulation? I am leaning toward another option; leaving the 4 inches of air and starting my next layer with sound board, then 1/2 inch particle board and drywall.

[DanDan]

Glad to hear it is floating and islolated. This is extremely difficult to achieve Is there absolutely no common ground between the walls/frame of this inner box and the entirely separate outer structure.
If so, can I hire you- ;-).
Without a lot more detail to be fully certain, I reckon it would be safe and best to go with Batts in the void. I can't see a downside if they are loosely fitted. I am unclear about the whole design concept. Is this in fact a four leaf walled box? Why the 'soundboard' etc. ? Also the half inch gap between the walls? That seems like a very small gap. Is this a design you found somewhere, and could you show the plans?
Dan FitzGerald

[Rick Sutton]

In my experience the batt insulation helps dampen the inner chamber that the wall makes. I have always filled both walls in a double wall situation. My walls are sound board with two layers of 5/8" rock and are quite effective.

[badboymusic]

Originally Posted by DanDan

Also the half inch gap between the walls? That seems like a very small gap. Is this a design you found somewhere?

It's specs I received from my local studio design guy. He said leave a half an inch, coupled with the empty studs I end up with 4 inches of air space. But, I am reading conflicting info on the web and am questioning having two hard surfaces facing each other. I am not sure if the resonation will be a problem or not. My intent with the sound board was to eliminate one of those hard surfaces. So I would end up with original insulated outside wall studs, 1/2" particle board, 1/2" sound board and 5/8" drywall then 4" air space, 1/2" sound board, 1/2" particle board and 5/8" drywall covered with 4" OC 703.

It is in fact a four leaf system which I did not know what that was until after I was too far into it. I can't change it now and am trying to make the best of the situation. I have gone to so much work to build a room that is completely isolated and solid, then to read that it could have been built better acoustically with a three leaf system, very discouraging.

Thanks to all for your input.

[Rick Sutton]

Originally Posted by badboymusic

I have gone to so much work to build a room that is completely isolated and solid, then to read that it could have been built better acoustically with a three leaf system, very discouraging.

Don't get discouraged. With all that mass and decoupling that you've worked so hard to get you're gonna be fine. Many successful rooms whave been built with the methods you are using. In my opinion (and experience) any slight coupling of the two hard surfaces facing each other is more than made up for with the extra mass, especially in the low frequencies.

[DanDan]

Indeed, I don't mean to discourage you, just to cause a pause for thought to make the best of the remaining build. More than two leaves can have strange LF effects, but your build sounds massive enough to over-ride these considerations. I am reading your descriptions but am still unsure of exactly what you have and how much is still possible. Including RC might still be a very useful and cheap addition if the 'float' is not 100%. A diagram or pictures would work wonders here. If I am understanding you correctly you have a 4 inch gap, gyp facing gyp. You are proposing soundboard to deaden one of those hard surfaces and to some extent the void? Fair enough. Unless the size and cost is enormous I would still recommend including batts. If you some doubts why not go a little thinner and or lighter than 703. I can't foresee a down side.
Dan FitzGerald

[badboymusic]

Thanks, I will put the batts in the wall.

[Rick Sutton]

Just curious. Is the 703 being used inside the wall structure or as the interior surface of the actual room?

[badboymusic]

Interior surface, covered with burlap.

[badboymusic]

I'll try to post some photos in the next week. This has been a project, there is not one parallel wall in the room and it is six sided not counting the ceiling or floor.

[nosebleedaudio]

I would pack it with pink...
Some people think air space means "true air space" NOTHING at all, absorption is superior to air only...
Air space is from hard surface to hard surface...
And there is NO substitute for a good air space, 6 to 8". or more...

[nosebleedaudio]

Originally Posted by DanDan

I do hope that your stud frames are floating and isolated from each other and the floor and ceiling as much as possible. i.e. separate stud systems floating on neoprene. If his is not the case, please read up on Resilient Channel which you might be able to include. One or the other technique is necessary.
Regarding your question. I guess insulation would probably improve performance. Hopefully you are not referring to pink loose fill attic insulation. Semi Rigid Batts or a 'blanket' are normally used in stud walls. They sort of hang out in there loosely damping the void. They touch the wall panels only lightly. A tightly stuffed fill of pink would actually start to connect the two walls at very low frequencies, diminishing isolation.
Best Regards, Dan FitzGerald
Sound Sound - Homepage

I would disagree with this, if it touches it WILL NOT hurt anything...