[sandbag]

I have some black MLV from another project and am thinking of using it on my ceiling instead of paint. Does anyone have experience with how this looks? I know the seams will be touchy, but with all that light absorbtion will it matter? Also, will I have to use more screws in the gg layer of drywall to support the extra weight of the MLV? I also have some MLV with closed cell foam backing. Would this work better or worse than plain MLV? By "work" I mean will it improve STL somewhat in the room above, assuming I've done everything I can to isolate/decouple/add mass/deflank?

I've always assumed MLV should "droop" to work best. For example, by securing it loosely between battens. What about securing it with green glue?

Is MLV ancient history in the age of Green Glue (I used to call this stuff contact cement because it was a gummy mess used to adhere Formica to MDF for countertops), or does MLV still have some fans? Obviously the cost is outrageous compared to drywall. Is that the main deterrent?

 

[Ted White]

The MLV offers mass. So does drywall.

The MLV doesn't perform better when limp, taught, or woven between studs. I've been in the labs when tested many times.

I would suggest using drywall and paint, as the MLV isn't bringing anything unique to the table.

 

[chadcummings]

I was in a similar delima with my ceiling as I want good sound absorption with the best performance vs cost. What I ended up deciding on was stuffing my ceiling joices with wither OC703 or acoustic cotton then using the greenglue strips to decouple the drywall and using 3 layers of drywall with greenglue in between. This gives me a lot of mass and should absorb tons of sound, giving exception to infrasonics from the IB of course.

 

[Ted White]

I was in a similar delima with my ceiling as I want good sound absorption with the best performance vs cost. What I ended up deciding on was stuffing my ceiling joices with wither OC703 or acoustic cotton then using the greenglue strips to decouple the drywall and using 3 layers of drywall with greenglue in between. This gives me a lot of mass and should absorb tons of sound, giving exception to infrasonics from the IB of course.

What Green Glue Strips decouple??

 

[chadcummings]

What Green Glue Strips decouple??

http://www.soundproofing.org/infopages/Tape.htm

I should not have used the words, Green glue, my brain was shot and while the tape is green it is not the same stuff.

Buy it at the same place though.

 

[Ted White]

OK I see. For clarity and accuracy foam tapes and compounds applied to the joists don't "decouple."

 

[chadcummings]

OK I see. For clarity and accuracy foam tapes and compounds applied to the joists don't "decouple."

We will agree to disagree on the link I sent. I have read several reports on the sound isolation padding vs resilient channel and until I am in a lab and can test it for myself, we will agree to disagree.

 

[Ted White]

Certainly don't seek an argument, but this is an extremely defined concept in the world of acoustics.

And I have been in such labs for the last 5 years testing these items, and have tested that exact tape on several occasions as well as resilient channel and all major resilient clips.

I say this because a great number of people read these threads and make decisions based on them.

 

[chadcummings]

Please enlighten me. I have done tons of reading and since you have the inside track I would love to have a clear understanding.

Not being sarcastic, I truely want to know before I screw up my own theater.

 

[Ted White]

Sure.

A common wall consists of a single frame, with one "leaf" of drywall on one side and a second leaf of drywall on the other side. Both leaves are attached to the same stud and therefore cannot move independent of one another. The system is therefore coupled, and the air cavity is fixed and cannot act as a spring.

"Decoupling" as an acoustic term refers to the physical disconnection of the two leaves. If we had a staggered stud or double stud frame assembly, and then attached the two drywall leaves, you would be able to push one side of the wall and have this move without causing the other layer of drywall to move. The two leaves move independantly and are therefore decoupled.

The air cavity in a decoupled system can therefore have the air compressed and then rarefied. Pressurized then unpressurized. This allows that air itself to act as a spring in this now decoupled mass-air-mass system.

This decoupling immediately moves the low frequency resonance point down considerably which is exactly what we want.

Foam tape on a stud is immediately compressed when screws (any fastener) are introduced. There is no flex, no resilience. This is still a coupled system. If used on each stud face, this foam can add a slight benefit by reducing a small amount of direct conduction through the studs. However the presence of all of the screws through the foam into the studs severely limits the reduction in conduction. In an ideal situation of a lab environment, you might expect a 1 point gain in the upper frequencies. True decoupling would give you 10 or more points.

By alternating the studs that have the foam you introduce another issue. The raw drywall is now sitting 1/16" away from the un-taped stud face. What that wall gets vibrating, you run the risk of the drywall slapping against the un-taped stud, introducing a whole new vibration.

 

[chadcummings]

Ok, that proves a couple of things:

1) I need to be reading articles from a more reputable source.
2) Never argue with someone who knows more than you.

I am using SS walls however.

But seriously, thanks for the further explanation.

 

[Ted White]

You have staggered stud wall framing? Then you're fine.

I would suggest you screw the drywall to all of the stud faces, not just the ones with tape (if you did the "tape every other stud" deal) to eliminate the possibility of that slapping / rattling possibility.