# Mass Loaded Vinyl



## Keysflyer1 (Nov 25, 2011)

Both the supply and return plenums form the HVAC system are running pretty much the width of my HT in the basement with five duct lines coming off and running the length of the room to the living area above.

Is using MLV on the bottom and sides of the plenum and around the duct lines to reduce noise worth the expense or will the the added insulation above the DD and GG ceiling suffice.

Also, if MLV is preferred, is there much gain between the 1lb. and 2lb.

Thanks for the help.

Brian


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## bpape (Sep 14, 2006)

Is the ducting tin or flex?


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## Ted White (May 4, 2009)

My thoughts are if the ducting above the decoupled massive ceiling is simply passing overhead then don't worry about it. Forget the MLV idea. 

If the ducting is a direct supply or return for the theater than you'll want to deal with those. Shoot me a PM if you'd like a few articles on the topic.


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## bpape (Sep 14, 2006)

My only thought was that if it was tin, you could damp it using something. Might not be MLV specifically but there are 'sticky mass' type of products (long day - can't remember the name) that would potentially help with it vibrating - though not specifically for isolation.

Bryan


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## Keysflyer1 (Nov 25, 2011)

Ted,

There is a supply vent that is cut into the bottom of the plenum that is there to heat the unfinished basement area. Had considered just useing it for the HT or possibly closing it off and running a different duct line.


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## MatrixDweller (Jul 24, 2007)

IF the duct has an opening into the HT room then damping the out of it is going to do very little because the sound will flank through the vent opening. You would be better of lining the inside of the duct with a product like Linacoustics and/or incorporating a duct silencer (like a muffler). 

In my HT I have a similar situation where the main trunk runs perpendicular to the room. I had to build a bulkhead around it. I stuffed the bulkhead with rockwool and used rockwool (but not much) between the duct and drywall. I put an elastomeric caulk on the wood where the drywall made contact, but only used 1/2 drywall. I could have done more, but sound wise it's pretty silent in there. The HT noise doesn't travel through the duct work at all. 

My return duct does have a membrane between it and the furnace to cancel out some vibration.


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## Owen Bartley (Oct 18, 2006)

When using MLV for ducts that don't directly vent into the room, would it be better to apply the adhesive type MLV directly around the duct (if you have access) or is it overkill? Would this method from the Acoustiguard website do the trick just as well?


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## Ted White (May 4, 2009)

Keep in mind that MLV is the most profitable item sold by many dealers of acoustic materials. Should give you some insight into the motivation for it' use / sale.

You don't need MLV in your ceiling or walls. Drywall is over 2x as massive and 1/5 the cost.

You should be shooting for something like this for supplies and returns that directly service your room:


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## MatrixDweller (Jul 24, 2007)

The way it is pictured is best. I wouldn't put it right on the ductwork for a couple reasons. The adhesive will eventually lose it's stick and the MLV will degrade faster than normal. Both conditions due to the fact the metal ductwork heats up and/or cools down. It might also not be legal (I'm not sure on that) to attach directly to ducts since it is plastic, even though it's UL94VO rated.


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## Ted White (May 4, 2009)

You'd be further ahead with a second sheet of drywall. Why the need for MLV?


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## Owen Bartley (Oct 18, 2006)

Thanks Ted, sometimes the simplest solutions are the best.


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## Ted White (May 4, 2009)

That's true!


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