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I am planning on a project to reduce the low-frequency noise (63HZ) and structural noise from multiple HVAC units which are directly sitting on top of a room. Right now, adding stuff right under HVAC units is not an option. So, would like to hear your experiences what works between if I am to add layers of drywall with GG or QuietRock to the ceiling of that room. Have read a bunch of good feedback on both products. Wondering if anyone has done any comparison in terms of the final effect. Since the room is quite small and budget is not a concern here.

Thanks a lot!
 

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Quiet rock definitely does what it says it will do but it is considerable more expensive and difficult to work with (generates alot of waste as well). I only use it when I need good soundproofing and am limited to 1/2" thickness(for example tying into an existing wall or ceiling) or if the customer insists on it.

With green glue the only expense is the tubes of glue themselves and you just build it up with standard 1/2" or 5/8" board. The extra thickness and mass of the assembly improves performance as well.

My general rule is for high frequency noise such as voices and music go accoustic insulation, for mechanical vibrations use added mass and dampening(quiet rock or green glue), for footsteps and loud noise you need mechanical seperation (sound bar or strapping) and all of the above.

If the noise from a mechanical room, laundry, or toilet may cause problems I generally recommend to customers to insulate and 2-ply walls with green glue simply because it's so easy to install and stock and is adequately effective. To take it to the next step add sound bar as well.

Cheers,
D'S
 

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From a first hand experience with both quiet rock and green glue, I prefer the green glue. Quiet Rock was way hard to work with and not as good (in my opinion, in this particular instance), in my opinion.

Green Glue does work, and it is not hype.

However, if I had my preference, I would go with 'separated walls' and the metal separation stuff (resilient channel) on the ceilings, if the ceilings are high enough (forgot the technical name, at the moment). These are both superior to green glue and quiet rock.

However, having used Green glue in my own home, it has DRAMATICALLY improved the room, but it has not soundproofed it (hard to 'soundproof' anything). It is just much quieter in the Green glue room now...

If you really want to get into it, you can start here on thread page 15, or read the whole thread: http://www.avsforum.com/avs-vb/showthread.php?t=456614&page=15
 

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Great comments all around. The issue is the glue. Quiet rock is standard drywall or cement board glued with quiet glue. Since there's nothing special about the board, it all boils down to which glue damps best.

on different occasions in different independent labs, green glue demonstrated a 4 to 1 advantage in damping.

So factoring in waste, a field assembled panel with green glue will be heavier (important) and more thoroughly damped. All of this is easily heard in the low frequency bass.
 

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However, if I had my preference, I would go with 'separated walls' and the metal separation stuff (resilient channel) on the ceilings, if the ceilings are high enough (forgot the technical name, at the moment). These are both superior to green glue and quiet rock.
I wouldn't spec resilient channel ever. The fact is there is no single standard for its construction. Some is 20 gauge, some 25, some in between. Some are slotted for flex, some are solid, some have holes.

Again, there isn't a standard for strength or flexability. Drywall Furring Channel, on the other hand, is specified by the Steel Stud Manufacturers Association, along with all other steel framing components.

This method of decoupling is effective if the steel can act like a spring. Since there's no manufacturing standard, the net result is that you have no idea if the resilient channel is too stiff (no spring) or too loose (no spring).

Much better to use the commodity resilient sound clips for a buck and a half and Drywall Furring Channel for $3 for a 12 foot stick. For a little over $40 you can install a ceiling with these steel clips + channel that would put any resilient channel ceiling to shame.
 
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