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I will be removing your link to quietrock , we dont permit flogging on our forum

 look up Acoustic "MASS LAW" now that you know every doubling of mass = around a 5db drop which is about 40% reduction of human speech. You have to understand that at a minimum you must double the wall mass.

MASS is MASS and as long as you have the space I dont mind what materials you use that are very heavy to achieve doubling of mass or more...I have even done mortar and chicken wire between studs.

Not a big fan of quiet rock as I have had to redo many of those jobs due to lack of mass.

Quiet Rock EZ snap - 2.6 lbs sqft around $50 a sheet  / Duroc 2.6 lbs sqft $18 a sheet
Quiet rock 510 - 2.13 lbs sqft / 5/8" drywall is better
525 - 2.7 lbs sqft  hardie backer or permabase cement board both exceed 525 and 527
527 - 3.0 lbs sqft
530 RF is for faraday cages / this one I have used in a few projects
and the only one that actually is something is 545 at 6.25lbs sqft but Ive seen upwards of $200 a sheet.
Which I can make myself for $60 a sheet.
Now if you saying the the magic stuff in the middle is doing the work dont forget you are driving screws right back into the frame sending sound and vibration into the studs unless you are on complex structure.
This is why I have seen green glue jobs not yield desired results and now I only use it for low frequency response of studios and theaters.

And the biggest mistake I have seen with quiet rock is the installers forget to butter the edges with acoustic caulking during install.

If you are trying to achieve higher then a 5DB drop based on mass law then you would have to go into complex structure ie. double frame/ clip and channel / resilient channel and you would still need to double or even triple the mass to get greater decibel reductions.

remember we can not talk through 6" concrete but if I hit it with a hammer you are going to hear it.
so it is important to decide what type of sound and how much reduction you are trying to reduce in order to design the assembly correctly.
Also keep in mind anytime you are doing single partition only you will have some value of flanking noise around the soundproof partition. this value I find to be unknown until the wall is complete.

And finally, yes every layer from start to finish has to be installed airtight / water tight without fail.

feel free to call me direct.

Best Regards,

Randy S.

I would be very skeptical of your approach. My office was terrible for STC (aka airborne) sound transfer. The contractors decided to put up a layer of rubber sheeting on top of the existing drywall, then homasote, then another layer of 5/8 inch drywall. Instead of sounding a foot away, the voices now sound like they are maybe 5 to 10 feet away. But I can still make out what the people are saying through all of that. And if they're at the perfect angle, then its no change - clear as day.  Caveat the building is a converted loft made of wood but I wouldn't bother doing this again to any rooms, it wasn't worth it.

If I were trying to kill STC sound, I would cut off the existing drywall on one side of the wall. Pack the joists with rockwol safe and sound or something similar (perhaps two layers - it isn't that expensive and is pretty easy to do yourself -- see youtube) then I would use Quietrock drywall (probably have to hire someone to hang it) and, if that didn't do it, try green glue and a layer of 5/8 inch drywall on top. If that doesn't do it, you're probably SOL, consider moving.

Quietrock is about 10x the cost of normal drywall but sounds legit from my reading. You should call Quietrock and talk to the guy there (forgetting his name). He is an awesome resource. Very helpful and into educating people on realities of sound transfer.

As for vents, I can't help much there. I've watched some videos on soundproofing vents and such but haven't done the same research. At some level, you should probably managed expectations on how much can be accomplished. As I've been told by many vendors on hours of calls about all of this, sound is like water, it finds a way through.
Hi Randy,

No the vent is on the wall just perpendicular to the wall in question. I'm not sure if it leads into the same air space or how that works.

So you are saying 2 layers of 5/8 drywall and 1 layer of 1/2 inch cement board. Should I use any green glue in between? Thank you so much for your answer!


replace one of the layers of drywall with cement board 1/2" 3lbs sqft to increase the weight. you need to double the wall mass ( 2 layers 5/8" - 4.6 lbs x 2 - 9.2 lbs ) 9.2 lbs is the goal.

you must treat the soffit the same way.

is that return vent on the wall you are trying to soundproof?

Randy S.
Soundproofing your Condo, Townhouse or Bed & Breakfast / Re: Rooftop AC Unit noise Q
« Last post by Randy S on May 08, 2019, 03:25:00 PM »
1) less contact points is better decoupling and more vibration reduction.
2) each pad is 7/8" thick, people do double up but reduction of vibration does not double, slight improvement but not expensive to do.
3) our durometer on those are 65.

I do have a company that is using our ssp foam mat 2" thick and claims to out do all the vib pads. just more expensive.

Randy S.
Other Soundproofing Questions / Re: WHERE CAN I BUY A SOUNDPROOFING MASK?
« Last post by homehouse on May 08, 2019, 06:39:02 AM »
You are looking for a stenomask to be used in conjunction with headphones. You might have to rig something to cross connect the headphones and microphone at same time. There are adapter cables for phones to do this. Search amazon for stenomask. Hope this helps.
Hello, I am trying to add soundproofing to a wall separating a newly built in-law apartment from the adjacent space. My contractor wants to use 3 layers of 5/8 drywall. He says this will be 'plenty to block the noise.' From my little bit of reading, it sounds like Green Glue would be a great thing to add between the layers of drywall. Do you agree? If so, should the Green Glue go between both layers of drywall? My other question is what to do about the soffit (if that's the right word) that you can see in the picture. It contains electrical wires. Do we need to soundproof that too, and if so how? We only have 1 7/8 inches to work with because there is a return vent at floor level we need to work around. Thanks so much for any advice you might have!!
I would also ask whether a larger pad (4x4) helps or hurts.
Hi there
Great site. I am learning so much about just about everything.

I live in an older condo on the top floor (floor 3), lucky me. Pretty good view. On my roof/ceiling right above my bedroom, are the six heat pump units for the units. Vibration from one or more of the units is causing vibration humming sounds. Before I reapproach the hoa, I have been trying to see if I can mitigate the problem by using isolation pads. Hoping it is not pipe vibrations.
Couple of questions.
(1) points of support - how many? The units are pretty small (300-400 lbs), so I see recommended four 2x2 pads (one in each corner). If four is good, does it make any sense to put more points of contact? i.e.: six? Add one more on each side or one in the center of the pan?
(2) thickness / how many layers? - if one layer is good, does it make sense to put a second layer (make a pad sandwich) just to be safe? I am looking at individual pad thickness of approx 5/8-3/4" for approx total double thickness of 1-1/2".
(3) D rating? - I see different durameter ratings available. All the way from d20 - d80.

Thanks in advance.
Hi I am new to the forum but have done some searching and still have some questions. I live less than a mile from an active earthquake fault and worry about too much ceiling weight if we get a big quake. Don't know if there are code stipulations in earthquake country about multiple sheets of sheetrock on RC channel etc. So we recently redid our foundation for earthquake safety and while doing so excavated another 2 feet so we now have 8 foot ceiling height. Our city, in a serious housing shortage, will now allow us to turn the basement into a secondary living unit and if we do so, I want to have excellent soundproofing separating main first floor living from tenants below. The ceiling, for the most part, is framed in 2x8 full dimensional doug fir joists. The floors above have 1x12 fir subfloors and maple or vg fir flooring. I was thinking of installing one layer of safe and sound followed by RC channel and then quietrock and using surface mounted lights. I have also seen the clips, which I assume block some vibration from the joists to the rc channel. At about 5 dollars a piece they seem costly for a 1400 square foot ceiling. Are they worth it and if so are any better or worse? Also, homasote does not seem that expensive or heavy. Does it make sense to rib sheets of homasote to 14" and install in the joist bays screwed to the subfloor (1x12 doug fir)? Is quietrock worth the money? Are 2 layers of safe and sound significantly better than one? Any other ideas?


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