Soundproofing Metal Ducts attached to Party Wall - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 38 Old 09-22-2019, 09:25 AM - Thread Starter
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Soundproofing Metal Ducts attached to Party Wall

Hello,

I live in a townhouse and I am soundproofing a party wall. The walls are already well-insulated so the only sounds I hear are the neighbors going up and down the steps and some bass music (if the neighbors have the stereo on full blast). I plan on decoupling the wall with RSIC-1 clips and hat channel, puddy pads, 1 lb MLV, fiberglass batt for the air cavity, and 5/8 drywall.

My only issue is that my townhouse has a forced air system with big metal ducts that is attached the party wall, and replacing the entire ventilation system is too costly. I realize quite a bit of sound is coming from the sound vibrations of the metal air ducts.

Is there anything I can line inside of the metal ducts to help dampen the sound vibrations? The metal ducts also have a narrow cavity, so it is difficult in getting more than just my arm through.

Thanks in advance guys for all your help,
Jason
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post #2 of 38 Old 09-22-2019, 11:44 AM
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Duct Liner is made for just this purpose, it would help if you posted a picture of the duct in question
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post #3 of 38 Old 09-22-2019, 03:09 PM - Thread Starter
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Old school metal duct. Narrow cavity though so can only put my arm through it
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post #4 of 38 Old 09-22-2019, 04:38 PM
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If only your arm can fit you won't be able to put 1 inch thick duct liner inside, it will narrow the passage too much. What kind of noise are you trying to manage?
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post #5 of 38 Old 09-22-2019, 05:41 PM - Thread Starter
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Footsteps going down steps (staircase is on other side of party wall) and bass music (with stereo on full blast).
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post #6 of 38 Old 09-22-2019, 08:00 PM
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you could decouple the metal duct from the wall and coat the outside with a product like Dynamat Extreme or cheaper Equivalent version.
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post #7 of 38 Old 09-22-2019, 09:00 PM - Thread Starter
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Thanks! One more question. Do you believe 1/4 inch drywall and 1lb mass vinyl have similar STC?

In an effort to lower costs, I'm thinking about substituting the MLV for 1/4 inch and 5/8 inch drywall (totalling 6/8 inches).
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post #8 of 38 Old 09-23-2019, 05:04 AM
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My formula for the wall would be remove the existing drywall, make sure all the air gaps to the adjoining space are blocked and well sealed, add putty pads or equiv to the adjoining space and your outlets, make sure it is well insulated than add A237 clips (Ebay) to the wall, insert 7/8 25 ga furring channel (hat). hang two layers of heavy firecode 5/8 drywall with Green Glue between the layers. Skip the MLV. If you want an over the top solution do three layers of Drywall.
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post #9 of 38 Old 09-23-2019, 05:02 PM - Thread Starter
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Thanks! In terms of a sealant, do you think it's best to go with the GG sealant, or would the generic versions work too?
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post #10 of 38 Old 09-23-2019, 06:15 PM
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I've not discovered a performance difference between the GG sealant and the OSI or USG brands of acoustical caulks
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post #11 of 38 Old 09-23-2019, 07:02 PM - Thread Starter
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Will save a few bucks there! Thanks for all your help!
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post #12 of 38 Old 09-24-2019, 04:53 AM
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I get the USG brand at $6 tube at a local drywall supplier.



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post #13 of 38 Old 09-25-2019, 06:35 PM - Thread Starter
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Will look into it, thanks! When putting up the two layers of drywall, do you caulk each drywall, or put both up with GG in between and then caulk?
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post #14 of 38 Old 09-25-2019, 09:28 PM
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the caulk is for inside corner joints, top and bottom gaps. Not for tightly butted tapered seams. Overdo the first layer of drywall and hide the mess with the second layer, on the second layer you have to be neater if you are going to tape an mud the joints and they will end up being visible. That is why going overboard on the first layer is important, You can be sloppy at the bottom if you intend to mount baseboard molding. Likewise any place that will be hidden by molding or acoustic treatments. Some projects the only place you do a traditional sanded smooth tape and mud is the ceiling if it is going to be painted, That means you can just slap it up on the walls if they will be covered.

The GG goes between every sheet, caulk is to make the room airtight. An average size theater will use a case of 12 large tubs of caulk.
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post #15 of 38 Old 09-26-2019, 03:57 AM - Thread Starter
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Thanks for advice! Do you suggest waiting 48 hours for caulk to dry before installing second layer of drywall with GG, or not necessary?
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post #16 of 38 Old 09-26-2019, 05:49 AM
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You can actually put the second layer up immediately as long as you don't use a motion that scrapes it out of the gaps. I worked on a project with a 8 guy drywall crew (I flew in for the day), As soon as they finished hanging a section resulting in an area to be caulked I was on the ladder caulk gun in hand. Parts of the room were getting the second layer before the first was completed. I managed to keep ahead of them and made sure they squirted the proper amount of GG. it was a 20x40x11 ft room and they installed drywalled on clips and channel in around 5 hours.

The perfect method would be to let it set up over night.
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post #17 of 38 Old 09-26-2019, 05:28 PM - Thread Starter
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Thanks! One more question - with the RSIC-1 clips, we only have a 1 inch air-gap or so before putting up the drywall. What should we use for insulation?
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post #18 of 38 Old 09-26-2019, 07:46 PM
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1- inch? sounds like you are planning on installing the decoupled wall on top of your existing drywall. That is a No No because it creates a triple leaf. https://www.soundproofingcompany.com...le-leaf-effect
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post #19 of 38 Old 09-27-2019, 04:14 AM - Thread Starter
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So I should remove the old drywall first, put up clips and hat channel, then the two layers of drywall with GG and acoustical caulk?

What do you suggest I use for insulation of the airgap? Fiberglass batt?

Also, I guess taking down the existing drywall, I'll be able to cover the air vent. What can I use to wrap it with?

Good thing I asked! 😀
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post #20 of 38 Old 09-27-2019, 05:02 AM
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post #21 of 38 Old 09-27-2019, 12:59 PM - Thread Starter
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Appreciate all the help! Will keep you posted on how it goes. I also plan on wrapping the metal vents with some sort of vinyl too so taking off the existing drywall seems like best option.
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post #22 of 38 Old 09-27-2019, 01:06 PM
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I haven't a clue how your condo was constructed and what is involved in taking off the existing drywall. As a general rule on serious sound isolation projects you need to get down to the studs and start over to avoid the triple layer effect and to actually see what other problems you have in the wall that can be addressed. It is entirely possible the sound you hear is not coming in only through the wall. It could be coming in through the ceilings and floors. What is referred to as flanking pathways.
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post #23 of 38 Old 09-27-2019, 07:02 PM
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Jeff, OT questions. How many db's reduction would I get simply adding GG (or comparable) adhesive and new layer of 5/8" drywall on one side to existing interior 2 x 4 wood wall with NO insulation and 1/2" drywall on both sides?


Also, the USG adhesive above seems already reasonably priced. But just wondering how would regular silicone work instead of specialty adhesives?
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post #24 of 38 Old 09-27-2019, 07:52 PM
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post #25 of 38 Old 09-27-2019, 07:56 PM
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Quote:
Originally Posted by spkrdbblr View Post
Also, the USG adhesive above seems already reasonably priced. But just wondering how would regular silicone work instead of specialty adhesives?

The USG is a caulk, Silicon is caulk. The USG is a mass weighted caulk, Silcon is airtight but lighter in weight. Probably 80% as effective but a lot more expensive per oz so why use it? Don't use the word adhesive.
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post #26 of 38 Old 09-27-2019, 08:04 PM
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Iirc, I've seen figures from 3-5 db reduction with added layer of drywall. I don't recall if it was 1/2" or 5/8" or if it had GG or substitute. Probably not worth the hassle for that level of attenuation. But if 5/8" with GG or USG gets something like 10-15 db attenuation. Then that would be an easy way to tame a wall with no windows, doors or carpet tacks for me...
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post #27 of 38 Old 09-28-2019, 09:42 AM
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USG is not the same as GG, not even close. Different physical properties. Keep in mind that there is GG dampening compound intended for use between sheets of material and GG caulk intended for air gaps. When people use the abbreviation GG 99.99% of the time talking about the dampening compound.

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post #28 of 38 Old 09-28-2019, 08:43 PM
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BIGmouthinDC,



To communicate clearer.


I've never worked with GG, so I don't know its properties. I was thinking it might be like silicone, softer than the 35 years (or so) siliconized caulking painters use. I was thinking (erroneously it seems) that the USG above is used like GG, used between sheets to dampen. I am aware from videos that GG has another product that goes on joints, corners, top and bottom of 1/4 gap that is left on purpose during hanging of drywall. If that is what USG above is intended for, then I wonder if they or another company has a comparable to GG product that goes in between the sheets to dampen?



And if so, how a 5/8" sheet with dampening material (GG or substitude) applied between existing 2 x 4 wall with 1/2 drywall on both sides would perform vs. just adding 5/8" for more mass. In both cases, one side of wall only and no channel.
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post #29 of 38 Old 09-28-2019, 10:26 PM
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Quote:
Originally Posted by BIGmouthinDC View Post
I get the USG brand at $6 tube at a local drywall supplier.




This is like my WD-40 whenever I'm looking for my best tools for acoustic quieting. Cheers!
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post #30 of 38 Old 09-29-2019, 05:14 AM
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Quote:
Originally Posted by spkrdbblr View Post
BIGmouthinDC, I wonder if they or another company has a comparable to GG product that goes in between the sheets to dampen?

And if so, how a 5/8" sheet with dampening material (GG or substitude) applied between existing 2 x 4 wall with 1/2 drywall on both sides would perform vs. just adding 5/8" for more mass. In both cases, one side of wall only and no channel.
here is a competitor product, the reviews indicate it has a curing problem: https://www.amazon.com/d/Studio-Supp...ail/B006FK4YQ0
There is another thread somewhere talking about using Robert's Carpet Adhesive as a substitute for GG.

I'm not sure I understand your question on putting a sheet of 5/8 between existing 2x4 wall, exactly where is between? If you are asking about adding it over top of a layer of 1/2 inch drywall skipping the isolation part of the room within a room design it will perform poorly. maybe 25% benefit just guessing, I know Ted White co-creator and vendor of GG has in the past told people who want to do just that to save their money, don't do it. The sound isolation formula is Mass-Isolation-Dampening-Absorbtion if you skip any one ingredient your results will likely disappoint.

Last edited by BIGmouthinDC; 09-29-2019 at 05:17 AM.
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