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Soundproofing Forum Topics => Other Soundproofing Questions => Topic started by: Melanie Mowery on September 05, 2003, 01:37:44 AM

Title: Sound proofing walls in duplex
Post by: Melanie Mowery on September 05, 2003, 01:37:44 AM
We  bought a duplex a few months ago and have not had any peace since.  Our neighbors are always yelling, slamming doors and thumping. We can hear conversations like they are in our home and we can even hear them going to the bathroom. We tried having insulation blown in  but it did not help at all (now we have all these holes in the walls. We have estimates on the rc with drywall and it looks like it is around 6,000. We want to make sure this is going to work.  What do you think is the best way to stop all the NOISE.  ??? ??? :'( I want the best method available so we do not have to hear them anymore.
Title: Re: Sound proofing walls in duplex
Post by: John Tower on September 07, 2003, 05:30:12 PM

  Yeah, the insulation won't do much. Problem is, much of the sound is coming through the studs, which insulation doesn't help at all. I have done quite a bit of research on these topics and it is clear to me that there is only 1 sure-fire way to solve these kinds of problems. Yes you can make a sandwich with Mass Loaded Vinyl between your existing drywall etc.. , But after looking at the facts, here is what I would do if I was you:

1. Rip off your old drywall

2. Put Viscoelastic strips on the studs where you are going to attach the resilient channel. These strips add another layer of resiliency. See for an example of this config.

3. Attach resilient channel (or Super Sound Clips with hat channel). They claim the Clips offer twice the soundproofing, but I haven't seen data to back that up, so I doubt it.  See, they are the ones that actually make the clips.

3. Put viscoelastic strips on the channel itself, where the drywall will rest on the channel, just another layer of resiliency here, worth the extra 20 minutes work.

4. Place a gasket material around the perimeter to seal out noise that gets through the edges.

5. Attach the first layer of drywall. Tape the seams and caulk

6. Place viscoelastic material (squares this time) about 24" on center on the first layer of drywall, yet another layer of resiliency (notice a pattern here, add resiliency wherever you can)

7. Attach the second layer of drywall

8. Caulk all the seams, tape the drywall and you are done.

This will give you a real reduction in sound. You could add a layer of Mass Loaded Vinyl between the sheets of drywall, but from my research, the Viscoelastic Squares are cheaper, better, and much easier to install (The vinyl weighs a ton, and getting it up on a wall is not easy) I have done tons of research on this, sorted through the misinformation (including some on this board) and the facts back up this design since I have seen the data to back it up, unlike other claims.  This will bring up the price, but this is the way to do it right, plain and simple.

Keep in mind that your contractor needs to know what they are doing here, as they could easily mess this up. Also, if you have electric outlets, switches, etc.. on the wall, you may need an electrician to bring them out a bit since the wall is going to be thicker now. Anyway, those are my thoughts, take em or leave em.

John Tower
Title: Re: Sound proofing walls in duplex
Post by: melanie mowery on September 17, 2003, 03:49:45 PM
Would it also help to get carpet installed.  The stairs and downstairs is all hardwood or vinyl.  Thanks for the help.
Title: Re: Sound proofing walls in duplex
Post by: Boborther on September 17, 2003, 11:29:28 PM

I am not really sure about  John Towers qualifications, but I do know what works, and I know that the resilience and soundproofing characteristics  of the SSP sound clips over Resilient Channels (RC-1), is indeed double. I don't get this information from labratory tests, but from real world applications and from Contractors and home owners who have installed the SSP sound clips, and have experienced remarkable soundproofing results. A lot of spec sheets tout their inflated STC's, IIC and NRC numbers, but the bottomline is simply  this, does it work in the real world?
Most of what John has told you is correct, I just disagree on a few of the details and some of his methods, but for the most part, his ideas are good ones.
It is best to take down the old drywall, but it is not absolutely necessary. You can still do a floated wall directly over the existing drywall. The reason for removing the existing drywall is so that you can seal off the dead air space inbetween the wall boards (drywall) and that sealed  dead air will work ffor you in your soundproofing effort.
 First I would line the open cavities as well as the studs themselves with a closed cell vinyl nitrile foam mat (usually 1/4" does the trick), and from there I would do my float using either the RC-1 or the SSP sound clips and metal furring channels. I do agree with the viscoelastic material on the face of the studs if you are unable to fully cover the studs with the closed cell foam mat, and it is also helpful on the face of the resilient channel flange ot the top section of the metal furring channel if you are using sound clips.
Once you have the sound clips and hat channel installed, you screw in your drywall, making sure that you leave a 1/4" gap from  the  ceiling, the adjoining walls and the floor. You will need vibration pads on the bottom of the hung drywall to isolate the drywall from the floor, and to also take the weight of the drywall off of the resilient channels or Sound Clips. You will caulk  this 1/4" gap around the perimeter of the new wall, and then tape mud and paint the new wall as usual. I would recomment the mesh drywall tape as opposed to the paper type.
It is that simple, and you have a very good soundproofed wall assembly.
Melanie, I hope you are not confused by all the advice and jargon. Remember, this is a forum, and opinions whether good or bad can and will be posted here. If you have any further questions, please feel free to call.

Bob Orther
Super Soundproofing Sales/Technical Associate.
Ph: (760) 752-3030    FAX: (760) 752-3040
Orders only (888) 942-7723
When Peace of Mind is all that Matters!
Title: Re: Sound proofing walls in duplex
Post by: John Tower on September 19, 2003, 11:09:22 PM

  My qualifications are that I have done an extraordinary amount of research in this area and seen actual facts. This all started with my own need to soundproof my condo. I started out planning to just add a layer of MLV under my hardwood like you recommended, but realized after more research that it simply would not suffice as I carried out the work.(reasons forthcoming)  I have read your board and do believe that much of your advice that you give is good, but some of it is false and misleading.

First of all, Pac International manufactures the Super SoundClips, which are technically referred to as RSIC-1. They performed a study comparing them to the Unimast RC-1 resilient channel.. See the following link , look at the section named RSIC-1 vs. RC-Deluxe. They measured an STC of 56 for the clips and 47 for the RC, though this is a specific design without damped channel offered elsewhere which are about an STC of 51. My point is, that is not double the soundproofing, especially over a pre-damped channel. It is better, I agree, but not double by any means, so you need to quit making false claims without proper evidence. How can you possibly get your results from contractors and homeowners, that advice would be anecdotal and they obviously didn’t set up the room with an RC-1 install, take careful measurements then tear it down and put up RSIC-1 to realize it was twice as good. You just can’t back that up, if you can, then let’s see it. Actual tests have been performed on various floor/ceiling and wall combinations that your readers can find. In fact, the very book you recommend on this site “Noise Control Manual for Residential Buildings” (see has much of this data in it including various assemblies and data on the STC of common building products, something you really need to look at Bob. Also, the Canadian Mortgage and Housing Corporation has done a tremendous amount of real world testing on various constructions, see the following link:

Additionally, it is much better to tear down the existing drywall if possible because adding RC or clips to an existing enclosure has the problem of mass-air resonance if the gap is not big enough and can cause the assembly to perform poorly at certain frequencies. The assembly can actually perform worse than with no channel if you aren’t careful. See the “Specific Wall Designs Section” of the following link:

This research states:

“Where two layers of gypsum board are indicated in Table 2, the layers are assumed to be screwed together. If resilient channels were used between two layers of gypsum board, the STC would be the same or lower than that for the same construction with a single layer, because of the mass--air--mass resonance for this small airspace.”

In other words, if you are going to disconnect a wall or ceiling through clips or RC, you should take it down first. If you want to just add a new sheet of drywall up there, then fine, since you won’t have the mass-air-mass resonance problem, though you won’t get the benefits of disconnection.

Finally, you need to get your facts straight on Mass Loaded Vinyl and some basic physics. You have stated, “This is a truly amazing and simple application that adds a minimum of 26 STC points to any wall or ceiling system”,

see the following link ;action=display;num=1063638474;start=1#1

First of all adding MLV to an existing structure will help, especially if you caulk everything. However, adding a sheet of 26 STC MLV to an existing 25 STC construction will simply NOT yield an STC of 25 + 26 = 51 (or anywhere near it), physics just don’t back you up there. Mass Law states that the doubling the mass of an existing wall/floor will give you about another 6 DB in sound reduction; got it? That is 6 DB for DOUBLING the mass in case you weren’t paying attention. For example, you can take a sheet of MLV and apply it on top of another sheet and you would get about 26DB (first sheet) + 6 DB (a doubling of the mass) = 32 for two sheets. In order to get to 38 you would need to add 2 more sheets for a total of 4.  MLV is good because it provides a high STC in a very thin package and is a limp-mass material, which means it doesn’t vibrate naturally at an audible frequency like wood or glass, but a sheet of drywall is also about an STC of 26, it is just bulkier, despite what you have said on this board. That information is available the book I mentioned above, page 350, table SIL-1. Check out National Research Councils work at for a treatment of Mass Law and Mass-Air-Mass Resonance also.

Like I said, you can say all you want about me, or my opinions, but I can back them all up. You do give good advice here, but you need to do your homework on some of these issues and be more realistic in the claims you give.

John Tower
Title: Re: Sound proofing walls in duplex
Post by: Mike Nixon on September 20, 2003, 05:28:39 PM
Dear Melanie,

An interesting discusion and some real meat and potatos information. One thing that seems to have been missed is the possibility of flanking sound transmission. it makes no sense to go to great deal of trouble and expense only to find out when all is said and done, that part of the problem maybe flanking transmission. For your information Melanie, flanking transmission is the noise that transmits over the ceiling, under the floor or around the ends of the party walls.

It is possible to get some sense of where the sound is intruding just by listening very carefully by placing your ear  close to the wall, floor and ceiling. Not a sure fire way to detect sound leakage but sometimes it will give you a clue. Alternatively, you could get a acoustical engineer to to run some tests.

Many times people do not find out they have a noise problem until they have moved into the dwelling and find out after the fact that there is a problem. If the dwelling is a new unit then it should have been built to comply with minimum sound control standards in compliance with the state and local building codes. If they do not, then you could have some legal recourse with the builder. If you simply purchased an existing unit and the noise problems were not disclosed in the buy/sell agreement you might likewise have some legal recourse. A simple phone call to an attorney might might clarify your position. And, it may very well relieve you of having to bear the cost of remediating the problem.

Insofar as selecting a method of remediating the noise transmisson problem, I do agree that it isa necessity to remove the gypsum board on one side of the wall and then start over from that point with, clips, resilient channel, insulation, caulking and one or more layers of drywall, depending on what construction assembly you select.

What ever design you select I believe it should be suprted by independent acoustical test lab data or at very worst actual field test data that quantifies what type of performance you can expect before you shell out mega bucks. If the system and products are good then the manufacturer should not be afraid to substantiate the claims. Subjective opinions are no good and very unscientific though subjective opinions can be used to support scientific data.

Good Luck

Mike Nixon

Title: Re: Sound proofing walls in duplex
Post by: John Tower on September 21, 2003, 05:20:13 AM
Mike has a good point about the flanking noise, you should definitely check if there are any sound leaks as well before doing any major work as even a small hole or path can let in a bunch of sound. Sound could be coming under the wall (through a gap between the drwall and the floor) or even through an electrical outlet. You can also pick up a cheap stethoscope from the feedstore to help find it.

John Tower
Title: Re: Sound proofing walls in duplex
Post by: Jeff Caves on September 25, 2003, 05:28:01 PM
Having read this forum and read Pac International's web page. I would have to agree with Bob that sound clips do provide a signifgant improvement over resilient channel. Pac states on its site that an existing structure with other materials adds up to an STC of 47 and the sound clip with the same materials adds up to 56 STC. It may seem confusing but those totals include other materials. The increase of 9 STC points clearly more than doubles the effectiveness of sound clips over resilient channel. There is a tremendous amount of facts and figures out there on several web pages. Again I would have to agree with Bob that as you read through these many of these so called facts and figures just do not add up. Common sense is what is needed here. So much of figuring STC points depends on how the material is put to use and in combination with  other materials used. Just like politics, differing opinions expressed can lead to a much clearer view for all. Bottom line is do not always trust the figures. It was stated in this thread that blown in celluse has had no effect for the first poster, yet I'm sure the people who manufacture that product can be very persuasive, spouting STCs and other figures. Hands on experience is always the best option.
Title: Re: Sound proofing walls in duplex
Post by: Boborther on September 26, 2003, 05:43:01 PM

Thanks for your encouraging words. A lot of people are confused when they see terms like: STC, FSTC, NRC, and IIC. These acromnyms mean a lot to the engineer in a laboratory setting,  but mean very little us common folk living in the "Real World". We simply want to know which products work and which do not.      
When was the last time you heard a manufacture state emphatically, I guarantee that this product does "NOT" work, and I will give you that in writing. Actually, if I ever did read something to that effect, I would be inclined to do business with that company due their sheer honesty.  
I personally know the soundproofing methods, techniques, and materials that work in the field (FSTC), but not necessarily those that are effective only in a clinical laboratory environment.  In the "real world", walls are not always sealed correctly, or necessarily straight, and the drywall usually does not go all the way down to the floor nor are studs always the insulated metal kind that  would be used in a perfect laboratory setting.
 Sure, we all like to deal in numbers and facts, but when you hear 'Ole Joe' the insulation Bubba swearing to you that blown in cellulose will add 48 STC points to your existing wall or ceiling assembly, and he can guarantee that in writing,  I have to seriously question his motives, sanity, and the validity of that claim.  That's where the common sense factor kicks in.
Manufacturers can make some pretty outrageous claims, and can generally get away with making these claims because they are seldom challenged by John Q. Public.  People seem to  trust companies like 3M,  Johns Mansville, Owens Corning, and Armstrong, should they?
 When it comes right down to it, there are only certain soundproofing agents that really do work and they have been tested and proven in the field and not just in a laboratory.
This discussion has become very provocative and enlightening  and I am sure Melanie is as surprised as I am about the response and reaction to her personal soundproofing issues.
 Lets keep this forum alive and well, and we can all learn a great deal from one another's  different points of view.
Thanks again for the kind, and for the "NOT" so kind comments, that's what Forums are all about!

Bob Orther
Super Soundproofing Sales/Technical Associate.
Ph: (760) 752-3030    FAX: (760) 752-3040
Orders only (888) 942-7723
When Peace of Mind is all that Matters!