# Soundproofing an Existing Interior Wall



## Peanut11

Is there anything on the market a DIYer can use to soundproof an existing interior wall between a bedroom and a bathroom to decrease the sound coming through?


----------



## Ted White

Do you know what your stud material is? Stud spacing?


----------



## NetWell

*Common Wall Soundproofing*



Peanut11 said:


> Is there anything on the market a DIYer can use to soundproof an existing interior wall between a bedroom and a bathroom to decrease the sound coming through?


A layering system is available that can be applied to most any common wall noise issue. Adding both "density" and "disconnection" to your surface can help force the collapse of the transmitting sound wave, and reduce up to 90% of the noise from passing through the wall. Results will vary depending on leakage, ventilation, plumbing, electrical, floors, ceiling, etc.


----------



## Ted White

MLV? Not so easy to work with, and is about the most expensive source of mass available. 

Also to the OP, is this pipe noise (you can hear the rushing of water through the waste pipe) or is this an airborne sound issue (people singing in shower, let's just say)? Also, does this wall have a door? If so, that's where you would initially focus your efforts.


----------



## NetWell

MLV is very easy to work with, and not expensive for a bathroom wall. There's hybrid products that are also made with MLV, including pipe and duct wrap lagging material that can help mitigate drain pipe or hvac noise if you have access to them. Bathrooms are tight treatments with many holes cut into perimeter walls, controlling leakage is key regardless of the treatment option. Also, vibration reduction, working to disassemble as best you can the common contact points in your wall, ceiling and floor assembly systems.


----------



## Ted White

Soundproofing solutions are largely a mass-based proposition. You'd like to decouple the mass, damp the mass, have some absorption between the mass, but at the end of the day it's all about the mass itself. Specifically, how much of it do we have available? The more the better. We are generally not concerned with the source of the mass, just how much of it there is. 

Drywall is 2X the mass and 1/5 the cost of MLV. Instant non-starter.


----------



## NetWell

The instant non starter is forcing a client to double drywall around a bathroom when there's no space to do it. Most of our clients seek to minimize the depth they are adding to a wall assembly, which plays to the advantage of dB-Bloc. MLV measures just .125" thick and requires a single layer of drywall. If there's ever a time to opt out of a double drywall layering system, which most constrained layer damping compounds require, in favor of MLV, it is a bathroom treatment. And no, if you took .125" of drywall and compared to .125" of MLV, MLV carries more density and wins every time. More density, less depth conceded, better collapse in sound bleed, more protection.


----------



## Ted White

hmmm. Not seeing any forcing. I think it's either pipes or door. 

Even if it _were_ the wall, no way to justify the high cost and relatively low mass of MLV. Wrapping ducts and pipes? Great product because it's flexible. Walls? Waste of funds.

If the OP has a question, I'll reply further


----------



## AngelArs

NetWell said:


> Apply to existing finished wall, or exposed frame, and follow the install techniques listed with material.


Been using MLV for a long time and you are right, it is better than drywall, but you're not suggesting they put this on the _outside_ of the wall like wallpaper are you?  There are less intrusive ways to cut down the noise from a wall. Also, the OP was not specific enough to say what *kind* of "noise" they want to get rid of. Using the term "soundproofing" is a bit unrealistic. Dampen would be more acurate.


----------



## Ted White

AngelArs, may I ask in what way you feel MLV is better than heavier drywall?


----------



## AngelArs

Ted White said:


> AngelArs, may I ask in what way you feel MLV is better than heavier drywall?


Hi Ted. Well for one it's lighter so you don't break your back :laughing: All kidding aside it's not a black or white question. First, MLV is not designed to be exposed to the room, so to use it as the manufacture intended the wall would need to be opened. Most people aren't going to do this. Regarding drywall; It would be a pain to add drywall to an existing wall, especially if that wall contained windows and/or a door. Then you've got to worry about the sound bleeding through the window and/or door. There is a new kind of drywall that came out that is lighter and yet stronger and more dense than standard drywall. It's only 1/2 inch thick and works really well but again, any drywall would be a pain to add to an existing wall. 

I have found that most people who aren't in the trade tend to misuse the terms 'soundproof' and 'sound'. Until the OP decodes what they meant, everyone else is just spinning their wheels by suggesting this or that. Something as simple as closed cell expanding insulation will cut down some noise, and it's much easier to install, but who knows if it's good for the type of noise that the OP wants to dampen. All things being equal, if a house was already built I wouldn't use MLV or drywall unless the customer had deep pockets. If the bathroom in question just has noisy plumbing, then just fix the noisy plumbing, after all, it's the source of the noise that they want to remove. If on the other hand they want to dampen the sound of someone singing in the shower, then they need to take other dampening measures. The point is that everyone needs more specific information from the OP before we know how to treat the problem. Bottom line, it's not that MLV is better or drywall is better, because each has their applications. In order to help the OP, they first need to tell everyone what their definition of "sound" is. :wink:


----------



## NetWell

dB-BLoc, or MLV, can be applied to an exposed frame or an existing finished surface and yes it is more dense than a .125" thick layer of drywall would be. True, if you double drywall, you trigger density, but the same could be held true if you built an 8' thick wall made out of chicken feathers. The key is to save space and go thin, which is exactly what dB-Bloc does. Layering it to an existing wall is easy, takes less depth, and triggers great STC values when properly installed. AngelArs is correct, each treatment is unique based on the starting point, so some fine tuning would be required to get the treatment right, but the treatment will perform. MLV is a component of an overall assembly system...layered beneath drywall. If the starting point is a finished surface, add the MLV and a firring strip system, then a new drywall layer. It is an easy, inexpensive procedure that works.


----------



## Ted White

NetWell said:


> If the starting point is a finished surface, add the MLV and a firring strip system, then a new drywall layer.


It's spelled "Furring"

Anyway that creates a triple leaf. Well documented mistake. Don't introduce a second air cavity. 

Drywall is 1/5 the cost, and 2x the mass. Keep it simple. If it's the wall, just install a second sheet of drywall from Lowes and call it a day.


----------



## AngelArs

NetWell said:


> MLV, can be applied to an exposed frame or an existing finished surface


I suppose any uninformed DIYer could install MLV any way they wanted to, BUT it would NOT be installed _correctly_. The correct way to install MLV is shown below. Even installed correctly there are better options available. 



> and yes it is more dense than a .125" thick layer of drywall would be.


Between standard 1/2 drywall and MLV, MLV will work better. HOWEVER, between something like Quietrock 510 drywall and MLV, Quietrock 510 drywall will _easily_ outperform MLV every time, and be much easier to install. If they also add some Quietzone insulation, then there is no contest and MLV could not even compete. If you are in the ’soundproofing’ industry and you are using blanket statements and telling your customers that "MLV is better than drywall" and you’re not being *specific* about _what kind_ of drywall, then you are being dishonest to them and doing a major disservice to your customers. 



> The key is to save space and go thin, which is exactly what dB-Bloc does.


There are better ways to "go thin" such as using a spray on form of MLV _inside_ the wall. Much easier and quicker to use yoo. The only downside of using it is the smell for the next 3 weeks while it cures :laughing:



> Layering it to an existing wall is easy, takes less depth, and triggers great STC values when properly installed.


Quietrock 510 has much better STC values than dB-Bloc (_MLV_).



> MLV is a component of an overall assembly system...layered beneath drywall.


Correct.












> If the starting point is a finished surface, add the MLV and a firring strip system, then a new drywall layer.


Not to nitpick but it seems you're talking out of both sides of your mouth :laughing: One minute you're preaching about _being thin_, and now you're talking about adding furring strips and drywal, Etc.l. Seriously, adding something like one sheet of Quietrock 510 will be much easier, quicker and more direct for the common DIYer, not to mention how much better it will perform.


----------



## Ted White

Angel, please don’t take this the wrong way, as I assume you’d rather know truth from fiction. Someone has sold you a bill of goods here. 

Once again, mass is mass. Could be Cheerios, Styrofoam, drywall, MLV, etc. Doesn’t matter where the mass comes from as long as there’s a lot of it. MLV does not work any better than other material of comparable mass. Since ½” drywall weighs 60% more than 1/8” MLV, drywall will yield better results, especially on a decoupled assembly. Such is Mass Law. MLV, being a heavy rubber, seems intuitively good for soundproofing, however lab data clearly shows that it’s simply another expensive source of mass. Nothing more.

The specialty drywall referenced is similar to the specialty factory-damped drywall from 4 other manufacturers as well. I have consulted with 3 out of the 5 manufacturers prior to their launching their particular drywall. I’m very familiar with it all and have formally tested various panels in independent labs since 2004. These panels are characterized as being very expensive per square foot (starting at $1.75 a square foot factoring in 11% waste). Second, they don’t weigh much relative to the cost. Given that soundproofing is a mass-driven thing, we want more inexpensive mass, not less mass for much more $$. This is why standard drywall is excellent. 

Spray foam is lab tested to be the WORST type of insulation you could consider installing for acoustics. Best for thermal, worst for acoustic. The greater density of the foam does not provide the absorption we need, and foam only serves to reduce our effective cavity depth, thereby further reducing sound isolation. Again, we go to Lowes or Home Depot, and while we’re buying their cheap and massive drywall, we’re also buying their cheap fiberglass insulation. 

Lastly, while that drawing is nice, virtually every detail of it is incorrect. There are either completely useless aspects (foam on channel, rubber vibraton pads) or expensive materials that have no business being there (closed cell foam, soundboard, metal tape). The RC-1 Resilient Channel is the one soundproofing product involved in the most lawsuits in the USA. Many acoustical consultants list “expert testimony in Resilient Channel litigation” among their services, that’s how commonly this product fails. I realize that a nice drawing implies truth, but not at all in this case.


----------



## AngelArs

Ted White said:


> Angel, please don’t take this the wrong way, as I assume you’d rather know truth from fiction.



Always open for interpretations and facts 



> MLV does not work any better than other material of comparable mass.


That's a blanket statement Ted and leaves out many factors. No one buys MLV because it is or isn't better than other materials of comparable mass. People buy it because it's easier to install, cheaper, and has less inherent issues than installing another material of comparable mass. For example; MLV is wear resistant and perfect as a carpet under-layment to dampen sound from basement areas, or first floor sound entering the second floor, etc. Go ahead, try using drywall under a carpet for sound proofing and see what kind of mess you have a month later :laughing: As I said before, every material has its application. Some MLV has around the same mass as a comparably sized piece of lead. That means MLV offers a lot of bang for the buck. Also not all MLV is equal. Some MLV is double weight which makes it even more desirable. If I was building a new house I would have no problem using MLV _inside_ the walls. After a house is built however I do not see any advantage to using it unless it's used under carpets areas. 

I don’t want to get too techie here but essentially sound is a form of energy. Energy can't be destroyed, only converted to another form of energy, so to dampen sound energy you have to convert it into heat. The simplest way to dampen any sound is to simply put a solid wall in its way. As you you double the mass of a wall, you roughly halve the amount of sound that is transmitted. But it’s not just about mass, because as a sounds frequency is reduced, the isolation provided by a structure also reduces. Basically for every octave drop in pitch, the sound isolation is halved. This is why it’s easy to muffle the sound of your neighbors annoying canary, but it’s hard to muffle the sound of their home theaters subwoofer. High frequencies are not too much of an issue to dampen, but deep bass is usually very hard. That is precisely why we need to know what KIND of sound the OP is trying to dampen. Just telling them to use this or that is like using a bazooka to kill an ant problem. Sure it might work, but there’s probably a better way to do it. 



> Since ½” drywall weighs 60% more than 1/8” MLV, drywall will yield better results


That's another blanket statement. Not all drywall weighs the same. Not all MLV weighs the same. Drywall does NOT always give better results. 



> however lab data clearly shows that it’s simply another expensive source of mass.


I've never seen anything like that. In fact, I've seen just the opposite. Feel free to post your links to prove your statement.



> Spray foam is lab tested to be the WORST type of insulation you could consider installing for acoustics.


That's not the point! We're on a DIY site and if the OP wants to muffle the sound of a leaky faucet then closed cell insulation is a cheap, easy and quick way to achieve that. 

No one is suggesting to use spray insulation in the walls of a recording studio :laughing:



> while that drawing is nice, virtually every detail of it is incorrect.


Not for the application it was drawn for. Every application is different.


----------



## Ted White

I appreciate your patience and demeanor, :thumbsup: and hope this sort of discussion isn’t outside the bounds of this forum. Generally people find this stuff interesting, I’ve found, so hopefully it’s OK.

Anyway, I think we’re just talking about a guy’s wall, not his floor, but I’d certainly agree you would not want drywall in a floor. I’d also agree that MLV under a carpet + pad is a great help if overall floor height can’t be increased much. That’s a great point I would also agree that after a house is built, there’s not much use for MLV, however if I were building a new wall, I’d start with 5/8” drywall, and if I needed more mass, I’d just add another layer of 5/8”. More mass for cheap.

Categorically, the great uses for MLV come from it being very thin and / or it being flexible and also being dense. That comes in mighty handy in some circumstances. Another fun fact is that due to it's flexibility it has an extremely high coincidence frequency . We'll save that for another day.

You bring up yet another good point in that it’s not all about mass. For higher sound isolation you would introduce decoupled framing, make sure there’s a little absorption (cheap fiberglass insulation) in the wall, and look to damp the mass. You quickly reach a point where the continued addition of mass alone becomes a diminishing return.

You mentioned about doubling the mass, which adds 6 STC points an assembly (rough lab rule of thumb). As far as how much sound the doubling of mass will affect, the answer is very frequency-dependent. Doubling the mass could very well stop 99% of frequencies above a certain point, while barely affecting lower frequencies, or any coincidence frequencies.


----------



## AngelArs

Ted White said:


> if I were building a new wall, I’d start with 5/8” drywall, and if I needed more mass, I’d just add another layer of 5/8”. More mass for cheap.


Next time I'm at Loews I'll have to check and see how much Quietrock 510 cost. I would think it would be cheaper than two pieces of standard drywall.


----------



## Ted White

Given that all of these pre-damped drywall panels are made from standard drywall and cement board that you can buy yourself along with readily available damping compound that you can buy yourself, it's no surprise that you can field assemble a much heavier, better damped panel for a fraction of the cost. And the seams will be stagered from the first layer to the next so better assurance against seal failure. 

This is an area where the DIYer will always do a better job for a lot less. Good news


----------

