Do Not Use MLV When Soundproofing
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Yup, you read that right. Don't do it! I am trying to stir up the internet on purpose. MLV is not as good at stopping sound as Green Glue with two layers of 5/8" drywall. I also am going to argue in the article that your soundproof room is only as strong as its weakest link, which in all rooms will most likely be the door.
1) You Are Only As Strong As Your Weakest Link
It is so important to understand that a soundproof wall with an STC rating of 63 and a soundproof door with an STC rating of 57 means that your room will have an overall STC of 57. Your wall will block a lot of sound, but those same sounds will come in your door that were blocked by your wall.
With this in mind it is extremely important to build your door so that it matches the STC of your wall.
So what does this have to do with MLV.
Let me explain.
2) MLV and Green Glue Increase Your Walls STC
That is a good thing right? Well, not so fast. If you build a doublle wall with just two layers of 5/8" drywall on both sides and achieve an STC of 63 then your door must also equal an STC of 63. To do this you must by a $5,000 plus door from a soundproof door supplier or build your own. To build your own you must match the mass of your two walls.
So, two walls with an a combined STC of 63 means you have 4.4lb/sqft on one side and 4.4lb/sqft on the other side. If you build a single door it must equal 8.8lb/sqft. Lets say your door is 36" x 80" or 20 sqft. Then your door must weight 176lb at least. This is the minimum and more is better.
Now, if you add Green Glue to your walls then we know that is the equivalent of adding 2 more layers of drywall to your wall. The reason we know this is from lab testing and this information is also in Rod Gervais's book: Home Recording Studio: Build It Like the Pros.
This would double our mass needed on our door to 352lb's. Yes, that is a very heavy door.
If you add MLV you will need to figure out how the added weight and damping effect of MLV will increase your soundproofing and adjust the door mass accordingly. Since Green Glue performs better than MLV my guess is you could build a slightly lighter door.
My point is that you may get enough soundproofing from just the two layers of drywall on each wall. This would mean you are wasting money on Green Glue or MLV. Or if you do use the damping products you must increase the mass of your doors and windows accordingly. This will increase cost overall and may, again not be needed.
3) Green Glue performs better than MLV
According to Lab Tests done by the Green Glue company with a private third party lab, Green Glue simply performs better than MLV. Look at this graph from the Green Glue company below.
You can see that Green Glue outperforms MLV except at 125hz. It performs better than MLV in general over the entire frequency spectrum. So, my question to you is why would you use MLV over Green Glue? Why would you use MLV over just two layers of 5/8" drywall?
Is it because MLV is advertised well all over the internet? That is true and most searches for soundproofing will lead you to MLV. That is called great SEO and it makes MLV suppliers a lot of money. The bummer is that you are the one losing out, not them.
Conclusion
My point is that adding damping in the form of MLV or Green Glue will improve the STC and Transmission Loss of your walls, but do you have the means to also increase the STC and TL of your door as well? If not, then do not bother with either MLV or Green Glue. Next, we know from lab tests that Green Glue performs better so if you are going to add a damping layer to your soundproof design please use Green Glue and not MLV.
