Please advise on SCT for this wall partition.

[Seatac]

Could someone please please help me to determine the SCT for the following wall partitions:

1.- 2"x6" wood studs c/w 1/2" drywall on both sides - adding one layer of 1/8" MLV membrane, 1/2" drywall on top, GG and a second layer of 1/2" drywall.

2.- 2"x6" wood studs c/w 1/2" drywall on both sides - then resilient channels, 1/2" drywall, GG and the final layer of 1/2" drywall.

3.- 2"x6" wood studs c/w 1/2" drywall on both sides - adding one layer of 1/8" MLV membrane and a single layer of 1/2" drywall on top.

Thanks!

[johnbergstromslc]

The wall configurations you mention are too unusual - I've never seen any independent, third-party tests on the STC of walls with MLV. 

The Green Glue company has done limited acoustical testing with their product.  Find them here:

http://www.greengluecompany.com/transmissionLossTests.php

[Seatac]

The wall configurations you mention are too unusual - I've never seen any independent, third-party tests on the STC of walls with MLV. 

The Green Glue company has done limited acoustical testing with their product.  Find them here:

http://www.greengluecompany.com/transmissionLossTests.php

J.B;

Yes, maybe I'm just a little too lost with my little project - I'm not really sure what to do with my wall. I'm trying to find a fit solution but maybe I'm going too far. I think that I'll just end up putting an extra sheet of drywall w/ some GG on top of my existing wall. But I am a little hesitant - don't know if that will be enough to quiet my neighbour.

Would you use soundboard + drywall over existing wall OR GG/ drywall over existing wall? what do you think?

Thanks a lot for your help!!!

[joel]

If you check out the independent third party tests on the Green Glue link jb provided in his post (was it the last one?, we lose track) you will see that MLV has been tested in wall assemblies.  There are numerous lab and field tests that have been done with MLV in wall/floor/ceiling assemblies.  Most of the tests done by competing materials will always sandwich MLV between sheets of rigid building materials - thus pinning it flat.  It is designed to be able to flex within the assembly - attached directly to studs/joists with rigid material next.  In fact, the UL approved method uses that assembly.
As a general rule of thumb, MLV adds 26 STC to an assembly when applied as described above.  When pinned flat between materials like dry wall it is reduced to between 10 to 17 STC - depending on who did the tests.  Adding sound deadening board to an existing drywall adds around the same as a second sheet of dry wall - 4 STC. 
If you want to send me an email ( joel@soundproofing.org) I will help you figure what your assembly STC would probably be.  As for Green Glue between sheets of dry wall you can estimate a minimum 10 STC improvement.  Since Green Glue is "squiggled" onto a rigid building material when it is used, it doesn't lend itself to standard STC testing methods - it's pretty hard to fill an open space in a test wall with a visco-elastick bead (it won't just hang there like a spider web).  More importantly, Green Glue will give a 13-15 dB (per test results) drop in low frequency sound - the hardest to block. 

[johnbergstromslc]

I just followed my own link and they have definitely added a few new wall specimens since I was there last.  Need to check in more often, I guess.  I found the MLV-wall acoustic tests interesting.

Joel, I do have to disagree with the "MLV adds 26 STC to a wall assembly" statement.  If you look at the tests, it clearly contradicts this. 

Test OL 05-1003 (5/8" drywall each side, insulation, studs 24" o.c., STC 40) versus test OL 05-0822 (same as above, with MLV added, STC 45) indicates a gain of only 5 points STC.  That's a long way from 26! 

A piece of MLV, by itself, hanging as a curtain might score 26 (as a 1/2" piece of drywall rates 28) but as part of a composite assembly it's not even close to that and never will be.

Also, a consideration of MLV is price.  The cheapest I've found is $1.50/sq.ft, or $48 bucks for a 4'X8' piece.  That's equivalent price-wise to 6 regular sheets of drywall.  Pretty expensive way to gain 5 STC points!

Green Glue aint cheap either ($30 for a 4'X8' area, in the recommended 'dosage'), but the low frequency isolation it provides makes it worthwhile.  Attaining good low frequency damping is most of the battle.

Seatac, you might want to invest in a sound level meter and take some measurements of your noise problem.  Multifamily dwellings are required to meet STC 50 between units; I suggest that be the minimum number to shoot for.

But 55-60 would be better....     

[joel]

If you check out the wall diagram it shows the MLV pinned flat between two sheets of dry wall - the worst way to use it (unless you use two layers).  Glad you re-checked the Green Glue lab tests.  You might want to check another site - acoustiblok - to see what their lab tests show.  Big difference. (by the way, Green Glue and acoustiblok did a project together a couple of years ago where Green Glue was used directly to MLV and covered with 1 sheet dry wall with "spectacular" results - but I could not get the test results from Green Glue as acoustiblok paid for the field test.  I have used this method to "fix" many already "soundproofed" home recording/practice rooms.)  My recommendations are based on the experience of the customers I work with and those that came before.  STC ratings are only a guideline.  When soundproofing anything, especially walls, the important factors are to decouple any vibrating surfaces from the structural's their attached to, absorb and block sound in a contained space (dead air space does not exist in the real construction world), and barrier the remaining air-borne sound.  Barrier materials work differently - different materials for different frequency ranges and amplitud (loudness).  Absorber/barriers work diffently also.  Combining the above with the type of sound and the results desired within a budget - that is how to solve soundproofing situationally.

[johnbergstromslc]

I think we need to agree to disagree on this point.

The wall test with MLV I cited is not for "MLV pinned flat between two sheets of drywall".  Both tests are single layers of 5/8" drywall on a regular stud wall and the diagram of the built wall shows the MLV installed in a loose, 'wavy' pattern underneath the drywall on one side. 

Page 2 clearly shows this:
http://www.greengluecompany.com/images/transmissionLossTests/OL05-0822_Report.pdf
And on page 6 it states: "The prefabricated mass-loaded vinyl sheets were limply hung and the seams sealed with lead tape."

I'm a convert to Green Glue and I use it whenever budget allows but I've used MLV several times on jobs and I have never seen "spectacular" results.  It has it's uses, but MLV is simply a way to add mass to a partition while adding marginal thickness. 

I can only speak for myself, but every customer of mine who has had MLV used on his/her project has been disappointed, considering the money they spent.  They bought into the MLV hype and expected a lot more than it could deliver. 

Details matter in soundproofing and it's too easy to cut corners and install MLV incorrectly (especially among the DIYer's you sell to) and it can quickly become a nearly worthless addition to the wall.

MLV is too-often touted as a 'magic sheet' type of product, something that you can put up and, voila, noise problems gone.  You know as well as I do that isn't true.  Maybe sometime in the future...   

The best ways to achieve 'spectacular' results in soundproofing are the old, tried and true ones: decoupling, mass, absorbtion and sealing.  Viscoelastic damping should be the 'icing' on the cake, not relied on as the main strategy.   

[Seatac]

Joel and J.B;

You guys are great - thanks so much for your interest and help. I'm sure that I speak for many when I say that your continuous support and dedication to this forum is very very much appreciated. Stay cool!