Author Topic: Advice please - Common wall between townhouses - Triple Leaf?  (Read 825 times)

jackmorgan

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Advice please - Common wall between townhouses - Triple Leaf?
« on: October 27, 2016, 07:43:50 PM »
Hi,

I recently moved into a townhome.  The shared wall with my neighbors consists of 1/2 inch drywall, 2x2 wood studs, 8 inch concrete block, 2x2 wood studs, 1/2 inch drywall.  The overall sound isolation is good, but certain frequencies of sound seem to go right through the wall - specifically talk radio early in the morning.  Through my research i believe i am experiencing a triple leaf effect due to the wall construction.  The frequencies of the radio voices are causing resonance in the wall and going right through without being damped, while most other frequencies are effectively damped.  I can still hear some impact noises. 

I want to add some soundproofing and can only access my side of the wall. 

I was thinking I should remove the existing drywall on my side, add a steel stud wall about 6 inches from the concrete block wall for decoupling, and fill the cavity with insulation.  This would still be a triple leaf issue (unless the different materials, ie concrete and drywall and differing gaps mitigate this effect?), but I'm hoping it will lower the resonant frequency of the wall enough so I can't hear the noise.  Is it better to leave the existing drywall in place? (this would obviously be easier).  Is 6 inches enough of a gap or should i sacrifice more space in the room (which is already tight).  Any thoughts or insights would be greatly appreciated.

Thank you.

Jack

Randy S

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Re: Advice please - Common wall between townhouses - Triple Leaf?
« Reply #1 on: October 27, 2016, 10:45:05 PM »
Jack,

You are experiencing a triple leaf effect, you should remove the drywall, most likely the cavity is hollow. This will give you a chance to inspect the concrete block..if cinder block they most likely left it porous which is why human speech is intelligible. 
You will need to seal the block, so paint it with a Henry's Elastomulsion.
You will only 1" space between the block wall and the new frame work.
rebuild the new wall with 2 x 4 wood studs, insulate R13 , staple up a layer of mass loaded vinyl to the studs, seal all penetrations and perimeter with acoustic caulk and tape field seams.
Install double 5/8" drywall with green glue in between and done.

As for impact, are you raised foundation? impact from footfall normally will go under the soundproof wall and since the floor joist system would be attached to the block wall this will most likely still exist.

feel free to contact me direct if you have any questions or concerns.

Randy S.
760-752-3030
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

jackmorgan

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Re: Advice please - Common wall between townhouses - Triple Leaf?
« Reply #2 on: October 28, 2016, 01:19:42 PM »
Thanks alot Randy, you've confirmed my theory.  I know this is the best solution, but my next question is, is there a cheaper way to do this?  I've priced out your solution and it comes in at around $900 cdn which is out of my price range.  I guess i'd like to know what's a must and what I can potentially leave out?  Green glue claims to be the most cost effective solution (according to their research) - especially around the 100hz frequency.  Is there any way to determine if the existing brick is porous or not (to eliminate the membrane)?  What weight MLV do i need (price is obviously more for a greater thickness), or can i leave that out? I'm willing to give up some extra space between the block wall and the new wall if that will help.

Thanks again!

Jack

Randy S

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Re: Advice please - Common wall between townhouses - Triple Leaf?
« Reply #3 on: November 01, 2016, 04:44:27 PM »
you must check the block, that must be sealed.

If you eliminated the MLV you must increase the added mass on the frame ...you can start by adding 2 layers of drywall assess the reduction and if you need more then add more sheets of drywall.

Randy S.
Randy Sieg

Super Soundproofing Co
www.soundproofing.org
888-942-7723
Ph. 760-752-3030
Fax.760-752-3040

 

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