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Author Topic: Limp Mass vs MDF  (Read 2811 times)

xAm

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Limp Mass vs MDF
« on: September 12, 2006, 07:52:43 pm »

OK, this is killing me to want to be able to do the numbers and figure it out, but I just can get it straight...

In a Room w/in Room construction, which offers the best STC for dollars invested...

Example one:
1. Stud
2. Cavity
3. Stud
4. MLV
5. Gypsum
6. Gypsum

OR

Example two:
1. Stud
2. Cavity
3. Stud
4. MDF
5. Gypsum
6. Gypsum

OR

?!??!?

X
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franman

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Re: Limp Mass vs MDF
« Reply #1 on: September 15, 2006, 03:58:01 pm »

Okay... if we're talking about using a Limp Membrane in combination (lamination) with other building materials... SKIP IT!! This type of buidling material CAN be very helpful, but the listed STC numbers are misleading. The membrane itself has decent numbers when used MONOLITHICALLY... not attached or sandwiched between anything else... If you are creating a multiple layer boundary wall, stick with Gyp Bd, MDF and other "heavy" materials. It's a mass thing, not a limp mass thing... Hmmmm.. that's what I told her!!
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xAm

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Re: Limp Mass vs MDF
« Reply #2 on: September 16, 2006, 05:47:00 am »

franman wrote on Fri, 15 September 2006 15:58

Okay... if we're talking about using a Limp Membrane in combination (lamination) with other building materials... SKIP IT!! This type of buidling material CAN be very helpful, but the listed STC numbers are misleading. The membrane itself has decent numbers when used MONOLITHICALLY... not attached or sandwiched between anything else... If you are creating a multiple layer boundary wall, stick with Gyp Bd, MDF and other "heavy" materials. It's a mass thing, not a limp mass thing... Hmmmm.. that's what I told her!!


Fran,

I shouldn't have had that cup of coffe in here... you owe me a keyboard!!  Laughing

I kinda suspected that the limp mass layer was only marginally improving the STC, but at a much higher cost per pound.

Thanx!!!

Max
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RKrizman

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Re: Limp Mass vs MDF
« Reply #3 on: September 21, 2006, 10:02:03 pm »

Is drywall a factor in bass absorption?  Do you approach treating a room differently if there are a lot of gypsum board walls versus stone or concrrete?

-R
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franman

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Re: Limp Mass vs MDF
« Reply #4 on: September 24, 2006, 11:53:33 pm »

As Lars has noted is some other posts, lighter drywall construction certainly does have some membrane effect for LF absorption. We normally build rigid shells out of multiple materials and don't calculate any membrane action from the drywall shells themselves. Make sense??

There are many different approaches to this.. Many folks design rooms with single (or double) layer drywall inner shells and calculate the membrane action from this construction based on weight per square foot and stud spacing. Snce Isolation is almost always a concern in our projects, we are building heavier walls. If they are masonry walls we treat them as infinite LF boudaries for the purposes of calculating modes and designing treatments.
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xAm

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Re: Limp Mass vs MDF
« Reply #5 on: September 25, 2006, 10:11:57 pm »

franman wrote on Sun, 24 September 2006 23:53

If they are masonry walls we treat them as infinite LF boudaries for the purposes of calculating modes and designing treatments.


What would the recommended construction method be for a masonry wall to avoid triple leaf, and therefore keep the infinite LF boundary?

It's my understanding that regardless of construction, a triple leaf system will indeed become less effective as a LF barrier.

Max
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franman

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Re: Limp Mass vs MDF
« Reply #6 on: September 28, 2006, 08:18:10 pm »

heavy CMU block at least 6" (8" is better), filled with concrete in the voids then rendered with concrete on both sides to "seal" the block.

Or, you can get into furring and drywall laminations and this will improve LF performance but you add some membrane effect from the drywall. I would still render (seal) the block wall.
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