Author Topic: Law of Diminishing Returns?  (Read 2999 times)

Craig Lyons

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Law of Diminishing Returns?
« on: February 17, 2003, 10:43:57 PM »
Hi,
I have a question as to if STC values are cumulative?
For example, say a double-wall construction with 2 layers of wallboard on the interior wall and exterior wall yield an STC of 63. If I were to add a layer of MLV (STC 26), would I then have an STC of 89 (63 + 26)?
Or, what if I just used 4 layers of MLV, would I have an STC of 104 (4 x 26)?
Thanks,
Craig


John Tower

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Re: Law of Diminishing Returns?
« Reply #1 on: February 18, 2003, 08:18:09 PM »
Craig,
 Despite what you may read, STCs are NOT cumulative. Mass Law states that for each doubling of mass, you get a 6 DB reduction in sound (factoring out any sound leaks of course), which of means you get diminishing returns as you add material.
Let's say you had a wall comprised solely of MLV (just for argument) and this wall had no sound leaks. You would get an STC of about 26. Add another layer of MLV, and you get about 32, then it would take another two layers to get to 38 (doubling the mass of the previous 2 layers. The MLV is still a good product because it allows you to add a lot of mass in only 1/8" increments, but don't be fooled, the laws of physics still apply.
A key point here, is that you should mix your approaches. You want to add adequate mass to a wall, and MLV can help, but you also want to decouple the wall, using RC or sound clips. These techniques in combination are they key.
John Tower
: Hi,
: I have a question as to if STC values are cumulative?
: For example, say a double-wall construction with 2 layers of wallboard on the interior wall and exterior wall yield an STC of 63. If I were to add a layer of MLV (STC 26), would I then have an STC of 89 (63 + 26)?
: Or, what if I just used 4 layers of MLV, would I have an STC of 104 (4 x 26)?
: Thanks,
: Craig