Your soundproofing is only as good as your weakest link, so in this case the sections with DD.
To take an extreme example - image a double cementboard room that is perfectly installed. Now add an open door to that room. No matter how perfect those walls and ceiling are, the open door defeats any sound proofing efforts.
The chain analogy doesn't really fit here. A chain will break and be useless, and thus is as only good as the weakest link. But 100% of a theater's sound doesn't escape out of the weakest point of a room. Every theater compromises in certain spots on sound isolation and other concerns (that is why we have doors to our theater
). My point is that the less weak spots you have, the better. If cement board improves sound isolation, and reduces the amount of weak spots, that can't be a bad thing in my opinion.
Originally Posted by Ted White
Standard Durock, etc isn't that much different in density to drywall. For this to work, you'd have to get the ultra-dense stuff from Joe Hardy Co.
$35-$45 a 4x8 sheet for 1/4" as I recall. Drywall is $7
Now we are talking numbers and making sense. 1/2 inch Durock weighs cement board is 3 pounds per square foot, while standard 1/2 dry wall is 2 pounds. 5/8 dry wall is 2.6 pounds per square foot. Joe Hardie 1/4 cement board is 1.9 pounds sq. ft, They make a .42 inch think board that is 2.6 pounds per foot. So the Durock, at least according to the websites, is actually heavier. An extra pound per square foot in increased density has to mean something, doesn't it?
You can buy the Durock in 3x5 sheets for $7.88 per sheet from Lowes, maybe cheaper in bulk. And I would be willing to spend a little more for improved performance.http://lowes.com/lowes/lkn?actio...964&lpage=none
Not sure if I'll do this in my theater, but I think its a reasonable option. Admittedly a base layer of cement board + GG and a finish layer of regular dry wall isn't as good as three layers of dry wall, but it has to be better than just two layers of regular dry wall, and the expense isn't much more.