Originally Posted by Robert Jones II
I'm still learning my way through this stuff, so I'm sorry if I misspoke. To my pedestrian brain isolation meant both keeping sound in and keeping sound out. My 3-year old son's bedroom is the only room that connects directly to the theater room. In an ideal world I would want to be able to watch movies with him sleeping next door without having my wife worrying about whether we are going to wake him by watching an action movie (keeping sound in). On the other hand, I don't want to hear the kids next door playing basketball while I'm watching a dialogue-intense movie (keeping sound out). The slope ceiling may have less to do with either, and more to do with how the room is treated, but these are all concerns that I would like to have a clear plan for before beginning any sort of construction.
I suppose my thread title ought to be: Sound isolation, sound proofing, and how to treat a sloped ceiling room.
Isolating the room will significantly reduce the amount of sound leaving the room. Sound isolation requirements outside the room is +3dB over ambient noise if done correctly. You'll have to determine what is more important...stopping low frequency waves (equals money and significant portions of your room being eaten for dead air space), or making the room quiet (~20dB) while significantly reducing the amount of sound leaving the room. Keep in mind, only the lowest frequencies will be transmitted, and often just a low rumble during dynamic low frequency reproduction (explosions, etc.)...if done right. That's the trick. Perhaps Dennis Erskine's paper on designing a home theater might help with some considerations.
Getting to Big's mention of the activated carbon...the paper he dug up and shared with me is this:
There are very few scholarly papers written on the subject. It is a true peer reviewed white paper, and gets into the thermodynamics of activated carbon low frequency aborption and adsorption. If you don't like dealing with partial differential equations, here are the take home messages:
1. The absorption coefficient for activated carbon is 0.24 around 50 Hz. This is significantly higher than sand which 0.04. However, keeping this in perspective, 0.24 still isn't much.
2. The authors found that only specific types of activated carbon seem to achieve the results. They didn't go into great details of which, but I get the gist you can't go burn pallets in the backyard and stick it in your walls (although it works well for water filtration!
3. The results seemed to surprise the authors, and no doubt further research is likely ongoing, but this area of acoustics is pretty young in the research department...so all the details are not yet in as to who, what, where, why and how. Your welcome to wait to build your room when all the research comes in!
4. It is an expensive solution compared to more conventional and cost effective means. Also, the cost of the solution, in my opinion, appears to yield diminishing results in cost vs. effectiveness. As I said, 0.24 isn't that much, but it is interesting. Not to say, that more material couldn't yield better results, but the cost also goes up along with it.
Just my two cents FWIW.