Has anyone used "Quiet Rock" sheet rock in room?

Rigid foam is a great way to go. You can get anywhere from 1/2 in to 2 inch in 4x8 foot sheets. I have this on the exterior walls of my house and you can't hear anything. You would just need to make sure you or someone doing the project understands vapor barriers.

Rives is right - a wholistic approach is by far the most cost-effective. Getting wall transmission down by 50 dB is of academic interest only if your doors only isolate by 25 dB and/or if your air conditioning ductwork acts like an intercom. You gotta pay attention to all the little things - the wall outlets themselves may be a significant sound transmission pathway. Sound can transmit by vibrating the air or by vibrating a large structure which in turn vibrates the air.

Also, if the walls of the room are somewhat lossy at low frequencies this works in your favor because it damps the low-frequency room modes. Consider using resiliant channels to hang the sheetrock; this is far more lossy than direct attachment to the studs and significantly reduces mechanical sound transmission. Insulation in the wallspace would reduce air-borne sound transmission between the walls. But, what about the door?

Nothing wrong with Quietrock, but don't blow your whole budget on that unless that's really the only problem you have. It's like having six leaks in your rowboat so you do a really really good job of fixing only one of them.

There are two chapters chapter devoted to this subject in Earl Geddes' book, "Premium Home Theater: Design and Construction". It will save you far more than its $44.00 price.

http://www.gedlee.com/Home_theatre.htm

Duke
dealer/manufacturer

I did not use the quietrock sheets in my room, but did use the safe n' sound insulation in between the walls and double drywall. It is very quiet outside the room but would not contain 120 db levels. I used to play drums for a living, and still play, and it would be hard to completely insulate that kind of vibration from leeking out of a room without building a 'room inside a room'. I also agree with Bjesien that you have to be careful about vapour barriers on outside walls. More important is the issue of heat buildup inside the room. You would need more than just a heat run to the room. You would need at minimum a cold air return as well and it would be critical that these were dealt with so that the sound would not be leaking through the ducts into the rest of the home, no matter how well the rest of your room was insulated. No sense in having a beautiful quiet room that is too hot to be in. You could build a 'hushbox' for these. There used to be good ideas on the 'www.hometheaterbuilder.com' website, as well as 'mufflers' you can buy already made to insert between ductwork pipes.
I built a room approx. 11' x 18', did all the work myself including the ductwork and electrical etc., and spent about five thousand dollars on materials. That did include a riser (insulated and ported) with several layers of plywood for the second row of seats though. Good luck!

Also, if you are going to insulate the best option is blown in poly spray foam, next would be blown in cellulose or laying blue jean batts. Stay away from fiberglass for insulation because it's junk.
Blueboard and plaster is better than sheetrock too. More $$ but it has a better finish and and is more solid, not flimsy.

Use tight, heavily weather stripped, exterior entrance doors inside. I've done that and it makes all the difference.