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

It is expensive, but does work. However, you should consider what your goals are. Is it to isolate the room? There are less expensive ways to do this reasonably well and you will likely have other sound leaks--so don't break the bank on one aspect of sound isolation and forget another.

Second aspect, if you build a really rigid wall it will increase your peaks for modal response. Thus by isolating room in one particular method (stiff walls), will actual reduce the performance of the in room frequency response.

Check out our resources. You will find an article on sound isolation (right column) that may be of help to you.

If want Metalica at 120 db and to be quiet outside--full on sound isolation, then separate wall structurs inlcluding Quiet rock (the heavy 160 lb a sheet stuff), floating floor, hung ceiling, windows are possible, but difficult and expensive, double fourier entry studio doors, specialized isolation for all penetrations including electrical and some very inventive HVAC solutions. Build cost would likely be $30k, maybe more depending on location and how complex the HVAC gets. And figure on losing 22" in length and width and close to the same in height to construct what's needed for isolation.

We do recording studies--where it IS Metalica or Ozzy not reproduced--but actually recording and producing music. Sometimes the studio is near a highway--always difficult. Then the same studio is used for a vocalist and it has to be absolutely quiet to hear every nuance--no HVAC noise at all because the ribbon mic will pick it up. The engineering is expensive, the build out is very expensive, but it can be and regularly is done for commercial endevours. It is very rarely done at this level for residential environments, but we have done it for a few clients.

Unclejeff--that's interesting and we will actually explore some possibilities of using that in combination with a layer of sheetrock and green glue in between. Same material layers (5/8 sheetrock) with green glue in between give really incredible results for $ spent. I think we may do some experimentation with this Densarmor board. Is it similar to blue or green board?

Field observations are sometimes where discoveries are first made. We regularly learn things from builders and then incorporate them into our plans so that everyone benefits.