Garage Listing room

From what I just read on the web, the STC rating is a limited frequency power rating apparently measured in dBs. Acoustic power says 10dBs is approximately what we perceive as twice as loud (or half as loud). So a rating of 43 vs 33 would be twice as quiet (approximately). But don't forget that is a limited frequency measurement, not the full audio spectrum. 

QuietRock 545 is better then drywall. (STC-rated Assemblies ASTM E90:

60-80)

https://www.quietrock.com/products

@hiend2 "Going to bring in a set of speakers and amps and listen to someting fimilair, the room the system is in now are almost the same dimensions, will report" there you go. Listen and see what you have.

Since you will still be using the space as your garage and/or shop you may consider putting some drywall at selected locations on the walls to help reduce the amount of absorption in the space. Less about isolation and more about room acoustics and reducing the amount of absorption. I would normally suggests just using plywood on the walls in a space like that so you could use it to hang shop/garage items but sheetgood products like plywood and particleboard are still very high cost relative to last year. Drywall is more expensive as well but nothing like plywood. If you have a shop I'm guessing your relatively handy and you can hang the drywall yourself. Don't need to finish it if looks aren't a concern but this will help reduce absorption in the space. Best of luck! 

@arch2 

Since you will still be using the space as your garage and/or shop you may consider putting some drywall at selected locations on the walls to help reduce the amount of absorption in the space. 

I was thinking the exact same thing. Perhaps 2' drywall strips (spaced 2' apart), and add more as necessary. Yep, needs reflection.

I would also consider plywood or OSB, but as you say, it's still costing a fortune compared to gyp board.

arch2

Yes on your reply, Take advantage of the absobtion of the insulation.

If I would cover all the walls with wall board would end up with a lively mess