Check out GIK acoustics art panels.  You can decorate those panels however you like.  Also check out the AMcoustics room simulator for help understanding what kind of room modes you are going to have.

https://amcoustics.com/tools/amroc

"...a dedicated room for audio?

Ahh, if only I could be so lucky!

If I was that lucky, I guess I'd be most concerned with just how lively I'd want the room to sound.

Just how lively you might prefer will be a matter of personal taste, but I certainly wouldn't want my room to be as anywhere near as acoustically dead as an anaechoic chamber. Far from it.

Then there's always the old handclap test to tell you quite a lot about the way your room behaves.

Perhaps the real problem will depend upon your speakers, and the amount of bass they produce.

But even here, you have resources such as isolation aids to help with any issues.

It's also certainly an interesting question to see if there's such a thing as a good room, one that's better for all equipment, all of the time, in all regard.

Good to hear that you can move the speakers out into the room. Otherwise, you'd be ruling out quite a few designs right off the bat.

I am fortunate enough to have an outstanding audio space. It was acquired quite by accident. The best my dealer/friend has heard in thirty years of installing high end systems, many are $200K+ systems built for the purpose. Unfortunately, it is the exact opposite of what you are planning.

First mine is underground. The quiet is palpable down here. Your plan is to subject the entire structure to vibrations and external noise by putting it above the garage is just a receptor to sound and vibration from the outside world.. My space is asymmetrical in every respect. Basically it is on the top half of a very large Z room. See my UserID to see my main system. The three basic things that makes my space great is: underground, highly asymmetric, and large. Another great thing is that the main bedroom (my partner sleeps during the day) is upstairs and far away from my listening space. She is a light sleeper and cannot hear my system no matter how loud I turn it up.

I am sorry to say, but you are completely on the wrong path to having a great listening space. The stud spacing is never going to make up for location, symmetry and size. I would reconsider everything.

I am really sorry to be so blunt. Your forthought is fantastic. I wish I had such great forthought… I did not… I was lucky.

Humbly, George

I have to agree somewhat with George. Although, not in the same league as his space, I’m in the basement too because it sounds so much better with concrete walls and floor. 

Sorry AGon has such a weird platform. See following:

Thanks for the responses so far. @erik_squires can you explain how to interpret the graphs associated with the room simulator software? @dweller thank you, I had read through that thread--very helpful. I am hoping that some members whose room is also a "bonus" over the garage can offer some suggestions to address the limitations George has cited. @ghdprentice I totally hear you. Big tradeoffs here--first, my son will need the basement for his own activities so that room is out. Also, while I can appreciate how block and cement will respond more favorably to vibration, the room I am building will have some nice natural light and views of the mountains and vineyards below. Better in my mind to try and tame the room problems and enjoy the view than lose the view in a basement scenario. Please keep the suggestions coming on how I can make the best of the space I have to work with!

Having a symmetric room definitely helps with soundstage and channel balance, but I don't think the dormer is going to be that big of a problem. With careful application of acoustic treatments, you can balance the reflections off the side walls and get a great presentation. 

Since you are not too concerned about leaking sound out of the room, I don't think it's necessary to go crazy with special construction techniques. Basic drywall (perhaps a bit thicker than normal) on 16" spaced studs works quite well.

You're probably going to want to beef up the floor joists (if that's not too difficult). A good solid floor makes a big difference in bass performance. I'd recommend hardwood floor with a high quality wool area rug instead of carpet, since this gives you more flexibility (size and thickness of the rug will alter the acoustics quite a bit), but this is a fair amount more expensive than going with carpet. 

The most important thing is to minimize noise from outside. If you don't live on a busy street, the most common cause of this is from HVAC equipment. If your furnace, water heater, etc. are in an adjacent space, you'll want to provide extra sound proofing on that wall (or between floors). With walls, it's relatively easy by using separate studs for the interior and exterior wall such that their is an air gap between the exterior wall and the studs supporting the interior wall, and add insulation in the internal space. I built my last dedicated home theater this way and it was very effective at minimizing sound transfer.

The other thing you need to look at is the venting into the room. Vents are an excellent conduit for noise, and can also generate noise on their own if the airflow is high relative to the ducting/vent size. Using significantly oversize ducting with a large plenum to allow the air to expand before entering the room with oversize ducts helps a lot. Adding some sound absorption material in the plenum will also help. 

You'll also want to make sure you incorporate the dedicated mains wiring you'll need. You may decide to move your equipment around or add additional, so install more lines and outlets than you think you'll need. It's MUCH easier to add these when the walls are open.

I'd also recommend consulting with an acoustics specialist to help with selection and placement of acoustic treatments. As I'm sure you're aware, proper treatments make a huge difference in the quality of sound you'll achieve. 

In addition to GIK Acoustics (which seems to take forever these days to delivery product), I'd recommend checking out ATS Acoustics. Their prices and quality are similar to GIK, but they are much faster and also willing to do custom sizes for a small upcharge. I've had excellent service from them.

@dodgealum Don't be put off by the nay sayers.  I built my listening room in a similar "bonus room" that extends over the garage.  14' x 23' with a ceiling that raises in the center to 11'.  I used some acoustic panels and used the 20% rule in placement of my system.  The front of the speakers are 20% of the room length off the back wall and 20% of the room width from side wall to speaker center.  The result is a great sounding system.  Is it perfect?  No.  Could I hear the differnce in a better room?  That's always the question.  Don't get bogged down chasing some ideal we can nver achieve.  Build your room, enjoy the music.  

Building a Listening Room

• by Robert Harley
• May 28th, 2019

Robert Harley - Building a listening room

I have read that article in the past.  While I found it interesting, who among us can affort the cost of a room like this?