Help Building an Audio Room

Thank you both for the level-headed input.  
I love the idea of a bookshelf/built-in wall to effectively build one wall out and provide some trap and diffusion in doing so. I think that will go a long way, and I can see in the pic they did something similar. 
If I did that on a side wall, I might explore building the front or back wall with a bit of angle; top edge of wall built out 6-10” more into the room than the bottom or vice versa. I’m thinking that may help and be barely noticeable. 
The cost is essentially the same to the builders/me, but as I socialized the idea with them a few weeks ago, they said, “That’s a first. Build it out of square?.. We can do that.” 
I’ll check out the book, too. 
Thank you again. 

Just ordered the book.  Thanks for the recommendation. 

Good job on getting the harley book. Best single source on audio.

I once had a dedicated room in a basement. It was 13, x 15, after framing the front wall and the right wall. Other walls were framed interior to basement.  I had stand mount speakers along the 13' wall about 2.5" from wall with nothing set in between.  Equipment was on a rack to my right. I had DIY acoustic panels behind speakers, at reflection points and behind listening chair which was ~3' from back wall.ceiling was 8.5'. Listening was nearfield. 

It as like having a front row seat in a club with great acoustics. 

I would frame in the three walls so to approach these dimentions. In the Harley book there is a discussion on best room HxWx L ratios. If you frame in the ceiling to reduce height you should consider adding a sound pannel into it at a reflection point. For that matter acoustic panels could be incorporated into the side and back walls as well.  

Good luck on a great project.  

Walls

Even if you do a great job of sound insulating the walls and ceiling, sound travels great through hvac air ducts.  Learned that one the hard way.  Good luck.

@jo1mtb i am also preparing to build a dedicated two channel listening room in my basement with 10 foot ceiling height. I have spent 3 months researching everything from room dimensions for least problematic room modes to optimized wall construction methods for noise isolation/best acoustical performance to best dedicated electrical service practices. 

Here are a few suggestions to consider:

1) Room dimensions have a significant influence on room modes that will give you fits and require big investment in room treatments to try to reduce these “built in” problematic room modes. Bottom line is that a) square rooms are most undesirable, b) any dimension that is a direct multiple of any other creates overlapping axial modes (the most problematic type to treat), c) small changes in any dimension (even a few inches) can have a large effect on resulting room modes.

So, your proposed 15’ x 15’ x 10’ room size is really a big problem (violates a and b above). Even a 15’x 20’ x 10’ room would be a real problem with overlapping axial modes. One of the best ratios is 1.4 x 1.9 x 1. Given our fixed 10’ ceiling height, that would be a 14’ x 19’ x 10’ room. This is the room size I plan to build.

If you want to play with different room dimensions scenarios to see their resulting room mode behavior, try this tool (and also Bob Gold’s calculator):

2) After talking with several big name acoustic design companies, I have chosen ASC. Their technical folks are readily available for consultation (at no fee), are super helpful, and never try to push their products as the solution to every need. I also have concrete block walls on two sides on my planned room space. Their advice here was to build the framed walls at a least a few inches away from the concrete block to give air space for pressure to escape, also using insulation between studs and even plywood sheet on the outer side of the framing.

Since our master bedroom is directly above the planned listening room, sound isolation through the ceiling (both to and from he bedroom) is a major concern. After thoroughly investigating several options, I chose ASC’s ISO-Wall resilient channel system for the construction method for my room. Not only does ASC’s system provide excellent sound isolation, the resilient channel system allows the walls to act as controlled membranes to improve low bass room modes. You can get details on this system form their website or by calling ASC.

3) My conclusion on insulation was that the more expensive types (rock wool, etc) are a poor cost/benefit proposition over standard fiberglass insulation. It is the millions of small fibers with ample air space between them that perform the work on acoustic dampening, so loosely packed fiberglass insulation (R-13:or R-19) works great between the studs in your wall. Consider using 2” x 6”:lumber for wall studs in your construction - much stiffer than standard 2” x 4” studs ad only about 20% more expensive. 

4) As for room acoustical treatment, that is a whole big enigma unto itself. Beware of companies that push “more is better” and “one size fits all” recommendations. Room size and construction have a great deal of impact on how much interior room treatments will be necessary. Poor decisions on room dimensions and construction techniques will cost you much more in subsequent interior room treatments to deal with the undesirable room modes and resonances that will result.

Hope this helps!