Most important fundamentals in your built/modded listening room?

Fantastic set of comments! I am copying these out into a list meant for a contractor. These ideas will be implemented. I hope there are more.

Some replies to you generous folks:

The room won’t have noise issues. Just master bedroom upstairs and my spouse is usually somewhere else in the house. No traffic to worry about.

Thus, regarding noise, my takeaway from the comments is that a modicum of noise reduction is in order, but no need to go crazy. I don’t think I need double walls, etc. Wall damp sounds great.

There are no moisture issues. Colorado is dry.

Electrical: dedicated lines for sure. Two should be enough, no? I have a fairly simple system but there’s a possibility of a home theater system down there, too. Perhaps put the stereo rig on one short wall and the home stereo on the other, with seating toward each in the center? So...three dedicated lines?

Regarding ceiling, this is a case where I might need to do something now and make a further decision later. Here’s why:

• The ceiling with drywall would be about 7’10" with the thicker sheetrock.
• The room is 27 feet long, but it could change when we continue a further basement and house renovation -- so, MC, for now, I suspect that leaving it at 9 feet with insulation and a fabric cover with sheetrock to be added later might make sense.
• Another person wrote to me that I might want to create a false wall at one end (shortening the length to about 25 feet) and have a place to put my electronics. That might help with the problem of "multiples" and also give a neatness to the space.
• I agree about not going crazy expensive.

Sounds like a great project and opportunity! You have been given much sage advice.

My approach would be to devote the space to audio, If wanting to add video, I would use my 2-channel system for it. Therefore devoting $$ to music as, I find that 2-channel can do wonders for video.  

Initially, I would pay attention to consideration of ideal ratios for a dedicated room. The Harley article discusses this. Consider the 8' ceiling to be 'fixed' and the reference. Insulate between joists with two layers of 6" insulation covered by 5/8' drywall. The 17' dimension can be played with by furring out the concrete walls as desired. Insulate between wall material and concrete. Use 5/8" drywall for wall.  Consider this the width. Frame in a cross wall to the desired length. Consider using the damping material between 2 sheets of drywall for this wall. Possibly only on the side of this wall interior to the audio room.

Given you are running Mono amps and a pre with digital source I would route 3 dedicated lines to the room for equipment, one to amps, one to pre, and one for digital front end. 

I would consider placing a equipment rack for sources and pre at one side of listening chair. Mono amps on stands where best suits. 
Have nothing between speakers. 

Enjoy!

So one thing I just discovered is the joy of diffusion.

I've heard well balanced rooms before, with a mix, but only recently have I been able to do A/B comparisons with and without them. 

If anything, incorporate diffusion into your planning as soon as you can.  They add air and shimmer without glare. 

@erik_squires
I agree about diffusion. I’ve now gone the over-damped route and am seeing how to make my space "alive" without brightness. So...

I have two of these: https://images.app.goo.gl/rkE6t1jUgAMBoHCm7

QUESTION: How would you lay the GROUNDWORK for diffusion?

@mesch

Thanks for your reply. Some questions below. I will design the space for audio, once the kids leave. I’d probably just have a different amp for video, as I don’t want to run tubes for video all the time. I already own a Denon AVR and klipsch speakers for A/V. Maybe I’d ditch the speakers or put them on surround duty.

Insulate between joists with two layers of 6" insulation covered by 5/8’ drywall.

QUESTION: What kind of insulation? R38?

The 17’ dimension can be played with by furring out the concrete walls as desired. Insulate between wall material and concrete. Use 5/8" drywall for wall. Consider this the width. Frame in a cross wall to the desired length.

Given you are running Mono amps and a pre with digital source I would route 3 dedicated lines to the room for equipment, one to amps, one to pre, and one for digital front end.

QUESTION: If I had a separate set of components for A/V would you do 4 dedicated lines? That seems like a lot.

I would consider placing a equipment rack for sources and pre at one side of listening chair. Mono amps on stands where best suits.
Have nothing between speakers.

QUESTION: Makes it hard to have a TV, but I suppose if there’s a "false wall" it could hide the TV. Sound ok?

Room ratio is a tough one. If one looks at various ratios, some say 1 H x 1.67 W x 2.7 L (P.S. Audio) and that works out, with an 8 foot ceiling to 21.6 x 13.3 x 8. That amounts to reducing width by almost 4 feet and the length by 6 feet. Not sure how that will work for various purposes. This is why I was thinking to keep the ceiling open (without drywall) and have it at 9 feet. That way I could have a ratio of 9 x 15 x 24 as a target and just need to pull off the walls by a couple feet. Still, I guess once you start building out from concrete (one exterior wall) you can probably bump out pretty easily, eh?

I had multiple goals.  I have a 50/100 Hz resonance in the room that needed treatment so I added GIK's 7" thick bass traps with diffusion panels on top. You don't have to go that thick, unless you lack where to put bass traps, but the GIK Impression panels are very effective and very affordable compared to the prices I have seen on some QRD types.