How do I build the best room

Kevin, my new basement listening room is 8x15x19, so I may be able to offer some advice. Re standing waves, the room height vs room width may be the main issue. If any part of your ceiling dips below the 8' level (or if your floor is elevated anywhere), that will exacerbate problems in the 60-90 Hz area. But a combination of bass traps and digital EQ helps enormously. I am using five Corner MondoTraps from RealTraps and couldn't believe the improvement once I got them put in. That, plus judicious use of the notch filter in my Anthem AVM20 for movie material. You may indeed be able to utilize built-in DIY fiberglass for the direct reflections, but bass traps commonly need some airspace to do their work (i.e., place them in room corners).

Be careful about speaker size and type. If I had it to do over, I would swap out my von Schweikert VR-4jr's for high-end, stand-mounted monitors (maybe like Usher BE-718s) and a (good) sub or two. The VS's are too big for my space--they too easily over-excite the room. Also, I presume you have a cement floor; this will be difficult to spike floorstanders to--will really trash the sound. I am spiking the VS's to hardwood platforms that rest on the carpet, but this is probably not a final solution.

I am not sure what to make of the suggestion to put the speakers along the long wall of the room. You may want to try both the long and short wall; my hunch is that short-wall placement will give you more "wiggle room" in terms of trying different speaker placements.

General rule of thumb is to put some acoustic absorptive material behind the speakers, and acoustic diffusors behind your listening chair(s). The Echo Busters and RealTraps Websites have good diagrams and advice on this.

Kevin: I built my room in the basement also. The biggest problem I am having is eliminating the upstair noise. Footsteps being the biggest problem. So far have disconnected the ceiling from the floor truss and put in ceiling joist. Not even the walls are touching the floor truss now.Used 4 inches of rigid mineral wool for insulation. In the process of laminating 2 layers of half inch mdf with green glue inbetween and half inch of quiet rock with green glue inbetween it and the mdf. I had a drop ceiling and will be putting that back in with 1 pound psf mass loaded vinyl on top of the tiles. The channels will be treated with silicone where necasary so they will be quiet. Perhaps your situation is different but for me the upatairs noise was more than I could handle. Plus to much of the music was getting upstairs in my opinion. I read a lot on soundproofing. There are 4 things: number 1 mass , 2 isolation, 3 damping, 4 absorption. My room is 14 by 20 by 8. Treatments are some absorption on long wall and 21 inch diamiter 1.5 thick inch pipe insulation for bass traps about 12 inches out from rear cornor.Big pipe insulation. The room is fantastic sonically hopefully it will be quite enough in a couple of months. Hope this helps and hope your room works well for you. Jeff

The room is a little on the smaller side for the 20.1, but we did (successfully) put a pair in a 13.5 x 18 x 7.75 room. The planars don't have a lot of energy dispersed towards the ceiling and they don't have a lot of bass, so they can actually work reasonably well in a smaller room. However, at this size the engineering is difficult. The smaller the room the more attention needs to be paid to room modes, diffusion, reverberation times. Small rooms are very unforgiving to design flaws--but it can be done.

Well, what a nice collection of responses for a first post! Thank you gentlemen.
I am not surprised at the comments of concern regarding placement of MG 20.1s in the proposed room. Does anyone have experience with a pair of hot rodded 3.6's with external X-over and multi channel amplification? Comments on the Magnepan Users Group forum lead one to believe success may lie therein.
The dimensions, excepting the floor to ceiling height, are somewhat flexible am considering at least two opposing non parallel walls- most likely the long walls. This may cause difficulty with long wall placement.
I will have a dip in the eiling to 7 feet one inch to box in the Header and plan on treating it with an absorbtant product as it appears to be at or very near to the first reflection point.
Thanks again gentlemen for your expertise in this matter.
Kevin