Ideal design for a new music room

I am no expert but in my there are advantages to having a dedicated listening room in the basement. 

Advantages:

1) No large windows, if any at all.
2) Concrete floor.
3) More design flexibility than if the room was in a more public area of the home. This includes the addition of acoustic treatments that only look attractive to the eyes of the audio enthusiast.
4) Easier to design such that music can be listened at high volume without disturbing other family members, especially in the late evening when the audio “magic” often occurs.
5) The option to have an adjacent equipment room to house a turntable that is well-isolated from the listening area.

Disadvantages:

1) Part of the enjoyment of the hobby is sharing music. Not many folks like to spend hours in a windowless basement listening to sonic perfection other than audiophiles.
2) If your system will include very large speakers betting them down into the listening room can be a pain.
3) Basements rarely have ceilings more than 8 feet high. This may partially be related to cost but also, the deeper the basement, the more concerns there may be with water inflow. Our neighbors rebuilt their home and deepened their basement. Their sump pump runs continuously. Our basement, less than 20 feet away but not as deep, is bone dry and our sump pump has never kicked in over the 14 years we have been in the house. 

Your idea is amazing. I have long dreamed of owning a stereo room. Wish you soon complete your ideal.
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Thanks for everyone's comments. I've had experience with 7 different listening rooms. I agree with many of the suggestions. Each room came with dimensions that I could not change. Each one sounded different. For sure room characteristics are big contributors to the sound you experience. So I wondered what characteristics an ideal room would have. So far there are excellent ideas but no one has come forward to say they've built a listening room (not a recording room) that is close to perfect in being able to create a satisfying sound stage. Even better, no one has suggested that an inexpensive system, say under $5,000, in a great room will deliver a better audio experience than systems costing multiples more in a poor room. Is it possible that fortunes are being spent on equipment that is fighting rooms with poor acoustics?

Hello encore, I can personally relate to your post and find it refreshing to see someone seriously identifying / questioning the elephant in the room. 
 You have hit the nail on the head and I will repeat your quote with an answer: 
 “...no one has suggested that an inexpensive system, say under $5000, in a great room will deliver a better audio experience than systems costing multiples more in a poor room. Is it possible that fortunes are being spent on equipment that is fighting rooms with poor acoustics?”
   And the answer is absolutely YES! 
And that’s exactly what’s going on in probably a major percentage of the rooms we see on our audio sights and hear in our visits to our audio friends and acquaintances. 
   An ‘excellent room’ for listening is almost always at odds with a room designed for anything else... 
    A dedicated listening toom will have the speakers placed EXACTLY in THE 2 spots where they will sound optimum in that specific room. 
    A dedicated listening room will have the listening chair ( or perhaps ‘love seat’ but you’d be pushing your luck a bit to try and use a couch)... in EXACTLY THE correct location for the speakers to sound their optimum....
    A dedicated listening room contains the requisite audio rack(s) necessary to properly serve the components and should be strategically positioned to have minimum influence on the acoustics of the environment.
    A dedicated listening room will be seriously addressed with corresponding acoustic room treatments placed where they ideally benefit the system’s prime directive of replicating the musical performance as realistically as possible. 
   With that said... most homes have a chosen room which can be deemed ‘the one’ where the system tries to do its best while still remaining a somewhat socially integrated venue. 
     In my humble opinion a properly set up $4000 system in a dedicated listening room utilizing $1000 in select room acoustic treatments and the available open space void of unnecessary furnishings will be very very tough to beat. 
    Commit to a room first.. work it all from there. 
    Lots more to talk about but just wanted to get started. 
     Happy Lissn’n.     Lissnr

Encore-

I actually designed and built my room. Not from scratch, it was added as part of a major remodel. Main thing I learned, its easy to say things like the ideal room when in reality there is no such thing. You are onto something when talking about great sums being wasted chasing what was made near impossible by the room itself. You are also onto something with the comment about the soundstage and the room. Yes the room matters but much more with some aspects than others.

Even though you are designing from scratch still you have restrictions of some kind. Physical, aesthetic, whatever. Point is only you know them. So my best advice is find a good architectural book and spend a bit of time studying basic construction.

A little knowledge here goes a long way. Here you will learn for example that 5/8" sheet rock stops sound about twice as good as 1/2", or that the relatively simple construction technique of offset wall studs is good for a good 6 to 10 dB of isolation. A solid core exterior door with weather-stripping is nowhere near recording studio performance, but hugely better than standard interior construction for hardly any more money. Just a very few examples of what you can quickly learn that can get you big results for a very small amount of money. 

You can probably tell I'm much more practical as opposed to theoretical oriented. Maybe that's because after having learned the theory and then done the physical I learned the practical is much more relevant. (Watch how those who argue this point have never actually done what I have actually done!) So learn all you can, but keep it real.

With that in mind, size matters. The bigger the better. The bigger the room the fewer the problems with bass response. Bass is the biggie. I can get you outstanding imaging in a closet. I cannot get you outstanding bass response in even a decent sized room. There's simply no substitute for size.

One last word on bass response. Everything else is easy compared to this. Vast sums can be thrown at this problem. You need to decide how important it is to you. If you want really deep, powerful, articulate bass and are building your own room then either you spend almost as much on just this one thing as everything else thrown together, or you design the room to include bass drivers mounted directly in the floor or wall. Few do this because of the obvious- cutting a great big hole in the floor or wall. I didn't do it because I only learned of it after the fact. But Fosgate did this, and SpeakerLab in Seattle, and the bass it delivers simply must be heard to be believed. For a tiny fraction of the cost of doing it any other way.

That's about all I can tell you in broad strokes. The devil is in the details. The more of yours I know the more I can help. Ultimately though nobody will ever be able to help you more than you yourself. (But I would definitely take Michael Green up on his offer!) You're on the right track. Good luck!