What is ideal dimension size for a home listening room?

brownsfan, I am not aware of any room mode calculators or  mathematical model for rooms with non-parallel walls. We started with a rectangle shape for a base line. Then we did some calcs and made some assumptions to come up with which walls to skew. About 60% of the room is made up of non-parallel walls. About another 20% of the walls are covered with diffusers and broadband absorption. About half of the skewed walls are actually built-in bass traps with reflective surfaces and tuned sections. I can't be absolutely positive we did it 100% correct, but it works great.

I started using non-parallel walls after a learning experience while exhibiting at an audio show in Los Vegas about fifteen years ago. A pair of very large and flat shipping crates placed staggered and skewed along the side wall saved the day.

My minimal experience with concave surfaces would suggest very diabolical.

What’s a California corner?
”ideal” is somewhat subjective and relevant to the objectives.
Please share your experiences with non-parallel walls as used in a dedicated room. I’m always eager to learn.

brownsfan made many good points. I suggest that you find a good on-line Room Mode Calculator which speaks of Schroeder Frequency,  Bolt Area, Bonello, etc. to help you better understand the consequences of room dimensions. You might consider consulting with a professional because once the walls are up you are stuck with the design.

You might also consider non-parallel walls. Our purpose built room was designed with non-parallel walls and the results are well worth the effort. The calculations are more complicated but worth it. They help minimize the need for absorption and diffusion. The end result is a lively (not bright) well balanced room. The next time you are at an indoor live venue check out the enclosure you are sitting in.

If possible, consider which family of speaker design (mono-pole, dipole, point source, line source, omni-directional) you will likely end up with. This consideration doesn't necessarily influence the optimal room dimensions which is more about distributed room modes and a smooth bass response but it will influence the interior room design and treatment needed.

Consider built in or free standing corner bass traps. There are real reasons why qualified professionals recommend corner and soffit bass traps. Don't believe the general statement that too many bass traps will absorb all the mids and highs and make a room sound over damped. Not all bass traps are created equal. For example, DIY "bass traps" that are basically a 4" thick block of Corning fiberglass wrapped in fabric are marginally effective as bass traps and are really broad band absorbers that can, if overly used, over dampen a room. A REAL bass trap (bass attenuation only) typically has a membrane covering the fiberglass which reflects the mids and highs back into the room and does not over dampen the room.