18 years ago I had a studio built in our new house. Shape was critical, 8ft x 13ft x 21ft, Fibonacci ratios. Size is secondary, but bigger is better up to a practical limit. Insulated well, double insulated staggered stud interior walls, insulated exterior fiberglass door with weather seals, and insulated/lined flexible fiberglass ductwork (can't hear the furnace fan). Had three 20 amp hospital grade duplex wall receptacles installed for audio and had them grounded separately from the rest of the house which is on our own transformer and uses a whole house surge protector.
Setup is mid-field, monitors are 8ft from the listening position and 7.5ft apart, 4ft from front wall, centered at ear level. Have ten GIK 2ft x 4ft 244 panels in the room, six full range panels at first reflection points (front, side, rear walls), and four bass traps straddling the front corners. And have three tall book cases on side walls acting as "casual" diffusers (that I can easily adjust). Back of the room is my office.
The room is dedicated to me. Wifey rarely visits, small audio club visits once a year or less. Current equipment consists of MacBook Air with Tidal and Buchardt A500SE with hub. The A500SE's are active 2.5/3-way designs with selectable "Master Tunings". The hub is a wireless preamp (from source and to monitors), server, and room EQ. The monitors use Purifi mid/woofers and are rated 25-40,000Hz +/- 1.5dB.
