Had a house built and made an effort to get a first class sound room. Lath & Plaster walls & ceiling. Soundproofing inside the walls and an exterior weight door to minimize disturbing the wife. Dimensions not especially large (is it12'X11X8'?) but I'm a guy who prefers tone quality & soundstaging over bass & deafness. I'm mainly a classical guy. Gorgeous Eucalyptus bare floor sourced from local wood. Double-glazed windows. No acoustic treatment other than a couple thousand LPs. What can I say? I love the sound I'm getting. There's a picture (edcyn's system) in this crazy website's picture ghetto.
