Hola Francisco.
Room resonance (shudder). (intentional pun)
The house that I own now is frame construction with drywall interior. It is amazing how much the walls get into the act at low frequencies. It is not just standing waves, but walls acting as secondary radiators that add coloration. I would love to do some inerferometry on walls to quantify the effect some time, but I don't see that happening in the near future. I am sure that somebody has mapped the phenomenon.
For LF I have had the best luck using my subwoofers in nearfield, and keeping the crossover below 70hz, with a steep slope. Ideal crossover point is a tradeoff between hearing the subwoofer location and room excitations due to the main (satelite) speakers. It typically requires larger subwoofers since you are no longer taking advantage of the room gain. Some of the servo-controlled types or heavily equalized units might also work. I haven't tried them. I tend to think of big cone motions as a bad thing.
I personally never cared for the effect of diffusers. My impression was that they lower signal to noise from the source by raising the ambient noise floor.
Outdoor listening is pretty neat, but has some obvious tradeoffs (like no thermostat). The bass response is astounding. It is tight, with no overhang at all. Very much headphone-like. The tradeoff is depth. There is only the ground plane for gain, so you don't get any of that 6db/octave lift that happens indoors. Fortunately there is plenty of room out there, so my 8 cubic foot (each) shotgun subs look downright diminutive.
I am still working out what is best for the rest of the spectrum. I am using a Morel top mount tweeter, with a peerless midwoofer in a bass reflex cabinet. My project satelites will use the same tweeter (at first) and an Eton woofer in a larger br cabinet. At some point I will probably go to a ribbon tweeter, then start fiddling with amplifiers. The experiment will never be complete.
I like your idea for a web-site. I think that room acoustics should be a higher priority for most serious listener's. It can, in many situations, make much bigger improvements than electronics and cables.
Later
