Five feet from the front wall

@mijostyn: Just for the record, I much prefer an "over"-damped room to an "under"-damped one. My current one is on the over-damped side, and I have found diffusion to keep all the output of my dipoles audible, whereas I believe damping (please, not dampening 😉) would absorb the high frequencies too much. But then I use dipole planars, which produce very little output to their sides, and therefore very little sidewall reflections. The loudspeaker/room is an integrated system, you can't separate the two.

@marco1: Reminds me of my stoner days, laying on the floor with the left and right speakers on either side of my head, like giant earphones.

@invalid: I believe you meant to direct your last post to @mijostyn, not me.

I somehow never managed to hear any Apogees, perhaps because there weren't many dealers on the West Coast. My dipole planar exposure is limited to Quad, Infinity, Dayton Wright, Magnepan, RTR, Beveridge, Acoustat, Martin Logan, SoundLabs, and Eminent Technology. 

Regarding the wall behind dipole planars: One of the hardcore Maggie owners on the Planar Speaker Asylum completely damps the wall behind his very-modified Tympani T-IVa’s (he also braces the panels to the walls), other owners prefer diffusers.

Both absorption and diffusion can work; when choosing between the two, one consideration is the acoustic properties of your entire room. If you have a very lively room, absorption is probably the way to go; if it’s on the dead side, perhaps diffusion. Too much absorption in a dead room can lead to lifeless sound.

My room is definitely on the dead/warm side, so I went with diffusion. I have stacked Vicoustic Multifuser DC3’s behind my planars, and have found them to work great. Diffusers don’t absorb high frequencies, they scatter them randomly, keeping the inherent sound of the room intact. The scattered reflections don’t head straight back to the planar (or listener), so it’s back wave doesn’t compromise the sound coming from it’s front side. But that back wave does enhance spaciousness and depth, not a bad thing imo.

To call the wall behind the loudspeakers the rear wall makes no sense. Sure, that wall is behind the speakers, but so what? The wall the listener is facing is the front wall, the one behind the listened the rear wall. Period.

@dsper: Yes, measurements are always made from the baffle the loudspeaker drivers are mounted onto. The 5' figure is especially apropos for dipole planar loudspeakers. 5' allows the speaker's front wave to be heard 10ms before the rear wave (sound travels at about 1' per ms: 5ms from the back of the planar to the front wall, 5ms for it to return to the planar after being reflected off that wall), the minimum required for our brains to hear those two waves as separate acoustic events. But that 5' distance is only one consideration in getting the best sound in your room.