Five feet from the front wall

@paulrandall 

I stated, I thought clearing, that the reference is the face of the driver, not anywhere else. 

@invalid 

It makes not difference whether or not you are direct driving ribbon speakers although you have to be careful. The tweeters have VERY low impedance, < 1 ohm and can burn up some amps. All planer dipoles benefit from subwoofers. It is not a mater of speed. Speed has nothing to do with it. Lack of spurious resonance's, time and phase coherence along with the right crossover point have a lot to do with it. 

@lanx0003 

That is the wrong way to look at it lanx. Sounds that reach your ear after 10 ms are perceived as an echo. Less than 10 ms and they are perceived as one with the direct sound. That does not mean these sounds are not distorting what you are hearing, they are in a big way. They are sound that was not present on the recording and as such are distortion. They change frequency response (amplitude) and screw up phase affecting the image.  

@bdp24 

If is extremely hard to over dampen a room. Most system/rooms that I have auditioned are under dampened. What people think is dull and lifeless is generally much more accurate, they are just use to sizzling hot with echoes and have a hard time reorienting themselves. Turn the volume up, way up to 95 dB. If the sound wants to cut your throat you are underdamped.

That is the wrong way to look at it lanx. Sounds that reach your ear after 10 ms are perceived as an echo. Less than 10 ms and they are perceived as one with the direct sound. 

I'm not sure where you received that information from. The reference to a 5 ms time interval was made by Haas (1951), who stated that a single reflection arriving within 5 to 35 ms can be up to 10 dB louder than the direct sound without being perceived as a secondary auditory event (echo). The shortest possible interval is 5 ms.  You can find this information in the following reference.  Should you need more details, let me know.

Haas, Helmut, The influence of a single echo on the audibility of speech, J. Audio Eng. Soc., Vol. 20, Issue 2, pp. 146-159, March 1972 (English translation by Dr. Ingr. K.P.R. Ehrenberg of Haas’ original German paper published in Acustica 1, pp. 49-58, 1951).

@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.

A long time ago I noticed a big improvement moving my speakers so the backs of them (which has ports for the bass) are 3 feet from the wall behind them. It was surprising because I didn't move them out all that much. Maybe 6 inches. I have a credenza between them that is about 2-1/2 feet high which probably increased the improvement a lot since the speakers are now an inch or two in front of the credenza.

FYI- the sound also improved a lot when putting my speakers (KEF R500s) on top of multilayered Symposium acoustics stealth platforms. Supposedly it cleans up the vibrations inside the cabinet while also isolating it from vibrations from my suspended floor. All I know is it sounds clearer and more focused.

Based on my extensive experience with speaker placement in various sized rooms over the years, I've found that speakers, in almost every case, sounded better farther out into the room.  Just go to any High End Audio Show, and in 99.9% of the exhibitors rooms, you'll find that these experts always place their speakers out into the room several to many feet from the front wall.  Placing the speakers out into the room helps to create greater depth of field within the soundstage, which creates spaciousness, and that lovely layering and airy effect that we all search for in our own rooms.

@mijostyn, I expect you intended "It is .  .  ." when you said, "If is extremely hard to over dampen a room."

But I guess it is not impossible.  Several years ago I had a friend who was a reviewer for one online audio magazine.  Being serious about the task he hired a then well-known acoustics company to advise him on room treatments.  That resulted in installation of a large number of Tube Traps plus several panel absorbers, along with an array of diffusers suspended from the ceiling.  At first he was pleased but after a few weeks became dissatisfied that so much dynamics and "life" seemed to be missing.

At his invitation another friend and myself came over to help.  One by one we eliminated most of the tube traps while he listened to a couple of reference recordings.  After about six traps had been removed he found the sense of dynamics and aliveness he'd been missing.  So he sold the excess traps.

it's easy to over damp a room for hi-fi..we generally like the reverb of our rooms...but control rooms don't want the room involved...they of course aren't listening for enjoyment. 

So this is the challenge...the panel sellers don't really understand hi-fi goals so they will tell you to kill your sidewall first reflections and also to put a cloud on your ceiling to kill that first ceiling reflection...all those spatial cues we love they correctly see as colorations.

Floyd Toole discovered during the Harmon studies that people generally don't like the first reflection absorbed for music...but the dogma to kill first reflection points persists and is repeated in every corner on the internet. ;-)