how far off the wall

Far enough out to reduce the chances of non-modal peaks and nulls being introduced...modal peaks and nulls are another story and problem...although the two tie together overall.

Non-modal peaks and nulls are caused by a freq's wavelength and in relation to it's distance from room boundaries. Bass wavelengths are very long so reach all walls within the room.

Odd points: 1/4-3/4-5/4...ect,ect cause nulls
Even points: 2/4-4/4-6/4...ect, ect cause peaks

As you move the speaker out...and away from the wall you will pass through these wavelength points. The important part for bass in many rooms is usually to get out past the first 1/4 wavelength (null) but maybe not into the 2/4 wavelength (peak)...somewere in between these two first measurement points may be fine also.

If we use 100hz as an example:

2 ft 10 inches is the 1/4 wavelength for that freq...null

5 ft 8 inches is the 2/4 wavelength for that freq...peak

Of course all the other bass freq's have a different wavelength so have different measurement points in relation to the wall for their peaks and nulls.

5 feet (or so) works so well because it's far enough away to clear the first null for almost all of the lower bass points.

These same problems effect the listening position in relation to room boundaries...I'm sure you have read at this or other forums advice for placing a subwoofer at the listening position while you crawl around the room listening for the best bass...and then swapping those points between yourself and the sub.

I'm not the best at explaining things... even a worse writer, so sorry if this is somewhat unclear.

Dave

Duke - I am currently researching diffusion options for some planar speakers I currently have 4' from the wall (Quad 988's). There are cheap diffusor options (Auralex), but the reasonably priced ones are either limited in depth (2-3 inches) or complexity (and randomness) of form. Then there are the more expensive RPG and Auralex forms, but that will cost a bunch to cover maybe 3'x5' behind the Quads. Do you have any recommendations for diffusor options?

Thanks, Peter S.

Sogood51, my head is about to explode. No i did not know to crawl around the room listening for the best bass. Could you our one of the members here suggest a entry level book on audio setup. thanks so much

Im so glad Im not using logans anymore. Never could find the perfect position, I was always moving them around because one area or the other suffered everytime they were moved. They are great speakers however, its just nice to just have to adjust at initial setup and be happy, like with my focus 20/20's.Its amazing how ever new logan owner battles with this issue.

Cj1capp - what are your room dimensions. Are there any windows behind speakers etc. With those informations I may be able to help or not. I also owned aerius i for 6 years.
Setting Martin Logans is a little tricky.