SoundLab Dealer and dipole designer/manufacturer, Duke LeJeune, posted the following in an Audiogon thread titled: “Dipole speakers, subwoofers and that rear wall”
“The ear does not perceive comb filter effects from reflections the same way a microphone registers them, so in general reflections are far more benign than they look “on paper”.” “But if reflections arrive too early, they still can be detrimental to clarity.” “According to acoustic and psychoacoustic researcher David Griesinger, ten milliseconds of essentially reflection-free time is sufficient.”
“Sound travels approximately one foot per millisecond, so the implication of Griesnger’s finding is that ideally we’d want to position dipole speakers about five feet out from the front wall, which would result in a backwave reflection path length of ten feet, and a delay of about ten milliseconds.”
“In my experience, if dipoles (or bipoles) are placed less than 3 feet from the wall behind them, aggressively treating the backwave is usually a good idea.” “This can be absorption or diffusion or re-directing the reflection away from the listening area.”
“At distances between 3 and 5 feet it’s more of a judgment call as to whether or not you need to treat the backwave.” “Imo in general re-directing the reflection and/or diffusion are preferable to absorption.”
My experience with two different rooms and 3-different pairs of SoundLabs, correlates with Duke’s recommendations.
With my Majestic 845’s pulled out into the room approx. 7′, the 6′ x 3′ free standing sound absorption panels I tried on the wall behind the speakers, removed the liveliness from the sound. Obviously, more than anything else, the room dictates what should, or should not be done.
I do have a partial wall of drapes between/behind my SoundLabs (see picture). However, the drapes were installed for room darkening, but they may also have a sonic effect.
A comment was made about a bookcase and books, for a similar result, I’ve also seen a bookcase housing 500 to over 1,000 vinyl albums, placed between and behind a pair of A1 SoundLabs.