I have tried several ways of dealing with the walls directly behind dipole speakers. I use 16" ASC bass traps behind my Martin Logan Summits which are 6' out from the front wall and 16" ASC bass traps for the Magneplanar Tympani bass panels which are 9' out from the wall. There are also full round 16" ASC bass traps in the corners. These traps
have the reflective membrane adjusted so the high frequencies are angled away from the speakers to prevent early reflections. Having a large distance behind the speakers reduces comb effects greatly and this provides a wide sound-stage and depth. There are also traps above and behind the speakers that also helps with early reflections. Hard wood flooring is placed behind the speakers to maintain ambience and kinetic energy and light weight, adjustable drapes provide some diffusion of highs as well. So bass trapping, diffusion and a large distance behind the speakers makes dipole speakers sound very realistic.
