@invalid I owned Divas for 6 years. I had just moved back to New England in 1987 and picked up my pair directly from the factory in Mass. My previous speakers were Acoustat 2+2s with Tympany 3s before that and several models of Acoustat before that going back to 1978. All dipoles. The Divas chased me right back to Acoustat 2+2s. I use Sound Labs 645-8s now, 8 foot 645s. All dipoles without exception, but only two full range line sources, the 2+2s and the current Sound Labs.
The reason you have to dampen the front wall behind dipoles that have thin membranes or ribbons is the sound reflected off the front wall at full volume comes right back at the speaker and is transmitted back through the diaphragms causing severe comb filtering. This creates response irregularities and really messes up imaging. In some cases the effect can be euphonic especially if you have not lived with a system that images properly. It can create a false sense of ambience at the expense of image specificity. At worse it can make things shrill and sibilant.
If you go to my virtual system page you can see a device called a SALLIE (Sound Attenuator of Low Level Interference Effects) These are sitting directly behind my speakers and are way more affective than the usual fare. Roger West of Sound Labs only makes them 1 foot wide and I needed them 2 feet wide. Left to my own devices I made them out of Walnut, god forbid someone should look behind the speaker. I had been using plain 4" acoustic foam tiles behind the speakers, but the remaining comb filtering was tying a new digital signal processor up in knots, so I had to do something more drastic. Fortunately it worked.