Open baffle speakers

@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.

@jasonbourne71 My very best friend in Miami, a Jewish journalist two decades my elder had DQ 10s. We met at Sound Components, Peter McGrath's high end store. I had just moved down there for med school and I was a fish out of water. Leo and his wife took me under their wing. I already had a pair of Acoustat Xs with their built in high voltage amp which had the most amazing image compared to what I was use to at the expense of bass and volume. Since I lived in the Nurses Dorm (don't ask) I couldn't play them loud anyway. So, I'm over Leo's for the first time sitting in front of his DQ 10s and I mean right in front. Leo listened to speakers like most of us listen to headphones. My response when he asked me what I though was, "Very transparent. I can't tell where anything is but they are very transparent." Thus began my career trying to fix other people's systems. I could never get them to image properly and at that point I had not been exposed to the high school teacher's system that permanently warped my brain, or the HQD system that came next. I did not achieve that level of performance until I got my first pair of Acoustat 2+2s some five years later. The DQ 10s downfall was undoubtedly it's crossover. Within a year Leo had moved over to Acoustat Monitor 4s on top of RH Labs subwoofers controlled by the Dalquist LP1 crossover. Biggest set of headphones you'll ever see. There was no way they were going to perform to their potential in that room, but they did image better than the DQ 10s. 

There are a couple of opinions referencing the Dahlquist DQ10 "...lack of imaging...".  In my experience Speaker imaging in most part is impacted by three components, placement of the  speaker(s), speaker design/build and the acoustic dynamics of the listening area.  Also to clarify the woofer in the DQ10 is a non-ported sealed unit so that driver is not "open baffle".  Jon Dahlquist and his engineering design staff described/introduced the DQ10 as a "5 speaker Phased Array, open baffle" design.  The vast majority of industry reviewers and audiophiles  then and now still view it in that light. It's ground breaking design remains a highly regarded speaker in the evolution of the audio industry.    I'll close by sharing that a brilliant university professor ended a lecture that I attended with the following, "Opinions, by their nature are always correct"  She then added as we were about to exit, Oh, do you agree with that observation, what is your opinion of that?  Consider that as we shall dialogue on that at our next gathering.  She was a pistol that always motivated us to think.

@mijostyn   agree for 100%  to produce bass 30 Hz  baffle size must be HUGE

common OB speakers  only can start from 100Hz, you say if anybody dont belived -measure , But no any Loved OB want to measure, Just happy what they get

agree for 100% to produce bass 30 Hz baffle size must be HUGE

Disagree. The Spatial Audio X3 with it’s powered 15" woofer could easily reach into the mid 20s with a baffle width of about 18". For all it’s other shortcomings, bass response and quality was not one of them.