Open baffle speakers

My woofer towers are H-frame open baffle with four servo-controlled 12" drivers. There is obviously cancellation at the lowest frequencies where the backwave wraps around, but the circuitry in the amp does an excellent job compensating for this. The measured response in my 29'x17'x8' room is not without some room interactions, but considerably less so than my previous conventional subs and is the deepest, tightest, and most natural sounding bass I've ever had in my system. 

To say that open baffle subs can't create excellent bass is hogwash. Yes, you need more power and more radiating area to compensate for the backwave cancellation, but if done properly the bass is superb.

Open baffle speakers need some room to sound their best. Most of the manufacturers say 3ft to the wall behind them, but in my experience you really need more than this. I have mine set up approximately 7ft from the front wall and 4ft from the side walls. The side wall distance is less critical since the backwave cancellation helps reduce side wall interactions. 

As long as I have the space for them, I wouldn't consider switching back to box speakers after living with the speakers I have now. 

@mijostyn : I have a nicely upgraded pair of DQ10's and have no complaints about the 3-D imaging qualities. Go read Harry Pearson's 1975 review in TAS. He praised them for their life-like presentation of space!

The Carver Amazing Platinum is a successful open-baffle speaker using four high-Q 12" woofers crossed over at 100hz to a 60 inch ribbon driver. They sound fine without the need for active amplification for the woofers.

@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.