The Shure V15 V with a Jico SAS/B stylus VS The Soundsmith Hyperion MR and Lyra Atlas SL

@lewm: If you want, take a look at the dipole woofer system in the Linkwitz LX521, or go onto the GR Research website, where you can see the dipole sub Danny Richie and Brian Ding of Rythmik Audio co-designed.

Siegfried’s dipole woofer is a W (or M, same thing) dipole frame, each woofer mounted on it’s own baffle, the baffles mounted in the frame 90 degrees offset from one another. In the GR Research/Rythmik dipole sub, the woofers can be mounted in M/W frame fashion, or in an H-frame, the latter more common. In an H-frame, the woofers (two or three, the user’s choice) can be mounted facing 180 reversed from each other (one cone facing the listener, the other with the rear of the cone facing the listener), or all facing forward. What makes it a dipole woofer system is not how the woofers are mounted in regard to each other, but that the output from both the front and back of the woofer propagates into the room, the front and back waves being 180 degrees apart. In fact, you can build an ob/dipole woofer system using just one woofer.

Yes, those front and rear waves---being of opposite polarity---meet on both sides of the dipole frame, with resulting dipole cancellation. A loss of output is therefore inherent in the ob/dipole sub. There’s no free lunch! But once you’ve heard an ob/dipole sub, you’ll know why people are willing to accept that design penalty in exchange for the sound quality produced by the sub.

For many years, I considered the sound QUALITY produced by the big Magnepan woofer panels (two of the panels in the 3-panel Tympani models, and the current MG30.7) to be the best reproduction of low frequencies I had ever heard (Harry Pearson agreed with me). Well, the GRR/Rythmik OB/Dipole woofer system sounds very similar to the Maggies. Brain Ding characterizes it as sounding "lean". The question is: is it lean, or are "normal" woofers "fat"? The ob/dipole sub reproducing an upright bass (or the lower registers of a grand piano) has to be heard to be believed! The "texture" of the fingers plucking the bass strings is clearly audible, with no added "weight" or "pluminess."

To offset the dipole cancellation, Brian Ding installs a dipole cancellation compensation circuit into the plate amp that comes with the OB/dipole sub kit. That of course means the power amp must provide more power than it would sans the compensation circuit. Power is cheap, and the woofers used are pretty sensitive/efficient. The sub also features Ding’s patented servo-feedback control of the woofers, which is what drew Danny Richie to Rythmik Audio. Danny was already marketing an ob/dipole woofer, and the idea of mating it with servo-feedback sounded like an idea worth exploring. It was.

I’ve owned servo-feedback woofers mated with planar loudspeakers before---the Infinity RS-1b, and this sub is a whole ’nother matter. State-Of-The-Art reproduction of low frequencies! Audiogon member @jaytor has the GR Research/Rythmik woofer system, with four woofers per side (left and right channels). Crappy bass? Uh, no.

Guys! All I was trying to do was to establish the definitions of bipole and dipole. But I must say I’m curious about a “dipole cancellation compensation circuit” or whatever Mr Ding calls it. I remember reading about subwoofers using two woofers in one sealed cabinet driven 180 degrees out of phase so there’s no back pressure build up in the closed box. That’s supposed to have its virtues too.

Listening to Big Band Monk on my Beveridge system where bass comes from my home made transmission line woofers. For me TL is the most undistorted bass imaginable but doesn’t go down to 10 Hz.

@lewm: Like you, transmissionline loading of woofers for bass reproduction holds a special place in my heart.

In 1971 my hi-fi education took a giant leap upward when I was first exposed to: 1- ESL loudspeakers, and 2- TL woofers. The ESL was the original Infinity Servo-Static I, as well as the ESL tweeter (made by RTR) array in the ESS Transtatic I. The TL woofer was also the design of the woofer in the Transtatic. ESS (this was before they introduced their Heil models) installed the well known KEF B139 woofer in a pretty long transmission line, and the KEF B110 midrange driver in a short one. David Wilson used that KEF woofer and the RTR ESL tweeters in his original WAMM loudspeaker.

Hearing the bass reproduction afforded by the Transtatic revealed to me that the bass of the AR-3a and Rectilinear III (two of the best box speakers of the late-60’s/early-70’s) was somewhat lacking. I was severely lusting for a pair, but at $1200 they were out of reach. In 1982 I saw a pair for sale in The Recycler (a weekly buy/sell rag published in Southern California) for $400, and snapped them up. One of the B139’s had been replaced with an imitation B139, so I gave ESS a call to get a real one. They had one woofer left, and for 39 bucks it was mine! I still have them, sitting in my spare room (along with a pair of Magneplanar Tympani T-IVa’s, acquired from Kent at Electrostatic Solutions).

And like @mijostyn, I love ESL’s. If I had the dough and a big enough room (and a capable amplifier), I too would own SoundLabs. In his review of the Eminent Technology LFT-8b and 8C planar-magnetics, Steve Guttenberg states that he doesn’t like ESL’s, finding them to sound a little "threadbare", lacking body and substance. Or as Art Dudley might have put it, lacking full "color saturation". I suppose I can understand what Steve means, though I don’t share that opinion. Speaking of the ET LFT’s, in the reviews Steve also states that he prefers them to every ESL and Magnepan he has ever heard. I'll bet he hasn't heard the Sanders ESL, imo a great loudspeaker.

I’m not on the Eminent Technology (or Sanders) payroll, honest.

@richardbrand You were talking about balanced force woofers which are bipoles in the context of speakers which are dipoles. As you correctly mention 57s are dipoles. There is a huge difference. The dipole nature of panel speakers is not the same issue as dipole subwoofers if you remove the low bass from them. Like every other dipole woofer they stink at it. There rear wave of a panel loudspeaker, at least above 200 Hz is relatively easy to control, below 100 Hz  you are totally helpless. Unless you can get panel loudspeakers 10 feet from the front wall, in order to achieve the best image, the rear wave has to be partially absorbed by at least 50%. People frequently prefer the sound without absorption, it is brighter, more airy and louder. It is also far less accurate and at times painful (sibilance). @bdp24  As far as subwoofers are concerned, low bass is omnidirectional. The rear of the subwoofer driver is just as omnidirectional as the front. Take two enclosed subwoofers and play a 30 Hz test tone. Walk around the room. As you move the bass will get louder and softer due to room modes. As you get close to walls the tone will get louder. This is barrier effect. Now wire one of the subs backwards 180 degrees out of phase. Now as you move around the room the tone goes from almost entirely gone to extremely loud. Where this happens changes with frequency. An open baffle subwoofer is exactly the same as two out of phase subwoofers, actually worse because in open baffle designs the drivers are inadequately braced. Put your hand on one while playing a 20 Hz test tone at 85 dB. It will be shaking and that is distortion. At some frequency, depending on the effective mass of the system, it will shake so badly you will be able to see it. This is the resonance frequency. There is absolutely no way you can overcome this. You can only live with it and the best way to live with it is to avoid dipole subs like the plague. 

I think what Steve Guttenberg is trying to express is that playing full range ESLs will not go all that loud and because they are dipoles, the low bass is compromised. They are also very difficult to drive and the amps used make an extreme difference. Look at the monsters Roger Sanders uses to power his speakers. Once you take 100 Hz and down away from ESLs it is a whole different story. Roger crosses to his transmission line woofers at 250 Hz using a dBx driverack. Without those frequencies it is harder to saturate the transformers and the diaphragm has a lot more room to go loud, very loud given enough power. I have no problem hitting 105 dB, ear splitting levels. At 95 dB they might as well be playing at a whisper in terms of distortion which is an order of magnitude below any planar magnetic or dynamic loudspeaker. I guarantee "threadbare" would never be a term anyone would use to describe my system or Roger Sanders speakers including Mr. Guttenberg. If anything he would think my system had too much bass and my response would be to compare it to live performances and not other systems. The only problem with Roger's speaker is it is extremely selfish, it beams like crazy. People sitting outside the listening position get no direct high frequencies.  The ETs are good speakers, better than most, but IMHO the Magneplanar 3.7i is even better. That ribbon tweeter is fabulous, arguably the best tweeter made. The ET's tweeter is too wide which will cause it to beam.  I once had a pair of Tympany IIIs. It was with great fortune that I met my wife at this time giving any other speaker a reasonable WAF. She loves the Sound Labs as they blend right into the room. People don't even notice them at first. 

Every audiophile should read Roger Sanders White Papers. https://www.sanderssoundsystems.com/technical-white-papers

Every one of those subwoofers you mention is challenged by bad enclosures and their bass is colored.  There is no such thing as too many drivers in a subwoofer system. The more surface area you have working for you the lower will be distortion levels. INHO the minimum is two 15" drivers or four 12" drivers. 

@lewm A dipole cancellation compensation circuit? Talking about wishful thinking. How many bad ideas does it take to make a good one?

The subwoofer design you mention is just as bad as the open baffle subwoofer except the drivers are more adequately braced. Like the open baffle subwoofer the only virtue it will have is terrible bass. Using drivers in phase at opposite ends of a symmetrical enclosure cancels Newtonian forces, the enclosure does not shake and the drivers brake each other improving transient response. The drivers have to have high BL products and very stiff cones, preferably aluminum to prevent paradoxical flexing. You also want drivers with a shorter X max and stiffer suspensions for the same reason. 

OMG! I once owned Tympani 1Us and then Tympani IIIs. Those were my only forays outside of the ESL paradigm since 1973. Without the ribbon tweeter, magnepans were dead sounding, utterly lifeless. It’s frightening to think how closely our bouts with audiophilia coincide, and yet how profoundly we differ with respect to digital processing and room equalization.