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

@richardbrand: While it appears the tweeter of the DIPTYQUE could be a little closer to the midrange/bass driver next to it, the distance between the two is not too bad. The crossover point is 1600Hz, the wavelength of which is 21.45 centimeters. Most loudspeakers are worse than that in terms of the two drivers creating comb filtering issues.

The distance between the ribbon tweeter and p-m driver in the Eminent Technology LFT-8b/c is even greater, AND the crossover point is at the very high frequency of 10kHz, the wavelength of which is only 3.4 centimeters! I’m seriously considering having a new filter built with a more sensible crossover frequency, in the neighborhood of 1500-2000, assuming the tweeter will play that low without distortion. I would love to hear why on Earth Bruce Thigpen chose such a high x/o frequency in the LFT-8.

On the other hand, the p-m driver in the LFT-8b reproduces 180Hz up to 10kHz, with no crossover in that range. And it has a relatively high modulus of impedance of around 8 ohms, the panel itself 11 ohms (the woofer and panel each have their own pair of binding posts, making bi-amping simple enough). Far better than Maggies for use with tube amps.

@rauliruegas: In the video below Danny Richie examines the Klipsch Forte 1, and in that examination the reason most horn loudspeakers are extremely colored (imo) becomes obvious. Low coloration is a high priority for me.

https://youtu.be/QlVG0Qx5Ds8?si=PamEu5u61kkTlXSl

THIS is the dipole/planar loudspeaker I find myself lusting to hear. At $17,000/pr I can’t buy them, so it’s purely academic.

https://youtu.be/KQh66jM7aLE?si=ia3J7sKU7Eh9Z-MT

I share with @lewm and @mijostyn admiration for the Magnepan ribbon tweeter, which is found in the Tympani T-IVa’s. The planar-magnetic midrange driver of the T-IVa (unfortunately single-ended), however, is somewhat veiled, especially in comparison with just about any and all ESL’s as well as the p-m midrange driver of the Eminent Technology LFT-8b and 8c, which is of push-pull design and construction, a big deal.

There are a group of guys active on the Planar Speaker Asylum forum who replaced the T-IVa’s midrange driver with eight of the fabulous NEO 8 p-m drivers, which with a little fiddling fit into the slot in the frame of the T-IVa’s for that Magnepan midrange driver. Mated with the Magnepan ribbon tweeter and the two Tympani bass panels (Harry Pearson made his "super speaker" using those bass panels with the Infinity EMIT and EMIM drivers), the resulting loudspeaker is reported to be significantly more transparent than the stock T-IVa.

While the Eminent Technology LFT-8b may not be up the level of the SoundLab ESL’s, they cost only $3200 a pair. That is just about the same price as a pair of Magnepan MG1.7i’s (also with a single ended midrange driver), which imo (and that of Steve Guttenberg) is not in the same league as the LFT-8. One problem with the LFT-8 is that the crossover point from the p-m midrange driver to the ribbon tweeter is located at 10kHz, with 1st-order filters. Those filters characteristics coupled with the short wavelength of 10kHz leads to the inevitable comb filter behavior of the driver interaction. I trust I don’t have to explain comb filtering. I’d love for Danny Richie to get a hold of a pair, and design a crossover with filters at, say, 2 to 3kHz.

Guttenberg found the sealed enclosure 8" woofer of the LFT-8 to mate very well with the planar-magnetic driver, but an 8" woofer can be expected to play only so low, and not at lifelike spl. However, since the crossover point between the woofer and midrange driver is at a very low 180Hz, the GR Research/Rythmik Audio OB/Dipole Sub (you can disregard the opinion of @mijostyn---he hasn’t heard it)---which is capable of playing up to 300Hz---can be substituted for the stock woofer. The resulting combination provides 100% open baffle/dipole operation, with deep, clean reproduction from 20Hz to 20kHz. Guttenberg found the sound of the LFT-8 to possess the best characterisics of ESL’s and planar-magnetics, without their (in his opinion) failings. Since getting my pair of LFT-8b’s, my Tympani T-IVa’s and QUADS have been relegated to a spare room.

@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.

@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.

I spoke with Roger Modjeski about using subs with the QUAD ESL. He recommended a crossover point of 100hz with a 4th-order filter (24dB/octave). In his own ESL speakers, he used those figures and an 8" sealed woofer. He also made a direct-drive OTL amp to power them.

No matter how many OB/Dipole sub users testify to the success they have achieved mating them with dipole planar loudspeakers, @mijostyn insists on repeating his opinion that OB/Dipole subs can't and don't "work". Yes they can, and yes they do.

Siegfried Linkwitz used them successfully, as does Danny Richie of GR Research. So does Audiogon member @jaytor, mating them with the fantastic NEO 3 and NEO 8 planar-magnetic drivers. They are also being used in conjunction with Magnepan and Eminent Technology p-m speakers, and assorted ESL's. Regular old dynamic speakers, too.

The Finnish company Gradient made ob/dipole subs for both the QUAD ESL and QUAD 63 back in the 1980’s/90’s, but they were not built to perfectionist standards. They were somewhat similar to the ob/dipole woofer system Siegfried Linkwitz used in his LX521 loudspeaker.

The OB/Dipole woofer system offered by GR Research in partnership with Rythmik Audio is similar, but of much higher quality and performance. Two or three (or more, your choice) 12" woofers (optimized for open baffle applications) installed in an H-frame (though the woofers may also be installed in an M/W frame, as Linkwitz did), with a Rythmik Audio plate amp that includes servo-feedback control of the woofers, along with a dipole cancellation compensation circuit. THE woofer to use if you want to add subs to your QUADS.