Why not more popular?

I owned quite a few floor standing monkey coffins/box speakers including; Nearfield Pipedream (10K prototypes), Genesis Vs (HPs personal pair), Usher 6371s...


and before all of those, Accoustat 2+2s with upgraded servo amps
and after the monkey coffins, Magnepan 3.5Rs, I found both of these to cut off the visual flow of my awesome multipurpose room.


I replaced the 3.5Rs with Emerald Physics KCIIs, with Clarity Cap upgrades, and wired with WireWorld OCC. Great for a regular size room, but mine is ~35 x 21 x 12. I tried to incorporate my SVS Plus and Ultra cylinder powered subs, but never could get a good seamless blend.

I replaced the KCIIs with EP 3.4s (12" concentric woofer with 1" polyester dome tweeter), which sound seamless down to ~ 40hz and blend much better with the SVS subs, but when I moved them out from ~6ft from the front wall to 7.5ft that freed them to come fully alive. IMO, the 3.4s will more than satisfactorily reproduce 95% of music we all enjoy in a more normal sized room. Quite the bargain if you can find them. There are a couple bigger EPs for sale in the classifieds


My subs are ~ 10 years old, and Im sure SVS sells vastly better subs now, but even theirs are expensive. What to do? Next up for me is EP 2.8s, which uses all carbon fiber drivers; a 12" concentric, plus 2 @ 15" subs per speaker. That should take me over the top

In summation; OBs are capable of life like reproduction at a reasonable price, and cost a lot less to ship

@mijostyn: I expected to see the response in your paragraph number one, but not from you ;-) . Yes of course, planars are technically open baffle (though there have been some ESL’s made in sealed boxes). My statement was made in response to the post in this thread claiming that "Open baffle is basically a version of what Martin Logan has been making for years."

If that’s true (and it’s not---the factory-built OB’s from Spatial Audio and Emerald Physics use dynamic---cone---drivers, as do the DIY kits from GR Research---though some with a magnetic-planar NEO3 tweeter---and Siegfried Linkwitz.), you could make the same claim about planars dating much further back than Martin Logan, all the way back to the QUAD ESL, introduced in 1957. Then the KLH 9 a little later, the Magneplanar Tympani I in the early 70’s, Sound Labs and Acoustat in the 80’s, and numerous others. Why single out the Martin Logans?! Martin Logans claim to fame is the curved ESL (designed by Roger Sanders) and the ESL/dynamic woofer hybrid (or at least popularizing it).

As for baffle size and dipole cancellation, of course that cancellation cannot be completely eliminated by increasing the front-to-back driver distance alone (that’s what Infinite Baffle is for ;-), but you can lower the frequency at which cancellation commences somewhat by doing that. What Siegfried Linkwitz and Danny Richie do is use an H-frame to create the front-to-back driver separation instead of a flat baffle, as the frame provides more resonant-free sound than does a "normal" flat baffle (an un-normal one is the 2-1/4" thick one made by Ric Schultz of EVS, mentioned above) . The depth of the H-frame is limited by the "cavity" resonance inherent in each of the frames enclosed spaces (the deeper the frame, the higher the frequency at which cavity resonance becomes audible). Both Siegfried and Danny limit that depth to around 14".

To further minimize the dipole cancellation inherent in dipoles, both Siegfried and Richie incorporate the 6dB/octave shelving circuit I mentioned above (commencing at around 100Hz, I believe). Siegfried does it in his digital filters, Danny had Brian Ding of Rythmik put it in the A370 plate amp that comes with the OB Sub kit---analog, of course.

The reason full-range planars are so big is for the reason you state---their bass output is restricted by the relatively-limited (compared to dynamic woofers) ability to move air: the thin Mylar film only moves back-and-forth a tiny distance. OB/Dipole dynamic woofers are also less able to move as much air as a sealed or vented sub, so more of them need to be used. The Linkwitz and basic GR Research use a pair of woofers (the former 10", the latter 12"), but GRR also offers a 3-woofer version. Plus, you can make multiple H-frames and stack them. What Danny does at Hi-Fi shows (and in his own listening room) is use OBs at the front of the room, and a pair of sealed subs at the rear. That set-up won GR Research "Best Bass At The Show" award several years running at RMAF (as reported in show reports in TAS and elsewhere).

Clayton Shaw at Spatial Audio and most DIY’ers go a different way: using a pair of 15" drivers on a big flat baffle. When you do that, the midrange driver (if any) and/or tweeter will also be on that baffle. For better or worse: Danny Richie is particularly adamant that it is for the worse (though he holds Clayton and his speakers in high regard).

As with everything in audio, there are trade-offs made in all loudspeaker designs. You have to pick your poison, find the loudspeaker at your price-point which gives you the most of what you are looking for. OB’s are one choice, planars another (ESL, magnetic-planar, or ribbon), horns, and of course normal dynamic (cone and dome). Infinite baffle are REALLY out-of-fashion, though they may come back in when kenjit introduces his version ;-) .

I've owned many good speakers from the DQ10 days, and yes they could do bass if you had a big enough amp, say the Threshold 400A they could sake the room, to Dynaudio Confidence speakers, ProAc, and Quad ESL's. I decided to try the Spatial Audio M3 Sapphires which are OB speakers. Like all new speakers, one had to allow them to burn in and learn how to set them up properly. Reading many of the anti-OB speaker comments and their sound, is nowhere what I am hearing in my system. Clayton woofers are designed for OB speakers period, in the past box woofers have been used and they suffer bass roll-off. The tweeter in the M3's was selected to work with the woofers and the open baffle and covers a large range from the midrange to the highs up to 40Khz. Once burned in the bottom end is so good, with detail, speed, and texture, that one does not need a subwoofer, in fact, I tried them and they ruined the coherence of this fine speaker. They are nowhere near boring, they make music sound alive, open, and tonally right. They produce what you feed them, you change a power cord or interconnect or speaker cable you will hear the change big time, meaning coloration is very low as well as distortion. They rock out, they play Jazz, they do baroque, large play symphonies, the piano is dead-on right, brass and horns also. They are also just enjoyable to listen to and as my wife says that sounds live. After being with my rebuilt Quads 63's by Kent at Electrostatic solutions, and enjoying them for almost 9 years, I wanted a change, I heard many speakers at my dealer and none for the money could match my Quads and they were 12-20K. Thus my research and finding Clayton Shaw speakers and after speaking with Clayton decided to take the plunge. Clayton is honest and upfront, I wanted the X5's but he suggested the M3's as the best speaker for my room and distance from the speakers. He was dead right, the wrong speaker for a given room is a waste of money because they just won't work. While no speaker is perfect, and you can always wish for if it only had this or that, but overall the M3's is one of the better sounding speakers I've heard or owned, and they are a real value vs. sound quality. After Quads, it is very hard to listen to a box speaker, with the M3's I not only listen but enjoy the difference from the Quads, and like the Quads, they just disappear when listening. Unless you hear them you cannot comment on OB designs of the past, because what these speakers do, do right is sound real as the recording and alive like few speakers can, like panel and stats, they are an open window to the recording. They cost $5,000 and worth every penny and then some. 

Great post @phillb!

The significance of your point about Clayton using drivers designed and built specifically for OB use cannot be overstated. All professional loudspeaker designers/builders know the importance of that, and proceed accordingly. I’m sure there are some DIYers who have used inappropriate drivers (those designed for use in enclosures), but we’re not taking about them.

Danny Richie of course also uses drivers made to his specs, drivers made with electrical and acoustic properties tailored specifically for OB use. These include his woofers, tweeters, and NEO3 magnetic-planar tweeter. One difference between the designs of Danny and Clayton is Danny’s use of a minimum-width front baffle, partnered with the use of side "wings" to increase the front-to-back driver separation the large baffles used by Clayton inherently provide. In spite of their different approaches, Clayton’s design talent and resulting OB loudspeakers have received high praise from Danny.

Also good is your mention of subs not blending well with OB’s. Planar loudspeaker lovers have for decades dealt with that reality. No matter how good the box sub was, it sounded "separate" from the planar loudspeaker. In the 1960’s the 24" Hartley was used by many QUAD ESL users, Mark Levinson using it in his HQD (Hartley sub, double QUAD ESL’s, Decca Ribbon Tweeter) loudspeaker. Infinity used servo-feedback sealed-enclosure subs with their IRS and RS-1b speakers, and many other attempts could be cited.

There are numerous reasons for the difficulty of achieving the desired blending---which I won’t go into here, except in one regard:

In the 1980’s, Finnish company Gradient introduced an OB/dipole sub designed and built specifically for the QUAD 63. They followed it up with an OB/dipole for the ESL (aka 57). Though compromised by sub-par design, build, and maximum SPL, it showed the way. OB sub design flourished amongst DIY loudspeaker designers/builders, including a very young Danny Richie.

Meanwhile, Harry Pearson at TAS had come up with the idea of replacing the sub towers of the Infinity IRS with the bass panels of the Magneplanar Tympani loudspeakers, two 16" X 72" panels per side. Mated with the m/t panels of the IRS (which housed line-source arrays of EMIM and EMIT planar drivers), the sound produced was the finest many people have ever heard---to this day. Finally: full-range (except for the bottom half-octave: below 30Hz) reproduction, completely planar. Unfortunately, the resulting combo required a LOT of floor space, so was impractical for most.

Along comes Danny Richie. His GR Research company was started to sell loudspeaker kits to the DIY community, with an emphasis on OB design. GR Research was offering a number of OB loudspeaker kits, along with a sealed sub. Though very much liking OB bass, he resigned himself to the fact that it’s limitations presented a challenge he was unable to resolve to his satisfaction.

But then Danny heard about a company introducing a new (patented) servo-feedback woofer (Rythmik), which just happened to also be in the State of Texas (in Austin). Danny proposed to Rythmik designer/owner Brian Ding his idea of mating Brian’s servo-feedback woofer/amplifier with a woofer designed by Danny for OB use, a pair of the servo-feedback woofers installed in an OB/dipole frame.

As I’m sure you know (or have guessed), the product came to market. If you have heard the bass produced by the Magneplanar Tympani loudspeaker, you already know what to expect from the GR Research OB/Dipole Sub, but without the latter’s missing bottom half-octave (and massive power amp requirements!). For any OB or planar loudspeaker owner who wants not just more bass, but bass that sounds like it’s being produced by their loudspeaker, it is now available.