Paul McGowan gets asked about rotary subs.


Paul McGowan of PS Audio has for years posted frequent (daily?) videos on YouTube in which he answers questions sent in by people from the world over. I just watched one in which he answers a question sent by a guy in India, inquiring as to why rotary subs are not more popular. Paul gets around to completely answering that question, but before doing so says this:

 

"The Rotary Sub was invented by a guy named Bruce Thigpen, and Bruce is a VERY (Paul’s emphasis, not mine) creative inventor who used to have a company---maybe he still does---called Eminent Technologies (sic. It’s actually named Eminent Technology). And Eminent Technologies, they made some GREAT (again, Paul’s emphasis) loudspeakers. They were---if I remember right---they were planar, or electrostatic---I think they were planars, they weren’t electrostatics, but they were REALLY (Paul again) good. And I don’t know what ever happened to that, but I DO know that Bruce figured out a way to make a subwoofer that could go well below what normal subwoofers do."

 

But this post is not about the Eminent Technology TRW-17 Rotary Subwoofer (there aren’t rotary "subwoofers", there is only one Rotary Subwoofer, the product of ET alone), it is about Eminent Technology itself. I mean geez, if Paul McGowan doesn’t know if Eminent Technology is still making planar loudspeakers, just how low IS the visibility of the company?!

To set the record straight: though Paul differentiates between a "planar" and an "electrostatic", while not all planars are electrostatics, all electrostatics are planars. I routinely see Magnepans referred to as planars (by Steve Guttenberg, for instance), which they of course are. But so are electrostatics. When Paul and Steve say planar, they are speaking of planar-magnetic loudspeakers. Both Magnepan and Eminent Technology make them.

 

The Eminent Technolgy LFT-8 planar-magnetic loudspeaker was introduced in 1989/90, and remains in production today. It has gone though a few revisions over the past thirty-three years: in 2007 an improved woofer replaced the original, with a change to it’s nomenclature: the LFT-8a. In 2015 an improved tweeter replaced the original, the new model designation being LFT-8b.

The LFT-8b remains available, and there is also a new version of the LFT-8: the 8c. The 8c consists of the same planar-magnetic panel as the 8b (which contains the midrange---180Hz up to 10kHz---and tweeter---10kHz and above---drivers), but with the monopole woofer of the 8b (for frequencies 180Hz and below) replace with a "gradient" dipole woofer (still a sealed enclosure, but with a 6.5" rear woofer added to the 8" in the front), which simply bolts on in place of the monopole woofer enclosure. Also included with the 8c is a power amp for the woofers, and DSP for the low-pass x/o filters for the woofers, time-alignment of the panels with the woofers, and equalization.

The LFT-8b retails for $3200, the 8c $4500, shipping in the U.S.A. included.

 

Magnepans are commonly discussed and owned (I own a pair), but the Eminent Technology LFT-8 remains virtually unknown (I also own a pair of the LFT-8b). Why is that? It has received rave reviews (REG in TAS, cudos from VPI’s Harry Weisfeld---who characterized the midrange of the LFT-8b as "the best I have ever heard", a number of reviews in the UK hi-fi mags), yet remains virtually unknown to the vast majority of audiophiles. I know ET has few dealers and does no advertising, but still.....

128x128bdp24

 

Thanks @wsrrsw: Thanks, I hadn’t seen that write-up on the TRW-17.

 

@uncledemp: Though "normal" recordings made in studios are limited in very low frequency content, some recordings made in very large "rooms"---cathedrals and churches, large theaters---contain very low (below 20Hz) information. That’s why you can hear the sound of the room itself (the dimensions of large spaces allow very low frequencies to propagate.). I have some EMI and Decca Classical LP’s in which the environment in which the recording was made is quite audible/evident---a HUGE space. I can only imagine what the ET TRW-17 would make them sound like!

 

@aldnorab: Some good questions. Here’s some answers to them:

 

1- Very true. That’s how I learned of the Magneplanar Tympani T-I’s (Gordon Holt’’s review of them---which was not entirely positive---had not yet appeared in Stereophile). In the Spring of 1972 I happened to visit a newly-opened hi-fi shop on the very day Bill Johnson was delivering and installing a complete ARC/Magneplanar system in the shop’s excellent sound room (Bill was a pilot and owned a plane, so flew himself and a demo system to new dealers who were located far from Minnesota). I made like a fly on the wall---keeping my mouth shut and my ears open, listening to Bill and Walter discuss all thing hi-fi. I got quite an education that day!

I had already heard the Infinity Servo-Static and Dayton Wright electrostatic loudspeakers, but was unprepared for the sound the ARC/Maggie system produced. Shortly thereafter I bought from that dealer (Audio Arts in Livermore, California, owned and operated by Walter Davies, as fine a man as I have ever known. He later created the Last Laboratories line of excellent LP and tape preservation products.) the same system: Tympani’s bi-amped with the ARC passive crossover and D-51 and D-75 power amps, an ARC SP-3 amplifying the signal from a Decca Blue cartridge mounted on a Thorens/Decca player. That was Johnson’s reference system, except he had brought along a prototype tonearm in development at ARC, which was never put into production. I remember it resembling the Weathers and Grado arms of the 1950’s and 60’s.

2- Prior to introducing the LFT-8, Eminent Technology had already marketed LFT models which were not hybrids: the LFT-3, LFT-4 (a pair of which I also own), and the LFT-6. Instead of a dynamic cone woofer, those three models had planar-magnetic woofer diaphragms, which were of course somewhat large (bass frequencies require drivers which have either large radiating surfaces---planars of course do---or considerable excursion capabilities---planars don’t---in order to be able to "move" enough air.

To make an LFT model of more modest proportions, Thigpen decided to use a dynamic woofer for the LFT-8. He readily admits the 8" woofer is the LFT-8’s weakness, but for those with a room big enough one could use the bass panels of the Tympani’s with the LFT-8 midrange/tweeter panels. Or, since the LFT-8 woofer operates up to only 180Hz, in place of it one could instead use a pair of the fantastic Rythmik Audio/GR Research OB/Dipole Subs (which---unlike "normal" subs---can be used up to 300Hz.). Or, get the new LFT-8c, which incorporates a new sealed dipole woofer. By the way, Magnepan has itself been working on their own dipole woofer for some time now, and it will eventually come on the market.

3- All drivers are made with compromises. Do the front-mounted magnets of the LFT driver cause diffraction? Remember, the more expensive Magnepans---the 20.7 and 30.7---themselves employ push-pull midrange drivers, with magnets front and rear. Which is worse: a small amount of diffraction, or a large amount of harmonic distortion? Only you can decide. ;-)

If you wish upon a star...

http://www.eminent-tech.com/index.html?fwd=LFT8.html

SOAF= Zero....unless vision-impaired..

Even then, with the 'hearing compensation' that's typically existing...

O, Lucky Man....;)

@avsjerry: That pic is with the front grill frame & cloth removed. With it in place, the LFT-8 looks no worse than do Maggies. Not pretty, but not horrible.

Would love to hear with my Acoustat Model X’s.  Over the years, I’ve tried probably ten subwoofers with them and have never found one yet that’s fast enough.

@bdp24, seems like we share a few perceptions.

For years I've set a goal for 40 Hz bass in speakers I've owned.  Not necessarily flat down to that frequency, but at least reasonable output.  I'm a big jazz fan and the 42 Hz (as I've typically read) of the open E string on a bass defines the minimum of what I expect to hear.

Basic need for lower bass.  Not that many instruments extend below 40 Hz, nor is there an abundance of music scored in that range.  But I too learned that the sense of space in large recording venues is better captured by systems which extend into the lowest octave.  So that elusive sense of realism of live experience is better supported by deep bass capabilities, even when not attempting 16 Hz organ notes.

I don't remember the year, but clearly recall the experience of Bill Johnson coming to a San Diego dealer to set up an ARC tube system with a pair of Tymphany speakers.  Still, one of the better audition experiences I've had after decades in this hobby.

Unfortunately, at my age I'm looking to simplify my system.  So while the larger rec room where I had hoped to set up a good second system (where ET 8Bs would have been contenders) was a dream, I must admit it is not likely to happen now.