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.....


@bdp24 thanks! I’ve read that in the user manual but I’ve just been afraid to mess with it. Really I need some time to adjust and listen, rinse and repeat. But they sound so wonderful even in their flawed state!


I do have the sound anchor stands- these are the large heavy thick metal legs that Thigpen recommends for his speakers, correct? I have them but they were a pain to screw into the woofer box- felt like I was probably causing some sort of new resonance due to the screws sticking out inside the box. My biggest worry though is that I’ll lose a nail and fracture my little toe on them. One of the speakers sits right in the path of my listening room door and I’ve accidentally caught my pinkie toe on it multiple times. The pain is awful. I’ve been on the search for some sort of rubbery material I can place over them to prevent losing a toe someday.

On the subjection of tensioning the ribbons on the panels- do you have any literature on how to go about it the right way? I don’t want to just be loosening/tightening hex screws without knowing what I need to be adjusting first.


Thanks for the tips! I can’t imagine these speakers sounding any better but there it is… something for me to chew on.

Yep, there it is. By the way, the recommendation of an aluminum wrench is a REAL good one. The magnets in the LFT drivers exert a pretty strong pull on ferrous materials (steel)!

@bdp24, yes...nothing like having a tool yanked from your hand. 😬

Brass wrenches are better, but mind the alloy and test cheap. *l*

Agreed, a nude Maggie isn't cute by no means and I'll give the 8's a nod for at least looking 'business-like' about being sans grilles... ;)
Some of us don't mind facing nudes..😏

I have my Heils...I know a good ribbon or planar when I stumble into them.
I'd give the 8s' my time. *S*