Paul McGowan gets asked about rotary subs.

@sandpat: Yup, they’ve gone up to $3200/pr, plus a coupla hundred for a pair of the Sound Anchor base/stand. But that does include shipping within the Continental U.S.A., making them imo a better value than the $3000/pr Magnepan MG1.7i (I auditioned them both).

@tomic601: Yeah Jim, Richard Vandersteen is not your typical high end audio designer and manufacturer. If I wasn’t a committed planar enthusiasts it would be Vandersteen’s I would probably own. I have listened to music through them for many hours at Brooks’ shop.

I had the pleasure of joining Brooks for dinner with Richard at the steak house in the venue Richard was showing at during one CES in the late-90’s, and found him to be very down-to-earth, a regular working-class kinda guy. No "snooty" pretenses at all, of which I saw a lot at various CES’ I attended.

Richard ordered the wine, he obviously knowing his stuff. I’m more of a whiskey drinker, and Brooks? Milk. I swear to God! ;-) Richard picked up the tab (Brooks and I had our women in tow, and there were a few others in our party), a good thing as it was the highest I’ve ever seen!

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)!

@sandpat:

1- To get rid of the wrinkles you adjust the LFT driver tensioning mechanism.

2- I take it you don’t have the speakers mounted on the stands made by Sound Anchors specifically for the LFT-8b? Get a pair, they’re pretty cheap!

3- Grant Mye has made his stands for the LFT-8. It includes support arms which extend from their base all the way to the top of the LFT panels. That provides increased structural stiffness and improved sound quality. By the way, the MDF frames of Maggies are even less stiff than the LFT panel of the ET’s. That’s a penalty you pay with a planar loudspeaker.

Not a problem @arion, at least for me. Yep, for dipole loudspeakers (of which most OB loudspeakers are) dipole woofers ARE are the way to go. And I complete agree with your calling drivers which reproduce "only" down to 20Hz woofers, not subwoofers. Separate enclosure with driver(s) became known as subwoofers because most "full" range loudspeakers are of course nothing of the sort. Since those speakers have woofers, what should the industry call a product which reproduces very-low frequencies, those below what the speaker's own woofers can't reproduce? Why subwoofers, of course!

@tomic601: Hey there Jim! Yep, I heard the Vandersteen subs many times over the years at Brooks Berdan Ltd., one of Richard's first and best dealers (he sold a LOT of Model's 2 and 3). When Brooks decided to not sell Richard's new higher-priced models (beginning with the Model 5, I believe) I knew he was making a big mistake. That was not acceptable to Richard, and Brooks was no longer a Vandersteen dealer. Brooks, you fool! ;-).

Brooks wanted to sell his customers (and potential customers) who were looking for higher-priced loudspeakers Wilsons, not Vandersteens. Why not offer your customers the choice of both? The more product you sell of one company, the better wholesale price you get, hence more profit. I sat in on a meeting Brooks took with Wilson's head of sales at CES, and witnessed how dealers are pressured to sell more product. It wasn't pretty.

@curiousjim: Allow me to suggest a subwoofer that is ideal for your Acoustats: The Rythmik Audio/GR Research OB/Dipole Subwoofer.

Planar lovers (especially electrostatics) have been looking for a sub which can "keep up" with their loudspeakers since QUAD and KLH introduced their ESL’s in the 1950’s. Everything form the 24" Hartley woofer in a huge enclosure to a transmissionline-loaded KEF B139 woofer (David Wilson used two B139’s in each of his original 1970’s WAMM model, for midbass frequencies.). The Finnish company Gradient was for a time making OB/Dipole subs for use with both the QUAD ESL and QUAD 63. The design was good, it’s execution not-so-hot. It was reviewed by Robert E. Greene in TAS, if I remember correctly.

Traditional engineers will tell you (the guys at SVS did me) that a woofer can’t be "slow", as it is reproducing only "slow" frequencies. That is of course an over-simplification of a more complex situation. In his excellent series of Tech Talk videos on YouTuve, Danny Ritchie of GR Research discusses all things loudspeakers, including subs. I won’t bore everyone with information better explained by Danny, but suffice it to say that the reason subs have never sounded "fast enough" to blend seamlessly with ESL’s can be explained. Which Danny does.

One important factor is that monopole subs (whether sealed or ported) don’t propagate sound in the same manner as do dipole loudspeakers, nor "load" the room the same way. Employing either dipole planar woofers (as Magnepan does) or traditional woofers used in dipole fashion (a woofer mounted both front and rear in an enclosure, in polarity opposite each other, just as the front and rear of a dipole loudspeaker) solves that problem.

Magnepan has been working on a dipole sub (but it is not open baffle) for a few years now, and has demoed it at a few high end dealers (and hi-fi shows, I believe) around the U.S. The woofer system is the basis for an upcoming Magnepan model: The 30.7 For Condos. It will have Magnepan planar-magnetic drivers for midrange and treble, the woofers of course for bass. Magenpan will also offer the dipole sub as a separate product, for use with their other models (or the loudspeakers of other companies). Eminent Technology already offers a similar woofer system, but it is available only in their LFT-8c loudspeaker. Perhaps ET will sell the woofer system separately? It is offered as an upgrade for current LFT-8b owners, $1500/pr, I believe. Complete with power amp and DSP for crossover functions, time alignment, and equalization.

But the best answer is the amazing OB/Dipole Sub from Rythmik Audio/GR Research. Either two or three (your choice) 12" servo-feedback "free-air" woofers mounted in an open baffle frame, low frequencies (up to 300Hz) propagated both front and rear, just like dipole loudspeakers. The best thing I’ve found for use with my QUAD ESL’s, Eminent Technology LFT’s (both -4 and -8b), and Magneplanar Tympani T-IVa midrange/tweeter panels (I have no room large enough for the Tympani’s bass panels. They are HUGE!).

The sub is available only as a kit (which contains the plate amp---which provides the best controls in the business---and the woofers.). The OB/dipole frames are your responsibility, but GR Research has a company in Canada which makes the required OB frame, shipped as a flat pack. I know that sounds like a lot of work, but the frame is very well designed and fabricated (on a CNC machine, the MDF very high quality and thick), and easily assembled (only wood glue and clamps needed). Reasonably priced, too.

The genius speaker/crossover designer Siegfried Linkwitz came to the conclusion that open baffle/dipole loudspeakers are the way to go, and designed and sold (he died back in 2018, but arranged to have a colleague continue to market his designs) a loudspeaker that includes a sub of the same design as that of GR Research. But the latter is the superior sub, imo.

End of sales pitch/shill. ;-)

@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.

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. ;-)

@pryso: Excellent point about the LFT’s avoidance of a crossover through much of the audible range. For those who missed it, the midrange planar-magnetic driver in the LFT-8 reproduces from 180Hz up to 10kHz, with NO crossover! That is a very big deal. Fans of single-driver designs take note!

Bruce Thigpen was very impressed with Jim Winey’s original Magnepan design (the Tympani), but thought he could do better. So he designed his LFT driver as a push-pull transducer, in contrast to the single-ended of the Tympani. A push-pull driver produces less distortion than a single-ended one, of course (the wires attached to the Mylar film of the drivers better remain in the field strength of the driver’s magnets). Winey eventually designed and built an excellent push-pull ribbon tweeter, but the midrange drivers of his MG.7, 1.7, and 3.7 remain single-ended. Also, the LFT driver is built into a substantial metal frame, as opposed to the Mylar of the Maggies being merely glued and stapled onto the speaker’s MDF frame.

The crossovers for all the LFT-8b drivers (the p-m midrange and tweeter, and the 8" dynamic woofer in a sealed enclosure) are simple 1st order/6dB-octave filters, with few parts. And the LFT-8, while very low in sensitivity, is an 8 ohm load. The m-t panel itself is an 11 ohm load, so great for tube amps. The LFT-8 comes with two sets of binding posts, for easy bi-wiring or (even better) bi-amping.

The ET TRW-17 Rotary Woofer has been described (by Peter Moncrieff in International Audio Review, I believe) as the world’s only true subwoofer. That is because it is designed and intended to reproduce "only" 20Hz and below. Most loudspeakers have a hard time reproducing even 40Hz at lifelike SPL with low distortion, and even the best subwoofers can’t do 20Hz very well (except perhaps the Rythmik’s).

The current Stereophile contains a review of the Klipsch La Scala AL5, and both the reviewer (Alex Harbestad, a name new to me) and John Atkinson’s measurements revealed the output of the AL5 to plunge rapidly at 50Hz. And that from a 15" woofer! Totally unacceptable, to me at least. The lowest note produced by a standard 4-string bass (electric and acoustic)---the E string played "open"---is located at approximately 41Hz. If a loudspeaker can’t reproduce 41Hz, I ain’t interested ;-) .

We all know that hi-fi’s are still---after 100 years or so of development---quite incapable of reproducing music that comes close to that which we experience when heard live. I have long believed a large part of that failing has to do with hi-fi’s failing to reproduce (and perhaps recordings failing to capture) the physical properties of live music. Live music is sensed not only by our ears, but by the rest of our bodies as well. While our hearing may not perceive frequencies below 20Hz or so, our bodies certainly do.

I would love to hear the TRW-17, and have seen pics of it in the system of one audiophile (he installed it in the floor of his listening room). He pairs it with his loudspeakers, which are a pair of Martin-Logan ESL’s augmented with the bass panels of the Magneplanar Tympani loudspeakers. Yeah, baby! I LOVE the sound of the Tympani bass panels (I own a pair of them as well, the T-IVa), but they are good down to only 30Hz at best (when braced and fed a LOT of power).