The criteria for loudspeaker choices.

@cbrunhaver: The sensitivity measurement Atkinson got was for the original iteration of the LFT-8, reviewed in Stereophile way back in 1993. In 2007 the original woofer and crossover were replaced with new ones (and renamed the LFT-8a), which raised the speakers sensitivity to it’s current 83dB spec. When the original tweeter was replaced with a new one, the speaker became the LFT-8b.

As other owners have found (as did Steve Guttenberg), while the LFT-8b has a rated sensitivity very close to that of Maggies, the ET’s require far less power than do Maggies (As I stated above, I have both). But the way to run the LFT-8 is bi-amped; when run that way the p-m panel itself is an 11 ohm load to the amp, and 50 watts is plenty for it alone. The woofer of the 8b can be powered by any ol’ amp, preferably a solid state one

By the way everyone, Steve Guttenberg recently reviewed another large planar-magnetic loudspeaker, made by the French company Diptyque. He likes it even more than the ET LFT-8b/c, but it costs far more, I believe four times the price of the LFT-8b.

@kennyc: The title of the thread was made in relation to what PS Audio had to say about planar-magnetic drivers, which they choose to employ as tweeters in all their loudspeaker models. In their promotional literature for their speakers, they cite all the ways in which p-m drivers meet their criteria for achieving superior quality reproduction of high frequencies (reread the op to refresh your memory if necessary).

The question I therefore asked was: If planar-magnetic drivers meet PS Audio’s criteria for superior reproduction of high frequencies, why not use a planar-magnetic driver for midrange frequencies as well? There are only a very limited number of loudspeakers employing p-m drivers to reproduce midrange frequencies, one being Eminent Technology. Another is of course Magnepan. I currently own both Magnepan and Eminent Technology models, and because everyone already knows about the former and few do about the latter, I felt compelled to once again bring the ET LFT-8 to everyone’s attention. If that now qualifies as shilling, so be it.

Everyone has their own criteria for choosing a loudspeaker, I posted this thread in response to the criteria stated by PS Audio as the reason for them choosing a p-m tweeter, not as a means of myself making the case for the superiority of planar-magnetic drivers or loudspeakers. I also own ESL’s (QUADS), but didn’t bring them into the discussion as PS Audio doesn’t use ESL drivers, nor make any claims as to their ability to reproduce music.

One listener who DID bring the subject of ESL’s into his review of the ET LFT-8b and 8c is Steve Guttenberg. In his reviews he states that he doesn’t care for the sound ESL’s make, preferring his dipole panel speakers to be of planar-magnetic design. He then goes on to say that he found the sound produced by the two ET models to be superior to that produced by every ESL he has heard, as well as all Magnepan’s he has had in his listening room.

I hope this post makes clear my motive and intent. I did my best to make it so!

@cbrunhaver: You raise some justified issues, and make some excellent points.

The shallow crossover filters employed in the ET LFT-8 (1st-order) are also used by Magnepan in their planar-magnetic loudspeakers (PS Audio’s Paul McGowan’s reference speaker for quite a few years was the MG3.6, which he was very happy with in spite of it’s low-order filters). When Danny Richie of GR Research measured the MG3.7, he found a lot of frequency response irregularities caused by phase cancellations between drivers, a result of the large expanses of driver overlap (inevitable with low-order filters).

The ET LFT-8 (both b and c iterations) employs a 1st-order high-pass crossover frequency of 180Hz for the LFT-8 planar-magnetic midrange driver, so phase cancellation between woofer and midrange driver is not a problem (due to the very long wavelength of 180Hz). What IS a problem is the out-of-band woofer resonance (seen at around 1800Hz in the Stereophile frequency response graph), but that may be eliminated in the LFT-8b by installing a cap onto the woofer, shunting the high end response of the woofer to ground (as detailed in a few posts in the Planar Speaker Asylum forums). That problem is eliminated in the LFT-8c, which has a different (dipole) woofer system. I eliminated the problem by using the Rythmik/GR Research OB/Dipole woofer system in place of the LFT-8b’s stock woofer (easy to do, as the 8b has separate woofer and planar-magnetic driver binding posts), which transforms the LFT-8b into a 100% OB/dipole design.

The criticism of the 1st-order high-pass and low-pass filters located at 10kHz IS quite valid. A 10kHz wavelength is only approximately 1.36" long, so small movements of the listener’s head can result in frequency response changes resulting from phase cancellations between the midrange and tweeter drivers. I’d love the hear the LFT-8 with a lower midrange-to-tweeter x/o frequency, and/or steeper filter values (perhaps 4th-order, as I believe Siegfried Linkwitz employs in his OB/Dipole designs). The phase relationship between tweeter and midrange drivers in the LFT-8 may be adjusted by small changes in loudspeaker toe-in.

I don’t know where the 77-78dB sensitivity figure came from, but it is not accurate (83-84 is more like it). The LFT-8 infact requires significantly less power that do Maggies (I have both). Steve Guttenberg found 50 watts to work pretty well with both the 8b and 8c. And if you bi-amp the speaker, the planar-magnetic driver itself presents an 11 ohm load to the amp, great for tubes

Regardless of all the above, the fact remains that the ET LFT-8 reproduces 180Hz up to 10kHz WITH A SINGLE PUSH-PULL PLANAR-MAGNETIC DRIVER (without a crossover in that frequency band!), resulting in high coherency and transparency, low coloration sound. I better wrap it up here, before I’m once again accused of shilling for Eminent Technology and Bruce Thigpen.

@ricevs: Your comments are always welcomed by me (by the way, I still own the Audible Illusions Modulus 2 pre-amp you "modified" for me about 25 years ago. Modified is an understatement; it is a complete redesign, turning the full-function pre into a phono-only gain stage).

I did just as you suggest, using the GR Research/Rythmik Audio Direct Servo-Feedback OB/Dipole Subwoofer (which you at one point were using in your own loudspeaker design, mated to the planar-magnetic m/t drivers that are no longer available. I forget the name of the company that was making them. Danny Richie of GR Research is now offering his own version of that fantastic p-m tweeter.) in place of the stock woofer in the ET LFT-8b.

The combination of the ET LFT-8 planar-magnetic drivers (180Hz and above) mated with the OB Sub is one way to achieve near-state-of-the-art sound at a peasant-income price. IMO. Far superior to the Infinity RS-Ib’s I used to own.

Such as? I also own Quads ("57"s), Maggies (Tympani T-IVa), and ESS (Transtatics). In the past I have also owned Infinities (RS-Ib), Fulton Industries (Model J), a few others.

It’s not that the ET LFT-8b is "better than the acknowledged masters of the category", but rather that at $3200/pr shipped they are a great bargain in a dipole planar design. Why are some people bothered by others feeling that way? Weird.

Steve Guttenberg’s review of the LFT-8b (and 8c) are as enthusiastic as any review of his I’ve seen. Robert E. Greene’s in TAS and a couple in the British press (readable on the ET website) were equally enthusiastic. I’m in good company.

As a dipole planar-lover, I feel almost obligated to let others like me know about the LFT-8, especially those contemplating the purchase of the MG1.7i. I compared the two, and though they are in some respects similar in design, they sound very different from one another. Is informing others of another speaker to audition before purchasing the MG1.7i now considered "shilling" for ET?

I have owned only one PS Audio piece (the old 200C power amp), which I consider to be well designed and built. So did J. Gordon Holt and Tony Cordesman, reviewed in Stereophile.

As for Eminent Technology (not "Emminant tech"), Bruce Thigpen manufactures his LFT drivers himself in Florida.

@kennyc: The reason I was linking and comparing the PS Audio FR5 and the ET LFT-8 was because the case PS Audio made for the superiority of a planar magnetic driver over a dynamic was quite adamant on their part. If they feel so strongly about planar magnetics (I like them too), why not make a speaker fully fitted with p-m drivers? Using a p-m driver for a tweeter is well and good, but the PS Audio FR5 reproduces the majority of the music with a 6.5" dynamic driver. The ET LFT-8 does it with a single large p-m driver. 180Hz to 10kHz!

The LFT-8b makes bi-amping a simple proposition, and allows a tube amp to be used on the Planar Magnetic drivers/panels (tubes love an 11 ohm load), and a solid state amp on the sealed dynamic woofer. Splitting the signal at 180Hz eliminates the need for a high current ss power amp. In contrast, the MG1.7i---having a single pair of speaker cable connectors, as well as wiring the various P-M drivers in series, not parallel---needs internal surgery to be bi-amped. The combination of a 4 ohm (and lower) load with an 83.5 dB sensitivity makes a high current amp mandatory with the 1.7i, which is not the case with the LFT-8b.

But back to the PS Audio FR5. I have no doubt it is a fine sounding loudspeaker, maybe even great. And a good choice for a small room. The point I want to draw to everyone’s attention is that if the case PSA makes for the Planar Magnetic driver is as strong as they obviously believe, the LFT-8b uses that technology all the way down to 180Hz, the FR5 only down to 1750Hz. That’s a drastic difference. A whole lot of the sound of music is found in the 180Hz to 1750Hz range.

But then the FR5 is a "box" speaker, the LFT-8 a dipole planar. Not everyone likes, wants, or can accommodate the latter. For those people the FR5 may be a welcome offering. I find a mini-monitor, especially one with a price tag of $3499 plus shipping---of little interest.

I am living in the southern most town in Washington State (Vancouver), just over the border/river from Portland, Oregon. If I were working for Eminent Technology I think I would be living in Florida. And being paid to do so.

I’m not a dealer, or a manufacture’s rep, or hold any other position in the hi-fi industry. What do I have to do, show my income tax return?!

Anyone wanting proof I bought the LFT-8b’s as a consumer, give Sheila Berdan at Brooks Berdan, Ltd. in Monrovia, California a call and ask her (I'll provide my name). Sheesh!