As he promised, Guttenberg reviews the Eminent Technology LFT-8c.

While Guttenberg's reviews of 8b and 8c are both positive, I feel he did not review the  8c quite as it was intended. He dismissed the DSP function of the speaker, saying it did not sound as good. However, the DSP is an integral part of the 8c. The entire signal chain goes through a A-D and D-A conversion, so that one is able to adjust the low pass level as well as time align the high pass signal. The speaker is preset with a -14.5db on the bass and a 0.6ms delay between the panel and the woofer. Both these functions allow the speakers to integrate better with the listening room, provide a much more coherent soundstage with better image depth and width, and a better integrated bass response. 

I know there are those who say they can hear a DSP in the signal chain and dislike it. Just like there are those who claim they can hear a step-up transformer in the vinyl signal chain and dislike it. But with the 8c, it is through the 'digitization' of the signal chain that certain sonic defects could be remedied. I just wished Steve could have made a little more effort in discussing the 8c with and without DSP. 

If it were an issue of more and better bass, than @bdp24 's comment on the Rythmik / GR Research open baffle sub-woofer must be a great solution. But even the Sanders system uses an integrated DSP solution to the design. I just wish the DSP design methodology could be discussed more insightfully. I asked Bruce about the use of DSP in an email. And he claimed that DSP technology has advanced so much  that he can use it to do things that were just impossible a decade before. And given the advancement, he felt that DSP is the lesser of two evils, the other being a passive  crossover design.  

Good points you raise @ledoux1238. I admit to having reservations about digitizing all signals passing through the DSP of the 8c (and the Sanders version of same). I accept the assertion that digital technology has improved to the point of it being as close to complete transparency as is much of analogue, but still, why do it if you don’t have to?

One thing to know is that the 0-180 degree phase control (which provides from zero to 16ms of delay), gain control, damping control (high/low/medium), extension filter (14Hz/20Hz/28HZ), and crossover frequency (up to 300Hz!) and slope (1st/2nd/4th order) controls (amongst others) included in the Rythmik Audio plate amp make possible the integration of the LFT-8 panels and OB/Dipole Sub just as well as does the DSP unit. In addition, the OB/Dipole Sub features Brian Ding’s Direct Servo Feedback control of the 12" woofers, which also provide full output down to slightly below 20Hz, over an octave lower than the LFT-8 b and c woofers.

At any rate, both the b and c version of the LFT-8 really deserve to be more widely known by audiophiles interested in planar-magnetic dipole loudspeakers. Why on Earth it took Guttenberg 33 years to get around to hearing them is what I would like to know! Everyone knows about Maggies, while the Eminent Technology LFT-8 remains virtually unknown. Bruce Thigpen may prefer to keep Eminent Technology at a manageable size, but sending a few pair of LFT-8c’s out for review by print mags may provide him with a better eventual retirement.😉

I remember going to a previous Axpona show where they did a demo of an unreleased speaker in the 6K range that sounded very good. Does anyone know that model number and when that is being released?

There are many paths up the mountain of good sound. If I had an 8B I would upgrade all the jacks and xover parts and wires with the best stuff (including 12 gauge wax foil coils that are cryoed and used in the best sounding direction.....going into the inside of the coil and out the outside). This would take them to a level that practically no one has ever heard. Then I would disconnect the woofer and on a separate flat open well braced baffle would mount either two Lii Audio or Acoustic Elegance 12 inch woofers and use a separate amp that has full eq to extend the woofs down to 20 hz and also get rid of all room nodes. I had the GR research servo woofs and they do not play above 150 hz even with the highest xover point. I always had a hole between the woofs and my planar speaker (heard and measured). Also you cannot equalize the bass with the servo system. I would use something like a Crown XTi 2002 to biamp. You run the mids and highs from your great normal amp and the woofs get their own amp with eq.....so they are driven directly with no coils.

You could also wait till next year when ET might bring out a speaker using the new 90db panels (not the two boxer he showed in Florida). This would need to have new woofers and bigger box on bottom to match. Also, I suggested to Bruce that he sell the new 90db drivers on the panel by itself.....with no woofers....so us DIY people can make our own super xover and bi-amp as described above. We will see what he does.

Here are some more ways to get tricked out planar sound:

Put two 12 inch woofs on an open baffle and above it mount 4 of the 8 inch planar drivers from Parts Express ($60 each...or optionally, use the way more expnsive Radian Planars)......now you have a 32 inch line source of planar drivers running from 300hz on up (high 90s sensitivity). You get the Minidsp Flex pure digital version...xover ($500) and make a super power supply for it.....and get two modified pure digital amps (VTV D300 or Peachtree GaN1) and use a stereo amp per channel mounted right behind the speaker. All xover and eq and delays done via the minidsp. This system would have no preamp, no DAC and no analog interconnects.....just some coax digital cables and very short speaker wires that are connected from the amps directly to the speaker drivers......this whole system with out streamer would be around $8-9K.....for everything including the wood for the baffle. Would be killer. Think about it.....No DAC, Preamp, analog cables, no long speaker wires. Xover and eq done totally in the digital domain......pure digital amps.....two state of the art 12 inch woofers per side and 4 highly efficient planars per side.....all perfectly equalized and time aligned for your listening position........

If you want to stay with analog class D or class A or whatever then you can get the new Danville dspNexus xover and bi or tri amp with it. Check out what Richard is doing at Hollis Audio Lab. He just showed a stack of 3 servo woofs and the mid/highs were a single planar 10 inch driver from Radian mounted on a small open baffle. He is now experimenting with adding a small tweeter to give better dispersion (tri-amping). Please check out his forum on Audio Circle. He has helped one person with ET speakers to use the Danville xover with it.

Damn Ric, you’re gonna scare off potential LFT-8b/c buyers!

Sure, an outright fanatic like Ric Schultz can concoct a Frankenstein LFT loudspeaker, but most audiophiles (including those reading this thread) are looking for a plug & play loudspeaker, not a complicated project. Heck, even building the Rythmik Audio/GR Research OB/Dipole Subwoofer is beyond the interest and/or capabilities of your "normal" audiophile. I found it to be relatively easy, and I’m no master cabinet builder.

The recommendation of the Eminent Technology LFT-8b/c was suggested as an alternative to the far more commonly known Magnepan planar-magnetic loudspeakers. In the opinion of myself and Steve Guttenberg, the LFT-8b is superior to the Maggies, only slightly higher in price to the clearly-inferior MG1.7i (I compared the two), and less than 1/2 the price of the MG3.7i. The 3.7i I have not heard, Steve has. Make of that what you will.