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Eminent Technology LFT-8c Robert Greene review

A friend of mine forwarded this review to me a couple days ago.  I hadn't seen it as it's just a week old at this point. 

Why would I be interested? I have a pair of LFT-8b speakers that I picked up about 7 months ago.  Wonderful speakers. I always wanted to try a set of panels and, as luck would have it, last summer I found a used pair of 8b's just a short drive from my home..I made the jump.  As it turns out, this was one of the best moves I've made in my 50+ year audio hobby. 

In the last few months, I was considering picking up the 8b to 8c upgrade components, but put it off as I had a number of other projects going on.  Well..the projects got completed and I started a few more projects, though this time around the 8c upgrade is one of them.  I ordered the 8c upgrade yesterday and I'm really looking forward to the adventure once it arrives. 

One thing I've noticed when reading discussions of the LFT-8(no a, b, c)  here on A-gon, is the discussion wanders over the now 36 year history of the LFT-8.  Issues identified in this or that review from 10-20-25 years ago are brought up as if they reflect what the LFT-8 is today.  LFT-8's had a great sound 30 years ago, with a few flaws, as any 30 year old speaker would, and it sounds better today. Nothing surprising there. Most companies cut ties with models as they age and come out with something new, whether they are really new or repackaged parts..that varies.. 

What's my point?  I just find it interesting that Bruce Thigpen (Eminent Technology) came out with the LFT-8 in about 1990 and has been continually improving the model 8 year after year, decade in and decade out, staying in business with no advertising, though with a few shows here and there. There are very few current speakers(let alone businesses) alive today that have a 30+ year history under largely the same name. (Though the Vandy 2 series comes to mind)  Pretty unique in this industry.  It's also pretty unique that a decades old pair of LFT-8 speakers can be upgraded to the current model at a very modest cost. And the upgrade is easily done by any owner. 

So..the latest review:

https://www.theabsolutesound.com/articles/eminent-technology-lft-8c-planar-loudspeaker/

Robert Greene goes into considerable depth in his review, which is specific to the 8c version, though he's done an 8b review in the past. I'm glad it came out as it pushed me over the edge in ordering the 8c upgrade.  I'm not getting any younger..time to give the 8c a spin. 

One last note, I've read in a number of older and current reviews that the LFT-8 speaker placement is..finicky.  I haven't found that to be the case at all.  In the last 7 months I've experimented extensively with placement and they respond well to various setups. My current setup is about 115 inches between the panels (on center) and maybe 30 degrees toe-ed  in from facing directly forward.  Each speaker is 45 inches off the front wall(on center) and 38 inches from the side walls.  I have a great soundstage and and equally great imaging.  My tweeter panels are on the inside. 

 

(...and no..I have no affiliation with ET..just a customer owning a used pair of the 2017 model 8b)

nogaps
ledoux1238
419 posts
 

Another factor to keep in mind is the fact that when the midrange drivers are repositioned, the speaker/room interaction is changed. 

@bdp24  Yes, I can hear the difference.

 

And with no toe-in, the phase relationship between midrange driver and tweeter is as well. An easy way to experiment with midrange/tweeter phase orientation is with varying degrees of speaker toe-in.

There is an electrical phase delay function in the 8c. Bruce recommends applying a 0.6ms delay between the bass and upper frequncies. The  speaker toe-in you suggest is a mechanical way to phase align the tweeter and the midrange. Am I understanding this correctly? 

Regarding toe-in, I have read from other sources that with planar speakers it is best not to toe-in. As planars are dipoles in nature, any toe-in would  alter the interaction of the back wave with the room. However, the LFTs' have  separate tweeter and midrange panels side by side, so it behaves a bit differently from true dioples. Apply a toe-in to time / pahse align the tweeter and midrange seems to make sense. But I have the sides of the speakers only 8'-9' to side walls. I wonder if toe-ins might not cause unwanted room interactions? I will experiemnt though.

bdp24's avatar
bdp24
10,487 posts
 

 

@ledoux1238:

Yep, physically moving a woofer about 8 inches from a planar loudspeaker causes a time differential between the two equal to a 0.6ms delay (sound travels at 343 meters per second, or 0.343 meters per ms). Is Bruce’s recommendation for the woofer to be delayed behind the LFT panel, or visa versa? I suspect the former.

By the way, the plate amp included with the Rythmik Audio/GR Research OB/Dipole Sub includes a Phase/Delay control, continuously variable from 0 to 16ms (0 to 180 degrees). That allows one to position the OB woofer for best room response, using the Phase control to align the woofer with the panels. That is accomplished in the analogue domain, no digital conversion.

Having separate midrange and tweeter drivers does NOT mean the ET LFT-8b/c is not a "true dipole." Magneplanars and other true dipoles also have separate bass, midrange, and tweeter drivers. Now the LFT-8b is not 100% dipole as it has a sealed box woofer. The LFT-8c is 100% dipole (front and rear firing woofers, opposite in polarity), but not open baffle like the Rythmik Audio/GR Research woofer.

Yes, changing the degree of toe-in affects the speaker/room interaction, but that is not necessarily a negative thing. For instance, with extreme toe-in---like the two LFT-8b/c panels positioned so that the back wave of each reflects first off the two side walls, that reflection reaching the wall behind the speakers where it is then reflected again. The time taken for the back wave to reach the listening position is thereby increased in time, potentially a good thing. It’s like having the speakers further away from the wall behind them. 3’ is the most common recommendation, but 5’ is better. That creates a 10ms delay between the front and back waves, which the brain interprets as two separate sounds, rather than the rear wave being a smearing of the front wave (a minimum of 10ms between the two sounds is required to achieve that).

 

peter_s
1,439 posts
 

@nogaps I have the same open baffle subwoofers as @bdp24   So all I’m really looking for are the mid range and tweeter drivers and whatever crossover would go between them. I guess I could build my own baffles, but it would be good to have the metal bolt on baffles for sure.

bdp24's avatar
bdp24
10,487 posts
 

 

@peter_s:

Keep your eyes peeled for a used pair of LFT=8b's. The last pair I saw were priced at $1500. A pair of those with the Rythmik/GRR OB/Dipole Subs is imo preferable to the LFT-8c, but I admittedly have not heard the 8c.

 

ledoux1238
419 posts
 

With the LFT-8 midrange driver on the inside, you are getting less driver output loss due to beaming (even at midrange frequencies, far below 10kHz) compared with that driver on the outside (where the listening position is further off axis).

@bdp24 After a further week of listening with the midrange panels on the inside edges of the speakers, I concur with your analysis. There must have been some loss of output in the midrange / upper midrange frequencies with the midrange panels on the outside edges. The frequency response seems more balanced in the midrange. This also allows the placement of instruments in the soundstage to be spread more ‘realistically’ rather than in amphitheater style. The depth of the soundstage is also enhanced. 
 

I would say that for a narrow room like mine, 11 ft, and speakers’ edges at 8” from side wall, turning the midrange panels to the inside makes for better room interaction. I have not done any measurements, purely through listening. 

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