Eminent Technology LFT8B’s reversing woofer polarity


Hi,

I have a pair of the Eminent Technology LFT8B’s and read Dr. Robert E Greene review in the Absolute Sound magazine (2014 I believe) of the speakers where in the review he reversed the polarity of the woofers and said it made a significant improvement. He was going to give the speakers a mediocre review (his words) before doing this and after reversing the woofer polarity he then said they were significantly better and proceeded to give them a rave review. Have any LFT8B owners out there ever tried this? Thank you.

Scot
scothurwitz
I suspect there may have been something wrong with the review pair for that to be effective. 

I reviewed the LFT-8A/B for Dagogo.com  and owned it, even did the "stacked" pairs for a while which was fun.

NO way that speaker gets mediocre rating for its design, build, sound and cost. I think there was something terribly wrong in previous review ( didn't read it, don't care to) to arrive at such a conclusion.   YMMV

To turn the LFT-8b in an absolute giant-killer (actually, even in stock form it is), use a pair of GR Research/Rythmik OB/Dipole Subs in place of the LFT’s 8" woofers. Unlike "normal" subs, the OB/Dipole will play up to the 8b’s x/o frequency of 180Hz.

Until you do that, there is a remedy for the resonance in the 8" woofers output (in the 1k-1.5kHz range, way above it's x/o frequency), heard as a low-level "whistle". "Davey" has posted on The Planar Speaker Asylum a simple, cheap low-pass filter that suppresses that resonance to the point of inaudibility. It is just a single cap and resister, placed across the woofer's terminals (on the back of the woofer, not the speaker terminals).

I am a newbie to the LFT-8b's having installed them for a little over a month. Robert Greene's review was fresh on my mind when I reversed polarity on the woofers. Expecting some kind of transformation, I heard none! I did it twice, once a week in, and then a few days ago with about 200-250 hrs on the speakers. ( Yes, I've been listening non-stop! )

To be honest, I really wasn't expecting anything major. The speakers wired in their correct polarity was, for me, extremely engaging. I spent most of my time on speaker placement which proved most enlightening. 

BTW @bdp24 turned me onto the ET's. I put the same question to him on another post. And It was Doug's review that moved things forward, having  no dealers nearby. 
Hi bdp24

I appreciate your input and suggestions. 

I went to GR Research's website and I don't see the Rythmik/OB dipole subs you're recommending. Does GR Research still sell these or have they been discontinued? Do you use one or two and where do you set the crossover point at. 

I don't hear that "low level whistle" from the woofer you mentioned. Just because I don't hear it doesn't mean it's not there and everything won't sound better if eliminated. Do you think it's on every LFT8B ot just on some? 

Thanks for your help.

Best
Scot

Scot, here’s the deal with GR Research, Rythmik, and the OB/Dipole Sub. GR Research is a 1-man company (Danny Richie) specializing in two things: 1- open baffle speakers; 2- kits for DIY speaker builders. Danny is also well known for his crossover expertise. Rythmik is also a 1-man company (Brian Ding), known for it’s patented Direct Servo Feedback subwoofer design and the sealed and ported subs incorporating the servo design.

Danny was already offering a sealed sub when he learned of Brian’s then new servo system, and thought combining an open baffle woofer with the servo system would make a killer sub. Danny contacted Brian (they are both located in Texas), the two put their heads together, and the result is the OB/Dipole Sub.

Both men and companies sell the sub, in kit form only. Rythmik lists the sub on their website in the "Custom Installation" section. The listing shows the A370 plate amp and 12" woofer that comprise the kit, not installed in the requisite OB frame into which the kit is installed (the consumer is responsible for the latter---see below).

GR Research lists the sub on it’s website in the "DIY Subwoofer Kits" section. In that section, all the various versions of the OB/Dipole Sub (1- economy plate amp and one woofer; 2- that plate amp and two woofers; 3- the more advanced A370 plate amp and one woofer; 4- the A370 plate amp and two woofers; and 5- the A370 and three woofers) are pictured, again as on the Rythmik site just the plate amp and woofers, no OB frame.

In each of the OB sub listings on the GRR site, links to diagrams for both W- and H-style OB frames are provided (just click on the highlighted link), as well as a link to a woodworker in Canada who is making fantastic H-frames (for one, two, and three woofers) in flat-pack form. The frames are CNC cut out of 1" (baffle) and 1.5" (top/bottom/sides) thick MDF, with dadoes and alignment dowel pins to make assembly very easy (only wood glue and clamps required).

For lots of info, pictures, and discussion of the OB/Dipole Sub, head over to the GR Research section on the Audiocircle Forum.

Hey bdp24

Thanks for the explanation, I’m sure I would have eventually figured all that out, only problem is I would have been 5 years older! Does Rythmik sell this sub already built? I would like to hear one. The other sub System I would like to hear is the “Swarm”. Thanks again, very interesting. Take care

Scot
No Scot, both Rythmik and GR Research sell the OB Sub as a kit only. But the Canadian woodworker offers his H-frame fully assembled (and finished if you want) in addition to shipping it as a flat pack. To see what it looks like, look up the Virtual System of Audiogon member kennythekey (using just "kenny" as your search word). Kenny had his frames built and veneered by the Canadian.