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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
bdp24's avatar
bdp24
10,248 posts
 

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.

scothurwitz OP
113 posts
 
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
bdp24's avatar
bdp24
10,248 posts
 
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.
djembeplay
179 posts
 
Not to hijack this thread, but many thanks to bdp24 for all your past posts about the LFT-8Bs -- I ended up purchasing a new pair a couple years ago from someone who purchased them but never ended up using them due to life changes (lucky find).  Funny side story -- the dealer he purchased them from mixed up the boxes for the matched pair of panels and woofers (they come in separate boxes).  I ended up with a new, but unmatched pair, and when trying to assemble them, the predrilled holes were too far off to make the connection, but too close to be able to make a clean new pilot hole!  The woodworkers and DIY guys will know what I'm talking about... SOOOO, before I could even hear these I had to spend some analyzing the issue, which led to some careful application of plastic wood and re-drilling... thank goodness I came into with with a woodworker background, so I was able to correct the issue cleanly -- lol, do we all go through this stuff, or am I somehow in debt to the karma police?

Anyways, what an incredible set of speakers.  When I was researching, I was on the fence between these and open baffle designs -- mainly the current offerings from Spatial.  I still would like to compare these to some Spatial Sapphire M3's someday, and would be highly interested in reading the opinions of anyone who has any about this, or even better has perhaps heard both designs.  

To my ears, and this is coming from a fairly long and varied experience with other very nice speakers, these are nearly perfect for my tastes.  The imaging is one of the things that people sometimes mention is just sort of mediocre, but in my case I'm finding it to be totally holographic and pinpoint accurate, while also being large and immersive... shrug.  They are *very* sensitive to placement -- micro adjustments in any way can bring a notable change.  Finicky position tweaks and experimentation has been a large part of my history with these, but I don't find this to be a fault in any way of the speaker... I look at it as the added care needed for adjusting and maintaining a precision instrument -- it needs more finesse and care than a generalists tool, but once set up properly, it excels.  A high level racing bicycle requires more careful alignment of all parts versus an el cheapo mountain bike, for example.

My one complaint, in my system, has been in regards to the treble.  Sometimes it's just a bit forward and hot for my ears, and I find it can be a little bit fatiguing.  However, I'm admittedly prone to being sensitive to this.  The effect varies widely from recording to recording, and I don't have other 'spare' high end gear on hand to mix-and-match to run a process of elimination.  I'm left wondering if it could be how they play with my upstream components, or some untamed room brightness exacerbated by the nature of the dipoles, or just the nature of the speakers.  It could also just be the mastering of the recordings themselves.  Maybe these are SO honest and revealing, that any harshness in a recording can easily grate on the ears.  It's usually in the mid to upper treble region, where saxophones, female vocals, electric guitars, and treble-leaning synths commonly venture.  I do only have a few diffusion panels in an otherwise fairly bare drywalled room -- maybe the answer is to add some carefully placed absorption panels.  Even though the speakers are almost 5 feet off my front wall and a few feet from the side walls, I could still be getting too much bounce.  It would help be to know if anyone else who knows or owns the LFT-8Bs has experienced this same 'peaky treble' - ?

Otherwise, I'm happy as a clam in audio nirvana... (are clams happy?)...


majorc
78 posts
 
My tech disconnected the tweeters and placed the speakers with the tweeters facing the outside - they sound and image much better. 
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