Eminent Technology LFT8B’s reversing woofer polarity

@ledoux1238: Yeah, the Marchand x/o’s are very well respected. They make filter "cards" for every conceivable need, the 1st-order you need being the most simple.

As for using the volume control of the Mactone to balance the panels and woofers, remember this: a volume control doesn’t provide gain, it only attenuates the signal sent it (with the volume control set fully clockwise, it is proving zero attenuation). For your plan to work, the Mactone will need to have greater gain than do the woofer amps. If the woofer amps have higher gain than does the Mactone, the volume control on the latter will not be able to bring that amp up to the level of the former. Even wide open, the gain of the Mactone will remain less that that of the woofer amps. On the other hand, if the Mactone has greater gain, that amp’s volume control will allow you to attenuate (lower) its output, thereby providing a means of balancing the panels and woofers. See what I mean?

@bdp24 Regarding the potential mismatch of the two amps, your point is crystal clear. I will know in two weeks time.

If there is a mismatch, the issue of which x/o remains. The initial thought was a passive x/o, 1st order. However, several comments, including yours, I believe, indicated that the particular passive x/o from Marchand was not as good as their active tube. You have pointed to the less than stellar parts quality in the passive. There is also a clear price difference between the two units.

I suppose going active will provide the most flexibility for future subwoofer upgrade, or, heaven forbid, a change from the ET’s to other transducers.

Regarding your earlier post on the TAS reviews of the ET’s, I think I’ve read all the available professional reviews and most of the forum posts on the LFT 8b’s before I contacted Bruce T. I have had the pair for over a year.  In terms of placement / interaction with my listening room, I believe they are optimized. I would like very much to push to optimize the speakers in other ways, hence the bi amp queries. And eventually, I ‘d like to upgrade the the internal x/o caps, and try OB subs. 

My list of active crossovers includes:

Marchand XM-44
Beveridge RM-3
Accuphase F-25

With each of these I have the flexibility for different slopes and frequencies. I can also attenuate (Beveridge, Accuphase, Marchand) or add gain (Marchand). I've used these frequency dividers with various panel speakers and I'll never go back to passive crossovers again. Unfortunately the LFT 8b's crossover is too high for my taste, I prefer to keep it under 100 Hz (and currently use 80 Hz). Not sure why Thigpen chose the higher crossover frequency, but I'm sure he had a reason.

@clio09, I believe the reason for the 180Hz x/o from the panel to the woofer is because the dual midrange LFT drivers don't produce enough output below 180Hz to do otherwise.

But remember, the LFT-8b wooder is just that: a woofer, not a sub. Looked at it that way, the 180Hz x/o in the speaker is unusually low. The LFT-8b is a 3-way design, and most 3-ways x/o from their midrange driver(s) to their woofer(s) at a frequency far higher than 180Hz.

On reason the GR Research/Rythmik OB Sub works so well with the LFT-8b is because the sub can be used up to a x/o frequency of 300Hz (the reasons why can be found on the GR Research and Rthmik websites). Used with the LFT-8b, the OB serves as both woofer AND sub.

@bdp24 Yes I realize the LFT-8b has just a woofer, and not an active sub. My bass array are just woofers too, based on the woofers Roger Modjeski used in his ESL system. His theory was to keep the crossover point low from the panel to the woofer, so his ESL panel (a two-way) was designed to go down to 100 Hz. He listened to a lot of Leon Redbone and some other male vocalists whose voices went low enough that at a higher crossover point than 100 Hz you could start hearing the vocals in the woofers.
I did not know the LFT-8b were three way. What's the other crossover point?