Sorry for the slow response, busy couple of weeks at work.
@bdp24, was it obvi that I love ET speakers? I’ll have to try to hide that better!
I did do all the xover and panel upgrades myself, if anyone is interested message me and I can send you a link to my ET Speaker folder on my Google Drive space and you can see the upgraded xovers for the IVs, Vis, and VIIIs along with the Dynamat on the LFT-VI panels. One thing that made the upgrades work on the IV’s and VI’s was being able to use the now unavailable Northcreek Audio 100uF and 200uF polyprops. I should have bought some additional 100uF when they still had them! I used these to replace the 470uF electrolytics in the originals.
While there are other caps in the 47uF-100uF range now available that will likely surpass them in performance, their price/performance was very good back in the late 1990’s / early 2000’s and an upgrade over the Solen that were the standard back then. Today I’d have to spend time looking over the Humble Homemade HiFi reviews along with scanning PCX and Soniccraft to see what’s available, likely a lot of good choices today (and great ones if you want to spend real $$$$$). A quick glance suggests the Auricap XO 100uF could be a good contender today, but upgrading a pair of LFT-IV/VI/VIII 470uF electrolytic caps would be a $1000+ purchase!
On the LFT-VIII xovers, there was some chatter on AudioAsylum about leaving out the 470uF in the midrange leg, so I did that there… no issues after running them that way for 14 years, knock on wood!
My read of the LFT-IV, VI, and VIII xover is that you should be able to duplicate the basic mostly 1st-order xover configurations with the B4 while retaining Bruce’s passive compensation networks directly on the drivers. Takes more good amps than I have, though! The LFT-III original xover was a bit more complex with some higher-order slopes, discussed at length in the IAR review. Since Bruce went to all 1st-order xovers for all speakers after that (except for the LFT-VIII mid-panel highpass where I believe the C6 2.2uF cap is there to compensate for a top-end rise in those panels), I wonder if he changed the LFT-III xover in the later ones.
BUT as you said, just biamping them with the bass-mids xovers at low-level before the amps and bypassing the in-speaker passive components will make a significant improvement even if you don’t go all the way to 3-way biamping. AND I never understood Bruce’s recommendation for the biamping split on the LFT-VI between the bass/mid and tweeter… bass – mid/tweeter makes more sense to me. AND that’s how he configured the LFT-III/IV and LFT-VIIIs, so not sure why the LFT-VI is setup differently. I guess I should ask him.
@riverdinaudio, I love your LFT speaker/driver collection and look forward to hearing about your experiments. I’ll keep your comments on the driver usage below 100hz in mind. My thought is to use the LFT-VI+VI bass panels to as low as they are effective… I’m guessing 40-50hz, maybe a tad lower. Then eventually cross over to a dipole cone sub setup to take it lower, likely something from GR Research.
One non-speaker revelation that has significantly improved the bass quality and extension of my setups in ways I didn’t expect and couldn’t imagine was using UC pair buffers on my DIY’d-ish DAC setups. I use an Allo.com USBBridge Signature as an I2S endpoint and feed either very modified versions of their Kali DAC or Ian Canada’s FiFoPi/DAC/output stage combos. In the last year or so I added a final buffer pair of 325F Ultracaps to the 2 DAC/interface rails (2x5V for the Allo Kali, 2x3.3V for the Ian Canada FiFoPi/DAC combo) and a pair of 3000F UCs on the 5V to the USBBridge Sigs. IF you DIY your digital gear and can handle the UCs safely (they will source welding-level current if shorted), I highly recommend this. Revelatory in many ways, with the bass improvements just a part of the overall jump upward.
BTW, does anyone have the IAR LFT-III review scanned? I have the hard-copy, but if someone has it scanned and can forward, that’ll save the scanning effort. Just lazy, I guess.
@riverdineaudio, really looking forward to your reports!
Greg in Mississippi
P.S. I’ve been an ET enthusiast since before he made speakers, getting an ET-1 tonearm not long after they first came out, upgrading it to an ET-2 when that became available, and now having 2 ET-2.5s.
