Minerva TB, or "Re-using the ET-CCT coaxial driver design with the TB W6-2313"

[JonMarsh]

Steve is probably going to kill me for this, or fire me as the pro bono West Coast SMJ design manager...

I still have the Minerva enclosures he sent me, but due to my frenetic work lifestyle up through the end of 2020 and other distractions like the Ardent D, I never got around to assembling them. I know where the cabinet parts and crossover parts are on a shelf in the garage, and I know where the Wavecor woofers and PRs are, and I've seen at least one of the C18EN001 coax drivers out here (in off site storage, I think, now), and I've got buckets of Speakon connectors and cables, but...

Having re-read the whole Minerva thread, and understanding some of the measurement and design issues Ergo and I were facing, and how things have evolved in the passing years (especially notable doing the measurements on the C18EN002 in Technodanvan's tower project, I had a flash back to the complexities of the original Minerva crossover and elliptical style filters necesary to get the sharp cut off rates required due to the driver's distortion versus frequency characteristics, and then a sense of peace settled on me, recalling how the TangBand W6-2313 worked out for the CC project for Sven... and how nice the Duelund style crossover is and how it sounds (Sven's main speakers, Ardent D derive, also are Duelund style designs).

One of the "quirky" things (of many) of the TB W6-2313 is how much it avoids behaving like a typical coax. The woofer cone is NOT used as a waveguide for the tweeter, and is deliberately kept shallow. The tweeter is an inverted dome using a carefully constructed aluminum-magnesium configuration, and has a very low Q apparent break up mode, at about 26kHz, and nearly none in my measurements- somewhat like the Scanspeak 6640, a Be dome part I selected for the Wavecor Ardent.








And the mechanicals are fairly compatible... with just a bit of tweaking (2-3 mm of trim on rebate diameter and driver opening) I think I could retrofit these to the original Minerva cabinets. Plus, I already have one extra, and buying a second one is relatively reasonable, at ~ $250. I checked in with PE sales when I bought my first ones, and they had about 40 more on hand. I doubt they've had a run on them.




This is the Duelund target used in the ET-CCT project. And would be used here...




I think this deserves some thought and investigation- but note, I have a complete crossover already for a 4 ohm woofer setup (the ET-CCT)! This could be fairly low development effort- just a few tweaks...

[technodanvan]

Looks awfully promising Jon! Just remember the final crossover has to fit in the base of the cabinets Steve made, if memory serves.

[theSven]

Looks awfully promising Jon! Just remember the final crossover has to fit in the base of the cabinets Steve made, if memory serves.

Those are gorgeous speakers that Steve built. My wallet hurts just thinking about this and reading this thread...

[JonMarsh]

Steve passed on to me some information about two SB Acoustics PRs, the SB34RNXX and RNX2. they seem to differ mainly in the default mass loading, the original version having a rather high Mms of 665g, and the RX2 version a more moderate 294g. No details are given about weight kits, they're just said to be easily adjustable.






More details and comparisons to come...

[ergo]

Jon, you do have many pies in the making... and this one again is of heightened interest for me for obvious reasons. I had Ardents as my main speakers for many years (still do in city home), but as we moved to countryside in spring I have been running Minerva's again as my mains. They got many years of idle time as I did not have as many systems as I had built Jon's designs. So I'll wait with interest and who knows - maybe I need to rework mine if the result come out as good as the preliminary data is suggesting.

[JonMarsh]

Thanks for telling me about your interest- I've been going through all of our old shared files- working on some related stuff for Steve (a new sub design, with CSS SDX12.

There's actually an SB 10" part I'm interesting in, too, but there's so much going on lately I haven't gotten to analyzing how it might contribute yet (looking at Cms, Qms, and Cms linearity, tradeoffs with response shaping at Fb corner).

And then other stuff keeps popping up- due to the gazebo, I'm behind on medical appointments, finally getting an eye exam this morning and ordering glasses, just mundane stuff that needs to be done! Car maintenance, winterization, prep for possible drive to Seattle for Thanksgiving, you get the idea!