I sold my big (bigger than Louis expected!) SEOS15+TD15M speakers today, with a promise that I'd do a passive crossover design for them. I had done a passive for them several years back, but wasn't entirely happy with it and switched to active before ever getting around to working the passive further. Before the boxes went, we got fresh measurements on the woofer and tweeter in a bigger area and re-established the z offset for them. Then today, I did a new PCD design on them, which I'm sending to Louis. Thought I'd post it here, too, for any TD15M owners who want to go with a SEOS15 top. The design simulation came out very nice, phase response is unusually smooth (doesn't even roll over once through the band). There's a PDF document here which has further data, schematic and Parts List: http://libinst.com/SEOS/SEOS15/SEOS15%20TD1M%20redo/TD15+SEOS15%20design.pdf Hope this works for you Louis!