One place where my plans changed a little was the throat – I measured the 902 exit expecting 1” but found it’s more like .875” so my tractrix throat will start with that dimension. I know it’s not much but I think it might be best to have a smooth transition from driver to horn throat without a .063” step in there.

I know a bunch of the software models say 4 to 5ft3 for flat alignment with these Altecs but in my experience, if you want full range, larger is better. I think you are in the right ballpark with the cabinets BillE is building. What baffle width are you using? As much as they look prettier, I found narrow baffle cabs sounded a little ‘thin’ in the upper bass lower mids with the 604’s and a 26” wide baffle (as used in the 620) yields better balance making that famous ‘604 midrange shout’ a touch less noticeable.

I sure would like to hear a purpose built round wood tractrix on an Alnico Altec 1.4” driver, if I ever find a pair of these at a reasonable price I’ll consider building some but with the price of Altecs these days, I don’t see this happening anytime soon.

No plans for travel anywhere near your place right now Ron, I really have to get down there! Do you ever get anywhere near Toronto? I’d love to have you over.