Hi Sam,Thanks for the info. I was able to locate Altec AN-9 at the Sound Practices website as you had suggested. The method of achieving acoustic alignment by changing the relative position of the drivers while wired in phase to produce a maximum null at the crossover, then reversing the driver phase (for 2nd order xover) is ingenious.
Now about destressing the 511b's... Just how much sawing/weld removal are we talking about? Just the fins, fins and flare, or the entire horn?
Regards,
AstroSonic