RobH,
Nice!
Looks quite natural with that 12".
Are you going to create a passive network for this ?
BTW, I've seen a few other references to these large Heils that seem to indicate they're not as sensitive as what you showed in your first post that had them reaching 105db ( something like 5db less than that ).
Did you measure/calibrate at 1M with 2.83 Volts ?