I recently picked up 3 empty 825 cabinets and have started working on them. I could not afford Altec woofers but I did find 2 AE TD15M woofers for a very reasonable price. I installed one with a 511B and 808A driver on top playing mono. I am using active crossovers with 18db slopes run through Ashly FET amps.

At low volumes they sound pretty good. As they get louder they get mushy which I attribute to all of the cabinet and horn ringing coupled with my concrete vault basement. I'm pretty sure that this can be made to go away and have read many posts about this. Also once they get moved out of the basement into the barn/theater and once deadened they will hopefully sound better.

My question concerns crossover points. After much experimenting by ear, but no measurements, I have settled on about 2000 as a good crossover point. The driver plays flat up to 4K but above 2.5K I start hearing changes in the sound as I move from side to side and around the room. Clearly at this point the off axis response from the 15" falls off and becomes audible. What surprises me is that the driver can play up to 2K without hearing off axis issues. Is this a side effect of the short horn on the woofer? Is it better to use the higher crossover or a lower crossover? Once dialed in I can listen to the same vocals over and over and even change the crossover mid note and not hear much, if any, difference from 800-2K. Below 800 the vocals seem a bit grainy, less smooth. The reason I ask is that I am looking at trying a compression driver (Radian 475) that wants to be crossed 1200+, preferably, 1600+ from what I read. Before trying that I wanted to see if there is any issue with using such a high crossover.

Thanks,
Greg