JLM said
But now the woofers are locked into a position that might be great for mids/highs, but terrible for bass proprogation. And you're still leaving the customer to adjust the bass output/roll-off.
Passive 3-way speakers do not provide for
any control over the bass level, which is needed for room gain effects, and personal preference. Active bass via bi-amping does. The bass EQ controls are used primarily to work with the room gain characteristic. Small room = set the EQ for a sagging bass. Large room = set the EQ for flat bass. In no case does the EQ setting de-calibrate the bass/mid crossover.
Because the bass units are a stereo pair, localization effect is not an issue, and the bass/mid cross point can be moved up (120Hz) so that even the monitor roll-off is not affected by the room gain curve.
By contrast, moving a separate subwoofer around in the room de-tunes the phase of the crossover, and you are right back into the syndrome of "why does the subwoofer not blend properly with the monitor?"
So I have presented the customer with the necessary controls to adjust overall level and EQ to his/her liking, but
without de-tuning the crossover in the process.
And of course the bi-amp 3-way overcomes other limitations as well. See
http://www.bamberglab.com/s5-tm-xls_features.shtml