Axiom Home Page Forums General Discussion Technical Questions 3dB frequency point of my M3's?

You were doing it the only way you can. The knob on the subwoofer that is probably labeled Crossover (even if it isn't technically that).

Oh, the volume of the subwoofer should also be set when the filter point is low, so the output of the sub, and the output of the main speakers is equal. So when you start to raise the filter frequency the two will meet at equal levels.