I have the Axiom M80Tis whose Freq Resp is +/-3dB (Hz) 34-22K and +3dB/-9dB (Hz) 25-22K and I cross them over at 80 Hz to my home built Shiva sonosub and it sounds best at this crossover. It's difficult to explain. I don't have the technical lingo. I just trust my ears. At 40 or 60, the bass didn't have that distinct punch, but at 80 there is magic! And my Shiva sonosub rocks. I have it pushed by 400 watts mono. The other 5 speakers are driven by my 770.