Thanks for the reply Wayne, can you think of a song that is good to test for intermod?
I tried listening earlier with my speakers set to full range vs 80hz crossover to my nearfield sub, the differences are quite subtle and most of that was probably how the response was changing in my room? ( haven't measured)
They do seem slightly brighter with the high pass engaged, is this the "cleaner sound " or is it just because there is less bass coming from that point?
I don't think I've ever heard modulation of vocals, my speakers are active and the bass driver is very well controlled.
Is the headroom thing a myth? I.e can a speaker actually play louder released of bass( I assume the theory is less energy is being wasted on bass) or is it that it can play louder without distortion?