Dear @lukaszwk : That was only and example. Normally 80hz id the one.
If you can't integrate subs to your mains through a high pass then you need to test and test to do it, it's not rocket science. Only patience and knowledge and ovbiously good subs as those Velodyne.
No black magic. If you have trouble in the past the problem with all respect is you and nothing but you.
Subs are for a 2 channel to reduce the IMD and system THD. It's the best quality sound level you can achieve in any system no matters what.
Sorry but that is it. Lu
R.

