1) At what point in the frequency spectrum does the signal become non-directional? Many believe that even though subbass is non-directional, two subs are still better than one.

2) Low-pass filter is always used to cross a sub with main speakers. Is there a need to apply a high-pass on the main speakers for better integration control or just rely on natural roll off?

3) What is the best way to cross a midrange with a woofer in a 3-way? Control with box (vented or closed)? or high pass?

4) Is there (and should there be) any difference between crossing a woofer in a 3way vs crossing a sub with main speakers, other than the crossover point?

5) Does quality of amplification matter below certain frequencies so long as the juice is delivered? For example, at 100Hz, 75Hz, or 50Hz, are there still sonic differences between SS, tube, class A/AB/B, SET, PP, etc? Can I get away with a bargin basement Class D amp?

thanks,
Gar.