Good questions.
I think that the 80hz is a rule of thumb and the actual frequency for humans for non-directional sound is differnt for everyone (probably within +/-10Hz max). 60hz is pretty low, i bet it is closer to 70 / 75 Hz. I bet this is why most recievers are in 20 Hz incrments under 100hz for crossover freq.
This is why I always recommend the QS8 over the of the QS4.
I have done some extensive testing and really don't notice that much, if any difference between setting my QS8 at 80 Hz or 100hz.
Some people like to have all their speakers in an Epic 80 st to 80Hz. I think that actually works great for movies, but for 2ch music, I like my M80's at 40hz.
I suspect the recommendation of keeping the crossover at 10Hz over the lowest tested freq. in theory can makes sense. However I really would be suprised if you could hear the difference between the QS8 set at 80Hz and 90Hz with a good sub like the EP500.
I don't think the timbre of a speaker is nearly as critical at lower frequences say below 80Hz. So, no subs don't have to be from the same manufacturer. It isn't like matching your mains with a center channel.
That is not to say there arn't very bad sounding subs out there, but it usually isn't because they don't match the rest of the speakers.
paul
