lots of great information here:
http://www.soundoctor.com/whitepapers/subs.htm
if you want to use an active XO, jl audio, bryston and marchand are the most common. if you're just looking for a line level high pass filter, Vandersteen makes a decent one (HP-5) but be aware of the slope - I believe it's only first order.
Another consideration is proper time alignment of the sub and mains. I ignored this for a long time, simply high passing my mains with the afore mentioned line level unit from Vandersteen, then a custom built set using V-Caps. Worked well enough, but I found a significant improvement in integration when I properly time aligned the mains and sub. Things really snapped into place perfectly - there is absolutely no differentiation between the sub and mains, just one perfectly cohesive soundfield.
http://www.soundoctor.com/whitepapers/subs.htm
if you want to use an active XO, jl audio, bryston and marchand are the most common. if you're just looking for a line level high pass filter, Vandersteen makes a decent one (HP-5) but be aware of the slope - I believe it's only first order.
Another consideration is proper time alignment of the sub and mains. I ignored this for a long time, simply high passing my mains with the afore mentioned line level unit from Vandersteen, then a custom built set using V-Caps. Worked well enough, but I found a significant improvement in integration when I properly time aligned the mains and sub. Things really snapped into place perfectly - there is absolutely no differentiation between the sub and mains, just one perfectly cohesive soundfield.