IMO, the main reason to low pass the mains is that they are (usually) out in the room away from the walls. This means that cancellation caused by reflected energy will cause seriously ragged response in the long wavelengths (low frequencies). If the mains are low passed and the subs are against the wall, all bass is generated close to a wall, low frequency cancellations are greatly reduced, and bass response will probably be MUCH smoother.
OTOH, if your mains are also against the wall and/or they produce little to no low frequency info and/or you are able to effectively EQ the low frequency issues, then the decision to low pass becomes less compelling. You still might choose to do so, depending on the specifics of your set-up, but it's not as straightforward a calculation.
Just MHO.
Marty
OTOH, if your mains are also against the wall and/or they produce little to no low frequency info and/or you are able to effectively EQ the low frequency issues, then the decision to low pass becomes less compelling. You still might choose to do so, depending on the specifics of your set-up, but it's not as straightforward a calculation.
Just MHO.
Marty