[JimC]

My sub (a Velodyne F-1800RII), includes line-level inputs and outputs
which permit high-frequency signals to be filtered out and sent through
the line-level outputs to the power amp, essentially removing the bass
from the signal fed to the power amp and providing bi-amplification.
There is a high-pass filter switch which can be set to either 80Hz or
100Hz (6 dB/octave). There is also a variable frequency low-pass filter
which can be adjusted between 40Hz and 120Hz (12 dB/octave initial,
48dB/octave ultimate).

My question is: Assuming the low-pass crossover is set to 40Hz, and the
high-pass filter is set to 80Hz, what happens to the frequencies between
40Hz and 80Hz (Ignoring signals that are outside the roll-off curves)?
Are they simply lost? In this system, the mains are Maggie 3.6 planars,
with response extending somewhat below 40Hz, and I would prefer to feed
bass above that frequency to the Maggies rather than have them
reproduced by the subwoofer. But with the above system, it seems that
they would not receive any substantial bass below 80Hz. Also, what
happens to signals sent to the mains when the Velodyne low-pass
crossover is adjusted, e.g., adjusted between 40Hz and 80Hz or above?

Presently I am not using the high-pass connections, and instead feed the
full audio frequency spectrum directly to both the sub and the power amp
(the preamp output is connected directly to the power amp and to the
sub). This is because I had concluded that signals fed directly from the
preamp to the power amp, without any processing or filtering, would be
cleaner and provide a more transparent sound from the Maggies. On the
other hand, it might be beneficial to remove the very low frequencies
from the amp and the Maggies for greater efficiency.

Any advice or suggestions? Do I need an external electronic crossover to
resolve this issue?

Jim