The first and third circuits duplicate the transfer function of the original 1.6 passive crossover.  The speaker components can then be removed and the amplifier channels hooked directly to the transducers for a true bi-amp setup.
These two circuits have some drawbacks which severely limit their use:
- Insertion loss which could be significant depending upon preamp/poweramp combination.
- Component values need to be adjusted for the particular preamp and amplifiers in use.
- Poor interconnect cable driving ability.
The active version solves all of the problems associated with the passive line level circuit.
It also adds a precision +/- 2.5db level control for the high pass output, and an input buffer that can be configured as a low frequency high-pass filter.
The level control circuit inverts polarity which necessitates reversing the speaker wires going to the quasi-ribbon driver.
* alternate email for Dave Reite