McIntosh MC901's internal active crossover & speaker's internal passive crossover

@erik_squires what you're essentially claiming is that any speaker that can be biwired can also be biamplified - that the two terms are interchangeable. That's simply mistaken and, as I noted, easily tested with a DMM or VOM.

When you biwire, you do not send the full amplifier output to the tweeter, do you? Of course not, you’d blow the bugger out. It still goes through the speaker’s x-over. It’s easy to verify with a DMM - just check for continuity. Spendors used to be wired that way, IIRC, and it always puzzled me.

I agree that you should check for continuity before bi-amping, Check hot to hot and ground to ground. I’ve seen all 3 cases:

1. Infinite impedance
2. Both internally shorted (0 Ohms)
3. Ground only shorted

In the case of 1, bi-amping is fully safe.

In the case of 2, no bi-amping at all is safe

In the case of 3, only unbalanced amps with 1 hot output are safe.

In all cases listed the internal crossover remains in place.  It's really a manufacturing choice whether or not the filters are joined internally. 

Want to point out that there’s a number of A’goners who are successfully passively bi-amping. 1 and 3 seem to be the most common situation.

In the case of 3, only unbalanced amps with 1 hot output are safe.

In case 3, higher possibility of ground loop noise.

Also should avoid many Class D amp as well.

However, case #3 is rare!