Does impedance of a speaker change when one bi-amps?

The impedance curve of the speaker is separated into two pieces: high and low. The amplifiers only get one of those respective load curves. With most bi-amp-able speakers, the low cutoff feeding the midrange and tweeter is still in the circuit. Likewise, the high-cutoff still rolls off the highs hitting the woofer. Put both together as one load to one amplifier, and additional interactions affect sound quality, usually for the worse. Bi-amping worked very well for my system, but ymmv. 

I have bi amped several systems and never heard a difference that would justify the additional amp. Bi wire, same thing. I did hear a difference with an active 3 way system with an external crossover though. It was a Linn isobarik Brik system. I also copied the the Linn system with 3 Bryston LP2's and a Behringer 3 way analogue crossover. It was awsome. And cool to talk about. :)

@pkvintage

 I have bi amped several systems and never heard a difference that would justify the additional amp. Bi wire, same thing. I did hear a difference with an active 3 way system with an external crossover though. It was a Linn isobarik Brik system. I also copied the the Linn system with 3 Bryston LP2's and a Behringer 3 way analogue crossover. It was awsome. And cool to talk about. :)

Kudos for going the extra mile.I have been promoting multiamping here for years. I designed the Beveridge RM3 crossover which allows easy  changes and has level controls for both outputs. It is all discrete analog. 

 Most here haven't the nerve to so what we have done so they just bad mouth what we are doing. They dont understand the advantage of removing the un-wanted signal Before the amplifier rather than after. They would rather waste their money on expensive crossover components for a less than optimum solution. 

Someting to think about. If the bass voltage is still present in the treble amplifier then the IM it creates is going to be the same. 

Keep at it man, I will support you.

bDP24 says  (this is true)

Beside the advantage of a bi-amped speaker presenting an impedance of less variation to each of the two power amps than one amp sees from a non-bi-amped speaker

@erik_squires  says

Sorry @BDP24 this is not really true as you put it. See from my blog post and any simulation, the min to max impedance is MUCH greater with a split crossover.

The overall current load however is always decreased. This may help the power supplies stiffen up.

While active bi-amping is good, it’s also complicated. It’s much easier to get top of the line parts and design in a passive. 

Sorry, erik. BDP24 is correct. Individual drivers have rather smooth impedance curves because they are mass loaded drivers and thats what mass loaded drivers do.. The wild impedance variations we see in complete speakers are due entirely to the passive crossover which we want to eliminate. 

The complication is not a large one and the benefit is enormous.  Any serious audiophile needs to give it a try and we are here to help at www.berkeleyhifischool.com

@rickytickytwo  

Yes for speakers with complex impedance dips and peaks there can be a significant change when you biamp. We dont care about the peaks, its the dips that bother the amplifier. Drivers themselves do not dip below their DC resistance. However when combined with inductors and capacitors this is no longer true (unless its 1st order). 

When you separate the high and low crossovers (unstrap them) the impedance of each will improve because it no longer sees the other.