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

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

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.

Being able to get rid of the speaker-level crossover parts is one of the two reasons for bi-amping (doing so has at least the potential for producing a worthwhile improvement in the sound quality of a loudspeaker). The other is, as Roger Modjeski said above, to separate the low frequencies from the mids/highs in the amplification (giving each it’s own amp, of course), thereby decreasing the potential for the creation of IM distortion in the amp(s).

Bi-amping need not be complicated and difficult. And, it can be cheaper than replacing stock speaker-level x/o parts with those pricey boutique ones. Not only that, you can use a brute-force amp on the woofers if you want, with a nice tube amp for the mids and highs. I first bi-amped with a pair of Magneplanar Tympani T-I loudspeakers in 1973, using the ARC passive x/o designed specifically for that task. Nelson Pass makes a great electronic x/o, but it’s not cheap. Fortunately he also makes (or made, it has just been discontinued) a modestly-priced 2-way x/o, the First Watt B4. It provides 1st/2nd/3rd/and 4th order filters in 25Hz increments from 25Hz to 3200Hz. All discrete (no opamps, no ic’s), retail price $1500. Reno Hi-Fi may have one left, I don’t know. For DIY’ers, it will soon be available as a kit.

Bi-amping need not be complicated and difficult. And, it can be cheaper than replacing stock speaker-level x/o parts with those pricey boutique ones.