Bi-amping vs. bridging

Gah, I meant to say:

The increase in the minimum impedance requirement when bridged is related to the maximum safe thermal dissipation of the amplifier, in watts.

This is the same reason why most power amps won't support 2 Ohms. The power dissipation needed would cause a thermal meltdown. Hopefully your amp will shut off before this happens! 

Best,

E

When you bridge you need to be careful of the amp manufacturer's specifications.

Usually they provide a minimum speaker impedance when bridging, which is 2x or more the minimum when un-bridged. It's all math, but as mentioned before when you bridge:

2x Max Voltage, therefore:
4x Power (at 8 Ohms) (since P proportional to V squared).

The increase in power is limited in large part by the thermal dissipation of the amplifier. 

Will you gain much? Meh. It takes 10x the power output to double the apparent volume (10dB). You'll only gain about 6 dB this way.

Bi-amping (without a crossover) is also kind of limited, but with weak power supplies can bring out a lot. Since the current for bass notes is now separate, the power supplies are stiffer, and you may experience more dynamic, faster and less muddy amplifier this way.  However this implies you have a separate power supply. With a multi-channel amp, this benefit is less clear.

Bi-amping WITH a crossover is where the magic, and complications lie. :) Best left to experts and active speaker makers.

Assuming your amplifier is spec'd for bridging with your speakers, I'd encourage you to try both and see if you find one you like best.

Best,

E