Why wouldn’t a single amplifier output of 100 watts through a passive crossover be just as good as two 50-watt channels with an active crossover ahead of the amplifier?

Using the example in the previous post, if I actively bi-amp through two 50-watt channels, I have 20 volts available to the woofer for low frequencies and 20 volts available to the tweeter for high frequencies including transient spikes’ headroom.

In order to make 20 volts available for the woofer and 20 volts available for the tweeter through an ideal passive crossover (no losses due to the crossover), my amplifier would have to output 40 volts cleanly. Doubling the available amplitude means quadrupling the available power, so my amplifier now has to be rated for 200 watts per channel to accomplish what 2 channels rated at 50 watts each can accomplish - true for a signal consisting of a myriad of upper and lower frequencies mixed together, not true if all frequencies present are within the range of only one of the drivers. While it would take an amplifier rated at 200 WPC in order to deliver the 100 WPC in this mixed-frequency scenario, 200 watts is not delivered – the amplitude of 200 WPC is needed, but not the full current that would mean 200 WPC was being delivered.

Note that, almost without fail, professional systems for large scale sound reinforcement use active crossovers ahead of amplification. This provides for, among other things, better overall power efficiency and better ‘control’ of drivers with direct-to-amp connections where lots of power transfer and excursion will occur.