Lets say a 4ohm tweeter is hooked up to a passive crossover and a 4 ohm midwoofer is also hooked up to the crossover.

If an amp is then hooked up to the same crossover, how much load will the amp see, 2ohms 4 ohms or 8 ohms?

 

the amp will see a 4ohm load

 

Yep.

It is the job of the passive crossover to separate the frequencies not only to suit the drivers but to also keep the amplifier from 'seeing' both speakers at the same time.

 

Alright, makes sense