But when it is over 500w ,use an active crossover which is cheaper than the passive crossover at 500w and above. Also the active crossover is better than the passive crossover,cos you can adjust the roll off point,and limit the frequencies.

So for example a 50hz-5 khz driver can be limited to 50hz,so 50hz and below doesn't damage the driver,also at this point you can crossover
to a sub bass bin - 20hz or so