Even though each driver in a 3-way, or a 2-way speaker, is wired to the input from the amp in parallel, the various filters in the crossover prevent the all the drivers from “seeing” a signal all at once. For the woofer, a low-pass filter at 300 Hz for example, effectively blocks signals an octave above that, 600 Hz or higher, from getting through to the woofer. Something similar works for the tweeter, where a high-pass filter, at say 3,000 Hz, effectively blocks signals much below 3,000 Hz from getting to the tweeter. For the midrange driver, a band pass filter from 300 to 3,000 Hz only allows signals in this range to reach it. The only time two drivers see the same signal at an equal level is near the crossover frequency.