Another way to look at it, is that some drivers are designed to handle high frequencies (tweeters), some are designed for miidrange (smaller to medium woofers) and some are designed for low frequencies (larger woofers, subwoofers). Filters or crossovers ensure that only the appropriate signals are being sent to each driver. You don't want mid and high frequencies heading to your subwoofer...hence the need for a low-pass filter. Similarly, you don't want low frequencies heading to a tweeter.
harry
harry