Fundamentals of car audio talkin' crossovers

摘要

Humans can hear frequencies ranging from 20 to 20,000 cycles per second, or Hertz (Hz), This huge range represents an unattainable feat for a single speaker: Since no driver can successfully cover all those frequencies with quality and quantity, specific speakers specialize in specific ranges. Most commonly, big and powerful subwoofers handle the low bass, tweeters take care of the highest notes and midranges reproduce the frequencies in between. In order for these specially designed drivers to perform their best, they must receive only the range of frequencies for which they are designed to operate. That's where crossovers come into play. For music reproduction, the name of the game is moving air, and low frequencies need to move a lot of it, If the intensity or loudness is to be kept constant, each time the frequency halves the cone or dome of a loudspeaker must move four times farther. So, all things equal, for a specific loudness, the bigger the cone diameter, the less excursion necessary to reproduce that loudness. The downside is that the bigger the cone, the heavier it is (and therefore the more inertia it has). So as frequency goes up, say 5,000Hz for a 12" woofer, it simply won't be able to start and stop fast enough to reproduce that frequency, It will try nonetheless, giving rise to several kinds of audible distortions. In order to avoid that, one should filter out the high frequencies. On the opposite end of the frequency spectrum, if a tweeter can start and stop 20,000 times per second without losing its breath, it certainly can move only 50 times, The problem is that in order for its small dome area to create any usable output, it should move several feet front and back, of course destroying itself while trying, That's why it is so critical to filter out low frequencies from tweeters-in order to keep them alive from over-excursion, In between these drivers, midranges suffer from both problems at both extremes of the audio band.