Please 'Boom' Responsibly As most of you have noticed, the noise ordinances have become much tougher lately. Most of this is due to idiots, yes IDIOTS, who drive through residential areas with their windows down while their system is playing at full power. To make things worse, the music they listen to has all sorts of foul language that's not suitable for small children, (who may be playing outside). There are even a few people, who are even beyond idiot status, that play their systems at full power through residential areas after 10:00 PM (when many people go to bed). I don't believe that this type of behavior is good for the industry. If the fines get too stiff, people will stop buying large systems. If this happens, more people will get out of car audio (who wants a mediocre system). People get interested in things because they're exciting. A deck and four 6.5" speakers are not going to interest many of the younger car audio enthusiasts. If car audio enthusiasts keep annoying more and more people, the fines will keep getting tougher. All of this will only reduce interest in the equipment that fuels the industry. If you want to listen to your system at full volume, get out on the highway where there's little chance of bothering anyone. When you get to a red light, turn it down. If the only thing attractive about you is your 'system', you have some work to do. Bottom line... Think about what you're doing. Think about other people. It's not the end of the world if you have to turn the volume down for a little while.

Crossover Basics:
A crossover is a filter. Passive crossovers use capacitors and/or inductors in between the amplifier and the speaker to block/pass different ranges of frequencies (e.g. block the bass from the mids, block the bass and mids from the tweeters, block mids and highs from the woofers...). Passive crossovers allow different types of speakers (woofers, mids, tweeters) to be driven from a single full range amplifier and will only allow the proper frequencies to go to each individual speaker. Electronic crossovers use op-amps to divide up the frequencies. Electronic crossovers go in the preamp line before the amplifier.
CROSSOVER ROLLOFF
Crossover rolloff (or slope) describes the rate which the audio level increases/decreases per octave as the frequency increases/decreases. It is usually given as a number (6, 12, 18, 24...) of dB per octave. Electronic crossovers commonly have a 12dB/octave slope. This means that every time the frequency of the audio signal is changed by a factor of 2 (one octave), the level of the audio signal will change by 12dB.
Graph Legend:

Cyan  =   6dB/octave
Red  =   12dB/octave
Green  =   18dB/octave
Violet  =   24dB/octave


The diagram above shows both high pass and low pass crossover filters with the 4 most common slopes. The crossover point is the frequency at which the level of the signal is 3dB down (for a Butterworth alignment - to be discussed later) from the level of the pass band (the crossover point is about 1000hz in this diagram). The pass band is simply the part of the audio band which is unaffected by the crossover's filters.
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