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Capacitors in Series with Speakers:
Earlier we discussed passive crossovers. The simplest form of high pass crossover is achieved by simply putting a capacitor in series with a speaker. The proper capacitor is determined by the desired frequency response and the speaker's rated impedance. A more in-depth discussion of capacitor selection will be covered on the passive crossover page.
Making the Connection:
For a 6dB/octave high pass crossover you simply connect the capacitor in series with one of the speaker connections (it doesn't matter whether it's the positive or the negative). There should be no positive or negative markings on the capacitor. If there are, you have a polarized capacitor and it will probably fail (which could cause the speaker to fail if the capacitor shorts when it fails). For best results, you should use a non-polarized or bi-polar (same thing) capacitor rated at 100 volts or more.
On the following graph, the green line shows how the signal level drops off (rolls off) as the frequency decreases. You can see the green line is virtually unaffected (there is virtually no decrease in the signal level) above ~2khz. At point A, you can see that the signal is down 3dB at 1khz. The 3dB down point is the crossover frequency (for Butterworth alignments). It represents the point where the power reaching the speaker is 1/2 of what it would be without the crossover. At point B, the signal level is down by 6dB. This represents the 1/4 power point. At point C (250hz), the signal is down by 12dB. This means that the amount of power reaching the speaker at 250hz is 1/16 as much as it would be without the capacitor.
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