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© 2003 TDM Audio, Inc. Electronic Crossover Owner’s Manual Page 8
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Figure 4 - 24 dB per Octave Filter Curve
To make a 2-way crossover, we feed the same signal into a high-pass filter and a low-pass filter
with the same cutoff frequency. This is called the crossover frequency. The output of the high-
pass filter is the high output of the crossover. The output of the low-pass filter is the low output
of the crossover. The crossover frequency knob simultaneously adjusts the cutoff frequencies of
both filters to vary the crossover frequency. Because the cutoff frequency of a filter is the point
at which the output signal is 6 dB below the input signal (which means that it has half of the
amplitude of the input signal), the crossover frequency is the frequency where half of the signal
goes to the low speaker and half goes to the high speaker. Below the crossover frequency,
progressively more signal is sent to the low speaker. Above the crossover frequency,
progressively more signal is sent to the high speaker. Thus, there is a smooth transition between
the low and high speakers. This is why we call it a crossover. To illustrate, Figure 5 shows the
frequency response curves of both filters in a 24 dB per octave 2-way crossover at 1000 Hz.
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Figure 5 - Crossover Frequency Response