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RC High-Pass Filter and Speaker Crossover

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Recipe #4 — RC high-pass filter

Move the capacitor into the signal path and the same two components now favor higher-frequency changes while reducing DC and lower-frequency content.

RC HIGH-PASS FILTER IN C = 0.1 µF OUT R = 1 kΩ high frequencies pass; DC and lower-frequency content are reduced

Same example values

R = 1 kΩ and C = 0.1 µF again produce a cutoff around 1.6 kHz. The parts are the same; their arrangement changes the job.

Real-world uses: coupling amplifier stages while blocking DC, removing slow drift or rumble, separating AC from a DC bias, and forming the high-frequency side of a simple crossover.
SIMPLE FIRST-ORDER SPEAKER CROSSOVER IDEA AMP C tweeter high-pass branch L woofer low-pass branch Real crossover values depend on speaker impedance and frequency.

A crossover is really a pair of filters

A simple two-way loudspeaker crossover sends higher frequencies toward the tweeter and lower frequencies toward the woofer.

The drawing above shows the basic first-order idea: a capacitor in the tweeter branch and an inductor in the woofer branch.

Speaker crossovers are not calculated like an unloaded RC example

The speaker's impedance is part of the circuit, and real loudspeaker impedance changes with frequency. Practical crossover design must also consider driver sensitivity, phase, acoustic response, power handling, and component losses.

Try these yourself

Which frequencies does an RC high-pass filter favor? RC HIGH-PASS FILTER IN C = 0.1 µF OUT R = 1 kΩ high frequencies pass; DC and lower-frequency content are reduced
A series capacitor increasingly blocks lower frequencies and passes higher-frequency changes more readily.
What is a common use of a coupling capacitor between amplifier stages?
A coupling capacitor forms a high-pass effect with surrounding resistance: it blocks DC and passes sufficiently high AC signal frequencies.
In a simple passive speaker crossover, which component is commonly placed in series with a tweeter?
A series capacitor is a classic first-order high-pass element for a tweeter.
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