What capacitor and inductor values do I need for a 4-ohm speaker crossover at 500 Hz?

Per the Component Guide, at 500 Hz with a 4 Ω speaker load you need a 1.3 mH inductor and an 80 µF capacitor.

What voltage rating should the crossover capacitors have?

Non-polarized capacitors rated at or over ±25 V should be used for C1 and C2, because of the amplifier's output voltage; this prevents a safety hazard.

What slope are these crossover filters?

All three filters shown — low-pass, high-pass, and band-pass — are 6 dB/octave designs.

How do I make a band-pass filter for a mid-bass/mid speaker?

Combine a low-pass and high-pass filter: an inductor (L2) and a capacitor (C2) in series with the speaker, giving a 6 dB/octave band-pass response.

Which component makes a low-pass filter for a subwoofer?

A low-pass filter for a subwoofer/woofer uses a series inductor (L1); the L value from the chart depends on speaker impedance and desired crossover frequency (fc).

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DIY Speaker Crossover Guide - 6 dB/Octave Filter Component Chart (2/4/8 Ohm)

Audio crossover filter manual page with filter circuit diagrams and speaker-impedance component table

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Manual page on setting filter constants with low/high/band-pass crossover circuits and an inductor/capacitor component guide table.

AI caption August 2007 · Photo 900 of 1028

This document is a car-audio reference page titled 'Setting the Filter Constant' and 'Component Guide,' explaining how to build simple 6 dB/octave passive speaker crossover filters. It shows three circuit diagrams with frequency-response curves: a low-pass filter using a series inductor (L1) for subwoofers/woofers, a high-pass filter using a series capacitor (C1) for mid/mid-high speakers, and a band-pass filter combining an inductor (L2) and capacitor (C2) for mid-bass/mid drivers. Notes explain that a multi-channel system can be set up with a combination of filters, that the inductance (L) and capacitance (C) determine the crossover frequency (fc), and that non-polarized capacitors rated at or over ±25 V must be used for C1 and C2 to prevent a safety hazard due to amplifier output voltage. The Component Guide table lists required inductor (mH) and capacitor (µF) values for 2 Ω, 4 Ω, and 8 Ω speaker load impedances across crossover frequencies from 50 Hz to 10,000 Hz (50, 80, 125, 200, 320, 500, 800, 1,250, 2,000, 3,200, 5,000, 8,000, and 10,000 Hz). A reader can use this page to select the correct coil and capacitor values for a homemade crossover at a chosen crossover frequency and speaker impedance.

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Frequently asked questions

What capacitor and inductor values do I need for a 4-ohm speaker crossover at 500 Hz?: Per the Component Guide, at 500 Hz with a 4 Ω speaker load you need a 1.3 mH inductor and an 80 µF capacitor.
What voltage rating should the crossover capacitors have?: Non-polarized capacitors rated at or over ±25 V should be used for C1 and C2, because of the amplifier's output voltage; this prevents a safety hazard.
What slope are these crossover filters?: All three filters shown — low-pass, high-pass, and band-pass — are 6 dB/octave designs.
How do I make a band-pass filter for a mid-bass/mid speaker?: Combine a low-pass and high-pass filter: an inductor (L2) and a capacitor (C2) in series with the speaker, giving a 6 dB/octave band-pass response.
Which component makes a low-pass filter for a subwoofer?: A low-pass filter for a subwoofer/woofer uses a series inductor (L1); the L value from the chart depends on speaker impedance and desired crossover frequency (fc).