Part 7 of 8 of the NB Audio beginner guide to speaker building. Start at Part 1 and the series contents.
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Most first crossovers are built from someone else's drawing. The job is to build exactly what's on it, and to know how to check you have.
Expansion Guide 6 starts there, then shows what one filter change does in software, then what designing your own adds.
The target
Follow the signal through the speaker: the woofer's branch, the tweeter's branch and the overlap between them. Then find the input and outputs on the drawing before you look at a single value.
The sum
Sort the parts by their labels, copy each part's whole specification rather than its headline number, and trace the circuit one junction at a time. Lay out the board, assemble it, and check it with the power off. Then try one filter change in software only, to see what it does.
The prototype
For a new design: the data you need, a baseline model you can go back to, one change at a time for one stated reason, then a prototype you measure. There's a section for active and DSP crossovers too.
Who it's for
It's written for a first build from a documented design, with the circuit drawing, parts list and wiring instructions beside you. The design section is there for when you're ready.
What it won't do is treat the frequency printed on a generic board as proof it suits your drivers.
Expansion Guide 6: Designing the Crossover
Free PDF, 10 pages. Every step and checklist in order, with the signal-path and software-exercise diagrams.
Check out for $0 and the download link comes by email.
Previous: Part 6: Your first speaker measurement: repeat it, then compare the pair (Beginner Guide, Part 6)
Next: Part 8: Testing and tuning your speakers: first sound, fault-finding and placement (Beginner Guide, Part 8)