Pair of Crossover PCBs for the Classix II DIY speaker design - PCB Board Kit | eBay
Amazon.com: Speaker Frequency Divider Board, Treble Alto Bass 3 Way Frequency Divider HiFi Audio Crossover Filter Module Board for 812 Inches Speaker, Free for Welding, Perfect for DIY : Electronics
Amazon.com: High Power 2 Way Audio Speaker Crossover for DIY, Fine Workmanship, Excellent Sound Experience, Dual Frequency Dividing, PCB Material, 180W Power, 3200Hz Crossover : Electronics