12V Low Pass Speaker Subwoofer Crossover for 8 Ohm or 4 Ohm
Passive crossover schematic - most types - Audio Judgement
Ghxamp 300w 600w Subwoofer Speaker Crossover Audio 1 Way Filter Frequency Divider Super Woofer For 12 Inch 15 Inch Speakers 1pcs - Speaker Accessories - AliExpress
Crossover For Subwoofer - EEWeb
How to make easy Tweeter crossover circuit at home - YouTube