I built a 2-way passive crossover (Bessel), with a cutoff frequency of 4600 hz. I needed a crossover for my DIY speakers, these speakers have a woofer and a tweeter. The woofer has an impedance of 8 ohm and the tweeter has an impedance of 6 ohm, and none of the already assembled crossovers seemed to work for my parts. 

Even though there are many crossover calculators online, I though it was interesting to derive the equations of the filter, and test my crossover, using a function generator and an oscilloscope.

To build a crossover, apart from the components, you will need a soldering iron, wire, and a glue gun (to keep the components attached to the plate).