active crossover

[elysir]

I need an active crossover for my woofer in car
a simple variable "low pass" about 0-500 Hz at 12 or 18dB/oct

I can see which project to build it?
or is there something cheaper to buy?

thanks

[Perry Babin]

The cheapest would be found on eBay. If you want to build something, include sallen-key filter/crossover and state-variable filter/crossover in your Google searches.

[dangus]

Or thrift stores, pawn shops, yard sales, flea markets. Don't overlook local car audio dealers... you never know what goodies you'll find on the bargain table.

If it looks like it's going to cost much money, you may be better off with a new (or used) sub amp that includes the crossover.