how to connect a sub on a 2 channels amplifier

[Mikka]

I'm not sure is this diagram right or wrong, cause planning to buy a unpowered subwoofer. please correct the diagram if somthing wrong.

 

[raindog]

in theory it's correct (if you add a crossover) but in practice it doesn't work very well(trust me! i tried) so you are better off buying or buildind a separate amp for the sub(and a crossover of course)