look at this question.

[beau]

i want something that i can put on my speaker outputs and it makes it low bass and not high treble, what is this called, i need to search on ebay.

 

[gaz.d]

low pass filter or lp - filters out all high frequencies - subs

high pass fileter pr hp - filters out all low frequencies - mids/comps etc

normal - anything goes

the only time i have seen these filters is on an amp, or a head unit with an output especially for subs

 

[beau]

cheers but i couldnt find any

 

[Luke]

they're called passive crossovers just make sure you get teh right ones - as stated by gaz