this might be a really dumb question... my head unit has three pairs (front, rear, and sub) of preamps. when i hook an amp up to the sub one, does it automatically filter out the highs? and the same with the front and rear with the lows? i have an alpine 9847... thanks.
RCA's that "automatically" filter: Sub-yes, most come with a LPF of around 120hz(The headunit might or might not have sound control to change this). Front and rear-no, these have to be set manually by the headunit(if it has the option to do so).
ok, so i dont have to worry about the subs, but for the speakers, why do i have to mess with the hu... isnt there a HPF on the amp for my speakers that should do the trick?
All the information you're asking for is clearly available in the manual. If you did not get one, you should complain to your reseller. You did get it from a legitimate reseller?