this year i plan on upgrading my speakers and plan to run them off an amp but my deck only has one set of rca outs and i was wondering if its ok to use an rca splitter that splits one rca connection into two (currently have a sub using the rca) or would the splitter reduce the sound?

 

No no no no no...You can't do that dude. You need to get a 2 or 3 way crossover to separate them.if you are running one set of components then use a 2 way. If you are runnin front, rear and sub then get a 3way crossover.

 

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A crossover is the best way to go but a pair of splitters will work in a pinch. Your amps probably have built in crossovers. The sub amp is probably already sent to LP (low pass) so set the amp for the components to HP (high pass)