Audio Systems: crossover, pioneer head unit, power cap

Question
I have a system in my truck including a pioneer head unit, 2 12s a power cap and sub amp. I noticed that some words and other frequencies were comming through the subs. What should I do to clear this up?

Answer
This will be all about a crossover and /or its' settings.
You must realize that even with a crossover enabled, you 'may' hear such sounds (though at a greatly reduced volume). Hearing some higher frequencies is normal when only playing the subs but they are reduced enough by a crossover to not be noticed when the other speakers are enabled.

If your current amplifier has a crossover built in, you may need to lower the frequency setting.
If all else fails you can disable an on board crossover and use a better stand alone unit between the headunit and the amplifier. A variable 18 DB/Octave crossover should to the trick.