Last night I replaced the stock head unit with the Pioneer AVH-p3400bh. I'm loving the added features, but noticed that the audio sounds "muffled", or rather it doesn't sound crisp or clear. Many people have stated that simply replacing the HU made all the difference and audio was much better.

Does anyone have any suggestions or advice of what I can try to make it sound better without replacing the stock speakers?

 

Did you use a harness, or did you hardwire it into the car?

I would pull the unit to verify you don't have one (or possibly more) of the speakers wired out of phase. Or while you are there you could also make sure that all four of the speakers are still working. The only other thing could be that you've got one of the wires or RCA's shorted to the speaker wiring.

 

Also, without knowing anything about this particular unit, some of the newer ones have built-in SPL tests that you have to run in order to calibrate the system. Just throwing that out there as another thing to rule out.

 

adjust the eq

 

The stock head unit is EQed with lots of bass and treble. If you have a bass model with no tweeters and change the head unit, you will be left with mostly mid-range.