Car audio gurus -- please help with phase problem

[Jeffs Black 97 Formula A4]

Ok, I just got the milhouse box from Subthump, and noticed with some songs that have higher mid-bass, the subwoofer (JL Audio 12W3v2) and main speakers (Kenwood components in front, 2-ways in rear) sound like they are out of phase. This is with the subwoofer hooked up normally (+ to +, - to -). Disconnect the sub, I hear midbass from the speakers as it should. Reverse polarity with the sub firing into the well, the phase problem seems to be gone. Little loss on the bottom end (not enough to care), sounds fine. But, if I flip the box up to make room for the t-tops, the system sounds better if I switch the polarity back to normal. Any ideas on why this is happening? Thanks.

[MN6WS6]

You have to think of your bass as a wave. Every wave has a high point and a low point. If your mids have the high point of the bass wave hitting your ears at the same time as the subs do, then you're okay. However, if the low point hits you when the high point does from the subs, they are out of phase. If you'll sit in other seats in the car, you'll notice that it may be more prevalent or less prevalent. It's just inherent in audio systems.

Why is it happening when you flip up the box? Because you've moved the subs but not yourself. So that's what's going on, you have the high point of a wave from one speaker meeting your ears at the same time as the low point of the wave of another speaker.

I don't have this problem because my box is not movable. I get to "set it and forget it". However, what you will need is a radio with phase shifting from the dash (like the Pioneer DEH-P77DH). With this radio you can leave your subs in phase or shift them 180 degrees out of phase from the dash. Basically what it does is it takes your sub out channel from the radio and makes the negative positive and the positive negative on the RCA side (same difference as swapping the wires at the box).

[Jeffs Black 97 Formula A4]

Actually, my Kenwood eXcelon head unit features a phase switch since I am using the non-fading preouts for my sub. Still trying to figure out which phase setting sounds better by listening to many different songs.