Phase Plugs, why and how

[OnYrMrk]

here is the fifth one

[OnYrMrk]

here is the baffle being mounted

[geolemon]

Pics look good, door looks pretty well sealed off, wooden baffle should actually if anything add a tiny degree of rigidity, which is good...

...so if you aren't getting any midbass, I'd suspect phase issues.
And unfortunately, there's TWO ways that can occur:

1) wiring the two speakers relatively out of phase. If you "click" the speaker with a 9v battery, you can visually see the phase - it's a nifty trick.
Disconnect the wire from the amp, and touch the wires to the battery, with the + wire touching the + battery terminal (and - to - obviously). The speaker cone should move OUT. If it moves IN, it's wired improperly - check the connection at the crossover, if you have one.

But more importantly than that - the cones should move the same direction on both sides. If the drivers side moves in, and the passenger side moves out, then that's what they'll do in operation as well - and the end result will be cancellation... but more importantly, increasing amounts of cancellation as the frequencies get lower and lower, due to the pathlength difference of your offset seating location (among other things).

I'd suspect that...
...but the OTHER way you can have phase issues has purely to do with car acoustics. My Civic suffers from a lack of midbass to some degree as well, and it has more to do with speaker placement / aiming / and interior acoustics than anything. Play with "time alignment" if your head unit has the feature - if this is the case, you'll find you can make an improvement with it.

Phase is a very interesting subject (OK, maybe you have to be a geek ) - and it has some serious implications on your sound.

[geolemon]

Oh, curious (forgot at this point):

These pictures are the Lincoln, right?
(those sort of look like Ford-style doorhandles, and something about the color... very Ford I think And the oval door speakers - no one else but Ford...)