Bought a 2010 Ford Escape XLT last August. It contained the standard CD-radio, 4-speakers-in-the-doors Ford system. Being a hi-end audiofool...cough, cough...
...that system wasn't nearly good enough--all the music came from around my knees, the music was gritty...edgy, the system had no low bass, etc. So first, new door speakers.
I again chose the SonicCraft 6-1/2" drivers I've bought literally by the several dozens over the years...
[That CC speaker had 4 of those in its bottom, too, for a total of 10. That system didn't last long.
...and installed them in the 4 doors...
Then, after installing and finding unsatisfactory a pair of top-mount tweeters, I installed a pair of Polk home-system TL1 Sat speakers atop the instrumentpanel. This got the orchestra in front of me, finally, and improved the overall sounds considerably. All this was still driven by the stock CD-radio.
Also around this time I rewired the LH- and RH-rear-door speakers in series and then wired them across the rear-channel-positive-only speaker leads. This of course reproduces only the difference between the 2 channels. The music is somewhat low in level and rather 'phasy' and spacious, and this added a bit of spaciousness to the overall sound.
For bass, and not wanting to add any kind of box that'd be in the way too often, I installed a Lanzar 10"-driver one-piece powered SW under the RF seat.
That added the missing midbass and some bottom-octave bass.
Replaced the head unit with an Axxera ...7200 CD-receiver, which is OK but not great (I think).
BUT...I felt things could be better still and started investigating poweramps. After a highly trusted audio 'guru' told me that I really wouldn't like the sounds of modern digital car-stereo amps and a long-time friend agreed and pointed me at the old Apine V12 series of amps, I found on eBay and bought an Alpine MRV-F303 amp in excellent condition for only $146 delivered. It's rated (14.4VDC in, 4 Ohms out) 50 Watts, continuous, times 4 channels. It had the hi-pass filters that would eliminate overdriving both the front-door and Polk TL1 speakers with too much bass, and under the LF seat it went*. I chose Audioquest cables for the front speakers--Type 2, 4-solid-long-grain-copper-conductor cable for the instrument-panel Polks and G2, a stranded type for the frontdoors.
WOW what a difference, all good. Then within the Polks, I removed the cheap 300uF 'lytic cap in series with the 'bass'/MR driver that was used to limit bass and increase power handling. Also replaced the cheap 'lytic in the tweeter network with my last of the great-sounding BlackGate NonPolar caps, and the sounds got even better. The system now sounds quite good on an absolute scale.
Of course, being an incorrigible tweak, I can't leave well-enough alone, so I bought another 'F303 amp and a Service Manual and started scheming on how to improve the sonic quality of the poweramp. So...
In the powersupply, I replaced both pairs of 'chicklet'-type 0.047uF and 0.056uF bypass caps with 0.047/100 MultiCap RTXs ('styrenes). Was tempted to replace a pair of 330uF/35s 'lytics bypassing the output-stage rails with maybe hi-Q Nichicons, but didn't.
1. Replaced all 4 coupling caps, cheap 'lytics, in channels 1 and 2 with 0.47/200 SoniCap Gen.2 'propylenes.
2. Replaced all 8 DC-rail-bypass caps, 4.7/50 'lytics, in all 4 channels with 4 7.5/200 SoniCap Gen.1s bypassed with 0.47/200 SC Gen.2s.
1. Pulled all 8 DC-rail bypass caps, 0.47/50 'lytics, in all 4 channels. Replaced with 4 5.1/200 SC Gen.1s bypassed with 4 0.47/200 SC Gen.2s plus 4 more of the latter on the board.
2. Replaced all 8 emitter resistors with 5W Mills MRA-5s, noninductive wirewounds.
Just for kicks, and every time I do something like this in this car-stereo amp I laugh at myself, I replaced all the magnetic, brass-plated-steel speaker- and power-wire hold-down screws with nonmagnetic stainless-steel screws and lockwashers and brass flatwashers.
Have turned the front-door drivers into woofers with 75Hz LP filters (and raised their level) and have lowered the HP filter on the Polks to 75Hz, both of which increased mid- and upperbass and overall warmth. The system sounds quite good, and I'm HAPPY.
* Meanwhile I had purchased a new Soundstream REF4.400 poweramp, but it was too long to install.