The DIY home speakers that are usable in car audio, are kind of like a diamond in the rough. Many of PE woofers have some of these issues:
8ohm impedance
long mounting depth
unusable with crossover above 2KHz
not optimized for IB
Of course, for the truly dedicated installers, some of these are not an issue.
tweeters:
very good, but tend to be very large for stock locations.
Madisound has a few interesting woofers and tweeters that are quite usable: the Seas Neo tweeters. Seans rnx woofers, silver flute woofers, sb acoustics woofers, maybe a few others.
good points Zako, but i'm not sure they are a hinderance
1. 8ohm impedance - not an issue for car audio. damping factor is higher, THD lower, and output only reduces by 3dB.
2. long mounting depth - you can find car audio speakers just as deep or buy new home audio
3. unusable with crossover above 2KHz - many home audio speakers have extended frequency response. the main issue with a car vs. home is aiming. but all speakers, regardless of who makes them for what purpose, have different response on- vs. off-axis. frequency response should always be evaluated at the same time as aiming. And with car audio you don't get freq response of the woofer only, nor at 30 deg and 60 deg. Home audio drivers are better documented.
4. not optimized for IB - IB doesn't exist so it's a moot point. a door is an enclosure - a large, leaky, resonant enclosure. nothing sounds good in an untreated door.
the tweeters with large flaceplates are certainly not suitable for a car. the tweeter selection is really driven by physical size, but i would argue that most factory tweeter locations are poor anyway. factory 3.5" locations are well suited for a larger tweeter as a drop-in replacement. otherwise, there are compact options.
the main challenges I see are as follows:
A. lack of grills for protection - more of an issue for tweeters than woofers, but can still be a challenge.
B. lack of water resistance treatments - water is a concern for any door speaker - baffles or channels should be used to direct water around the speaker opening.
C. crossovers - custom made crossovers are not cheap, and it takes some R&D to come up with a good pair of tweeters and woofers and a crossover.
as mentioned, running active makes using individual car/home/pro speakers much easier to implement. it resolves issues with impedance and frequency response.
...
which is why i do it. //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif
my front stage cost a whopping $150 and it sounds great... after a few hundred hours of install, testing, install, testing, install, testing, etc...
but a great sounding system doesn't happen with drop-in speakers anyway. i've finally reached a point where my weakest link is my speakers and not my install.