btw the fundamental frequency may not always be the most desirable freq. its more the freq that has the most energy.
for example looking at my sound desk right this second, for a tv show on voices. I would EQ someones voice as follows. shelf cut at 160Hz, -4dB notch at about 380Hz, then a +3Db at about 4.5Khz, then a high shelf cut starting at 12Khz.
the reason i cut below 160HZ and above about 12Khz is for voice there is nothing in there that is desirable for a normal "talking heads" type tv/radio show, often this is the same for music.
for a kick drum or a bass guitar for example i would depending on the day, boost the 60 to 160Hz range, and might cut everything above say 4Khz.
its all about shaping the sound so it fits into its own gap in the frequency range, two things trying to fight for the same frequencies will just get mushed up and be hard to hear.
in a car its along the same lines, for best results you want one thing doing one range of frequencies. personally this is what i prefer....
a sub does the lows 10" or 12"(40Hz to 120Hz)
rear speakers 6x9's or 8" mid bass subs (110Hz to 4Khz ish) ive been known to cut the tweeters out of rear speakers before if they are harsh.
front main drivers 6" (150Hz to 4Khz ish)
front tweeters (3Khz up)
different speakers will sound different so you need to tune your car to find out what works, and what gives you a balance thats isnt heavy in one area.
something like this xover (same sort of thing as what i have) where you can tweak the high and low freq range of each feed before it gets to the amp makes a huge difference. also there is a gain on each channel so yu can get it all sitting just right in relation to each other.