you need to learn your monitors properly
your noticing the difference in levels more on your car speakers, because (as a rule) the frequency response of them is massively hyped around the vocal reigon.

mixing on headphones is a bit of a no no too.

you just need to really really listen to your monitors and hear what they sound like, and get used to where a vocal sits within a mix.
spend a day or two listening (i mean really listen) to some tracks that you know from your car.
its a matter of you not hearing your monitors correctly
x

you need to learn your monitors properly

It make sens because I'm listening my car speakers a LOT!

I think that you are right. However I've tried adjust levels on my AKG 240 vocals (only vocals!) and now trying to hear on KRK's... level seems to be perfect.

Maybe a combination of both is giving me a right settings now.

I have to spend some time on my speakers.

Thanks for your help!

Again about those levels. Just bought speakers for my PC. Cheap Logitech $30.00 speakers.

When listen to my music, I've noted that I can hear very precisely difference in levels.

Quick adjustment and levels are perfect.

I didn't spent time of listening on these ones. But I can hear very easy any difference.

So... here we go.... :D

Yeah I really don't understand all the fuss in monitors after all $30.00 logitechs are probably the answer. All those engineers devoting hundreds or thousands of dollars on monitors must just be for bragging rights huh? Why not just mix in your car? It may be illegal to talk on your cellphone and drive but there aren't any laws about mixing while driving, well unless it's scotch and soda type of mixing anyway.

Mix down until you get a good sound on your main monitors which should be "accoustically true" and then tweak things a bit until you get get a good sound on another cheap set of monitors... while still maintaining a good mix in your main monitors. The school where I studied had a cheap set of speakers sitting right on the top of the board for just that purpose.
I know this might sound too obvious but make sure there wasn't any compression affecting what you heard in the studio monitors.

If you want your mixes to translate everywhere, learn your monitors. This means listening to commercial recordings you are VERY familiar with on those monitors.
Sound different than your car? Adjust your ears.
Once you learn what a good mix sounds like on your monitors, you can then compare your mixes, and try and make them sound the same.

I am learning my own monitors/room now, and it's getting better all the time.

That said, it doesn't hurt to check things on crappy speakers occasionally, as that is what a lot of people will be listening on.

I've owned my Creative speakers for, err, 2 years now.
And my HD280s for about 18 months, heh.

I still can't mix anything on them properly! If I mix on the speakers, certain aspects end up flooded with mush in the cans, but sound OK on the speakers.
If I mix on the cans, the levels end up crap but the EQing is a little better.