Perhaps your car is acting as a 'resonant cavity'... or your head is : )

Sammy, my best guess is that the room you are mixing in doesn't have enough acoustic treatment. What you are experiencing ("it sounds good in my room but crappy everywhere else") is the most common symptom for that.

Basically, what happens is that sound reflects off the walls in your mixing room, cancelling some frequencies and reinforcing others. So when we mix in a room like that, we aren't hearing an accurate picture of the music, and as such any EQ decisions we make are (unconcsiously) trying to compensate for a bad room, rather than making the music sound good.

Get some acoustic treatment (fiberglass, rockwool, or cotton are imho better than foam) in the room, and it will be easier for you to hear what's going on, then you can make better decisions at mixdown.

Of course, it could also be that your car system has a peaky response, that happen to coincide with frequencies you like to boost in your mixes.... but I'd bet the farm that your mix room isn't optimized.

JWL:

Thanks for the advice. I should have mentioned, I can actualy hear the same problem frequencies in my control room whilst mixing, its just more apparent in my car. I think this is because as you mentioned, my car does tend to emphisize a few frequencies, as a result, also accentuating the trouble spots im talking about.

What do you think is the best approach in the studio for this problem?

cheers!

Sammyg
p.s. I do have auralex style acoustic tiles in my control room in order to control things a little.

well, it's a good sign if you can hear it in the control room, because that means you can do something about it. Try to identify which instrument is offending at those frequencies (use mutes and solos to be sure). Once you know which instrument it is, try to find where those frequencies are with a parametric EQ.

Set the band to a very narrow Q (like 12 or higher), and a dramatic boost (12dB or more) and slowly sweep that EQ across the frequency spectrum. Find the EQ that offends (sweep until your ears explode), and then cut that frequency, possibly also widening the Q a bit so that it sounds good in the context of the mix.

As far as the room, generally most small rooms need a lot of absorption, especially in the corners of the room. Plus, make sure you have a listening zone with reflections being absorbed from the side walls and ceiling. See the acoustics forum for more.