I've got a stereo WAV file after mixing down in Sonar.   

I wanted to test how the mix sounds on the car stereo, so dragged the WAV file over into my iPhone folder.   When I hook up the phone in the car, is the iPhone actually playing the WAV file itself, or has it automatically converted it to some other format?  The mix is sounding very bass heavy - even boomy - in the car ... not sure if that is the iPhone conversion or the car stereo itself, or both ... ?

your EQ on your iphone / car flat ? if not you might want to look into that.. don't use an iphone so can't comment on it

Maybe your car stereo is bass heavy or your mix is.

Assuming an iPhone can play wave files, there should be no conversion involved. The device might have some EQ (I'm not an iAnything user so I don't know) so you'll want to verify that if there is, it's set to Flat.

A more likely explanation is that it's not the iPhone's fault, but rather the limitations of your car's sound system causing the mix to not translate well. That's the real challenge in this business: making mixes that sound acceptable no matter what you play them on. It's not easy! 

I would caution you, however, against tailoring your mix for the car, as that is a losing proposition that will just have you chasing your tail. A car is an acoustically-challenged environment, with lots of reflections and resonances. Think about how automotive engineers literally design car doors to be drums, so that they make a satisfying thump when you close them. Those doors are resonant cavities! And where are your speakers mounted? In the doors. And if you have tweeters in the dashboard, look at how their aimed: in most cars they're aimed at the frickin' windshield! Can you say "comb filtering"?

On top of that, most car stereos have a built-in bass boost to disguise the fact that you can't get good bass response in such a small space. They typically have an artificial bump somewhere around 60-100Hz. Consumers generally don't care if it's flat, they just want to feel the bass. But it sucks as an EQ reference.

Which is not to say it's a waste of time to check mixes in the car. For me, it's the ultimate test. If it sounds OK in the car I know I've got a good translatable mix. What I don't do, though, is alter the mix specifically for the car. It will never sound as good in your car as it does in your studio, and if you do manage to get a great EQ in the car it will probably sound bad everywhere else.

ipods can play wavs.

No universal rule, but every ordinary car stereo I try always sounds bass heavy even when eq is flat.  But that is important input because I want a compromise that works most places.

Hi Ultrabra,
What you're describing is very likely a classic mix portability problem. There are some different ideas about solving those kinds of problems but the generally accepted industry answer is with room construction and acoustic treatment (google images of recording studios and see how many of them have some kind of treatment on the walls and ceiling). It's a big topic but I'd start here:

http://www.ethanwiner.com/acoustics.html

Good luck,
Dean

It just needs to be mixed and mastered in a tuned environment so it can translate properly on all sound systems.

Cj

Thanks for all the feedback but ... OUCH!    That feels like I've been diagnosed with some kind of illness I'd rather not have .... as a "start here" point, that looks kind of scary :-)

Seriously though ... I have read quite a few posts on room treatment - I must admit my room is not treated in any way -  I'm just wondering what the average home user does to a room?   There's no way I can properly treat the room I am currently using for mixing.   Does that mean my mixes are destined to be forever .... what's the word ... untranslatable?

It feels like ... you learn your DAW ... you learn your instruments ... you figure out compression ... you finally understand EQ ... reverb, delay, sorted ... yes, now we're getting some place ... then BAM! ................. your room isn't treated, so .....  

Hi Ultrabra,
Yeah, it's a daunting process. Not sure about the average home user, but you will likely hear various anecdotal accounts of all kinds of work-arounds...various corrective EQ's, headphones, "knowing" your room etc, but there is a reason why all those google images of studios look like they do: this is how folks do it. There's math behind it. I've seen and worked with folks who don't treat their rooms and get good results (though rarely in a professional capacity), but they really are outliers and, while my room isn't perfect, I certainly don't want to go to an untreated space. Ethan Winer's site is great for theory and he makes good products but there are lots of other treatment products out there...Auralex, Primacoustic, and good, cheap DIY products that work well (this one springs to mind http://www.ethanwiner.com/basstrap.html). Some good nearfields and a few DIY bass traps hung around the room will go a long way.

Dean 

All that doesn't mean you couldn't do proper mixes in an untreated room, as long as you know the room and its tricks. The acoustics of an average room with some soft furniture, book shelves etc. isn't necessarily that bad - not ideal, very likely, but very possibly quite tolerable. The positioning of loudspeakers can be the crucial thing. Something like monitors with the bass reflex hole in the rear positioned against the wall can do things really difficult.

For the ones of us who don't have a dedicated room for our hobby, acoustic treatment is not always an option. You can't position, say, bass traps in a room with corner to corner bookshelf on one wall and a cloth closet on the other and a doorway in the one free corner.