
to the forums...
Most factory style speakers do not have a very good frequency response, regardless of make. BMWs do a little better than most other imports and WAY better than the domestics. You wont find any bass response, and not much in the high end either. They really focus on the midrange, because thats where most of the music is. If I had to guess, I'd say 60hz-10khz with a boost @ 800-2000hz (thats the frequencies the human ear is most sensitive).
Long story short....replace them, you'll be much happier in the long run.
I (along with some others) use Infinity, the Reference series are a good speaker for the money, the Kappa series are well worth the little bit extra. Go to an audio store you can trust, bring in a CD listen to the same song, same headunit, same bass/treble settings, and switch between the speakers. Dont listen to me or anyone else that tries to tell you this brand is best, or that brand is best. There is no best, or everyone would be selling it and it would be high priced. The differences built into speakers are there to appeal to your particular hearing, not your buddies, not mine, but yours. Take a REALLY good listen (by yourself if the salesperson will leave you alone) before making your purchase.
Good luck, hope that helps....