Car audio question

[JustLearning]

I don't know if this is a question for Click and Clack, the Car Talk brothers?

I thought it might get a more useful answer if I ask you sound pros. So here it is:

Why does the volume seem to be less on my car CD player when I'm driving?

Is the volume more a factor of interference? That is, does the road, tire sound, engine, outside wind, etc interfere with the CD audio?

Or is it a matter of phase cancelation? Do the frequencies of ambient driving sound actually cancel frequencies in the audio?

Is it a combination of these factors? If so, is it more of one or the other, or is it something else?

All I know is when I slow down, stop or idle, the CD volume is louder than I think it should be.

Protecting my ears,
Benjamin

[DAS]

It really is just the ambient noise from driving (road/wind noise, etc.) interfering with your perception of the loudness. Some fancy stereos actually have automatic level controls that turn the volume up a few dB based on your driving speed.