What do you do about the obvious problem?

10 Someone opens a window.
20 Wind makes the noise level in the car go up.
30 The empeg turns the volume up.
40 Louder music makes the noise level in the car go up.
50 GOTO 30

Not to mention what happens when a song ends: as it fades out, the ambient noise level goes down so the volume goes down... all songs start out quiet.

I like the speed-sensitive idea of linking into OBD II.
_________________________
--The Amigo