I'm not pyros
, but a while ago I wanted to quickly test if I can get sound out of my carpc so I brought in my logitech speaker set and powered it by an inverter. It was still a quality set. In house, it sounded loud and clear. In the car, it sounded like total ****. The sound is all muffed because of the various surfaces like Red mentioned. I cranked it up high and still couldn't hear crap with all the road and engine noise.
Even a good old cheapass $10 cassette adapter would kick the crap out of most of these PC speaker systems.
Mind you, I never wanted to put PC speakers in the car but it was unbearable even just for testing.