Idea for dealing with Lower frequencies

A lot of mixes have come out sounding much muddier once I put them into a car or home stereo than they sound coming out of my Samson monitors.. I have an old sub-woofer from a set of PC speakers, that runs straight out the headphone jack. I'm thinking of hooking this up so that I'll get a better feel for how mid-to-lower frequencies are coming through.. Thoughts on how effective this might be?? Thanks!

yeh replicate the car sound and adjust frequencies as necessary