Annoying sounds from cars at stop light

" You are correct about very low bass notes having very long waves. Not sure those 6" speakers in the door or even a 12" sub in the trunk are pumping out 30Hz bass loud enough that I can hear it from my car in open air."

Chances are you are not hearing the speakers in the door as much as the subs located somewhere else in the vehicle. Since low bass is non-directional, placement is not crucial. The sub or subs might have dedicated high power amps too. Some systems I have seen have their own battery & capacitor circuit, separate from the vehicles. 

Yes,  I know it’s a good question. I only ask good questions. How do you get low bass with zero volume? You don’t have to have any experience with headphones to see what I mean.

It's possible I used to be one of those snot-nosed kids.  Now, it's annoying for this curmudgeon.

"How do you get low bass with zero volume? 
You don't, you need gain.

Good one! 🤪