how can i boost my voltage in my car to say 15 volts? and what other bass enhancment devices can i get besides a crossover and EQ

 

new alternator (not cheap) and new battery

 

Try getting a Capacitor. I know this improve your bass response because the power will be right next to the amp. It's basically like adding another battery to your system without the headache of the battery isolator. You generally want to go with 1 farad per 1000w. So if you're running like 800w max power, you'd go with a 1 farad capacitor. Also, make sure you have good cables hooked up to your amp, you generally want to go with an amp kit that is made for a step above your amp. My amp is 400w, it says to use 10 gauge, I put 8 guage on it to reduce resistance. Another thing, use fat speaker cable(Monster cable), this helps in the low signal transfers of bass, and reduces resistance. Hope this helps.