With an Audison stereo volt meter, you’ll know at a glance whether the system is performing up to snuff. Their Superfarad Capacitor, which stores extra electrical power for the subwoofer, doubles as a car stereo bass tester. It comes with a blue digital volt meter so you can see whether the system is getting the necessary juice. With a 20-volt reserve, it can stem the tide until repairs are made. Add one today with free shipping in the lower 48 states.