Not Quite
Capacitors in an auto sound system are actually used to provide a constant amount of current to the amps so as not to have a voltage drop. They are especially good in todays lower wattage, highre amperage amps. It is the quality of the current that has a more direct effect on the sound level and quality than the amount of raw wattage that you are pushing. If you want decibles, push wattage. If you want quality push amperage.
Capacitors are used in several different ways in electronic circuits:
* Sometimes, capacitors are used to store charge for high-speed use. That's what a flash does. Big lasers use this technique as well to get very bright, instantaneous flashes.
* Capacitors can also eliminate ripples. If a line carrying DC voltage has ripples or spikes in it, a big capacitor can even out the voltage by absorbing the peaks and filling in the valleys.
Like a Water Tower
One way to visualize the action of a capacitor is to imagine it as a water tower hooked to a pipe. A water tower "stores" water pressure -- when the water system pumps produce more water than a town needs, the excess is stored in the water tower. Then, at times of high demand, the excess water flows out of the tower to keep the pressure up. A capacitor stores electrons in the same way, and can then release them later.