Guys you shud know that the car audio system will not at all perform at its best (imo not even decently) when the car is switched off and the load is only on battery...
since battery's idle voltage is 12.5v +/- and during bass notes this will significantly drop to around 10.2v....that will make the equipments perform not at all on par...and not to mention is VERY harmful for our equipment .. (any voltage at or below 11v will damage equipment)...especially amps...
whereas with the engine on the voltage around 14.4-14.8v and if ur alternator is decent enough ...during bass notes it will drop to max 12.4v ... which will still make the equipment perform very nicely indeed...
now with a capacitor....ur voltage drops are highly minimized during these demanding bass notes... even with engine off and engine on....this is because it can provide power isntantly to the amp when it needs it and charge quickly to provide that burst again...thats the beauty of these things...
A capacitor has its own place in the car audio Electrical...and nothing can replace that...sure some things must be done prior to others but it is a really important part of the setup...
and lets face it guys we install car audio entertainment systems so we can enjoy it while driving....for stationary entertainment we have our home stereos, home theatres and tv's etc