Power: The amount of electricity each speaker can use before exploding (okay, before being damaged). Measured in watts (W), most components carry two numbers: normal and maximum power (which is almost always twice normal). For example, a component is marked "75W RMS/150W peak power" or "75W continuous/150W peak". RMS is "root-mean-square;" a meaningless phrase unless you’re an engineer, except that it describes steady power use. Peak is the maximum safe load. Think of wind -- RMS is a breeze, peak is a gust; too much and your audio speakers will look like the first two little pigs after the big, bad wolf got done with them! Impedance: Wires and microchips are solid objects, so they impede (ever so slightly) the flow of electricity. Think of a water pump connected to two pipes -- the larger pipe has lower impedance because more water can flow through. Measured in ohms (abbreviated by omega, that horseshoe-looking Greek letter), stereo amplifiers and speakers are usually rated at 4, 8 or 16Ohms; they work best when numbers match; mismatched components can give you bad sound or damage each other.
Having decided on your car audio goal, let’s kick the tires:
Price: Even at Overstock.com’s clearance-sale-every-day-prices, you can spend a lot of money on car audio (we know, it’s hard to believe, but it is possible). You can buy a discount car audio system (but never cheap car audio) or the most expensive car stereo system with all the bells and whistles. Before you begin, set a budget; then pick the components that fit your budget. Scope: If you don’t care about bells and whistles, pick up a basic car radio, car amplifier (car amp, for short), a car CD player and car stereo speakers and you are good to go. If you want all the toys, you can add a satellite radio, a car CD changer or portable DVD player (or both), subwoofers, big auto speakers in big speaker boxes--as much for show-off as for show tunes--the list is as long as the line at the DMV. Priorities: Now that you have an audio system in mind, make a list of the audio equipment that fits your budget and rank the features: How many speakers? Are you replacing the OEM or adding to them? Do they fit under the seats or will they be trunk-mounted? DIY or shop installation (an added expense)? The more questions you ask, the more you’ll know exactly what to buy.