I wrote this a few years ago for another site but thought I would add it to our knowledge base here. It is pretty basic but may help a beginner decide what to buy.
How to choose a car CD receiver.
First of all, the best advice I can possibly give on choosing ANY audio component is to LISTEN TO IT before you buy it. Buy what you think sounds good, ignoring the specs and features. The only person who ultimately must be satisfied with your decision is YOU, the person who has to live with a piece of equipment every day. Audio is a subjective thing. Two pieces of equipment with the exact same on-paper specifications might sound entirely different to your ears. Listen and be critical. The worst thing that can happen is to be stuck with something that sounds harsh and grating to your ears. Also remember that the sound can never get "better" than the way it starts, which means the best sound quality always begins with the best source unit.
That said, it must also be noted that what sounds good in a shop may not always sound good in your car. The difficult acoustical environment of an automobile can make the best components sound like tin cans on a string. So the second bit of advice I can offer is make sure the installation of whatever component you choose is completed properly.
The first question to ask yourself is what features do you want or need? Do you want a light show in your dash with a deck that draws attention to itself simply by being there or do you want a head unit that blends in with the OEM look of your dash? Do you want the security of a removable or hide-away faceplate? Do you need to control a CD changer? Are you planning to use external amps, subwoofers, or other external processing equipment? Do you need to plug in a portable music player? Do you want the highest sound quality, or are you interested mainly in being loud? Is there a specific brand you like or are biased towards or against for some reason? These questions should be answered by you in the privacy of your home, not under the watchful eye (read PRESSURE) of the audio store sales clerk.
Sometimes people look for a specific piece of equipment simply for one feature they find intriguing (such as the auto-EQ system in the Blaupunkt San Francisco or the no-buttons-on-the-face all-remote-control Sony XPlode 860.) If this is the case, articles like this one are useless to you and you are wasting your time reading! Go out and shop for the best price on the gear you already know you want!
Speaking of audio sales clerks, many of them are quite knowledgeable about car audio in general and especially about the components carried in their shops. Use them if you feel comfortable with them. But beware of a sales person who seems to always want to steer you towards the most expensive components, or towards a particular brand or model that doesn't exactly meet your needs. Sounds to me like that person is on commission or the store is trying to move a particular brand and they could care less about your wants or needs. This is especially common in some of the large chain stores that have become very popular around the country. While it is true you can often get the best prices with those big box guys, the selection tends to be very limited and the help from the staff often leaves much to be desired. Always purchase from authorized dealers, as that is the only way you can ensure yourself of getting a full factory warranty and that the gear you purchase is what it claims to be. There are lots of folks selling refurbished or damaged or even counterfeit gear these days, especially on the Internet. Buyer beware if shopping on line!
The main component of your car audio system is called the "head unit." This is the part usually installed in your dash that normally includes an AM-FM radio receiver, a cassette player and/or CD player, and often contains internal amplifiers and other electronic components to allow you some control over your car's audio environment. This article will focus on this component.
Some common head unit terminology you should know:
Power. This is the power output from built-in amplifiers given in watts per channel, with modern powered head units rated anywhere from 30 to 60 watts per channel. This rating, by the way, is almost always a peak rating, meaning this is the maximum power the unit can spit out during the loudest peaks of the music without exceeding the heat dissipation limits of the amplifier. This is NOT the same as the RMS or continuous rating. The RMS rating is the average power the amplifier can put out all day long without distorting. This is a much more realistic rating for any amplifier in real-world use, and especially for the built-in head unit amps which tend to be prone to overheating because they are crammed into such a small area. A 40-watt peak amp might be rated at a realistic 12 watts RMS. This is normal. Look for a head unit with the highest RMS rating, ignoring the peak numbers usually blasted across the front of the unit as marketing hype. Usually a higher RMS number means better components used in the construction, better design, and higher quality. Ask the salesperson what the RMS rating is on a head unit they are trying to sell you. If they have no idea what you are talking about ("Hey, it says 160 watts, man!") then you probably do not want to deal with that salesperson. They are probably on summer break from college or high school and know about as much about car stereo as you do about the goat roping methods of Laplanders.
DIN. This is a European size standard (German I believe) that refers to the physical dimensions of the head unit face. Standard sizes are single-DIN, 1.5-DIN and double-DIN. Many cars come from the factory with 1.5 or double-DIN radios, or some non-standard variation (most notably American branded cars.) Be aware that while many fine manufacturers make head units in those sizes, you do not have to find a replacement head unit of the same configuration. Almost any standard single-DIN head unit will fit into almost any car. There are adapter kits (the most common being made by Metra) that perfectly fill the "hole in your dash" and allow you to mount a standard single-DIN head unit. Metra also makes wiring harness kits for almost any car of recent vintage. If you have your new head unit professionally installed, expect additional fees to pay for these items as they cost money and are not given away free to the installers. It is well worth the $30 or $40 for the proper kits. (Unless, of course, you like the look of a large gaping void or cardboard filler with duct tape in your dash.) If you install your new head unit yourself, it is well worth the money to get the proper kit for your car and to do it right. Chopping off the OEM wiring harness is the first sign of an amature install and means you will have a much harder time doing the job, and especially if you ever want to change the head unit or replace the factory unit. Most car stereo shops can order these kits for you or they are available on line.
Pre-outs. These are non-powered line level outputs designed to drive an external amplifier or to interface with an external processor like an equalizer or other device. These outputs are generally in the form of RCA (standard stereo) connectors. Most high quality head units these days have pre-outs. Even if you have no plans to use them, they are good to have for two reasons: One, if you ever upgrade or expand your system, such as adding a subwoofer or other external amplification, you will get much better results with these than with a deck lacking them. Two, they will give you a "warm and fuzzy" feeling that the electronics in your chosen head unit are high enough quality that the manufacturer felt it could be used in a high-end installation. Look for a head unit with three sets or pre-outs: front, rear, and sub woofer (also called "non-fading") for the best flexibility, although two or even one set will still allow expansion of the basic system.
I've mentioned subwoofers and external devices several times now. This article is not about choosing those; however, I must say one thing here. When you upgrade your head unit, especially from a factory stereo, you SHOULD consider upgrading your speakers at the same time. Most factory stereos are rated at much lower power than most after-market head units and the factory-installed speakers are matched to the low power of the factory head unit. Also, most OEM head units contain equalization systems to tailor the sound of the cheap OEM speakers to provide the "best" sound. Your new head unit will not have this EQ built in. If you install your new high-end 50 watt-per-channel head unit to drive your factory 10-watt peak speakers, you will be left scratching your head wondering why the factory speakers are now squawking and twitching like tin roofing in a hurricane. You will wonder if you messed up the installation and why you wasted $300 on such a high-end head unit if it sounds so bad. It's the OEM speakers, not the head unit.
If you want a subwoofer, which in my opinion is probably the one car audio component that can make the biggest difference in the quality of the sound, you will want to power it off an external amplifier. The built-in amplifier on most head units CAN be used to drive a sub, but you will never be satisfied with the results as large woofers simply require more power than the average head unit can deliver. Get help from your friendly sales technician at the local car stereo shop, not from a chain store, if you are interested in installing subs. This is how they make their living, and they will give you the best advice.
Other things to look for include ease of use and remote control. Remember that you will use your car stereo most often while you are driving, so the controls should be in a logical location. I have seen some decks (Kenwood CD receivers, for example) with very small buttons in awkward locations, requiring the operator to stare at the deck trying to find how to switch away from the all-Groucho Marx AM station. Taking ones eyes off the road for that kind of time can lead to problems much worse than Groucho's one-liners. A remote control, if you have never used one, may seem like a ridiculous proposition in the car. You cannot be more than arm's length away from the head unit while driving, can you? But as soon as you learn the button layout on the remote, you will find it is much easier, more convenient and safer to use it than to stare at the head unit trying to find the MUTE button.
And speaking of staring at the head unit, I am disturbed by the current trend toward animated displays and large LCD screens on the head unit face. They are neat, to be sure. The first time I saw one I sat and stared at it, stabbing the buttons to see how many different movies I could make it play. But the first time I drove a car with one installed (a Pioneer DEH-P7300) I found it distracting, annoying, and wished I could shut the damn dolphins OFF! If I had one of these in my car, I believe I would have to cover the display with a piece of masking tape to avoid a road-rage accident. To each his own. Some people would not consider a head unit that did not flash and demand attention. Others prefer plain fronts. As in sound quality, when it comes to aesthetics, choose whatever makes you happy.
Also remember that it is illegal in all 50 states to have a video screen capable of displaying moving images while the car is in motion installed so it can be viewed from the driver's seat. All currently available in-dash DVD players have safety circuits to disable the video on the screen when the car is able to move. Do not disable this system as it is unsafe and can cause accidents, and it can get you a fine if you are caught.
The final consideration (at least the final one I'm going to discuss in this article!) is, of course, price. You can spend anywhere from $20 for a head unit that fell off the back of someones truck to far more than $1000 for the top of the line. I suggest you find the model of your heart's desire at whatever stereo shop you prefer, write down the exact model number and asking price, and leave the shop. Don't succumb to on the spot sales pressure. The unit WILL be there tomorrow, and they WILL give you the same price, no matter what the sales person tries to tell you. Research the model you like at different retailers. Check on line if you must.
Once you find the lowest price available for the deck you are convinced you need, try going back to the best local stereo shop and see if they will meet that price. Often they will, or they will come very close, and buying locally is always preferable to on-line or mail order or buying from out of town if only for service if needed and for the full factory warranty, plus no waiting for delivery and the price often includes basic installation.
So listen to the head units, even ones you do not think you want. Find one you think sounds best. Get the features you like, want or need. Get a good price. Install it properly. Drive safely and enjoy.