| Build quality:Some head units are flimsy and | | | | face:When the unit is off, the head unit has |
| weak. Some are built to last. Usually the | | | | a completely black face with no visible |
| best way to determine this is by the weight | | | | buttons or controls. Come on. Criminals |
| of the unit. Also, check to see if anything | | | | aren't so stupid that they can't see that the |
| doesn't "fit", or if there are parts that are | | | | head unit still has its face attached.Hidden |
| cheap or flimsy. The truth is this: The | | | | faceplate:This is common for DVD players with |
| bigger name units tend to be better. Also, | | | | screens, and one unit that I used to own, the |
| the more expensive units tend to be better. | | | | Alpine CDA-7998. Basically, the face folds |
| This isn't always a big deal for everyone, | | | | into the head unit, and looks exactly like a |
| but I believe that build quality is very | | | | unit with the faceplate removed. Neat, but |
| important.Basic Head Unit Features:Power | | | | the unit is still vulnerable.In short, all of |
| output:Most head units have built-in | | | | these tactics are imperfect. Pick the one |
| amplifiers. These drive the speakers. Some | | | | that makes the most sense to you, however |
| head units do not have internal amps, and | | | | most units only have a detachable faceplate |
| therefore, require the use of an external | | | | feature.CD Changer controls/Optional |
| amp. Head units without amps are usually | | | | equipment interface:This is a feature that |
| high-end models. Anyway, power is measured in | | | | allows you to connect other peripherals to |
| WATTS. We'll talk more about watts later, but | | | | your head unit. These peripherals are often |
| for now, just see more watts as more volume. | | | | CD changers, digital music players, satellite |
| Most head units (unfortunately) are deceptive | | | | radio units, and video equipment. With this |
| about the power output. Usually, the power | | | | feature on your head unit, you'll be able to |
| output spec on a unit will say "50Wx4 MAX | | | | add additional capabilities to your stereo |
| output". This means that when the laws of | | | | system in a convenient way. However, most of |
| physics are on your side, it's a clear day | | | | these interfaces are only compatible with the |
| everywhere in the world, the planets are | | | | same brand. In other words, you'll need an |
| aligned, the bass hits really really low and | | | | Alpine head unit with the Ai-net interface |
| hard, and for about a tenth of a second, | | | | connected to an Alpine CD changer with the |
| yeah, your head unit will put out 50Wx4. | | | | Ai-net interface.Remote Controls:Some head |
| However, most of the time, your head unit is | | | | units have remote control capability. This is |
| probably putting out a quarter of that. It's | | | | a handy feature because you can control the |
| not that the head unit manufacturer is lying, | | | | headunit without taking your eyes off of the |
| it's just that they are exaggerating the | | | | road.OK, so these are some of the features of |
| truth, AND MOST PEOPLE DON'T KNOW BETTER. So, | | | | head units. Now, let's look at the specs of |
| anyway, many people put a lot of importance | | | | specific types of head units.Tuner |
| on a head unit's power output. I don't | | | | Features:Most head units have AM/FM |
| because head unit amps suck, and no serious | | | | capability built in. Check out this |
| car audio person uses the head unit's amp | | | | information on getting the best AM/FM |
| anyway. Most head unit brands have about the | | | | performance possible.Presets: This feature |
| same power output anyway. 9 times out of 10, | | | | allows you to save your favorite radio |
| an aftermarket head unit will put out more | | | | stations, and instantly recall them at the |
| power than your factory head unit, and as | | | | push of a button.HD Radio: A new radio format |
| such, will sound better.RCA Preouts:These are | | | | that is close in sound quality to CDs. |
| used to connect external amps to your head | | | | Basically, a radio station broadcasts their |
| unit. These are the same red and white cables | | | | usual programming, but with an additional |
| that you use for your home system. Basic head | | | | signal that can be received by units with "HD |
| units usually have one set of preouts (front | | | | radio" capability. The availability of units |
| left, front right). Some head units have two | | | | with this feature is still small, and most |
| sets (front left, front right, rear left, | | | | radio stations haven't yet embraced the |
| rear right), but most decent head units have | | | | technology. I do expect this technology to |
| 3 sets (front left, front right, rear left, | | | | take off, however because the sound quality |
| rear right, subwoofer left, subwoofer right). | | | | is better, and not everyone wants to pay for |
| One quick note about subwoofer outputs: | | | | satellite radio.RDS: AKA "Radio Data System". |
| Sometimes they're called "non-fading" outputs | | | | A new feature for FM radios. This technology |
| because they are not effected by the head | | | | makes it possible for radio stations to |
| unit's fade control (front to back balance). | | | | transmit text to your receiver. This text can |
| If you're not planning on adding an external | | | | be used to show the station title or the |
| amp, you don't need to worry about RCA | | | | artist name, and other information.FM |
| pre-outs. If you want to add an external amp | | | | Sensitivity: The ability of your unit to tune |
| (or amps), I would always recommend getting a | | | | into a weak signalFM Selectivity: The ability |
| unit with three pre-outs.RCA Pre-out | | | | of your unit to reject interference from |
| voltage:Usually this spec is next to pre-out | | | | other stations.FM Stereo Seperation: The |
| spec. It is measured in VOLTS (which we'll go | | | | ability of a tuner to recreate the proper |
| over later). Basically, the higher the | | | | left/right channel sepearation.CD |
| voltage, the LOUDER the music will be at your | | | | Players:CD-R/CD-RW Playback: This feature |
| amp. Don't look at this as "free power" | | | | guarantees that your unit will play a CD-R or |
| because it is not. In addition, the higher | | | | CD-RW that was made with a CD recording |
| the voltage, the less noise that will be | | | | device.CD-Text: This feature displays CD text |
| introduced to your system. Again, this spec | | | | information that is encoded on some CDs. This |
| doesn't matter if you don't plan on using an | | | | information includes artist names, song |
| external amp. If you do plan on using an | | | | titles and album titles.MP3/WMA/iTunes |
| external amp, try to find the HIGHEST voltage | | | | Playback: This spec assures you that certain |
| you can. 2 volts is basic, 4 is standard for | | | | digital file formats can be played back on |
| a good unit, sometimes you'll see units with | | | | certain units.ID3 Tag Display: Displays text |
| 5 volts. I know Eclipse units have 8V(!) | | | | (such as song title and album name) encoded |
| pre-outs. In short, more voltage=less noise | | | | into MP3 files.DAC: Digital to Analog |
| and cleaner sound.Digital time | | | | converter. This device takes the digital |
| correction:This is used to simulate a perfect | | | | signal from your CD, and turns it into an |
| stereo environment. If you're at home | | | | analog signal for your amp. The better your |
| listening to music, you want to situate | | | | DAC, the more "real" your sound will be.CD |
| yourself in the middle of the two speakers to | | | | Frequency Response: The range of frequencies |
| get the best sound. The same is true in the | | | | that the CD player can reproduce. It should |
| car, EXCEPT that it's a hell of a lot more | | | | at least cover the 20hz-20,000hz |
| difficult. Usually, the passenger side | | | | range.Electronic Shock Protection: This |
| speaker will be farther from your ear than | | | | feature prevents your CDs from skipping. If |
| the driver side. Since sound travels fairly | | | | your head unit doesn't offer this, don't buy |
| slow (comparfed to light), you'll have one | | | | it. However, most players have it, and |
| ear receiving a portion of sound before the | | | | technology has gotten pretty good lately, so |
| other ear. The digital time correction delays | | | | it's unlikely that you'll have any problems |
| the music slightly so your ears will be | | | | with skipping.Signal to noise ratio (s/n): A |
| perceiving the same music at the same time. | | | | measure of how well a CD player silences |
| This is a very important feature if you are | | | | noise. The higher the rating, the less |
| planning an SQ system.Crossover:This feature | | | | noise.Zero Bit Detect mute: When the CD |
| is incorporated into many components in a car | | | | player detects a series of 0's on the CD |
| audio system. If your head unit doesn't have | | | | (such as between songs), it will |
| it, don't worry. Just be sure your amps have | | | | automatically mute the output. This feature |
| it. Basically, this makes sure the right | | | | isn't really important, but is often |
| speakers are playing the right sounds. I will | | | | advertised.Oversampling: The CD Audio format |
| go into more detail about crossovers | | | | has a resolution of 16 bits, with a sampling |
| later.Equalizer aka EQ:This feature allows | | | | rate of 44.1khz. What the hell does that |
| you to tweak the sound. The most basic EQ is | | | | mean? I really don't know, but think of a |
| a two-band, and controls BASS and TREBLE. | | | | digital picture. Zoom in really close to this |
| Some head units have 3-bands, BASS, MIDS, | | | | picture, and you see pixels. Think of each |
| TREBLE. More advanced head units have 5-band | | | | pixel as a sample. When you increase the |
| EQs. If you are serious about tweaking your | | | | pixels, you increase the sharpness and |
| sound to perfection, you won't use your head | | | | quality of the picture. When a CD player has |
| unit's EQ; You will get an external unit, and | | | | oversampling, it takes the 44.1khz, and turns |
| some of these units have 30 bands! I will go | | | | it into a bigger number. More samples=More |
| into much more detail about EQs later.Theft | | | | realistic sound. Confused? I know. I am too, |
| Deterents/Security Features:There are a few | | | | but a unit with oversampling will sound |
| options when it comes to head unit | | | | better than one without. Of course, the good |
| security:Detachable Faceplate:The most common | | | | news is that pretty much every unit these |
| method is a detachable faceplate. Basically, | | | | days has this feature.Tape decks:Auto |
| you remove the faceplate of the unit (where | | | | Reverse: A feature that will automatically |
| the screen and controls are), and the unit | | | | play the reverse side of a tape at the end of |
| won't function. This will deter thieves, but | | | | a side.Dolby noise reduction: There are many |
| please don't leave the faceplate in your car. | | | | Dolby technologies incorporated into tape |
| Thieves know most people do this, and will | | | | decks. Most of these features exist to lower |
| still break into your car, find the faceplate | | | | tape hiss, and raise the signal to noise |
| and steal your head unit.Password:Some other | | | | ratio.Frequency response: Again, the |
| units have a password function. When the unit | | | | frequencies the tape deck respond to. Normal |
| is disconnected from power, then reconnected, | | | | human hearning is from 20 to 20,000 hz.Wow |
| the unit will require some sort of password. | | | | and flutter: This spec tells you how stable |
| The unit will not function until the password | | | | the tape deck playback speed is.Now that you |
| is provided.Key CD:A few units use a key CD. | | | | know some of the features of head units, you |
| Basically, the first time the unit is used, | | | | are ready to buy the right unit for YOU.Alan |
| the unit will ask for a key CD. You insert | | | | Bayer is an entrepreneur and Car Audio |
| any CD, and the unit will now designate that | | | | enthusiast. He currently resides in some lame |
| CD as the key CD. If the power is | | | | suburb in northern California.He owns an eBay |
| disconnected, the unit will ask for the key | | | | business and the website also have a |
| CD before it will function again.Black out | | | | newsletter at my website. Check it out! |