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