Is Your car tech savy
The Media Center
The Head Unit
A high-end home audio system uses separate electronic components — a radio tuner, CD player, preamp, amplifier — connected by various cables. Since space is at a premium in a vehicle, automakers have to cram as many of these components as possible into one device: the head unit. Because of this, the head unit performs multiple duties, but its two main functions are controlling the overall system volume and the various audio sources in a vehicle.
When you look back at automotive history, AM radio was the only audio source in a car for years. Then came FM and tape formats such as 8-track and cassette. A CD player is now standard in most vehicles, and many factory head units can also receive Dab or Dab+. HD Radio has recently given AM and FM better sound and extra features, such as additional channels and information.
Head units can also be used to control media players like the iPod or navigate the content of a USB flash drive that's connected to the stereo system. Head units with Bluetooth audio can also play music that's streamed wirelessly from a compatible mobile phone.
Most modern head units offer some way to integrate portable music players like the iPod into a car's audio system and control them through the head unit. The most basic connector is the "aux-in jack." You plug an inexpensive accessory cable into the aux-in jack, which in turn connects to the headphone jack of an iPod or other music player. You operate the device using its own controls with an aux-in jack, although a car's head unit will adjust the volume. An aux-in jack also won't charge a music player's battery.
Car head units also play recorded material from various sources. Eight-track and cassette players had their heyday. Even record players briefly appeared in cars in the 1960s.
A compact disc player is the main non-radio audio source in cars today. Some head units can control remotely mounted CD changers. Head units that play both CDs and DVDs are also popular, since they let consumers play DVD videos on separate screens in the back — and in the front, provided the car is parked.
Many modern CD players can also play MP3 music files that have been burned onto a disc, which makes many more songs available. Most head units that play DVDs can also play MP3 files burned onto those discs. DVDs can hold significantly more files than a CD.
Some head units also have a built-in hard-disk drive that can store music files transferred from a CD or DVD. These disk drives range in size from 10GB to 30GB, with larger sizes allowing more music storage.
Many head units have a small, built-in low-power amplifier that can "drive" smaller speakers. This allows the audio system to be reduced to just a head unit and a few speakers. But better sound requires more power. So higher-end systems have separate power amplifiers that are mounted away from the head unit due to their size and the heat they generate.
The pre-amp takes data from a radio tuner, CD player or other audio source and slightly boosts it before sending it to the power amplifier. The power amplifier further strengthens that signal so it's powerful enough to move the voice coils of the speakers in the system. (You'll find more about speakers in a separate installment.)
In addition to controlling the system's volume, head units usually include basic tone controls such as bass and treble to tailor the sound to the listener's taste. Many audio systems also include signal processing that automatically adjusts the volume, depending on the ambient noise in a moving vehicle. Some high-end OEM audio systems also have a separate sub-woofer and sub-woofer level controls.
