The Head Unit: Digging Deeper Into Car Stereos

If you just joined my column, we’re knee-deep into discussing car stereos and how they work. In the last segment, I provided a quick overview of the parts that comprise the system. We talked about the head unit, speakers, power amp and preamp, and other ancillary devices that can be connected to it. But, as I’m sure you can imagine, there’s a lot more detail to uncover.

Today, we’re going to take a closer look at the brains of the system. You might remember my mentioning that the head unit is the component that controls everything else. I’ll describe the parts that comprise it, including the radio tuner and the CD player (or cassette player, for those of you who are a decade behind the times).

The Audio System’s CPU

Your computer has a CPU that controls other parts, such as the disk drive, motherboard, and video card. That’s the manner in which you should consider your car stereo’s head unit. In essence, it’s the command center of the audio system. This wasn’t the decision of the car manufacturers, but rather the competition among car stereo companies such as Kenwood and Blaupunkt.

The Tuner

The purpose of the tuner is the receive radio signals which can be output through the speakers. A long time ago, vehicles came equipped with antennas that were connected to the exterior to help improve the clarity of the signals. Today, those antennas are usually built directly into the windshield.

CD And Cassette Components

If you’re driving a vehicle that has a cassette player within the head unit, you may have noticed that it’s prone to failing. They can malfunction because they use multiple moving parts. By definition, the moving parts experience wear and tear, eventually failing to work. CD players also have moving parts and can fail after several years of use.

It’s important to note that while both the cassette and CD player are parts of the head unit, they can malfunction while the tuner continues to work properly. Further, a technician can usually repair both types of players.

Pumping Up The Volume

Each of the above components - the tuner, CD unit, and cassette player - generates a signal. Without the amplifier, those signals can’t reach the speakers. In an upcoming article, I’ll explain in detail how the power amp works. For now, understand that the signals must travel through the amplifiers (first the preamp, then the power amp) prior to reaching the speakers. It’s the power amp that ultimately “jumpstarts” the signal into a range that we can hear.

Frankly, you may never need this information. But, the more firmly you grasp how every part in your vehicle works (and how it can be repaired), the better.

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Overview Of Your Car’s Audio System

For enthusiasts, what I’m about to describe will seem elementary. To be fair, car audio systems have a huge base of aficionados that spend entirely too much time on their pride and joy. That said, I’m a realist and understand that the experience you have while driving is directly linked to your stereo (or, rather, the music coming out of it).

In this article, I’m going to give you an overview of the components which comprise your car’s audio system. We’re going to explore the speakers, the amplifier, radio, and supporting devices. I can imagine I’m going to receive angry emails from devotees who’ll argue that I’ve left a lot out. Remember, this is an overview for those who don’t spend half of their income on stereo equipment.

Radios

All car audio systems that are installed at the factory have a radio. Sometimes, it’s called the “head unit.” While you might think that the radio is only good for tuning into bad DJs and “talking heads,” it actually runs the entire show. All of the controls, including your bass, treble, and volume, begin with the head unit. What’s more, it encases the supporting devices, which we’ll get to in a moment.

Amplifiers

You’ve likely overheard someone mention that they’re planning to buy an amplifier for their car stereo. In truth, your audio system already has one; the person you overheard is probably planning to buy a unit with more power. All amplifiers - factory installed or aftermarket - come with 2 main parts: the preamp and the power amplifier. Most of the time, the entire unit is installed in a different location from the radio.

Speakers

Your car’s speakers basically receive the signal generated from the power amplifier before delivering it to you. Speaker design is more complicated than a lot of people think, so we’ll leave that discussion for another time. For now, it’s enough to understand that the system uses woofers for the low-range frequencies, tweeters to deliver the high-end, and drivers to take care of everything between the woofers and tweeters.

Supporting Devices

There was a time when your radio was all you had to work with. Today, you can plug a number of different devices into the head unit; some of them are already installed at the factory. For example, you might have a GPS unit or CD changer installed. Also, keep in mind that more vehicles today are coming from the factory floor already equipped with MP3 players. All of these devices need the head unit - the brain of your car’s audio system - to function.

Only The Basics

For the average motorist, what I’ve just described is enough to get you by. You’ll be able to make reasonably educated decisions regarding the type of components you’d like to have installed. For the stereo enthusiasts who are groaning over this bird’s eye view, be patient. In a future column, we’ll dig into the details.

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