In the last decade or so, automakers have placed increasing importance on in-car entertainment systems.
The core of these technologies has always been the audio system -- the noisemaker, if you will. What appeared in our dashboards more than 50 years ago as a tube radio the size of a breadbox now rivals the technical complexity of a 767.
This series is not written for aficionados, but for the average consumer who wants to gain a working knowledge of the basics of car audio design. By the end, we trust you'll have a better understanding of this technology.
What are the basics of car audio systems? How does each of the separate components operate? In the series to follow, we'll address these questions in a user-friendly and approachable format.
One note before we get started. This series will cover only original equipment manufacturer's (OEM) systems, the ones that come in your car from the factory. Unfortunately, in our limited space for this column, we're unable to deal with the vastness of the car audio aftermarket, which changes every day. Perhaps in future
A car audio system is composed of four different groups of components. These are: head units, amplifiers, speakers, and auxiliary input devices (such as a CD changer or a graphic equalizer). Let's take a look at each.
The Head Unit
This is the heart and soul of your system. Without this component, your car audio system can't and won't work. The head unit, or, more simply, the radio, is the central processing device in the system.
Consider the way your mind works. Let's say you want to shout at somebody. Your brain tells your vocals chords to raise to a certain volume level. The words form in your mind, your mouth opens, and out comes a shout.
In a similar fashion, the head unit controls all the functions in your car audio system. Music too loud? Turn down the volume. Too soft? Turn it up. Want more bass? Add bass input.
All changes and controls come through the head unit. If you could see behind the radio in your dash, you'd find a dozen or so wires going off in all different directions to other systems in the car. These are like the nerves in your body, transmitting signals to and from the various components.
In addition to volume, bass, etc., the head unit may contain other systems within its casing. These include: tuner, cassette, equalizer, CD or amplifier. Some of these words look familiar? That's because we mentioned them above.
You see, in a home music system, where you have much more room, many stereo setups will include a separate box for each one of these components -- CD, cassette, etc. You may have a home system like that yourself. In a car, with its space limitations, these components are often crammed into one box -- the head unit. This depends upon a number of factors, such as heat, space, cosmetic design and other concerns, and every car is different.
The Amplifier
All car audio systems have an amplifier, even if it's a small one (and based upon the factory systems we've been listening to lately, a lot of them are really dinky).
Occasionally the amplifier will be attached to the rear of the head unit; however, in most systems it is hidden elsewhere in the car to better dissipate heat.
Signal amplification is actually a two-stage process, handled by two separate components. These are the preamplifier and the power amplifier.
The preamplifier (preamp, for short) is like that little voice whispering in your ear not to eat ice cream at midnight. It's a very tiny signal coming directly from the radio (in fact, the preamp resides inside the head unit). Whether it's reproducing a cassette signal, a CD signal, or an FM broadcast, the preamp puts out a signal inaudible to the human ear. This is where the power amplifier takes over.
It's the power amp's job to take the signal from the preamp and boost it into the audible range. We'll cover this in more depth in our Amplifier column in this series. Again, because of heat, most amplifiers are located away from the head unit.
The Speakers
The speakers take the boosted signal from the power amp and deliver it to your ears. The way loudspeakers work is a fascinating process and will be dealt with at length in our Speaker column in this series. Essentially, loudspeakers transform electrical energy (the amplified signal) into mechanical energy (the motion of the speaker cone).
For now, know that all sound is vibration. When you snap your fingers, this action sets off a chain of frequencies in the air that eventually vibrate the membranes in your eardrums. You hear: "Snap!"
Sound energy is measured in wavelengths, known as hertz, and goes from 20 to 20,000 cycles. A cycle is the distance from the top of one wavelength to the top of the next.
Traditional loudspeaker design calls for three components to reproduce sound energy: woofers, tweeters and midrange drivers.
As the name implies, the woofer reproduces the lower frequencies, such as a large dog barking. The tweeter, also aptly named, replicates the higher register -- a bird singing. The midrange handles the frequencies in between.
Car audio manufacturers use various assortments of these drivers to achieve the sound they want. We'll go into this at length in a future installment.
Auxiliary Input Devices
Components such as CD changers and equalizers, not to mention cell phones, navigation systems, MP3 players and many of the newer technologies, interface with the head unit for amplification and signal processing. We'll delve into this area in our final installment.
We hope this helps you gather a basic understanding of car audio technology. Look for an in-depth view inside the head unit in our next column.
