Car Audio Systems

The audio system installed in today's customised cars are becoming increasingly more important. Choosing the right system for your car is predominately determined by music taste, financial restrictions and space.

Car Audio Subwoofers

Car audio subwoofers are responsible for the bass frequencies of your car audio system. They are typically large, usually greater than 8 inches, and have a frequency response that falls below 100Hz. To get the best from your car audio subwoofer it should be fitted into a sealed enclosure. This could be as simple as the boot space of your car to a specially enclosure that is tuned to give the best performance.

Picking a subwoofer for your car

When choosing a subwoofer for your car there are several things to bear in mind before you start.

Enclosure type:

The enclosure type is directly related to the size of you chosen subwoofer with ported enclosures being about 30-40% larger than their sealed counterparts. In some cases where space is at a premium it maybe better to choose smaller subwoofer and use more power.

Power Handling:

This is the amount of power that the subwoofer can withstand if it is used continuously. It is typically quoted as the RMS power and should not be confused with peak power. Peak power is simply a measure of how much power can be generated in short bursts.

If a subwoofer quotes the RMS rating as 100 Watts then you will need an amplifier with an RMS output of no more than 100 Watts RMS. If the output is any higher then you risk damaging the subwoofer.

Sensitivity:

This is a measure of the speaker loudness at 1 metre for a given power input. You should be careful when comparing these values since some manufacturers use a shorter distance when calculating this value giving a higher value.

Fs:

This is the frequency that the speaker naturally resonates ie the peak output frequency when the speaker is not mounted in an enclosure. The lower that this frequency is the lower the subwoofer will play naturally.

X-MAX:

This is a measure of the amount of movement that the voice coils have. The voice coils are responsible for moving the speaker in and out. The more that these coils can move the larger the volume of air that can be displaced will be.

BL:

This is related to the force generated by the voice coil. The greater that this value is the greater the control over the cone the voice coil will have.

Midrange Car Speakers

The midrange speakers are typically smaller 8 inches and have a frequency range of approximately 300 Hz to 5 KHz. These speakers are responsible for reproduction of the heart of the music such as instruments and vocals. The midrange speaker is designed to provide greater efficiency and therefore does not require as much power as a subwoofer.

Tweeters

Tweeters are the smallest speaker components that you can buy. They are used to replicate the highest frequencies in your system care must be taken when placing them due to their very directional nature.

2 Way, 3 Way, 4 Way and Component Car Speakers

As most people are probably aware car speakers can be bought in pre-determined packages. The individual parts have been chosen to give optimum performance at a particular cost. These are discussed below.

2 Way Car Speakers

Two way or co-axial car speaker systems give a reasonable performance using two speakers. They use a dedicated crossover to distribute the sound between a low-mid range larger speaker and a mid-high range smaller speaker.

These speakers are available is a range of shapes and sizes.

3 Way Car Speakers

Three way or tri-axial car speaker systems have dedicated speakers for each frequency range. They have a large woofer for low bass frequencies, a dedicated midrange for vocals and instruments and a tweeter for the high range frequencies.

These speakers give an excellent full range response.

4 Way Car Speakers

As the name suggests these speakers comprise of four components. They often add a separate 'super tweeter" that extends the frequency range above 20 KHz. This will feature will offer little advantage to many people since the majority of peoples hearing only extends to 20 KHz at best.

Car Speaker Component Systems

This is used to describe a system that uses a set of pre-chosen components that are fitted separately. Typically mid range speaker will be mounted to the side, usually in the door panel, and tweeter will be mounted in the dashboard. Each speaker is driven via a separate crossover which distributes power between the low-mid and mid-high range speakers.

Crossovers

A crossover is used to distribute the audio between the various speakers in your car audio system. They are available in two varieties which are active and passive.

Active crossovers are placed between your car stereo output and the amplifiers feeding your speakers. They offer many advantages over their passive counterparts. Most crossovers offer the ability to alter the frequency ranges and levels dedicated to each amplifier. The main disadvantage is that they are more expensive than their passive counterparts.

Passive crossovers consist of capacitors and inductors. A capacitor's impedance reduces as the frequency increases whereas an inductor's impedance increases with frequency. These characteristics can be used to filter the frequencies fed to each speaker in the system. The choice of these components is very simple and can be found using some simple equations.

The advantages of a passive crossover is that they are very cheap, easy to build and can be tailored exactly to your requirements.

The disadvantages are that they have to be placed between the amplifier and the speaker. This introduces a loss in the system which means less power to the speakers! Another disadvantage is that the crossover is tailored to a set of speakers. If these speakers are changed the crossover may require redesigning.

Equalisers

An equaliser enables the frequency response of the system to be 'tweaked'. It allows adjustment of various frequencies across the audio spectrum for example 20, 40, 80, 160, 315, 630 Hz and so on.

The purpose of an equaliser is not to fix problems with the system such as too much mid range or too much bass. If this is the case these issues should be addressed by reducing and increasing the appropriate amplifier gains. An equaliser should be used to flatten the audio response of the entire system. This means that if it is used correctly the gain/cut controls should remain very close to the centre.

Car Audio Amplifiers

There maybe several amplifiers in the car audio system, each one responsible for a chosen frequency range. The purpose of the amplifier is to reproduce the audio input faithfully with as little distortion as possible but at a higher output power. The ability of the amplifier to do this is given by the total harmonic distortion (THD). A THD of less than 1% will be barely detectable by most people.

Other important things to look for when buying an car audio amplifier are as follows;

Power Bandwidth

This is the frequency range that the amplifier can be used over.

Signal to Noise Ratio

This is the amount of background noise that is generated within the amplifier by its components. All electronic components generate noise which is usually detected as a 'hiss' when the no music is playing and the volume level is high. The higher this value is the better.

Power Output Rating

This is the power that is produced at the output terminals of the amplifier. It is normally rated at its RMS. However, sometimes only the peak value is quoted. For comparison this value should be halved.

Bridged Power

Some amplifiers allow to single outputs to be combined giving a single output of at least twice the single output power.

Car Audio Capacitors

Fuses

This is one component that is often overlooked but is very important and will protect your car audio system in the event of an accident. Ideally the fuse should be located as close to the battery as possible. To choose the correct size fuse you will need to find out how much current each component in your system will be drawing. For instance if you have two amplifiers drawing 30Amps then you will need a fuse rated above and close to 60 Amps.

Understanding Amplifiers
http://www.electronixwarehouse.com/education/amplifiers/main.htm
Calculating Fuse Sizes
http://www.caraudiohelp.com/newsletter/fuse_size.htm
Equalizers
http://www.css.exl.info/eqs.html
Amplifiers
http://www.css.exl.info/amps.html
Designing Passive Crossovers
http://www.termpro.com/articles/xover2.html
2-Way, 3-Way & Component Speaker
http://www.electronixwarehouse.com/education/speakers/whatscomponent.htm
What's a midrange
http://www.electronixwarehouse.com/education/speakers/whatsmid.htm
Choosing the Right Amplifier
http://www.carausioresources.com/content/installation_tips/38/1
Car Subwoofers
http://www.caraudiohelp.com/car_subwoofers/car_subwoofers.htm
Car Audio Amplifiers
http://www.caraudiohelp.com/car_audio_amplifiers/car_audio_amplifiers.htm
Car Audio - Passive Crossovers
http://www.the12volt.com/caraudiocross.asp
Understanding and Designing Passive and Active Crossovers
http://www.termpro.com/articles/xover.html