Before you start to upgrade your car audio sytem, you need to understand how each component in the system works and how it interacts with the other components. You will then be able to allocate your budget in the most appropriate areas to best improve your system.

First of all, the basic components of an audio system.

HEAD UNIT - reproduces the audio signal from the music source.

AMPLIFIER - amplifies the audio signal produced by the head unit.

SPEAKERS - converts high and low frequency audio signals from the amplifier into audible sound.

SUB WOOFER (bass speaker) - reproduces the sub 200Hz audio signals into sound.

HEAD UNIT - this is the heart of all audio systems. It is responsable for reproducing the sound from the original music source, ie. radio, cd, usb, ipod etc. if this signal is of poor quality, then no matter how good your speakers are, the sound quality will still be poor. For this reason, it makes sense to buy the best head unit that you can afford. Buy a brand that is well known (alpine, sony, kenwood,  jvc, panasonic, pioneer, clarion, blaupunkt) cheaper unknown brands may offer lots of functions and are fine if you only want to produce a noise, but if you want quality music, then you need a quality brand.

AMPLIFIER - as the name sugests, this amplifies the audio signal so that you can hear it at high volume. The basic amplifier is contained within the head unit, (another reason to buy a good one) most head unit amps are around 50watt output per channel. This will produce a good quality sound at lower volumes but as the volume increases, so the sound will gradualy deteriorate or distort. If you want to retain a good quality sound at higher volumes then a seperate amplifier is the answer. These are much more powerful and can produce quality sound at all volumes, but again it is important to buy reputable brands. A big misconception with amplifiers is that a 200watt amplifier will be twice as load as a 100watt amplifier, infact doubling the wattage only increases the sound output by about 10%. Amplifiers are rated in watts as an output, usualy stated as an RMS output figure and a MAX output figure. The RMS figure is the true output figure and is measured using a mathematical equation, the MAX output figure is basicly made up by the manufacturer and has no real relevance. As a rough guide to find the true wattage of an amp is to see what the fuse in the amp is rated at and then multiply that by the voltage it runs at, so if the fuse is 20AMPS and the car runs at 12VOLTS then 20 x 12 = 240WATTS

SPEAKERS -  probably the most complex part of an audio system, a pair of speakers can vary in price from just a few pounds upto as much as a thousand pounds. The difference in quality at the higher end of the market may only be appreciated by true audiophiles, but at the lower end of the market the difference in sound quality can be quite amazing. As with amplifiers, speakers are measured in  watts, but this is measured as an input value rather than an output value. So a speaker rated at 100WATTS RMS means it will withstand 100WATTS input  from the amplifier without suffering any damage. A speaker can only output the same amount of WATTS that is put into it from the amp, so a 300WATT speaker running on a 50WATT amp can only output a maximum of 50WATTS. A high wattage speaker will have a strong magnet and so needs more watts to make it work properly, a 600WATT speaker will not work properly if running on a 50WATT amp. This means it is important to match the speakers output to the amplifiers output to get the best performance from both components.

SUB WOOFER - probably the thing that most dramaticaly changes an audio system, the subwoofer gives a totaly new sound dimension.  Bass sound is not only heard, but also felt, as its low frequency sound waves reverberate round your body. Bass sounds are what cause distortion in speakers as they can make the speaker cone move to its physical limits. If you add a subwoofer to your system, then most of the bass can be directed to the sub rather than the speakers, which means the speakers can then run at higher volume with less distortion. You do not need a huge 15" double bass box that shakes the car, you will be amazed what difference even a small 10" bass box will make to your system.