1.) DIRECT REPLACEMENT SPEAKERS
Most cars have 4 speakers. You will find that manufacturers such as Kenwood and Pioneer do direct replacement speakers, that fit into the factory standard holes. These will better the sound quite a bit, make sure you go for 'Co-Axial' speakers, these are sectioned into 2 parts of the speaker for better sound.
2.) 6 X 9's
There was a fashion at one time to fit 6 X 9's into the rear shelf of your car. The 6 x 9's are able to offer more 'mid-bass' sound (as well as higher frequencies provided by other speakers in the car). The fashion was to cut dirty great holes out of your parcel shelf to fit them in. Not only does this get expensive if you want to by a new shelf when you sell the car (or build one out of MDF - handy andy's fave) but it only really adds to the rear fill sound in the car. Use 6 x 9's if you want a loud system, for quality use:
3.) COMPONENT SPEAKERS
These are 2 seperate speakers, normally fitted in the front of the vehicle to produce mid range and high range (through the 'TWEETER') sound. It might be necessary to make some room in your front doors for the speakers to go. Fitting Components will give you an excellent front sound stage. If fitted correctly (angled slightly towards the drivers ears) the sound stage should be like it is filling the car up from dashboard level.
Sub Woofers are the larger speakers which produce Bass. There are 2 main types:
a. Free Air - can be fitted to parcel shelf or ported sub-box
b. Boxed - require an enclosure (sealed or ported depending on manufacturers spec)
For the reasons of size, Subs are normally fitted into the boot of the car. Most require a box in which to fit them, if yours does not have one, check with the manufacturer as to what size box your sub requires. Box sizes are very specific to each sub, a wrong size box could make your expensive sub sound pants.
Many people choose to use multiple subs so that when they are at the traffic lights their car vibrates (normally Ford Orion drivers - or Novas). This is all a matter of choice.
WARNING: Using multiple sub set ups seriously encroach on your boot space!!!
If you try to run all your speakers off of your head unit, there will
a. not be enough power
b. Sound quality will suffer
Most people tend to fit Amplifiers which run straight off the battery and are linked to your head unit to increase the power signal of the sound. Most Amp's require RCA leads, check that these connections are available at the back of your head unit. If they are not, you can patch the sound to SOME amps by using the ordinary wire speaker outs (the AMP will require the ability for 'HI-LEVEL INPUTS' make sure you remember this!!)
Amps come in all shapes and sizes. Most people start by amping up their sub for more bass. It is important to match the power figures up.
XX IMPORTANT NOTE XX
When looking at power figures, look at the RMS figure, not the peak power figure. The peak figures are often over exaggerated and mismatching can result in a blown AMP/Speaker or just poor quailty sound.
6.) CROSS OVERS
What a cross over basically does is seperate the different levels of sound (I mentioned high end, mid range and Sub bass) and sends the RIGHT SOUND to the RIGHT SPEAKER.
Amps often have built in X-Overs to send bass signals to your sub. This can help keep the best sound and prevent the wrong ones going to the Sub and damaging it.
Passive cross overs are connected just before the speakers and are often used with the component sets mentioned.
Active X-Overs are used before the Signal is Amplified and seperate the sound to the correct amp. These are especially useful for multiple-amp set-ups.
6.) EXTRA GOODIES
If you are like me and love a gadget, you can fit some more advanced parts to your I.C.E system.
Sat Nav is a like an on-board route and traffic planner.
You can get T.V tuners and screens for either video, DVD, games consoles or even your lap top if you want!
There is really no limit to what you can do to your I.C.E. You can spend as little or as much as you want.