When buying speakers it is important that they are suitable to use with your amplifier or head unit. If they are not suitably matched the speakers could draw too much current and damage equipment, or not enough current, and the speakers themselves will be damaged.
Do I need new speakers?
Are you using an amplifier?
If not you probably won't need better speakers, and a good quality head unit will eliminate all of your distortion problems, especially in higher end cars. If your speakers are paper coned and old, then it is advisable to change them.
A lot of car audio shops will plug in a cheap head unit to your car and then make it distort, and suggest you buy new speakers. This is not the case. Did they use a good head unit? Probably not!
A good quality Alpine head unit in a car such as a Mercedes or BMW will not need a new set of speakers.
If you are installing a better head unit into an old car with paper speakers, then you would obviously want some new ones. It is advisable to test your new head unit with your old speakers before buying new ones.
If you’re installing an Amplifier:
It's advisable to upgrade your speakers.
A lot of people fail to upgrade the front speakers in their cars. If you think about this fact though, where do you sit in a car? The front!
Even though it is difficult to amplify the front of a car it will be greatly beneficial. If you are closer to the speakers they will be louder, and less prone to distortion, so you won't need to spend as much on them.
For the best sound a component speaker system would be used.
These have tweeters to play the High frequencies, and the main speaker plays the mid range. A lot of speakers come with a tweeter already built into them, but for superior sound the tweeters must be positioned nearer to ear level, rather than down low.
If you are installing these you will need crossovers. These often cause a bit of confusion, but are actually very simple to fit. The power from you amplifier source be it a head unit or an Amp goes to the crossover box. Next you join wires to the speaker, and the tweeter.
What does the crossover do?
This is actually a filter made up of capacitors and inductors. When the input is filtered it can be directed towards the right speakers. You wouldn’t want lots of bass being sent to your tweeter as it would break, and also you wouldn’t want to send a load of high pitched sounds to the main speakers as it wouldn’t be able to play them, and would sound terrible.
Where to put the crossover?
The crossovers are usually quite small. These can be put inside of the doors, if these are front speakers, or even beneath the dashboard. If they were rear speakers then the boot would be the best place for them.
Which speakers do I need?
A lot of speakers now come with super stiff cones made of composite materials to reduce distortion. Vibe and infinity make a lot of high-end powerful speakers. For better quality but not necessary such high power, consider the alpine and pioneer ranges.
The alpine Type-R has high quality and high power, but is very expensive.
Of course these are not the only speakers to consider, these are just used as examples of what I have tested myself. You must remember that Sony car audio is not the same as Sony home audio. The quality is not quite so good. Their X-plod sub woofer range is actually quite good though, and unique in the fact that they do not use round cones.
Your sub woofer is just a giant speaker design for bass. It is built a lot stronger and can handle a lot more power. Aim to get a sub with a high RMS power.
As a sub gets larger its response will get slower. If you are after fast punchy bass then a 10” will be suitable. If you want big bass then a 15” will be good.
Don’t forget that you can have one of each, to hit every frequency you want.