Basic Upgrade Tips

Remember, people.... you only get what you pay for. If you spend $100 on your head unit (deck) then it won't sound like the person that spent $400. Just do the math! You get what you pay for like anywhere else. If you purchase decent middle-of-the-road price range equipment you can usually take it along with you when you decide to build a bigger system, but the cheap stuff usually gets dumped as it's no good. It's tempting to cut corners when you first get into this hobby but in the long run it doesn't pay.

TIP: If you are on a severe budget I recommend you look for a new cd deck with removeable faceplate (for security). You can pick up a JVC cd deck for instance under $200 bucks. You'll need some RCA cables ($25) to run to a subwoofer amplifier and 8 gauge power & ground cables. 1/2 of a 4'x8' sheet ($20) of 3/4 inch thick medite board (like particle board but very fine grain particles). Borrow a friend's table saw. Some 10 or 12 gauge speaker wire (not long). A tube of silicone and drywall screws ($10). A decent 12 inch subwoofer ($120-300). A 100-200wrms amplifier, preferrably with built-in low-pass crossover filter ($200+).

So... for under $600 plus your install time you can add some substantial BASS to your vehicle.

Replacing your factory "head unit" (the part in the dashboard) with an aftermarket unit. Essentially it doesn't matter which brand you prefer and basically anything over $180 will sound fairly good. Depending on the features you are looking for most of the time a decent head unit will run you around $200-500 bucks. One of the features that appeals to me the most, and this is what my Sony head unit has, is the ability to play a single cd in the deck itself as well as being able to control a 10 disc cd-changer installed somewhere else in the vehicle. This is a nice feature because you may have some friends in the car that want to try their cd or perhaps you just bought a new cd at A&B Sound and want to try it out. It's less of a pain to just insert it in the deck than to open the changer. You can save some cash though by buying an am/fm cassette deck with changer controller. The newer cd decks also have mp3 playing capability and with that you can have around 100 music tracks on a single cdr disc. Those decks are more expensive than regular cd decks.
Replacing your factory speakers. The newer vehicles seem to come with fairly decent speakers so unless they're crap or you've blown them up or they sound terrible you can usually leave them alone.
Add a pair of tweeters to the front speakers, either dash mounted (not preferred) or hidden in the dash or under the factory speaker grills. In car audio your "front stage" sound is very important and if your legs cover the speakers in the door panel then it will sound like more sound is coming from the back than the front. You want to try and emulate the sound you get at a live concert... coming mostly from the centre stage.
Add a subwoofer. There are many ways to approach this upgrade. It's cheapest to add a subwoofer to your factory stereo system that will make your ok sounding OEM stereo sound rich and full. You can buy ready made systems like Bazooka tubes with built-in amplifiers or you can make a system from scratch with a separate amplifier, separate wooden box which houses a subwoofer driver. Personally I prefer to make my own box to the subwoofer manufacturer's design specifications. Many of the newest subwoofers can be put into boxes with 1 cu.ft. of air volume or less so it won't take up very much grocery space. If you have a circular saw and a little bit of woodworking experience then you too can build your own system. There is great satisfaction in building your own.
If you go the subwoofer route you will need to upgrade your vehicle's electrical system. Anything over 100 watts rms (real power - not peak output!) will need at least 8 or 10 gauge power and ground wires preferably directly from the battery with a fuse at the battery. I run a single Rodek 2150i amplifier with a 60A fuse at the battery on 4 gauge (thick as your pinky) power and ground cables. The cables run straight from the battery under the vehicle and come into the passenger compartment through an existing rubber grommet. No need to drill holes in the vehicle's chassis here!
Upgrade your factory front and rear speakers and add a 4 channel amplifier to power them. You can easily make do with a 4x50 watts rms amplifier or 4x75 watts rms. Much more than that and you'll be deaf too soon. You'll need to run preferably 8 gauge power and ground cables directly from the battery to power it.
For running a subwoofer you will need to add an electronic crossover. This device takes the full-range audio signal from your head unit and separates the low tones from the high tones. The extra low tones are sent to the subwoofer amplifier and the high tones are passed along to the front/rear full-range speakers if you have an amplifier for those. Most people chose to run their front/rear speakers from the amplifier built-into the head unit, and use a relatively inexpensive crossover just for supplying the subwoofer with low frequencies. Some amplifiers have a built-in crossover as well. From experience, the external crossovers usually have better sound quality than what you get built into an amplifier.