MikeG - I used to be an installer, so lemme shed some light on a couple things. Firstly, like one guy said, everyone's an expert and everyone has their favorite brand of equipment. For quick reference on what will fit, Crutchfield.com is a pretty good tool. Their equipment is a little pricey, but their customer service is fantastic. Anyway, some important things to note: Buy a book on car audio and read it. It will shed light on a lot of things. There's a lot more to understanding power output/input than you'd think. For example, your head unit DOES NOT actually deliver 25x4 Watts. Manufacturers rate these by powering the unit in the lab with nominal voltages (14.4-16.0 V). The literature in better quality brand head units and amps will give you two readings. The one on the box says "1400 WATTS!" and in small print you'll see (1400Wx1 @ 1ohm assuming 16 VDC input). In actuality, at 12.4V (which is around normal vehicle voltages) the efficiency of an amp (unless it has what is know as a "regulated power supply") decreases exponentially. Also, most people dont place 1 Ohm loads on their amps - and most amps cant handle such a load for long. Same goes for your head unit. 25x4 with 12VDC is actually 5-10 watts.

An important note: Most companies make a wide range of componets. Also, most companies make varying degrees of quality "lines," because they cater to a wide range of $ people are willing to spend. Pioneers higher quality stuff is called "Premier" and so on. Also, I have found that most companies make one or two good items. No company I have found had excellent everything. Anyway, some better companies include what people call a "birth certificate" with mid to higher end amps such as Precision Power, Kicker and MTX that show EXACTLY what THAT amp did in the lab, such as WATTAGE OUTPUT @ 12VDC at 4 Ohm: Rated 50x4 ACTUAL 43x4.

So, amplifiers depend on four things to determine actual clean power output: Power Voltage In (also affected by current flow i.e. do you have the recommended guage feeding the amp and is your ground solid), Line Voltage In (is there good audio signal fed to the amp from your head unit or processor), Ohm load from speakers (check out JLAudio.com's sub wiring tutorial which shows wiring of 1-6 subwoofers with both single and dual voice coils), and lastly heat: Is there adequate air exchange/cooling. Most people do not concern themself with this until their amps go into thermal protection).

Speakers and Amps: Someone told you that if you supply 50W rated speakers with a 60W rated amp, the speakers will blow. This is not correct. The fastest way to destroy speakers is to underpower them. The volume is lower, so people turn it up, which causes speaker distortion - the killer of speakers. Providing a relatively higher power to speakers allows them to play more efficiently. For example, if you have a speaker that desires 50W RMS (average) input, having an amp that delivers, say, 70W RMS will most likely NOT damage it. The speaker will pull what it needs for the volume you desire and the volume level dictates the demand it will place on the amp. Think of it like this: Let's say your lungs are the speaker and a straw is your amp. If you try to breathe through a coffee straw, you are going to strain and it will not support you. You will put out maximum effort but eventually lack of air exchange will cause you to fail. Likewise, if you have a regular size straw (MATCHING speaker to amp wattage), you will work well, but if you need a sudden demand for air (want volume loud, but not distorted) you will still not be able to draw large amounts of air. But, if you have a LARGER diameter straw, you can draw as much as you need. If you only desire a small amount of air, (smaller wattage demand will be placed on your amp), you will not have to work much at all to breathe in. With a larger straw (amp), if you need large amounts of air flow, it will be readily available and you will not have to work to inhale. Get the idea? That being said, note that applying an amp with larger ratings than the speakers depends on the SIZE of the speakers. The smaller the speaker, the more delicate. Do not feed a tweeter rated at 30 Watts, 500 Watts. Conversely, if your subwoofer is rated for 500 Watts, feeding it with an 800 Watt amp will help you get the most out of the sub. I'm beginning to get carpal tunnel syndrome so I'll wrap this up:

Look to comparison tests in car audio magazines and books when shopping for equipment. If you buy from a retail car audio store ask them if they work on commission. If they do, leave. All car audio stores sell different brands and their brand is always the best. If you're having someone install your system, ask to hear THEIR system. A good installer will happily show off his work in his own car. If it sounds like crap, yours will too. That being said, most car audio components are pretty easy to install yourself - and you'll save A LOT of $. Get a friend to help you AFTER you've educated yourself on basics. If any part of this friend's car audio system incorporates Duct Tape, DONT let them help. DONT skimp on wire and RCA cables! This is a largest weak link seen in stereo systems! Use 1 size larger power wire than called for and if you have a stereo of 300 watts or more, BOLT the ground wire to the FRAME. Any other questions, just ask.

 

To ACTUALLY answer your question, your aftermarket head unit will power aftermarket speakers, regardless of what they call for (50W, 100W). However, you will not achieve the volume you could nor the clarity - and you will slowly damage the speakers. Save a few more bucks and buy a good 4-channel amp rated around 100x4 Watts for 4-Ohm load (the speakers you'd buy for your car ARE 4 Ohm). I could complicate your decision by discussing parallelling speakers and such, but go with the above suggestion. You should be able to find a 100x4-ish watt amp for about $300-$400. Each REAL watt should generally cost $1.00. Anything more and you're paying for a company to send their CEO to Jamaica. Look for an amp with a regulated power supply. Ebay is actually a good place to shop, as you'll find wholesale prices. Make sure the seller has a good rating. If a price is too good to be true, it is.

 

i went to the crutchfield link, http://www.crutchfield.com/cgi-bin/S...01&vehicleid=0 , I picked everything out, and it tells me I have 6x9's in the front doors, and 5 1/4 in the back.... so i look some more and it tells me none of the 6x9's they carry fit!! but all of the 5 1/4's fit fine.... is the 6x9 in the front door a 'shallow mount' or what?

 

It shouldn't be that shallow. You'll find the factory speaker is a 6x8 - which is the same thing as a 6x9 with holes more proximal to the surround of the speaker. Get the largest speaker you can fit. Measure the depth with the window down and look as speaker dimensions. Dont worry if holes dont match up exactly - they rarely do. Get some self-tapping steel screws from Lowes, they work well. Make your own mounting holes. Do NOT get a 5 1/4" speaker for the front just because it will fit. You'll get 500 times better sound from a 6x9.