This is only meant as a simple guide for people who want to learn more about car audio. It is broken up into 3 segments: Cabin speakers, subwoofers, and Amplifiers. These explanations can get a whole lot more technical, but this is just to provide people with a good understanding of what to look for. Feel free to post any more questions, I'll try and answer them and then edit this post to include them. Cabin Speakers Q: What's the difference between Coaxials and Components? A: This is a really common question for people just getting into car audio, one that some people are afraid to ask . Component speakers usually come in 2 pairs: a pair of midrange speakers and a pair of tweeters. The speakers are completely seperate, and are dedicated to a certain range of frequencies so that music can be recreated as life-like as possible. Coaxials can include a basic midrange and tweeter, but can also include a supertweeter, etc. This is what determines the number when you hear "2-way Pioneers" or whatever. The "2-way" refers to the speaker: it has a midrange and a tweeter. A 3-way includes a supertweeter, and so on. While components are completely seperate pieces, so that they can be mounted in different locations, Coaxials combine these into one speaker. component: Coaxial: Q: Which is better then? Coaxials or components? A: This depends on what you want out of your system. Components allow for better staging. Staging is trying to reproduce the music so it feels like your at a concert, where the music comes from in front & above you. Because you can mount the midrange and the tweeter in seperate locations, component speakers are better at this, and therefore sound cleaner. However, because component systems dedicate certain ranges to a specific speaker, you need to use crossovers with components, which also cost more money. Coaxials are good for someone who doesn't want to mess with the installation, or higher price, of component speakers. Coaxials can be mounted as a direct replacement for your factory speakers, and require nothing extra to work (other than a wiring harness). Many coaxials rival the sound quality of component speakers, but they cannot provide the staging benefits. To most, the staging benefits of component speakers don't appeal to them, becasue many people just wouldn't notice it. Subwoofers Q: Why are there so many different sizes of subwoofers? A: A subwoofer creates b*** by moving air. Larger subwoofers displace more air, so their generally louder. The problem with bigger subwoofers though, is their size means that they cannot respond as quickly. This is definitely not true for all larger subs, but more of a generalization. The main reason why some larger subs aren't as responsive, or "tight", is because they take more material to make they generally have more moving m*** as well. Just like how weight affects how fast a car can accelerate and stop, its the same with speakers. With better quality, sound-quality oriented brands, larger subwoofers are mostly engineered to reduce the effect the larger cone will have on the sub's response. The response rate of a sub is important when listening to rock, punk, etc where there are fast drum solos. With larger (low quality) subwoofers, these fast-paced b*** beats are often blurred into one messy note. Smaller subwoofers are better for faster-paced music, because their smaller size allows them to respond more quickly to the changing beat. So, there are difference sized subwoofers to meet the needs of different people for both musical tastes, desired loudness, and size restrictions in any installation. How much of a difference there is usually relates directly to the quality of the product, with higher quality (but more expensive) subwoofers not really being subject to these generalizations. Q: So which subwoofer is best for ______ music? A: Smaller quality subwoofers can recreate any kind of music you throw at them. The problem with small subwoofers is they cannot come close to the output of larger subs. Because output (volume/loudness) is determined by how much air is being moved, the size of the speaker obviously plays a large part. The surface area of circles also increases exponentially, meaning that a 12" subwoofer will be exponentially louder than a 6" midwoofer. The problem with automatically jumping to a large subwoofer (15-18") is that you need to do some research and read reviews to make sure that subwoofer isn't "sloppy", "muddy", "boomy" or any other word that people use to describe the sound when subwoofers have poor response. 12" is somewhat of a universal size, because it provides the air displacement of a larger sub with the response rates of a smaller sub. The bigger the sub, the more output, but the smaller the sub, the better sound quality (in most cases). However there are always exceptions, and other factors contribute to sound quality (SQ) and loudness as well. Q: What about subwoofer enclosures / boxes? A: This is another common question. There are 3 basic kinds of boxes: Bandp***, ported, and sealed. Bandp*** boxes take up m***ive amounts of space, but require the least amount of amplifier power than the other kinds of sub boxes. However, they usually they have the worst sound quality. They are designed to get loud in a certain frequency range and that's pretty much it. Sealed boxes require the least amount of space, but require the most power. Sealed boxes can also help a sub to sound very very clean, with excellent SQ. One of the advantages of a sealed box, is the air pressure inside the box acts as a spring on the subwoofer as the cone moves back and forth, which is why sealed boxes are often able to reproduce the tightest musical reproduction. Ported boxes are a compromise between the other 2. They take up less space than a bandp*** box, but they are not as clean as sealed boxes (although much cleaner than bandp***es). They require a moderate amount of amplifier power. Ported boxes are often ideal for someone who wants to retain a certain level of SQ, but wants more output than they think they can get from a sealed box. Ported boxes are tuned to a certain frequency, usually somewhere between 28-35 hz for music. The thing to remember about ported boxes though, is because they do not have air pressure acting as a spring inside the box like sealed boxes do, you can damage the subwoofer if you send it too much power while playing music below its frequency. Below the tuning frequency of the ported box, the subwoofer will reach maximum linear excursion easier than its supposed to, which is why some people use a subsonic filter with a ported box to be safe. A good summary of this is: Your box can make or break your entire system. A poor quality box can make the loudest sub barely hit, and make the most expensive JL sound like crap. Q: So why can't I just make a box from scratch? A: Well, you can make your own box. I don't recommend attempting a bandp*** box if you're a first-timer, but with some basic knowledge and a free program called WIN ISD (see the bottom of this thread), you can make your own sealed or ported box. The main thing to remember when building a ported box is that the size and length of the port determine everything. Too big of a port in a smaller box can cause your sub to "bottom out", and damage/destroy your sub, whereas too small of a port can cause what's known as port noise, where the air is being moved very fast through a small area (the port) and creates turbulence. Ported boxes are "tuned" by the size and length of the port, to give a dB jump at a certain frequency. A ported box tuned at 60 hz will be about 5dB at that frequency than other notes. This allows you to custom tune your box & system to hit louder for a specific type of music. With a bit of knowledge though, building or having someone build a box designed for your needs & specific subwoofer will always be better than buying an off the shelf box from the local store. Amplifiers Q: What kind of amps are used for what? A: There are two basic kinds of amps: monoblock amps and multi-channel amps. Monoblock amps cost a little more, but are designed to stand the higher temperatures and loads of running subwoofers. Multichannel amps are typically A/B power, which provides better sound quality but also requires a larger current draw to produce its power, and also creates more heat. Most subwoofer amplifiers (monoblock) are D cl*** power, which is much more efficient, requires less power, and creates less heat than A/B amps but at a slight SQ cost. Because subs play a much smaller frequency range than coaxial or component speakers, the SQ sacrifice that you make with D cl*** amps is negligible. Multichannel amps are usually used with coaxial or component speakers. Q: Can I use a multichannel amp for subs? A: Yes, although it isn't as efficient as a monoblock amp. This is done with a 2 channel amp, bridged to present a lower load. Bridging an amp is also called "Parallel Wiring" (see image). The purpose of "bridging" an amp is to run your system at fewer ohms. Ohms simply represent the electrical resistance. An 8 ohm speaker doesn't flow electricity as well as a 4 ohm speaker, so less power actually makes it to the speaker. Here is an example of wiring a 2 channel amp in bridge mode (make sure you're amp is capable of doing so first, as more power means more heat and if you don't know what you're doing you can fry your amp by bridging below the electrical resistance it was made for): Q: What are the important things to look for in an amp? The main thing is to look at the power ratings. An amp will have two ratings: RMS and Peak power. The one you need to be worried about is the RMS power, because RMS is what the amp will run at 95% of the time. Your amp will rarely hit its peak power, because as the name implies, peak power is just what the amp is capable of for a very brief time. If an amp is ran at peak power for too long, it will melt down. Most brands label their amp with peak power, so a 1000 watt amp might only put out 600 watts in reality. Other things to look for are distortion rates, because you don't want the signal to get crappy when you go to turn up your amp. When distortion is amplified, the signal begins to "clip" (I'm not going to explain clipping in this thread) which is what usually kills speakers. Also, you'll want an amp with some sort of heat protection. Some of the larger amps have fans, to help keep the amp cool and diffuse heat. Other amps have Mosfet or circuit overload protection, where the amp will shut itself off if its gets too hot to keep it from melting down. Either way, you want an amp that will protect itself, because this is your money at risk! Also make sure that the amp is capable of doing what you want. Some multi-channel amps really don't like to be bridged, and will show it by frequently overheating. Capacitors Capacitors are similiar to batteries in that they hold & discharge electricity. At certain frequencies, your amp will draw more power than normal, which is usually exhibited by dimming headlights or panel lights as your sound system hogs the available power in your car. Capacitors are installed in between the power supply & your amp, and during normal power draws do nothing but recharge. Then, when there is a peak in the amount of power your amp is trying to draw, a capacitor tries to help supplement the car's electrical system for a very short period of time, discharging its stored up energy to the amplifier. Once your amp calms down and doesn't need any extra power again, then the capacitor siphons off a small amount of power to recharge itself. This series of discharging & recharging happens many times, basically non-stop while you are listening to music. Keep in mind while capacitors are helpful, they are really just a work-around or bandaid for a larger problem. Electrical problems in your car are better solved by upgrading your grounds (see sticky), better quality batteries & high output alternators. DIY Links Big 3 - Upgrading Grounds - I thought another member also did a DIY for this that was more inclusive than mine, if anyone sees it please post the link Replacing front door speakers Replacing Headunit 1 Feel free to post other useful DIYs to be included Some useful links: http://www.bcae1.com - by far the most informative site I've found so far http://www.partsexpress.com http://www.crutchfieldadvisor.com/S-YspqtS5sZKB/learningcenter/car/ http://www.sounddomain.com http://www.carstereo.com http://www.icixsound.com The WinIsd program mentioned earlier, useful in building boxes can be found here: http://www.linearteam.dk/ This is by no means an all-inclusive FAQ. I'm tired, and I'm sure I've left out some topics while writing this. Please post any other comments you have, so I can answer them and edit the FAQ to include them.