The problem with car audio is this.

1. A lot of so called professionals - do not know everything they should and are easy with the truth if they think it will get them a sale (Remember they are also trying to sell you product) Many are general retailers who happen to sell audio and don't really know that much about it.

2. Everyone has a mate named "Dave" who is a world expert on car audio, a little knowledge is sometimes dangerous - i could entertain you all day with stories of the horrors we've seen over the years from within the industry.

3. Manufacturers aren't exactly honest about the spec of their products - power figures for example.

With these three things in mind its hard for true professionals such as ourselves who have worked with manufacturers designing and testing product to educate consumers who are often mislead. At JBC we intend to write several basic guides on ebay to try and help the general consumer. When we sell audio we always try to give the customer whats best for them according to their budget, vehicle and listening taste - even if we then lose a sale because of it.

However we will try to wade through the minefield, this guide is designed to be a little simplistic, another pro would quibble with parts of it but its aimed at general principles for consumers.

Types of amps:

There are three main types of amps:

Monoblock (For Subwoofers only - Including Dual Voice Coil)

2 Channel (For Speakers and usually Single Voice Coil Subs)

4 Channel/Multi Channel (For Speakers and usually Single Voice Coil Subs)

Note: You CAN wire a Dual Voice Coil Sub to a 2 or 4 Channel Amp - it just isn't the best way of doing it and if you do it wrong.... Bye Bye Amplifier, theres plenty of DVC wiring diagrams from reputable companies on the net for people to look at as manufacturers are tired of end users fitting products themselves with little knowledge and blowing amps up.

Some 2 channel amps ARE 2 ohm mono stable rather than just 2ohm stereo stable - you CAN use these for DVC subs but always ASK to make sure.

Power Figures (The confusing bit!)

1. 4000 watts? MAGIC! - Wrong - Manufacturers Lie.

Theres many different benchmarks within car audio as to what actually constitues a "peak" or "RMS" (Constant) power figure. Also both figures are usually quoted at 14.4v by manufacturers and unless you have a large diesel car your probably running around 12.5-12.8 on your vehicle. For every volt you lose (Depending on the efficiency of your amplifier) you can lose huge amounts of power. Also again even if you had an accurate figure, if the amp isn't particularly efficient much of that power may be wasted, how the amp is setup to deliver the power to the speakers (Crossover Settings) will also affect how much power your speakers actually recieve from the amp. Then there's cabling: If your running thin, cheap cabling you'll not be supplying your amp with full power delivery in the first place or if your using poor speaker wire your speakers won't recieve full power from the amp.

Car Audio is a system not individual peices - if one part of your system is weak then it creates a "Choke point" and affects the overall system performance sometimes quite drastically.

2. Amp A is 1000w and 50 Quid - Amp B is 1000w and 250quid - Whats going on?

Amp A is a budget amp - at that price the real RMS is probably 35w per channel or lower which is actually fine for most lightly upgraded speakers (your headunit which says its 50w x4 usually kicks out a massive 5-10w depending on how good the internal amp is), its features are likely to be basic, the crossover will be cheap, its unlikely to be tri mode capable, is probably 4ohm stable not going as low as 2ohm and probably doesn't have proper Gold RCA inputs (yes it may say it has on the features list lol). The circuitry won't be as expensive, the heatsink won't be brilliant and the sound quality will undoubtably be lower.

However its a 50 quid amp so if you have a set of 25 quid speakers this is probably the right amp for you - theres no point putting a great amp on budget speakers at the end of the day.

Amp B is probably telling the truth - its RMS is probably in the region of 150w or higher (Despite the fact Amp A may have said it is also) the RCA inputs are likely to be good, the circuitry and features are likely to be impressive and it will properly supply say a 125 Quid set of speakers. the sound quality will be miles ahead - so yes its the better amp but unless your running decent speakers it probably isn't for you.

A trick to compare power!

An amp can't put out more power than its rated to take in - find out the fuse size of the amp from the seller or manufacturer!

For example a 40amp fused amplifier can put out up to around 500w RMS in theory depending on which conversion factor you use - how efficient it is then determines how close it gets to that figure, anything over 75% (in this case would be around 400w) would indicate a relatively efficient amp.

As you move up fuse levels this becomes slightly less accurate and some manufacturers over fuse their amps however as a basic comparison of two amps at the same price it serves it purpose.

3. So what Amp do i need?

The best advice we can give is this - if you don't know the product ranges inside out (Which only an installer working with it day to day would) is match your system carefully and always ask advice of a professional - if you think you can trust them.

For instance if you have a set of speakers from "Brand A's" budget speaker range - use a budget "Brand A" amp to power them - that way you know the two were designed to work together.

Unfortunately most manufacturers aren't good at everything so you may want to mix and match speakers from one brand, subs from another etc - in this case we've drawn up some simple rules.

1. Don't skimp on your amp - Your amp will usually cost you at least twice what your speakers do (Be careful if using that rule if you bought your speakers cheaper than they should have been retail, take it into account when looking for an amp), amps are like engines - just because they will run flat out doesn't mean they'll do it forever. A larger amp than your speakers really need just means its not straining itself to do its job, a speaker is more likely to blow from being underpowered than anything else especially if they are powerful and expensive as they will demand a certain amount of minimum power to operate. (See our upcoming speaker guide for info on "clipping" and other little known speaker facts)

2. Don't create a weak point in your system - Make sure the speakers, amp, cabling and headunit are all of the same quality - that way they will work together at the best of their ability. Start with your headunit (Your only as good as your source unit) and work from there.

3. Ask for help from someone who does know - its difficult because any specialist is also a retailer and wants your money - however if you find a seller who you think you trust, who offers free advice - take it - if you've picked a real enthusiast it will mean you get the most out of your full system.

4. Don't fit yourself unless you really know what your doing - the majority of failures in audio systems (and most systems that are truly poor) come from self done installs. Distortion is not volume, your boot lock is not a good earth point and the gain control is a gain control not a volume knob - i promise you there are reasons good installers charge for their services, nor does the average consumer have the test equipment to set the system up properly from a sound point of view.

This is just a few basics - not everything by any stretch but we hope we've helped even if its just a little!