What You should Know About Car Audio Amplifiers
First of all, amplifiers
The real measure of the power of an amplifier is the continuous power rating (R.M.S. rating - Root Mean Square). This refers to the average power output. Some of the lower quality brands may oversell the output of their amplifiers, so beware and best stick to well known manufacturers.
Extra features that are built into a power amplifier include equalizers, active crossovers, signal processing, and speaker level inputs. Keep in mind that doubling the amplifier power does not mean that you are doubling the sound output. This adds only 3dB of volume to the output. It takes a 10dB increase to double the sound.
A good indication of quality and the power of an amplifier are the size and the weight of the unit itself. The Class D amplifier however, is now designed more efficiently and has a smaller power supply and a smaller heatsink.
Another indication of the true output of the amplifier is the size of the fuse. A ten-amp fuse cannot be used in a 2000watt amplifier.
If you are concerned about price, you may consider buying a multi-channel amplifier with the built-in features you require. Although the quality will be a little less, this can save you space and quite a bit of money.
Common Terms pertaining to amplifiers
Bridgeable: This allows a pair of channels to be combined into one channel with greater power, usually used for driving a subwoofer.
Channels: A channel is one power output of an amplifier. The more channels you have, the greater the flexibility for installation and the possibility for future add-ones.
Class: This is the way the amplifier operates -A, A/B, and D. Class A are the least efficient, but also have better sound. These are extremely rare for cars. Class A/B are the most common type. Class D amplifiers are usually for high power subwoofer amplifiers, reaching efficiencies in the 80% range, therefore using less current and produces less heat than the other classes. Connectors: These are the method wire connections to the amplifier, the most common being the screw terminal strip. The other is the "Molex" type connector.
Crossover/Filter: A filter is a crossover that only impacts one channel by reducing a range. Built-in filters have the option for either LP or HP. AP means "all pass" which means the filter is turned off.
Distortion: (T.H.D) This is the measure of how much change there will be in the output signal from the input signal it is given. Measures below 0.1% will probably not be heard. Anything in the 3% range will not be heard, but all high quality amplifiers have a T.H.D. below 0.1%.
Efficiency: This is the ratio of power from the battery to the speakers. A 100-watt amplifier with an efficiency of 50% would take 200 watts of power from the battery and the output would be 100 watts of power to the speakers.
Power Supply: The two most common are the IC chip and the MOSFET supply. The IC chip is used in most source units and are only produce about eighteen watts. MOSFET is more common and have a smoother sound.
Separate Gain Controls: This lets the gain of each channel to be set independently, allowing for more evenly matched channels.
Speaker Level Inputs: This feature may be used instead of a pre-amp level output to take the signal from the speaker leads of the source unit.
Stability: This is a measure in ohms of how low of impedance an amplifier can handle. A good quality amplifier will be two ohm stable.
Tri-Mode Output: This is the ability of an amplifier to run a stereo pair of speakers and also a mono from two channels.
Tube amplifiers: These are the most uncommon and most expensive. They use vacuum tubes and claim to produce a warmer sound.
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