Sony XM4S

The "class" of an amplifier assists in determining the different performance characteristics because the "class" refers to the amplifier's internal circuitry:

The common number of channels for amplifiers are: Mono (generally for subs), 2-channel and 4-channel; however, amplifiers are manufactured in 3, 5, and 6 channels too.

The amount of continuous power, measured in watts, that an amplifier produces at 4 ohms.

The amount of continuous power, measured in watts, that an amplifier produces at 2 ohms.

The majority of amplifiers are not stable at an impedance level of 1 ohm. High Current and Class D amps are generally best suited for such a low impedance.

The RMS output wattage per bridged channel. Be sure to also check the "minimum impedance bridged" value to see what impedance level (ohms) the system must be running at to achieve the value stated here.

Total RMS power is measured by multiplying RMS power per channel by the number of channels, and is calculated at the lowest level of operating impedance.

RMS power is the amount of continuous power, measured in watts, that an amplifier produces is called RMS power. The higher the RMS figure, the louder and cleaner your music sounds.

The RMS output figure is much more accurate than the peak rating when comparing products.

Peak power is measured during a brief musical burst, such as a sudden drum accent. Some manufacturers display peak power ratings on the face of their products to increase the appeal.

The RMS power rating is more accurate, and we recommend using it for product comparison.

The total peak power output is measured as the wattage per channel multiplied by the number of channels, and is calculated at the lowest level of operating impedance.

It is measured during a brief musical burst, such as a sudden drum accent. Some manufacturers display peak power ratings on the face of their products to increase the appeal.

The RMS power rating is more accurate, and we recommend using it for product comparison.

This number refers to the maximum gauge of wire that will fit into the input connector(s) of the capacitor, amplifier, connector, or any other item that is receiving a wire.

The lowest impedance the amplifier will handle when it is not bridged.

The lowest impedance the amplifier will handle when it is bridged.

The amount of change in harmonic content of the signal as it is amplified. A lower figure indicates less change and a more accurate amp. THD below 0.10% is inaudible.

This feature is useful only if you plan on running your amplifier from a factory receiver or if you have no remaining preamp outputs left on your aftermarket receiver.

An RCA preamp output lets you pass the preamp signal to additional amps, and in some cases the internal crossover from the first amp can send a filtered signal, eliminating the need for an additional crossover.

A high-pass crossover will permit signals above a specified frequency to pass through, while a low-pass crossover will permit frequencies below a specified frequency.

The high-pass crossover frequency can be a fixed crossover point or a variable crossover range. A variable high-pass crossover allows you to select a specific crossover point which allows frequencies above the set crossover point to pass, while making frequencies below the set point gently or harshly roll-off, depending on the steepness of the slope.

The steepness of the roll-off slope is measured in dB/octave and refers to the rate of attenuation (lowering of volume) outside their pass bands.

The low-pass crossover frequency is typically used for subwoofers. It can be a fixed crossover point or a variable crossover range. A variable low-pass crossover allows you to select a specific crossover point which allows frequencies below the set crossover point to pass, while making frequencies above the set point gently or harshly roll-off, depending on the steepness of the slope.

The steepness of the roll-off slope is measured in dB/octave and refers to the rate of attenuation (lowering of volume) outside their pass bands.

Allows you to block (filter) ultra-low frequencies that your subs cannot reproduce.

This spec compares the strength of the signal to the level of background noise. A higher value indicates less background noise.

Also referred to as crosstalk. The amount of interference on one stereo channel caused by the leaking of the other stereo channel. The higher the rating in decibels (dB), the better the Channel Separation.

With the simple switch of a button or turn of knob, this feature can allow you to boost the bass output.

If the amp comes with a bass/gain remote you will be able to control the level of your bass from your dashboard. Typically bass remotes also include a 16-20 ft. wire for installation.

A great feature to have if an amp generates a large amount of heat. Cooling fans can help regulate the temperature to prevent the amp from overheating (burning).

The amperage and the number of fuse(s) an amp requires.

CEA-2006 Compliant amplifiers are those that have been tested to meet specific standards. When a car amplifier meets these standards, you can be sure that it will be able to produce the amount of power specified by the official CEA-2006 rating. Usually, these rating consist of the following items: