Everyone knows you need an amplifier in your car’s audio system if you want thumping, window rattling, trunk vibrating bass, but adding an amplifier will provide so much more. With an amplifier you’ll get much better overall sound quality. And if you’ve upgraded your speakers or added a subwoofer, a separate amplifier will provide the power needed to get the most out of them; power that the amp inside a dash mounted receiver just can’t deliver.

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Amplifiers are categorized according to classification, number of channels, and power rating in watts. The class of an amplifier refers to its circuit design. There are Class A, Class B, Class A/B and Class D amplifiers, with the latter two being the ones most commonly used in car stereo applications. Class A amplifiers produce the best sound quality, but are inefficient because current flows through their output transistors all the time.

Class B amplifiers are the most efficient because the output transistors pass current only when there is an audio signal, but they produce a lot of distortion. Class A/B amplifiers are a compromise, with a small amount of current flowing all the time, even when there is no audio signal, which results in greater efficiency with almost no distortion. In a Class D amplifier the transistors are switched on and off. Class D amplifiers are more efficient than Class A/B but produce more distortion. However, this distortion can be removed with a filter.

Select an amplifier with channels to match the number of speakers in your system. As the name suggests, a mono amplifier is designed for one speaker, usually a subwoofer, however two subwoofers can be connected to a mono amplifier. 2-channel amplifiers are for two speaker systems, 4-channel for 4 speaker systems, and 5-channel amplifiers are for 4 speakers and a subwoofer. Some amplifiers can be “bridged”, meaning 2 channels can be combined into one for more power. A 4-channel amp could power two speakers and then have the remaining channels bridged to power a subwoofer.

The amplifier’s power rating should coincide with your speakers’ RMS, or continuous power rating. If this rating is given in a range, go with the higher number. This is especially important to get maximum performance from aftermarket speakers. For best sound quality the amplifier should deliver at least 75% of the speaker’s RMS rating, and the average speaker can handle up to 150% of this rating without any problems. It’s always better to overpower speakers rather than under power them. If you’re building a system from scratch, a small car with a quiet cabin won’t need as much power as a larger, noisier, vehicle.

In addition to the above, there are other features that you’ll commonly see in amplifier listings, like filters and bass boost. There are high pass and low pass filters. A high pass filter removes low frequencies so the amplifier is only boosting the high frequencies sent to small speakers for high notes, while the low pass filter takes out the high frequencies, such as would be common when powering a subwoofer. Variable filters allow you to select the frequency to be filtered. Variable bass boost control allows you to increase the bass level to tailor the sound quality.

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Guides & Articles

  • Audio & Electronics
    In this article, we'll discuss the basics of your vehicle's audio system wiring. Specifically, we'll look at the addition of one or two amplifiers to your system, and examine the steps involved for both the mechanical and electrical installation. Refer back to these two illustrations while reviewing the text.
  • Audio & Electronics
    The purchase of a new stereo (also called "receiver" or "head unit") brings the promise of better sound, the thrill of new features, and the enjoyment of simply experiencing music in a way that is not possible with a factory sound system. We hear the excitement and anticipation in our customers' voices every day as they select and order their new equipment, and we help guide them through the process of stereo installation all the time. We know our customers' questions, and we see the most common roadblocks they come across.

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