Amplifier Types: 2-Channel, 4-Channel, Class D / Mono, and Multi-Channel

First up are 2 Channel amplifiers. These are traditionally found as Class A and Class AB amplifiers. The Class type refers to the circuit configuration. Class A and Class AB amps are designed for sound quality and are ideal for both subwoofers and speakers. Class A amplifiers are an older design and feature transistors that always have current running though them regardless if the amplifier is receiving audio signal or not.  Class AB shares a similar design however in this case the transistors ONLY have power running though them when the amplifier is receiving audio signal. A Class AB amplifier will run more efficiently and cooler. Remember anytime an amplifier is generating heat that is a by product of wasted energy. For most amplifiers made today the standard is now Class AB.

Most 2 channel amplifiers feature a built in high, low, and full pass crossover which is ideal for running either full range speakers or subs however not both at the same time. The 2 channel refers to the ability for the amplifier to handle LEFT and RIGHT audio or the amplifier can be BRIDGED to run a subwoofer. Bridging refers to the ability to combine the left and right channel into a mono output to produce more power. Keep in mind though most amplifiers only handle down to a 4 Ohm bridged load. Since bass is non-directional there is no left and right. The human ear cannot distinguish where bass frequencies are coming from which is why when a subwoofer system is installed in a trunk it does not actually sound like it is coming from the rear.

This is an example of a 2 channel amplifier running mid range speakers and then a sub configuration. Keep in mind you can run most 2 channel amps down to a 2 Ohm stereo load to achieve more power. So in theory you can run both your front and rear speakers using two sets of 4 Ohm aftermarket speakers. The disadvantage to this is since the amplifier is only two channels you lost the ability to fade (no rear right or rear left) your speakers but the amplifier produces more power.

Next we will look 4 and 6 Channel amplifiers. These tend to be the most versatile type of amplifier and can be used for many different applications. These amplifiers like 2-channel are normally Class A and Class AB models. Most 4 Channel amplifiers will also include a built in low, full, and high pass crossover. A 4 channel amplifier is able to handle Front Left, Front Right, Rear Left and Rear right. You also have the ability to bridge the front two and rear two channels or you can run a combination of the two, The front two channels and rear two channels actually feature independent crossovers and gain adjustments. The easiest way to imagine this is, a 4 Channel amplifier is basically a combination of two, 2 channel amps all built into one package. You can run the amplifier in a 4 Ohm stereo load on High Pass and just run your front and rear speakers on it (Example 1). Or you could run the front two channels as High Pass and run mids and highs on it, and then set the rear channels on Low Pass and bridge them to a sub (Example 2). Or you could run the front and rear channels bridged as Low Pass in (Example 3). It is actually possible to run an entire system on one of these amplifiers which is much more efficient in terms of current draw and also saves space.

The next type of amplifier we will look at are Mono Channel amps, these are generally usually Class D amplifiers are designed for subwoofers only. They will normally only have a Low Pass crossover only and are more efficient in terms of power output vs. wasted energy. These amplifiers can also handle a lower Ohm load which is ideal when running multiple subwoofers on a single amplifier. Most Class D amplifier are also smaller in terms of physical dimensions than comparable 2 channel and 4 channel amplifiers rated at the same power. Overall there is no better way to run subwoofers. If you have a 1 Ohm Class D amplifier here are a couple examples for wiring subs.

The last type of amplifier we will look at are 3 and 5 Channel, these are hybrid amplifiers normally feature both a Class D and Class AB circuit rolled all into one amplifier. A 3 and 5 channel amplifier will typically have a mid range speaker output and a subwoofer output both with independent crossovers. These amplifiers are both more power efficient and easier to install since all of the wiring goes into one place. This is a typical wiring diagram for a 3 and 5 channel amp: