When you’re deciding on what amplifier to buy for your audio system, one of the biggest factors is how many channels it has.
If you’re looking for an amp to power subwoofers, in most cases you only need a single or “mono” channel Class D amplifier, even if you’re running multiple subs.
This can be achieved by wiring the voice coils of multiple subs together in series or parallel configurations which will present a certain ohm load to the amp depending on how it’s wired and what the ohm rating of the voice coils are (usually 2 ohm or 4 ohm).
Here is an example of some voice coil wiring configurations:
While your voice coils are either going to be wired in series or parallel, some subs have only one voice coil while others are dual voice coil and each voice coil will be rated at either a 2 ohm or 4 ohm load, so there are quite a few different wiring configurations possible, the main thing to remember is that your amp must be capable of running the ohm configuration that it is presented to it.
Many amps for instance are not 1 ohm stable and can overheat if the subs are wired incorrectly.
Now what about amplifiers with multiple channels? Most 2 – 4 channel amps are going to be in the Class A/B category and are designed for powering your front stage (mid-bass and tweeters).
Coaxial speakers combine the mid-bass and tweeter into one speaker with the tweeter being mounted in the center above the woofer cone (as well as a small crossover, usually some type of small resistor).
Component speakers separate the woofer and tweeter for better imaging and typically include an external passive crossover network. While the woofer and tweeter are physically separated, the crossover provides the ability to use one amp channel to power them instead of two.
In most cases component speaker systems will only need two amp channels to provide power to all four speakers.
When it comes to getting the best possible sound quality, a lot of people will utilize an active crossover system, which means that each speaker has its own amp channel and the passive crossovers are not used, as each speaker channel feeds into a DSP/EQ unit that allows each speaker to be set to a specific crossover frequency and power setting.
This means that a component speaker set being run actively would require four channels for a two way system and six channels for a three way system.
Some higher end passive crossovers are bi-amp capable, meaning you can power each speaker with its own amp channel and still use the passive crossover instead of a dedicated DSP unit.
4 Channel Amps: What For?
Another typical scenario is using a 4 channel amp to run both speakers and subwoofers. We did a comparison on 4 channel amps that you should read.
In this setup the amp is typically put into a bridged mode for the rear channels meaning that the front two channels power the front coaxial/component speakers while the two rear channels are bridge into a single, more powerful channel to run the subwoofer(s).
This can be a helpful option for saving the space and cost associated with running multiple amps for speakers and subwoofers.
The downside is that most aren't going to put out a lot of power, which can be required for larger subwoofer setups.
What About 5 Channels then?
5 Channel amplifiers can be a combination of amplifiers, for example, the two front and two rear channels are Class A/B for running mid-bass and tweeters while the fifth channel can be its own Class D subwoofer amplifier.
5 Channel amps are a good option if you want to run four speakers instead of two for your front stage while still providing an extra subwoofer channel.
Again, this can be an effective space and cost saving measure but like a 4 channel amp in bridged mode, it still does not provide adequate power for large subwoofers.
Active crossover systems commonly take this a step further and utilize a separate amp for tweeters, mid-bass and subwoofers.
This gives a more precise ability for delivering the correct amount of power to each type of speaker.
With all of these different options and different amplifiers available, it can be confusing to decide what is best for you.
Typically cost is going to be the main factor in your decision making, but you should also factor in how much space you are willing to dedicate to audio equipment in your vehicle.
The good news is that with advancements in Class D amp technology as well as the shrinking size of amplifier components, you can get larger amounts of power out of smaller packages.
A good example of this is the JL Audio HD1200/1. It delivers 1200 watts of power out of an amp that is 8.5 x 11” or about the size of a standard sheet of notebook paper.
Another example is the Alpine MRV-M1200, which puts out up to 600 watts @ 4 ohms and 1200 watts @ 2 ohms, at a size that is comparable to the JL Audio HD1200/1.
As you can see, size is less of an issue than in the past for amplifiers but still needs to be taken into consideration especially when factoring in subwoofers and their enclosures.
As I’ve explained in the article, the number of speakers you plan to run should be the other deciding factor on selecting an amp.
Also, don’t forget that you also need to account for the power that will need to be supplied to the amp.
A lot of people over look this necessity when designing a car audio system.
Some amps are more power hungry/less efficient than others. Take a look at this article on amplifiers for more information on amplifier types and efficiencies.
How to power all this
Amplifiers are powered by your vehicle’s alternator and depending on how many amps your alternator puts out, you might need to upgrade to a high output alternator.
Adding or upgrading batteries can help as well but keep in mind that if you don’t have sufficient alternator amperage to charge those batteries, they aren’t going to provide enough power.
Typically stock alternators on most vehicles should be sufficient for powering a system up to 800 – 1000 watts, again depending on what your alternator amperage is rated at.
This article is meant to give a basic description of different kinds of amps based on number of channels and different scenarios in which they are used.
As always, if you need help selecting an amp or have questions about your specific vehicle and amplifier needs; please don’t hesitate to ask!