To clarify regarding the number of channel amps needed for 4 speakers, I will start in an order of sequence (let’s follow the general to specific rule).
Mono channel amp
A one-channel or mono amplifier uses less power and emits less heat when powering the subwoofer added to your sound system.
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A two-channel amp can power two woofers, two coaxial speakers, a single subwoofer and also, two sets of coaxial speakers. However, two- and four- channel amps are widely used to power door speakers (to be specific ;)).
A three-channel amp is ideal for powering a subwoofer and a pair of speakers. This configuration is perfect if you solely wish to power your front or rear speakers with an aftermarket amp.
A four-channel amp operates to power four speakers, two speakers and a subwoofer—you can use a four-channel amplifier to power a subwoofer and two rear full-range speakers by bridging two of the channels to power the sub.
What if you want to add a subwoofer?
If you desire to add a subwoofer, you can use a four-channel amp to power your four coaxial speakers and a mono-channel amp to power your subwoofer.
An amp with five channels can power an entire car audio system:
- Two speakers in the front;
- Two speakers in the rear; and,
- One subwoofer.
How to pick the right amplifier that suits your needs ?
As with most elements of car audio equipment, the amount of choice when it comes to amplifiers is mind-boggling. One of the most typical questions that experts get asked by people who are looking to buy their first car amplifier is “How many channels do I need”?
How do you plan to build your system?
The answer is relatively simple, and it entirely depends on how you plan to build, or how your current system is built at present moment. See how I got to details that you probably did not expect will be discussed concerning the titled query? It is because I am aware of the millions of hidden questions hidden in this one apparent question.
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Let’s go back to the basics-what is a channel?
Getting back to the topic, “channels” refer to the number of outputs that can be connected to an amplifier at one time, with the outputs being speakers and subwoofers.
If you wish to amplify a system with two speakers, you will need a 2-channel amplifier. If you want to power a system with 4 speakers, you will need a 4-channel amplifier. Simple, right?
When to go for a three- and a four- channel amplifier?
One thing to consider, however, is that if you want to include a subwoofer in your system (which you definitely should), you will require either a three-channel amplifier or a four-channel amplifier. Hopefully, the info shared is enough to answer your question.