A four-channel amplifier is similar to its two- and five-channel counterparts in that it uses a single power supply to step up the 12V output and supply higher power. Standard car stereos usually rely on the 12V current directly from the car’s battery, which doesn’t provide enough power for sub-woofers. A four-channel amplifier gives you the versatility of adding up to four separate speakers and bridging the channels for even more power.
However, there are important considerations when buying a 4 channel amp.
Ideally, you want your amplifier to have both high-pass and low-pass crossovers. It’s even better if they are adjustable, but this is not essential. A high-pass crossover allows frequencies above the chosen cut-off frequencies to pass through to your speakers. A low-pass crossover allows frequencies below the chosen cut-off. Put simply, these block frequencies from getting to speakers that cannot handle them, preventing distortion or even blown speakers. It also gives you far cleaner audio quality.
A/B Class and D class
Another important consideration is your choice of amplifier class. The main difference comes down to efficiency. Class A/B amps are the least efficient but offer the best sound fidelity. Class D amps will give you far more efficiency, but less audio quality.
The class of amplifier is defined by the way the amp combines power and signal. Every amp will consume more power than it can feasibly put out. An amp’s efficiency rating is in the ratio of what it can put out, divided by its power consumption. No amplifier can be 100% efficient. This means that it can never put out an equal or higher amount of power than what it draws. Power being drawn and not used for the output of audio creates heat. Too much heat equals a burned-out amplifier.
A/B class amplifiers
These amplifiers are usually around 60% percent efficient, the transistors inside being on only around half the time, even when there is no audio signal present. Until recently, these amps have always been the go-to due to their high audio quality, lack of noise and distortion, and full-range application. Class D amps have yet to come close when it comes to accurate sound production.
However, class D amplifiers are catching up quickly to the audio quality produced by A/B class amplifiers. They have the benefit of fitting into a much smaller chassis, making them far more compact and giving them the ability to be stowed away conveniently under the seat. They are also almost 90% efficient in some models, resulting in less heat than A/B amps.
The one drawback of class D amps is noise. Because of the way they function, when the gain is up, there is a noticeable hiss coming from the speakers. A higher-quality class D will produce less of this signal noise, but it will cost you.
How much power you need is subjective. For the average user who is not relying on massive bass output with sub-woofers, a 50-watt RMS rating will give you great volume and clarity. Although it is possible to bridge channels for higher power output, it will leave you with fewer speaker options.
However, for more dedicated audiophiles, 50watts probably won’t do it. If you want to connect an additional sub-woofer, it will be safer to go for 75 watts or above. This will mitigate the problem of overdriven and distorted speakers and give you plenty of extra power for bass response and additional tweeters.
When possible, it’s a good idea to go for a well-known brand name to ensure quality and prevent overheating issues. A high-quality MOSFET (metal-oxide-semiconductor field-effect transistor) is designed to handle high power levels, giving you high efficiency at low voltage. Choosing an amplifier with a MOSFET installed will help both your power efficiency and audio quality.
Overall, the Alpine MRV-F300 is our best pick for quality, power output, and affordability. Its class D designation makes it compact and efficient, and it will give you high-quality audio fidelity.
The best four-channel amp for the money is the Boss R1004. It’s an affordable and trustworthy class A/B full-range amplifier, giving you the power and audio quality you’d expect from a class A/B amp without breaking the bank.
There are many features and considerations within the world of four-channel amplifiers, from power to clarity and quality, and it can be somewhat overwhelming. Hopefully, our reviews have helped you navigate the abundance of four-channel options and choose the right amp for your needs.