What Class Amp Is Best For Subs? [Ask The Expert]

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Typically, subwoofers are powered with Class D amplifiers.

Why is this done and what kinds of different amplifier classes are available and what is the difference between them?

There are many technical aspects to car audio that can be confusing and a bit intimidating to the non-audiophile.

You don’t have to be an audio engineer or an electronic engineer to understand the basic concepts to amp design and function although things tend to get convoluted pretty quickly and the more you research, the more terms are used which most people don’t understand and are hard to make sense of without an in-depth understanding of electronics.

Don’t worry if you set out to try and learn about amp design and end up more confused than when you started!

Some engineers tend to have a bad habit of gleaning enjoyment from making you feel stupid when they “talk shop” and the quicker they see that expression of WTF on your face, they happier they get.

Fear not though! Your friends here at Gear4Wheels are here to help you get a better understanding of car audio amplifiers in a way that, hopefully, does not make your brain explode.

For the sake of transparency, I’ll make it clear that I am not an audio engineer or an electronics engineer, however I have been in the industry for over 20 years and being involved in both the Car Audio world and Information Technology, I have quite a bit of real-world and technical electronics experience at hand.

Brain explode

So let’s roll up our proverbial sleeves and dive into the wonderful world of mobile audio amplification!!

What are Class D amplifiers and why are they used for subwoofers?

What are Class D amplifiers and why are they used for subwoofers-

Before we get too far into Class D amplifiers exclusively, let’s do a little primer on amp classes and what distinguishes one amp from another by class.

For starters, there are really only two different kinds of amps; analog amps and switching amps.

Related: Best 2 Channel Amplifier 2017

This could be broken down as analog and digital as well, however most amps use a combination of technologies and both use forms of switching, be it analog or digital.

Out of all the different classes of amplifiers, the four most commonly used types are Class A, Class B, Class AB and Class D.

  • Class A
  • Class B
  • Class AB
  • Class D.
  • Class A
  • CLASS B:
  • CLASS D:

Back in the day, all mobile audio amps were Class A or Class A/B as the more efficient Class D amps had not yet made their debut.

With the development of more efficient technology, transistors and the shrinking size of components, Class D amplifiers were ready to make their way to the mobile audio environment.


The main factor distinguishing Class A and A/B from Class D is the “D” for digital.

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Ok, not really, but as advancements were made in transistor switching methods, Class D amps employ a switching method in which the transistors are switched on and off at a very high rate of speed, effectively creating a digitally switched or “pulsed” output signal that’s nearly consistent with the analog input signal.

While this creates an extremely efficient amplifier, the difference in this digital signal compared to its analog signal creates a certain amount of distortion at higher frequencies.

However since subwoofers primarily reproduce low frequencies, and with the incorporation of low pass crossover filters, this distortion is minimized and is the reason why Class D amps are an excellent solution for subwoofer amplification.

Hopefully this has given you some insight as to why Class A/B amps are better suited for full range i.e. front speakers, and why Class D amps are more suitable for subwoofer amplification.

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Let’s do a quick recap in the form of a Pros/Cons list for each amp class:



Class A:

  • High Audio Fidelity
  • Low Signal to Noise ratio
  • Low Total Harmonic
  • Distortion
  • Larger Size
  • Lower Efficiency
  • More Heat

Class B:

  • More Efficient Than Class A 
  • Smaller Size
  • Creates Less Heat
  • Lower Audio Fidelity
  • Higher Signal to Noise ratio

Class A/B:

  • More Efficient Than Class A
  • Less Distortion Than Class B
  • Less Efficient Than Class B
  • More Signal To Noise Ratio Than Class A
  • Slightly Higher Total Harmonic Distortion Than Class A

Class D:

  • Extremely Efficient Compared to Class A
  • Much Smaller Size (Depending on power requirements and design)
  • Notable Distortion at Higher Frequencies
  • Higher Signal to Noise Ratio
  • Higher Total Harmonic Distortion

As you can see, there are many different amplifier designs and technologies, and while this guide should give you a general idea of the differences between amplifier classes and how they are used, it is by no means a complete explanation (I left out the really technical stuff on purpose) .

Related: Best 4 Channel Amplifier of 2017

External factors

Since amplification technologies continue to advance, as well as lots of other external factors such as the mobile audio environment, power needs and availability of different vehicles and audio systems, there may be exceptions to the basic rules (as always!)

And sometimes rules are made to be broken (engineers and physics majors hate that phrase I’m sure).

For instance: with recent advancements in Class D technology, there are more and more Class D amps on the market that are suitable for full range applications as well.

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