WooferGuy is reader-supported. When you buy through an Amazon link on this page we may earn a commission, at no extra cost to you. It never decides what we recommend. How this works.
Almost every car subwoofer amp sold today is Class D, while Class AB still turns up in some speaker amps and is loved by a section of the car-audio crowd for its sound. The difference matters most for your car’s electrical system: a Class D amp turns much more of its input power into music and much less into heat. Here’s what each design does, the real-world numbers and which to buy.
The short version
- For subwoofers: buy Class D. It draws far less current for the same output and runs cooler.
- For speakers: either works. Good modern Class D full-range amps are clean; Class AB is a valid choice if you have the space and power.
- Efficiency: Class D is typically around 80–90%; Class AB around 50–60%.
- Size: Class D amps are much smaller for the same power, which helps under seats.
- “Class BD” is Rockford Fosgate’s name for its high-efficiency switching design, in the Class D family.
How each design works
- Class AB uses output transistors that conduct continuously and follow the music signal smoothly. It’s simple and linear, but transistors that are partly on all the time turn a lot of energy into heat.
- Class D switches its output transistors fully on and off very quickly, then filters the result back into an audio signal. Transistors that are either fully on or fully off waste little power, so efficiency is high.
Side-by-side
| Class D | Class AB | |
|---|---|---|
| Typical efficiency | About 80–90% | About 50–60% |
| Heat | Low | High |
| Size for the same power | Small | Large |
| Current draw | Lower | Higher |
| Best use | Subwoofers, compact full-range amps | Speakers, sound-quality builds with room to spare |
| Typical price per watt | Lower | Higher |
What efficiency means for your car
Here’s the current drawn from a 13.8 V electrical system to make 1,000 W RMS of output, using typical efficiency figures:
| Amp type | Efficiency | Current at 1,000 W output |
|---|---|---|
| Class D | 80% | About 91 A |
| Class D (high-efficiency) | 86% | About 84 A |
| Class AB | 55% | About 132 A |
That extra 40-odd amps for the Class AB amp is heat inside the amp and load on your alternator. It’s why big subwoofer systems are almost always Class D, and why the current figures in our wire gauge calculator assume a Class D amp. Rockford Fosgate rates its Punch P1000X1bd at 86% efficiency at 4 Ω, for example.
Does Class AB sound better?
Early Class D amps had a reputation for harshness at high frequencies, which is where Class AB earned its sound-quality following. For subwoofers, that argument never really applied: bass sits far below the frequencies where Class D designs historically struggled. For full-range speakers, modern Class D designs measure very well, and the difference is often smaller than the difference between two amps of the same class. If you prefer Class AB for your front speakers and have the space, power and cooling, it remains a reasonable choice.
Which should you buy?
| Your system | Recommendation |
|---|---|
| One or two subs | Class D mono amp. See our monoblock picks. |
| Factory radio, sub-only install | Class D mono amp with speaker-level inputs |
| Front speakers, sound quality focus | Either; Class AB if space and power allow |
| Full system, limited space | Class D multi-channel or 5-channel amp |
| Big system above about 1,500 W | Class D, plus electrical upgrades like the Big 3 |
For a sub, the two amps we point most readers to are both Class D: the Rockford Fosgate P1000X1bd and the Kicker CXA1200.1. Our amp sizing guide helps you choose the power.
FAQs
Is Class D only for subwoofers?
No. Many full-range and multi-channel amps are Class D now. Older Class D designs were mostly mono sub amps, which is where the idea comes from.
What is Class BD?
A name Rockford Fosgate uses for its high-efficiency switching amplifier design. In practice it sits in the Class D family.
Do Class AB amps need bigger wire?
For the same output, yes, because they draw more current. Size the wire to the amp’s current draw.
Will a Class D amp cause radio interference?
A well-designed amp with a good ground shouldn’t. Route power and signal cables on opposite sides of the car.