Key Takeaways
- The real difference between Class AB and Class D is efficiency, heat, size, and cost, not sound quality.
- Class D runs at roughly 85 to 95 percent efficiency; Class AB sits around 50 to 65 percent and runs hotter.
- Modern full-range Class D measures excellently. The old "Class D is only for subs" rule is outdated.
- Use Class D for subwoofers, high power, and tight installs where heat and space are limited.
- Either class works for a full-range front stage; pick on build quality, power, and fit rather than the class letter.
Class AB and Class D are the two amplifier classes you will actually choose between in car audio, and the honest answer is that the sound-quality gap that used to separate them has mostly closed. What still separates them is efficiency, heat, size, and cost. This compares the two on the terms that matter in a vehicle, and tells you which to pick for each job.
This is the head-to-head. For a deeper look at Class AB on its own, read our Class AB guide, and for the sound-quality benchmark class, see the best Class A amplifier. When you are ready to buy, browse Class AB amplifiers and Class D amplifiers.
How do Class AB and Class D amps work?
Class AB and Class D differ in how the output stage delivers power. A Class AB amp runs its output devices in a linear mode, conducting most of the waveform continuously, which is simple and clean but turns a large share of the drawn power into heat. A Class D amp switches its output devices fully on and off at high frequency and reconstructs the waveform through an output filter, which wastes very little power as heat.
That switching design is the whole reason Class D is so efficient, and it is also why early Class D amps had a sound-quality reputation to overcome. The switching and filtering in those early designs added artifacts at high frequencies. Modern Class D has largely engineered that out. For the full Class AB circuit explanation, the Class AB guide goes deeper.
Here is a side-by-side comparison of the two classes on sound, heat, and efficiency:
Does Class AB really sound better than Class D?
Not anymore, and that is the single most important thing to understand before you choose. The idea that Class AB sounds warmer and cleaner while Class D is only fit for subwoofers comes from early Class D designs. Today, a well-built full-range Class D amp measures excellently and is used in serious sound-quality front stages. The audible gap between a good modern Class D and a good Class AB is small to nonexistent.
What that means practically is that you should not pick Class AB expecting better sound on its own. Pick on the amp's actual measured performance, its power into your load, and its build quality. The class letter is not a sound-quality grade.
For the traditional case in favor of Class AB, this video makes the argument:
Efficiency and heat: the real difference
This is where the two classes genuinely separate. Class D converts most of the power it draws into output; Class AB converts a large fraction into heat. In a vehicle, where electrical power and airflow are both limited, that gap drives most of the practical decisions.
| Metric | Class AB | Class D |
|---|---|---|
| Efficiency | ~50 to 65% | ~85 to 95% |
| Heat generated | High | Low |
| Current draw for same output | Higher | Lower |
| Heatsink size needed | Large | Small |
Size, cost, and installation
Efficiency drives size and cost. Because Class D wastes so little power as heat, it needs less heatsink material and a smaller power supply to make a given wattage, so a Class D amp is usually smaller and often cheaper at high power. That also makes it the easier amp to install in a tight space, since it does not need the airflow a hot Class AB amp does.
Class AB amps tend to be physically larger for the same power and run hotter, so they want an open mounting location with room to breathe. Neither is hard to install correctly, but the Class D advantage in a cramped modern vehicle is real. Whichever you choose, wire and fuse it properly; the amplifier install guide covers gauge, fusing, and grounding.
Which should you choose?
Match the class to the job. For subwoofers, high power, and tight installs, Class D is the clear pick. For a full-range front stage, either class works, so choose on the specific amp rather than the class letter.
| Your job | Best pick |
|---|---|
| Subwoofer / high power | Class D |
| Tight install, limited airflow | Class D |
| Full-range / component front stage | Either, pick on the amp |
| Lowest cost at high power | Class D |
| You already run and prefer a Class AB amp | Class AB, no reason to switch |
Many builds use both: Class D on the subwoofers where efficiency matters most, and either class on the front stage. If you are running a processor, the DSP does the tuning work regardless of amp class, and the DSP tuning guide walks that through.
Frequently Asked Questions
Is Class AB better than Class D for sound quality?
Are Class D amps good for full-range speakers?
Which is more efficient, Class AB or Class D?
Should I use Class D or Class AB for a subwoofer?
Do Class AB amps run hotter than Class D?
Is Class D cheaper than Class AB?
Which amp class is best for a tight install?
Where to go next
Ready to shop by class? Browse Class AB amplifiers and Class D amplifiers. For the theory on each class, read the Class AB guide and the Class A guide. Once the amp is in, use the install guide and gain guide.
Not sure which class fits your speakers, your power system, and your goals? Contact us. We build and tune these systems ourselves and will point you to the right amp for the job, not the biggest number on the box.
About the Author
Scott Welch is a Multi Time IASCA National and MECA World Sound Quality Champion, an active SQ judge since 2019, and the owner of Audio Intensity in Tullahoma, Tennessee. He cuts every Proline X enclosure on the shop's CNCs and tunes every customer system before it leaves. Audio Intensity is the original US importer for Goldhorn DSP and an authorized dealer for Prodigy, Crescendo, Image Dynamics, Wavtech, Tru Technology, and more.
