What’s Impedance in Headphones?

You can think of impedance as how much something "resists" the flow of electricity. For headphones, impedance is a measure of how much they resist the power coming from a device, such as a phone, computer, or headphone amplifier.

Simply put: the higher the impedance, the less power the player can deliver. That’s why you’ll see specs like “224 mW @ 16Ω / 200 mW @ 32Ω / 24 mW @ 300Ω” on audio devices. This means the device delivers:

• 224 mW to headphones with 16Ω impedance,
• 200 mW to headphones with 32Ω,
• 24 mW to headphones with 300Ω.

Basically, the higher the impedance of the headphones, the harder it is for the player to supply power.

But Wait, There’s More!

The headphone output on any device whether it’s a player, amp, phone, or computer also has its own impedance, which affects how much power it can deliver. What does this mean? You need to consider both the headphone impedance and the output impedance of your device. To get the best performance, you should aim for an output impedance that’s at least 1/8th the impedance of your headphones. 

The lower the output impedance of your device, the better. This ensures:

• No alterations to the headphones’ frequency response,
• No distortion,
• Avoidance of unwanted resonances (a.k.a. damping factor issues).

Low vs. High Impedance Headphones

• Low Impedance Headphones These tend to sound louder and are more efficient because the player can supply more power. However, they need amplifiers with very low output impedance to avoid distortion.
• High Impedance Headphones These are more forgiving of an amp’s limitations but will generally sound quieter because they resist power delivery more.

Basically, low-impedance headphones are simpler to control and have more precise expectations of the amp's quality, whereas high-ideapher headphones require less power but can handle faulty amps with greater precision.