Impedance (in ohms) and sensitivity (in dB) together decide how much power a pair of headphones needs to play loudly and cleanly. Low-impedance, high-sensitivity headphones run well from a phone or laptop. High-impedance or low-sensitivity headphones, common among open-back and planar models, often need a dedicated headphone amplifier.
Two numbers on a headphone spec sheet tell you whether your phone, laptop or amplifier can drive them properly: impedance and sensitivity.
Impedance
Impedance, measured in ohms (Ω), is how much a pair of headphones resists the electrical signal. As a rough guide:
| Impedance | Typical examples | What to expect |
|---|---|---|
| Under 32 Ω | Most earbuds, IEMs, wireless and portable headphones | Easy to drive from a phone |
| 32 to 80 Ω | Many home and studio headphones | Usually fine from a laptop; better with a dongle DAC |
| 150 to 600 Ω | Some studio and audiophile headphones | Usually need a headphone amplifier |
Sensitivity
Sensitivity tells you how loud headphones get for a given input. Brands quote it as dB SPL per milliwatt (dB/mW) or per volt (dB/V). Higher numbers mean louder at the same setting. A pair with low impedance but low sensitivity, which is common among planar magnetic headphones, can still need plenty of power.
Do you need an amplifier?
You probably need one if:
- Your headphones are rated 150 Ω or higher.
- Your headphones are planar magnetic with sensitivity under about 95 dB/mW.
- You turn your phone or laptop to maximum and it still sounds quiet or flat.
You probably do not if you use IEMs, wireless headphones or portable headphones under 32 Ω.
Matching tips
- Sensitive IEMs can pick up hiss from powerful amplifiers. Look for a low noise floor and low output impedance.
- Output impedance of the amp should be low, ideally under one eighth of your headphone impedance, so the tonal balance stays as designed.
- Balanced outputs often deliver more power from the same device, which helps demanding headphones.
Start with whether you need a DAC, compare open-back and closed-back designs, or browse DACs and amps.
Common questions
What impedance can a phone drive?
Most phones and laptops drive headphones under about 50 ohms with reasonable sensitivity to a comfortable volume. Above that, check sensitivity: 250 and 300 ohm headphones usually sound quiet or thin without an amplifier.
Is higher impedance better quality?
No. Impedance describes the electrical load, not sound quality. Many excellent headphones are low impedance; some studio favourites are high impedance for historical and technical reasons.
Why do planar magnetic headphones need power?
Many planar models have low impedance but low sensitivity, so they need more current to reach the same volume. A desktop amp or a strong portable DAC/amp helps.
What is dB/mW versus dB/V?
They are two ways of quoting sensitivity: loudness per milliwatt of power or per volt of signal. You cannot compare them directly without the impedance, so check which one a brand uses.