Headphone impedance: what the ohms figure means for your amp
Impedance is the opposition a headphone presents to the signal from an amplifier, measured in ohms, and it changes with frequency. It doesn't tell you how loud a headphone will play, which is what sensitivity is for. It tells you how the power has to arrive, as voltage for high-impedance models and current for low ones, and how your source's own output impedance will affect the sound.
- By Jakub Charkiewicz
- Published
- Updated
- 4 min read
Glossary definition
- Impedance
- The total opposition (resistance + reactance) a speaker or headphone presents to the driving current, measured in ohms and varying with frequency.
What the ohms figure measures
A headphone driver is an electrical load. Its impedance combines the plain resistance of its wire with the effects of the coil's inductance and of the driver's own motion, and together they set how much current flows for a given voltage. The figure on the spec sheet is a nominal value, often measured at 1 kHz: the Kiwi Ears Belle's review, for example, gives its 32 ohms at 1 kHz.
The curve itself moves with frequency, and how it moves depends on the driver. A dynamic driver rises to a peak at its bass resonance and often climbs again in the treble. A planar magnetic driver stays nearly flat across the band. A multi-driver IEM with balanced armatures and a crossover can swing a long way from one region to the next. Keep that in mind whenever a single number is all you have.
Voltage for high impedance, current for low
Power, voltage and impedance are tied together: power equals voltage squared divided by impedance. So the same milliwatt arrives in different forms. Into 32 ohms, 1 mW takes about 0.18 V and 5.6 mA. Into 300 ohms it takes about 0.55 V and 1.8 mA. Into 8 ohms it takes only 0.09 V, but 11 mA.
A source can run out of either. Battery-powered sources are limited in how much voltage they can swing, which is where a high-impedance headphone finds them out, while a very low impedance asks for current that small amplifiers may not have. The Verum Audio Verum 1 is an 8-ohm planar, and its review warns that it "demands real current from the amplifier".
This is also why an amplifier's power rating always names a load. The same amplifier makes different power into 32 ohms and into 300, and a rating quoted into one says little about the other.
Why impedance needs sensitivity beside it
How loud a headphone plays for a given input is set by its sensitivity, and impedance only matters in combination with it. The HIFIMAN HE-R9 is 60 ohms, higher than many headphones, and its review calls it extremely easy to drive at 100 dB sensitivity. The HIFIMAN Arya Unveiled is a lower 27 ohms, yet its reviewer warns that you might think a phone can drive it from the impedance alone, and not to try: at 94 dB it wants a dedicated amplifier with good current delivery.
The pattern that trips people up is low impedance paired with low sensitivity. That combination needs real power delivered as current, and current is what small sources tend to run short of. The sensitivity explainer covers the two sensitivity units and how to convert between them, since that conversion needs the impedance too.
High impedance isn't a mark of quality either. The winding is a design choice made to suit a class of source, and some headphones are sold in several impedance versions of the same model for that reason.
Output impedance and the one-eighth rule
Every amplifier has an output impedance of its own, and it sits in series with the headphone. The two form a voltage divider: the headphone receives the share of the signal that its impedance bears to the total. If the headphone's impedance were the same at every frequency, that share would be constant and the only effect would be a slightly lower level.
It rarely is. Where a dynamic headphone's impedance peaks in the bass, it gets a larger share of the voltage than elsewhere, so a source with a high output impedance adds a bass hump the headphone does not have on its own. With a multi-armature IEM, whose curve swings further, the change can reach the midrange and treble; the balanced armature explainer covers that case. A planar's flat curve is barely affected.
The usual guidance is to keep the source's output impedance at or below one-eighth of the headphone's lowest impedance. At that ratio the response can shift by no more than about 1 dB anywhere in the band. For most dynamic headphones the lowest point is close to the nominal figure, so a 32-ohm pair wants a source under 4 ohms. The same ratio is sometimes quoted as damping factor, the headphone's impedance divided by the source's output impedance, and the rule asks for a damping factor of at least 8.
Reading impedance on a spec sheet
Start with both figures together: impedance and sensitivity, with the sensitivity's unit. The table further down this page lists every reviewed headphone that records an impedance, beside its sensitivity, and a figure such as the HIFIMAN RE2000 PRO Silver's 60 ohms reads differently in context: fairly high for an IEM, its review notes, yet easy to drive at 103 dB.
Then check your source at the headphone's impedance. Look for its rated output into that load, or the nearest one listed, and for its output impedance if the headphone is a dynamic or a multi-armature design. The headphone power calculator turns impedance, sensitivity and a target level into the power, RMS voltage and peak voltage swing you need, and the best headphone amplifiers guide ranks the headphone amps reviewed here.
Impedance across the headphones we have reviewed
24 of 30 headphone reviews record a nominal impedance; the other 6 are left out rather than guessed. Sorted low to high, with the figure it has to be read against beside it.
| Headphone | Impedance | Sensitivity | Price | Score | Bracket |
|---|---|---|---|---|---|
| Verum Audio Verum 1 | 8 Ω | 107 dB/mW | $349 | 8.0/10 | Low (< 32 Ω) |
| HIFIMAN Ananda Stealth | 16 Ω | 93 dB† | $359 | 8.8/10 | Low (< 32 Ω) |
| HIFIMAN Arya Organic | 16 Ω | 94 dB/mW | $1,099 | 9.2/10 | Low (< 32 Ω) |
| Kiwi Ears Orchestra Lite | 16 Ω | 112 dB† | $249 | 8.0/10 | Low (< 32 Ω) |
| HIFIMAN Edition XS | 18 Ω | 92 dB/mW | $269 | 8.7/10 | Low (< 32 Ω) |
| HIFIMAN Sundara Closed-back | 20 Ω | 98 dB† | $229 | 6.8/10 | Low (< 32 Ω) |
| Simgot EM6L | 26 Ω | 119 dB/V | $109 | 7.6/10 | Low (< 32 Ω) |
| HIFIMAN Arya Unveiled | 27 Ω | 94 dB† | $1,299 | 9.1/10 | Low (< 32 Ω) |
| HIFIMAN Arya Stealth | 32 Ω | 94 dB/mW | $759 | 8.7/10 | Medium (32-100 Ω) |
| Kiwi Ears Atheia | 32 Ω | 102 dB/mW | $349 | 7.9/10 | Medium (32-100 Ω) |
| HarmonicDyne Eris | 32 Ω | 118 dB† | $249 | 6.8/10 | Medium (32-100 Ω) |
| HIFIMAN HE1000 Stealth | 32 Ω | 93 dB† | $1,119 | 8.5/10 | Medium (32-100 Ω) |
| HIFIMAN HE400se | 32 Ω | 91 dB/mW | $109 | 7.6/10 | Medium (32-100 Ω) |
| Sivga Robin SV021 | 32 Ω | 105 dB† | $149 | 7.8/10 | Medium (32-100 Ω) |
| HIFIMAN Sundara | 32 Ω | 92 dB/mW | $299 | 9.0/10 | Medium (32-100 Ω) |
| OLLO Audio X1 | 32 Ω | 101 dB† | $549 | 8.9/10 | Medium (32-100 Ω) |
| HIFIMAN HE1000se | 35 Ω | 96 dB/mW | $1,700 | 9.3/10 | Medium (32-100 Ω) |
| Sivga Anser | 38 Ω | 105 dB† | $199 | 8.0/10 | Medium (32-100 Ω) |
| Sivga Luan | 38 Ω | 100 dB† | $299 | 8.1/10 | Medium (32-100 Ω) |
| Meze 105 Silva | 42 Ω | 112 dB† | $499 | 8.7/10 | Medium (32-100 Ω) |
| Sivga SV021 Pro | 45 Ω | 106 dB† | $179 | 7.6/10 | Medium (32-100 Ω) |
| HIFIMAN HE-R9 | 60 Ω | 100 dB† | $199 | 6.9/10 | Medium (32-100 Ω) |
| HIFIMAN RE2000 PRO Silver | 60 Ω | 103 dB† | $349 | 8.8/10 | Medium (32-100 Ω) |
| HIFIMAN RE800 Silver | 60 Ω | 105 dB† | $99 | 8.0/10 | Medium (32-100 Ω) |
† The maker gives no reference for this sensitivity (dB/mW or dB/V), so it cannot be read against the other figures as they stand.
What our reviews say about impedance
8 reviews raise it in their pros and cons: 5 lines credit it and 3 fault it. 6 are shown, each quoted as its review states it.
- Strength:
Easy-to-drive flagship: 35 ohms / 96 dB, three cables incl. balanced XLR
- HIFIMAN HE1000se, 9.3/10 - Flaw:
High output impedance (625Ω RCA / 1250Ω XLR)
- Denafrips Enyo 15th Anniversary, 9.1/10 - Strength:
Halved impedance (16Ω) - drives easily
- HIFIMAN Arya Organic, 9.2/10 - Flaw:
Impedance dips to 3Ω - not the easiest load
- Triangle Australe EZ, 8.1/10 - Strength:
Easy to drive at 106dB / 45 ohms - scales nicely with a dongle or amp
- Sivga SV021 Pro, 7.6/10 - Flaw:
8Ω impedance demands real current from the amplifier
- Verum Audio Verum 1, 8.0/10
Compared head to head
Comparisons between products on this page, each weighing the two reviews side by side.
Put it to use
Sources and further reading
- IEC 60268-7: Headphones and earphones
Standard International Electrotechnical Commission Paid full text
The international standard for the headphone characteristics makers specify, and how each should be measured.
- HyperPhysics: Impedance matching of audio components
Reference Georgia State University
Explains why modern amplifiers use low output impedance and drive voltage, instead of matching impedance to the load.
- Wikipedia: Electrical impedance
Encyclopedia Wikipedia
Keep reading
Balanced
A signal transmission method using two opposite-polarity signal lines plus a ground; noise induced on both lines is canceled at the differential input.
Sensitivity
The output sound pressure level for a standardized input: dBSPL at 1W/1m for speakers, or dBSPL at 1mW or 1V for headphones.
Gain
The multiplication factor applied to a signal by an amplifier, expressed in dB; proper gain staging is critical for minimizing noise.