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You buy a pair of highly rated studio headphones, plug them into your phone and hear a thin, quiet whisper. Nothing is broken. The most likely culprit is impedance, a number on the spec sheet that many buyers skip. beyerdynamic, the German headphone maker behind the DT 770 PRO, DT 880 PRO and DT 990 PRO, has explained this exact scenario in its own guidance. This guide covers what impedance means, why it changes volume and how to match headphones to what you plug them into.
What impedance is
In its guide to headphone impedance, beyerdynamic defines impedance, measured in ohms (Ω), as the electrical resistance of the voice coils in the transducer of wired headphones. It is tested during production with a standardized audio signal so that each headphone reaches its intended nominal impedance, the figure you see on the box.
To see why it matters, look at how a headphone makes sound. A diaphragm in the transducer vibrates the air to create sound waves, and it is moved by an electromagnet. The key part is the copper voice coil connected to the diaphragm. beyerdynamic explains that the lighter the coil, and so the thinner the wire, the clearer and more precise the transducer sounds. But a lighter coil also means greater resistance, which means higher impedance.
How impedance affects volume
Put simply, beyerdynamic says, the higher the impedance, the more voltage is needed for the headphones to sound loud enough. Most smartphones and notebooks do not provide as much power as a dedicated player or a stereo system. So beyerdynamic's rule of thumb is:
- Below 100 Ω: designed for mobile use with phones, tablets and laptops
- Above 100 Ω: great for stationary systems with a headphone amplifier, or for professional settings
beyerdynamic adds that a well equipped stereo system or studio usually supplies enough voltage, so high impedance causes no issues there. On phones and tablets, high impedance headphones will often sound too quiet. The company's rule of thumb is that headphones with higher impedance often produce a higher resolution sound, while lower impedance models are better suited to mobile devices.
The math, made simple
beyerdynamic gives a handy example. Assume a phone puts out 1 volt at the headphone jack. Power equals voltage squared divided by impedance:
- DT 770 PRO (80 Ω): 1 V squared divided by 80 Ω is 12.5 mW
- DT 990 Edition (600 Ω): 1 V squared divided by 600 Ω is 1.6 mW
On the same phone, the 80 ohm headphone gets almost eight times the power, which means much higher volume. To get the same power into the 600 ohm model, you would need more voltage, which mobile devices struggle to supply. An amplifier solves that. The example also shows why the same headphone can sound full on a studio interface and weak on a phone, even though nothing about the headphone has changed.
Common impedance levels
beyerdynamic groups headphones into broad bands, with a typical source for each:
- 16 Ω: smartphones and tablets
- 30 to 50 Ω: laptops, mobile devices, interfaces and headphone amplifiers
- 80 Ω: several studio applications, laptops, PCs and portable players
- 250 Ω: headphone amplifiers, stereo systems, audio interfaces and the studio
- 600 Ω: high end headphone amplifiers
It describes 16, 32 and 80 Ω as the common low impedance increments, and 250 Ω as a common high impedance value. If your system can supply the power, beyerdynamic suggests a 600 Ω model to get the most out of it.
Real world examples
Here is how some well known studio and hi-fi headphones line up, using their makers' official specs:
- beyerdynamic DT 990 PRO: 250 Ω, open
- beyerdynamic DT 880 PRO: 250 Ω, semi open
- Sennheiser HD 650: 300 Ω, open
- Sennheiser HD 560S: 120 Ω, open
The first three all belong in the high impedance group and will be happiest with an interface or a dedicated amp. Sennheiser describes the HD 560S as using low impedance drivers that work on virtually any device, which makes it a friendlier choice if you also listen on a laptop.
A caveat on comparing numbers
Impedance alone does not tell you exactly how loud a headphone will be. beyerdynamic explains that a 32 ohm headphone will be louder than a 48 ohm headphone at the same signal voltage only when both share the same driver design, with the same coil configuration. Within its own DT classic range, it says, volume decreases as impedance increases at the same signal voltage. Across different brands and drivers, also check the sensitivity, or nominal sound pressure level, on the data sheet.
How to choose
beyerdynamic's advice is to think first about which devices you will mainly use. If you mostly listen on a phone, stick to low impedance. If you work at a desk with an audio interface or a stereo, a 250 ohm studio headphone is a great fit. And if your gear at home cannot supply enough power, beyerdynamic says an additional headphone amplifier can seriously enhance the sound, while a portable DAC with a built in amp is an option on the go. See our picks for the best portable DACs and headphone amps.
Impedance is only part of the decision. The other big choice is the design: closed, semi open or open. Our guide to open back vs closed back headphones covers that next.
For more studio gear, browse our home studio picks.
