Headphone Impedance Explained: Do You Need a Headphone Amp?

What is headphone impedance?

Headphone impedance is the electrical resistance a headphone presents to an alternating audio signal, measured in ohms (Ω). A higher number means the headphone draws less current, so it needs more voltage to reach the same power.

The spec sheet lists one number, but real impedance changes with frequency. Sonarworks explains that a headphone's impedance varies across the spectrum, so some frequencies can be affected more than others depending on what drives it^[1]. Keep that in mind, because it is the reason output impedance matters later in this guide.

• Impedance (ohms) How hard the headphone resists current. Tells you whether you need voltage or current to drive it.
• Sensitivity (dB SPL/mW or dB SPL/V) How loud the headphone plays for a given input. This decides real-world loudness.
• Output impedance (ohms) The internal resistance of your interface or amp's headphone jack. Too high relative to the headphone can color the sound.
• Max output (volts, dBu or mW) How much signal your headphone jack can deliver. Compare it with what your headphones need.

Is higher impedance better for headphones?

Higher impedance is not automatically better. It is a design choice that suits certain sources. Low-impedance headphones are easy to drive from phones and laptops, while high-impedance versions are built for studio gear that has plenty of voltage.

beyerdynamic makes this explicit with the DT 770 PRO, which comes in three versions: 32 ohms for mobile devices, 80 ohms for universal studio use and 250 ohms for professional devices^[2]. Same model, different match for different outputs. For most bedroom producers using a USB interface, the middle option is the safe pick.

Why does sensitivity matter more than impedance?

Sensitivity tells you how loud a headphone plays for a given signal, which is what you actually care about. Two headphones with the same impedance can play at very different levels from the same volume setting.

Makers quote sensitivity in two ways. dB SPL/V tells you the level at 1 volt, which maps directly to your interface's voltage spec. dB SPL/mW tells you the level at 1 milliwatt. Sennheiser lists the 300 ohm HD 600 at 97 dB SPL at 1 V^[5]. Every doubling of voltage adds about 6 dB.

Converting between dB/mW and dB/V

One volt into a headphone of Z ohms delivers 1000/Z milliwatts. So dB SPL/V = dB SPL/mW + 10 × log10(1000/Z). For a 300 ohm headphone that is a difference of about 5.2 dB; for a 32 ohm headphone it is about 15 dB. Low-impedance headphones reach high levels from very little voltage, which is why they work from phones.

What is output impedance and the 1/8 rule?

Output impedance is the resistance built into the headphone jack itself. When it is high relative to the headphone's impedance, the headphone's changing impedance curve turns into a changing frequency response, so bass or treble shifts depending on the model.

The common guideline is the 1/8 rule: the source's output impedance should be one eighth or less of the headphone's impedance. Sonarworks gives the example that 32 ohm headphones want a source of 4 ohms or less, and reports measured response changes ranging from inaudible, around 1 dB, up to 7 dB in worst cases^[1].

Check your interface's spec sheet

Output impedance varies more than people expect. Focusrite lists the Scarlett 2i2 4th Gen headphone output at 50 ohms output impedance^[6]. By the 1/8 rule that suits headphones of 400 ohms and above. With low-impedance headphones the result depends on how flat each model's impedance curve is, so check measurements of your exact pair, or trust your ears and a correction profile. If you are shopping for an interface, compare headphone output specs alongside the picks in our budget audio interface guide.

How loud will your interface drive your headphones?

Here is the math: take the headphone's sensitivity in dB SPL/V, then add 20 × log10 of the maximum voltage your jack delivers. The result is the loudest level you can reach. If it sits comfortably above the level you mix at, you do not need an amp.

Focusrite lists the 2i2 4th Gen headphone output at +10 dBu maximum into 300 ohms, or 22 mW^[6]. Since 0 dBu is about 0.775 V^[7], +10 dBu is about 2.45 V. Apple says Macs with its adaptive headphone jack deliver up to 1.25 V RMS for lower-impedance headphones and 3 V RMS for headphones between 150 ohms and 1k ohms^[8].

These are peak ceilings for a sine wave. Music has peaks well above its average level, so a source that tops out near 97 dB will sound quiet on a dynamic, unmastered mix, while 105 dB leaves reasonable room for everyday mixing at moderate levels. Protect your hearing: loud headphone sessions cause fatigue fast, and quieter mixing also improves your judgment.

How do you know if you need a headphone amp?

You need a headphone amp when your headphones sound too quiet at full volume, or when they distort, thin out or lose bass as you push the level. If none of that happens with your quietest reference tracks, an amp will not improve your mixes.

• Volume knob near maximum If you need 80 to 100 percent of the dial for normal mixing, you have no headroom for quiet material. An amp or a more sensitive pair fixes that.
• Distortion on loud peaks Crunchy kicks or harsh vocals only at high volume mean the output is clipping before the headphone reaches its limit.
• Sound changes between sources If the same headphones sound bassier or brighter on another device, output impedance is likely the cause.
• Several listeners Tracking a band or a feature artist often needs a multi-output headphone amp simply for more jacks.
• No amp needed Your headphones get loud enough at around half to three quarters of the dial and sound the same on other good sources.

A quick checklist before you buy headphones or an amp

Match the headphones to the source you already own, then test before spending on an amp. The numbers are all on spec sheets and take five minutes to compare.

1. Find the headphone specs
   Note impedance and sensitivity, and whether sensitivity is per volt or per milliwatt.
2. Find the jack specs
   Look up your interface's headphone output: maximum level in volts or dBu at a load close to your headphone's impedance, and output impedance.
3. Estimate max loudness
   Sensitivity in dB/V plus 20 × log10(max volts). Around 105 dB or more is comfortable for mixing.
4. Check the 1/8 rule
   If output impedance is more than an eighth of the headphone impedance, listen for tonal shifts against another source.
5. Listen at your real level
   Play a quiet, dynamic reference track at your usual mixing level and note where the knob sits.
6. Decide
   Plenty of level and no tonal shift: no amp. Too quiet or colored: choose a lower-impedance version of your headphone or add an amp with low output impedance.

Impedance is only one part of choosing headphones. Cup design changes isolation and stereo image, which our open-back vs closed-back comparison covers, and our list of mixing headphones under $200 helps narrow the models. Once you settle on a pair, the headphone-only mixing workflow helps your mixes translate.