Headphone Sensitivity Converter: voltage to power (dB/V ↔ dB/mW)

Headphone sensitivity is printed either per volt (dB/V, a voltage reference) or per milliwatt (dB/mW, a power reference). This converts one into the other at any impedance. It matters because two headphones can list the same "105 dB" and be wildly different in how hard they are to drive — makers quote both units and rarely label which one. Paste in whatever the spec sheet says, add the impedance, and get both.

Why the gap gets bigger as impedance drops

One volt into 600Ω delivers 1.7 mW. The same volt into 16Ω delivers 62 mW — about 37 times more power. So for a high-impedance headphone the two numbers sit fairly close together, while for a low-impedance IEM they can be more than 15 dB apart. That is why the unit confusion does the most damage exactly where people are most likely to get burned: cheap, sensitive IEMs.

The conversion at every impedance that matters

The tool above converts one figure at a time. This is the same arithmetic laid out for every impedance in this database shared by at least 3 models — 45 values from 5.8 to 600 Ω, covering 503 of the 567 non-electrostatic models here. Find your impedance and read across.

Column two is the whole conversion: dB/mW = dB/V − 10 log₁₀(1000 / Z). Column three shows what it does to a concrete number — what “100 dB” on a spec sheet really means if the maker meant per volt. Column four is why it matters: the factor by which you have misjudged the power required if you read a per-volt figure as per-milliwatt. At 5.8 Ω that factor is 172; at 600 Ω it is 1.7.

Two things follow from the shape of this table. The gap never disappears — even at 600 Ω, the highest impedance here, it is 2.2 dB, and 1.7 times the power is still the difference between sizing an amplifier right and sizing it by half. And it is worst exactly where it is least likely to be caught: the single-digit and teen impedances at the top of the table belong to in-ears, where the figure is most often printed without a unit in the first place. Which makers print which unit, and how many print none, is counted model by model.

Two headphones, the same number, a different amplifier

That opening line is not a hypothetical. These are real pairs from this database: in each row both makers printed the same sensitivity figure, one of them per milliwatt and one per volt, and the last column is how much more power the second one actually needs to reach 100 dB.

The table is built, not picked: it takes every sensitivity figure that appears in both conventions somewhere in this database, sorts the pairs by how far apart they really are, and keeps the first four — with the one condition that no maker appears twice, so it cannot be one brand's quirk. Quote the per-volt number as if it were per-milliwatt and you have not made a rounding error. You have picked the wrong amplifier.

How big the gap is across the whole database

The gap depends on one thing only: impedance. It is 10 × log₁₀(1000 / Z), so it is 14.9 dB at the median impedance here, and it grows as the impedance falls.

• 521 of the 567 models — 92% — have a gap of ten decibels or more.
• 280 have a gap of fifteen or more. That is roughly the difference between a dongle being enough and not being enough.
• The widest is the Symphonium Titan at 3Ω: 25.2 dB between the two readings of one printed number.

High-impedance headphones are the forgiving case. At 300Ω the two readings sit 5.2 dB apart, which is annoying but survivable. At 16Ω they are 18 dB apart, and at single-digit impedances more than twenty. The confusion does its damage exactly where the buyers are least experienced.

Which makers use which

Counted from this database, over figures that come from the makers' own documents: Moondrop, AKG, Truthear, Symphonium, Austrian Audio, Tanchjim, Elysian Acoustic Labs and Campfire Audio publish per volt on every model here and never per milliwatt. Audio-Technica, Audeze, Fostex, Shure, Meze, Grado, Beyerdynamic, Sony, ZMF, Dan Clark Audio and 64 Audio do the opposite.

Two things are worth knowing before you use that as a rule. First, plenty of makers are not consistent even with themselves — the same catalogue will carry both conventions, sometimes on the same page. Second, a large part of this database prints a decibel figure with no reference unit at all, in which case no rule helps and neither does this converter. The full count is in the spec sheet audit.