Audit

A third of headphone spec sheets don't say what their numbers mean

Every headphone in this database was checked against the manufacturer's own documentation — 402 models, one spec sheet at a time. The point of the exercise was to record not just the sensitivity figure but the unit it was printed in. That turned out to be the more interesting number.

Sensitivity can be stated per milliwatt or per volt. The two differ by 10 × log10(1000/Z): about 5 dB on a 300 ohm headphone, 18 dB on a 16 ohm in-ear. Read one as the other and you will conclude a headphone is easy to drive when it is not, or buy an amplifier you did not need.

Of the 392 non-electrostatic models here, 173 publish per milliwatt and 82 publish per volt. The remaining 137 — 35% — publish a number you cannot use: either a bare decibel figure with no reference at all, or no sensitivity figure whatsoever.

Per milliwattPer voltMaker does not say
How each maker states headphone sensitivityHorizontal stacked bars, one per brand, showing how many of that brand's models publish sensitivity per milliwatt, per volt, or with no reference unit at all. The full figures are in the table below.BeyerdynamicBeyerdynamic — Per milliwatt: 9 of 29Beyerdynamic — Maker does not say: 20 of 2929SennheiserSennheiser — Per milliwatt: 1 of 27Sennheiser — Per volt: 21 of 27Sennheiser — Maker does not say: 5 of 2727HiFiMANHiFiMAN — Maker does not say: 25 of 2525Audio-TechnicaAudio-Technica — Per milliwatt: 22 of 23Audio-Technica — Maker does not say: 1 of 2323AudezeAudeze — Per milliwatt: 17 of 1717MoondropMoondrop — Per volt: 14 of 15Moondrop — Maker does not say: 1 of 1515ShureShure — Per milliwatt: 15 of 1515AKGAKG — Per volt: 13 of 14AKG — Maker does not say: 1 of 1414FocalFocal — Per milliwatt: 13 of 14Focal — Maker does not say: 1 of 1414ZMFZMF — Per milliwatt: 11 of 1111MezeMeze — Per milliwatt: 8 of 11Meze — Maker does not say: 3 of 1111ThieaudioThieaudio — Per volt: 1 of 11Thieaudio — Maker does not say: 10 of 1111GradoGrado — Per milliwatt: 8 of 10Grado — Maker does not say: 2 of 1010SonySony — Per milliwatt: 9 of 99Dan Clark AudioDan Clark Audio — Per milliwatt: 7 of 8Dan Clark Audio — Maker does not say: 1 of 88FostexFostex — Per milliwatt: 7 of 8Fostex — Maker does not say: 1 of 88SimgotSimgot — Per volt: 7 of 77TruthearTruthear — Per volt: 5 of 6Truthear — Maker does not say: 1 of 66Kiwi EarsKiwi Ears — Per milliwatt: 3 of 6Kiwi Ears — Maker does not say: 3 of 66EtymoticEtymotic — Per milliwatt: 6 of 66Campfire AudioCampfire Audio — Per volt: 1 of 6Campfire Audio — Maker does not say: 5 of 6664 Audio64 Audio — Per milliwatt: 6 of 66PhilipsPhilips — Per milliwatt: 2 of 6Philips — Maker does not say: 4 of 66FiiOFiiO — Per milliwatt: 3 of 6FiiO — Per volt: 3 of 66AbyssAbyss — Per milliwatt: 2 of 5Abyss — Maker does not say: 3 of 55Final AudioFinal Audio — Per milliwatt: 5 of 557Hz7Hz — Per volt: 3 of 57Hz — Maker does not say: 2 of 55LetshuoerLetshuoer — Per milliwatt: 2 of 5Letshuoer — Maker does not say: 3 of 55DenonDenon — Per milliwatt: 4 of 5Denon — Maker does not say: 1 of 55KennertonKennerton — Maker does not say: 4 of 44KossKoss — Per milliwatt: 2 of 4Koss — Maker does not say: 2 of 44Austrian AudioAustrian Audio — Per volt: 4 of 44SivgaSivga — Maker does not say: 4 of 44SoftearsSoftears — Per volt: 4 of 44Tin HiFiTin HiFi — Maker does not say: 4 of 44
One bar per brand for every brand with four or more models, longest first. The 26 smaller brands are in the table below rather than the chart, since a bucket of unrelated makers has no house convention to show. Electrostatic models are left out throughout: they are specified on a different scale entirely.

It is not that makers disagree. It is that many do not say.

Disagreement would be manageable. AKG, Austrian Audio, Moondrop, Simgot, Softears and Symphonium publish per volt across their whole catalogue — consistently, every model, so a reader who knows the convention can convert and move on. Sennheiser does the same on every consumer model but one: the HD 600's “97 dB” is per volt, which at 300 ohms makes it 91.8 dB/mW — a headphone with a reputation for needing an amplifier, and this is the arithmetic behind that reputation. That is a solvable problem, and this site solves it on every page.

The unsolvable ones are the makers who print a figure and stop. Dunu, HiFiMAN, Sivga, Tangzu and Tin HiFi state a sensitivity with no reference unit anywhere on the page, in the manual, or in the datasheet. The spec sheet says “94 dB” and that is the end of it. There is no honest way to convert a number whose unit nobody states — so on those pages this site shows both readings and the gap between them, rather than picking one and hoping.

Several makers are not even consistent with themselves. Beyerdynamic prints the reference on its newer models (“1 mW / 500 Hz”) and omits it on the DT 770, 880 and 990 — then quotes the same 96 dB for the 32, 80 and 250 ohm versions of the same headphone, which cannot be a per-milliwatt figure at three different loads. FiiO publishes both units on one line for the FT1 and FT5, and per-volt only for the FT3. Kiwi Ears prints “dB SPL/mW” on one model and a bare dB on the next two.

Brand ModelsPer mWPer volt Unusable
Beyerdynamic299020
Sennheiser271215
HiFiMAN250025
Audio-Technica232201
Audeze171700
Moondrop150141
Shure151500
AKG140131
Focal141301
ZMF111100
Meze11803
Thieaudio110110
Grado10802
Sony9900
Dan Clark Audio8701
Fostex8701
Simgot7070
Truthear6051
Kiwi Ears6303
Etymotic6600
Campfire Audio6015
64 Audio6600
Philips6204
FiiO6330
Abyss5203
Final Audio5500
7Hz5032
Letshuoer5203
Denon5401
Kennerton4004
Koss4202
Austrian Audio4040
Sivga4004
Softears4040
Tin HiFi4004
26 smaller brands4711630

Four specific things worth knowing

Superlux rates a headphone in watts it cannot take. The HD 668B datasheet gives 98 dB SPL referenced to one watt. The same datasheet caps input power at 300 milliwatts. Converted honestly, one watt puts the figure 30 dB below anything a headphone could plausibly measure — so the reference is wrong, not the number, and there is no way to tell what the real figure is.

Campfire Audio publishes an SPL at 11.84 millivolts. Not per milliwatt, not per volt — at one specific drive voltage. It is perfectly convertible and this site converts it, but nothing else in the database is stated that way, and a reader comparing it to anything else without doing the arithmetic will be out by more than 16 dB.

Three products in wide circulation do not exist. A Limited Edition DT 1990 PRO, a Focal Utopia in-ear and a KZ ZA10 all had entries in this database, carried over from secondary sources. Beyerdynamic has never made the first, Focal has never made an in-ear at all, and KZ's nearest real models are the AZ10, AS10, ZS10 and ZAX. Specifications circulate for products that were never built.

Amplifiers have the same disease in a different form. Of the sources checked for this site, 42 were excluded outright — most of them because the maker publishes a wattage with no stated load. “1 W” means nothing without the impedance it was measured into; it is not a specification, it is a number. Others were dropped because two of the maker's own documents disagreed with each other.

What to do about it

If you are comparing two headphones, check what unit each figure is in before you compare them. If one is per volt and the other per milliwatt, the difference between them is mostly the unit, not the headphone. The converter does that arithmetic, and every model page here states which unit its maker printed.

If a spec sheet gives you a bare decibel number, treat it as an indication and nothing more. Ask what the impedance is, work out what the gap would be, and see whether the answer changes your decision. Often it does not — most headphones are easy to drive either way. When it does, it changes it completely.

The full method, including what was excluded and why, is set out in how this data was built. Every model page links the manufacturer document its figures came from.

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