Questyle M15: power output and what it will drive

The Questyle M15 is a USB dongle at $250. It delivers 300 mW into 32Ω and 55 mW into 300Ω, which ranks it 132 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 549 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 14, only marginal on 2 and not enough power for 2. Questyle publishes power at 300Ω only, and their own site could not be reached during this check. A figure at 300Ω says nothing reliable about what a source does into 32Ω, so the low-impedance numbers here are carried over unverified rather than derived.

Nothing in the table above could be traced to a document this manufacturer publishes. The figures come from the material this database was first built from — independent measurement and reviewer reports — and every one of them is labelled unverified for that reason. They are being re-sourced one model at a time, and this page will change when the maker publishes something or a document turns up.

Nothing here is derived: every figure in the table is either a number the maker published at that exact load or a number marked unverified. The method behind the labels is written up here.

Ordered from easiest to hardest to drive. Headroom is measured at 100 dB SPL, which is louder than almost anyone listens — a small negative number means the source still plays loud, just without reserve for peaks.

These figures come from each manufacturer's own sensitivity rating. A handful of planars — the HiFiMAN Susvara and the Abyss AB-1266 in particular — are widely reported to need far more than their published sensitivity implies, so treat a bare pass on those as optimistic rather than settled.

At 3 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

That noise figure has not been traced to a document from the maker, so the levels below are as good as the number they start from.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 31 dB SPL, which you will hear between tracks and in quiet passages.

At 0.5Ω output impedance, the one-eighth rule says this source suits headphones of 4.0Ω and above. 1 of the 567 models here falls below that. The one model below that line is the Symphonium Titan, and the mismatch tilts the frequency response audibly rather than subtly.

That output impedance has not been traced to a document from the maker, so the count above is only as good as the number it starts from.

The rule is a rule of thumb, not physics: a source impedance below one eighth of the headphone's keeps the interaction under about 1 dB. The checker works it out for any pair.

Of the 280 sources here, 42 do everything the Questyle M15 does as a headphone output: reach 100 dB on every headphone it reaches. The cheapest of them is the FiiO KA11 at $29, against this one’s $250 — $221 less.

The cheaper one also publishes an output impedance and a noise figure, which the Questyle M15 does not — so on the paperwork it is ahead, not merely level.

This counts a headphone output and nothing else. Inputs, converters, microphone preamps, balanced outputs, the volume control, the case and the warranty are all outside it, and any of them can be the reason to buy the dearer box. What the count does say is that the three numbers a maker can be held to do not separate them.

Worked out in advance against its closest rivals: vs Astell&Kern HC3 · vs Cayin RU7 · vs ddHiFi TC44Grip · vs Shanling UA5. Each of those pages lists the headphones that tell the two apart.

Or put any two side by side in the source comparison tool, or run your own headphones through the amplifier matcher. Or see every Questyle source in the database, and how much of what this site says about them came from Questyle’s own documents.