The AKG K240 MKII is 55Ω with a sensitivity of 91.4 dB/mW, which is 104.0 dB/V. To reach 100 dB SPL — genuinely loud, louder than most people listen — it needs 7.2 mW, or 0.63 V across the drivers.
That is a moderate load. Most USB dongles handle it without complaint; the weakest phone outputs will run out of volume before they run out of quality. 276 of 280 sources here have enough headroom. The cheapest portable source that does the job is the Apple USB-C dongle (US) at $9.
Sensitivity here is in dB per milliwatt. Why the unit matters.
AKG publishes this as 104 dB SPL/V (1 V at 1 kHz (AKG heads the column 'Sensitivity (dB SPL/V @ 1 kHz)')) — a figure per volt, not per milliwatt. At 55Ω the two differ by 12.6 dB, so the 91.4 dB/mW above is that published number converted, not a different measurement.
This is the conversion that online calculators skip. Quote the per-volt number as if it were per-milliwatt and this headphone looks 13 dB easier to drive than it is — which is roughly the difference between a dongle being enough and not being enough.
Source: akg.com. How this data was built.
| As it is labelled | As printed | Tolerance | Standard |
|---|---|---|---|
| Audio frequency bandwidth (Hz) | 15 - 25000 | not printed | not printed |
AKG prints 15 - 25000 for the AKG K240 MKII, under the heading “Audio frequency bandwidth (Hz)”. Source: akg.com.
No tolerance is printed with it, so “15 - 25000” says nothing about how loud this headphone actually is at 15 Hz.
Only what the maker printed; maker by maker.
| Level | What it is | Power | Voltage | Current |
|---|---|---|---|---|
| 85 dB SPL | quiet background listening | 0.23 mW | 0.11 V | 2.0 mA |
| 95 dB SPL | normal listening | 2.3 mW | 0.35 V | 6.5 mA |
| 100 dB SPL | loud listening | 7.2 mW | 0.63 V | 11.5 mA |
| 105 dB SPL | very loud | 23 mW | 1.12 V | 20.4 mA |
| 110 dB SPL | peaks on dynamic music | 72 mW | 2.00 V | 36.3 mA |
Most people listen between 75 and 85 dB; the 100 dB row leaves room for peaks.
The 15 cheapest of the 280 sources here that reach 100 dB SPL into 55Ω with at least 10 dB of headroom and no known hiss or output-impedance problem with these headphones. All 280 sources, judged for these headphones.
| Source | Type | Price | Power into 55Ω | Headroom | Verdict |
|---|---|---|---|---|---|
| FiiO KA11 | USB dongle | $29 | 117 mW | +12 dB | Comfortable |
| ddHiFi TC35AL | USB dongle | $46 | 122 mW | +12 dB | Comfortable |
| ddHiFi TC35Air | USB dongle | $46 | 122 mW | +12 dB | Comfortable |
| Fosi Audio N3 | Bluetooth receiver | $50 | 80 mW | +10 dB | Comfortable |
| Tempotec Sonata BHD Pro | USB dongle | $60 | 163 mW | +14 dB | Comfortable |
| Tanchjim Space | USB dongle | $70 | 73 mW | +10 dB | Comfortable |
| Truthear SHIO | USB dongle | $70 | 73 mW | +10 dB | Comfortable |
| Aiyima A2 Pro | desktop DAC/amp | $75 | 87 mW | +11 dB | Comfortable |
| Moondrop Dawn Pro | USB dongle | $75 | 73 mW | +10 dB | Comfortable |
| FiiO KA3 | USB dongle | $79 | 76 mW | +10 dB | Comfortable |
| JDS Labs Atom+ (2nd gen) | desktop amplifier | $99 | 725 mW | +20 dB | Comfortable |
| Schiit Magni Heresy | desktop amplifier | $99 | 1.5 W | +23 dB | Comfortable |
| ddHiFi TC44 Pro E2 | USB dongle | $99 | 145 mW | +13 dB | Comfortable |
| Fosi Audio SK02 | desktop amplifier | $100 | 111 mW | +12 dB | Comfortable |
| FiiO BTR15 | Bluetooth receiver | $109 | 73 mW | +10 dB | Comfortable |
Hiss. At 104.0 dB/V these are sensitive enough to reveal a source's own noise floor. The noisiest source in the database, the Schiit Mjolnir 3, would put its hiss at roughly 12 dB SPL in these headphones — clearly audible in quiet passages. Check your own source.
Output impedance. At 55Ω these want a source output impedance below 6.88Ω to satisfy the one-eighth rule; 34 of the 192 sources that publish one miss it. Check yours here.
55Ω · 91.4 dB/mW · Moderate
See requirements →55Ω · 91.4 dB/mW · Moderate
See requirements →62Ω · 92.9 dB/mW · Moderate
See requirements →200Ω · 97.0 dB/mW · Moderate
See requirements →120Ω · 94.8 dB/mW · Moderate
See requirements →50Ω · 91.0 dB/mW · Moderate
See requirements →