The Truthear ZERO:BLUE2 is 5.8Ω with a sensitivity of 97.1 dB/mW, which is 119.5 dB/V. To reach 100 dB SPL — genuinely loud, louder than most people listen — it needs 1.9 mW, or 0.11 V across the drivers.
That puts it in the easy category. A phone, a laptop headphone jack or the cheapest USB dongle will drive it to painful levels. Of the 280 sources in the database, 221 have at least 10 dB of headroom and another 53 have enough. 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.
Truthear publishes this as 119.5 dB/Vrms (@1KHz) — a figure per volt, not per milliwatt. At 5.8Ω the two differ by 22.4 dB, so the 97.1 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 22 dB easier to drive than it is — which is roughly the difference between a dongle being enough and not being enough.
Truthear prints the impedance as 5.8Ω±15% @1KHz, not as a bare number. Everything on this page is calculated with the nominal 5.8Ω, and the rest of that line is quoted here rather than tidied away, because how a figure is qualified is part of the specification too.
Source: truthear.com. How this data was built.
| As it is labelled | As printed | Tolerance | Standard |
|---|---|---|---|
| Frequency Response Range | 20-41kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| Effective Frequency Response Range | 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 |
Truthear prints two frequency ranges for the Truthear ZERO:BLUE2. The wide one carries no conditions at all; the narrow one names a measurement standard and a tolerance. Only the second is a specification — the first is a headline.
This is one of only 58 models — out of the 490 whose maker prints a range at all — that also print the tolerance. That is what makes it a specification rather than a headline.
Only what the maker printed; maker by maker.
| Level | What it is | Power | Voltage | Current |
|---|---|---|---|---|
| 85 dB SPL | quiet background listening | 0.06 mW | 19 mV | 3.3 mA |
| 95 dB SPL | normal listening | 0.62 mW | 60 mV | 10.3 mA |
| 100 dB SPL | loud listening | 1.9 mW | 0.11 V | 18.3 mA |
| 105 dB SPL | very loud | 6.2 mW | 0.19 V | 32.6 mA |
| 110 dB SPL | peaks on dynamic music | 19 mW | 0.34 V | 58.0 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 5.8Ω 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 5.8Ω | Headroom | Verdict |
|---|---|---|---|---|---|
| Tanchjim Stargate II | USB dongle | $40 | 30 mW | +12 dB | Comfortable |
| ddHiFi TC35AL | USB dongle | $46 | 38 mW | +13 dB | Comfortable |
| ddHiFi TC35Air | USB dongle | $46 | 38 mW | +13 dB | Comfortable |
| Fosi Audio N3 | Bluetooth receiver | $50 | 25 mW | +11 dB | Comfortable |
| FiiO BTR13 | Bluetooth receiver | $59 | 44 mW | +13 dB | Comfortable |
| EPZ TP35 Pro | USB dongle | $70 | 20 mW | +10 dB | Comfortable |
| Aiyima A2 Pro | desktop DAC/amp | $75 | 27 mW | +11 dB | Comfortable |
| ddHiFi TC44 Pro E2 | USB dongle | $99 | 45 mW | +14 dB | Comfortable |
| Onix Alpha XI1 | USB dongle | $109 | 33 mW | +12 dB | Comfortable |
| Hidizs S9 Pro Plus | USB dongle | $139 | 25 mW | +11 dB | Comfortable |
| Topping L30 II | desktop amplifier | $149 | 1.3 W | +28 dB | Comfortable |
| Shanling H2 | portable amplifier | $169 | 123 mW | +18 dB | Comfortable |
| xDuoo MT-604 | desktop amplifier | $169 | 363 mW | +23 dB | Comfortable |
| TempoTec Variations V3 Blaze | portable player | $179 | 150 mW | +19 dB | Comfortable |
| Surfans F28 | portable player | $180 | 23 mW | +11 dB | Comfortable |
Hiss. At 119.5 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 27 dB SPL in these headphones — clearly audible in quiet passages. Check your own source.
Output impedance. At 5.8Ω these want a source output impedance below 0.72Ω to satisfy the one-eighth rule; 90 of the 192 sources that publish one miss it. Check yours here.
5.8Ω · 97.1 dB/mW · Easy
See requirements →10Ω · 97.5 dB/mW · Easy
See requirements →13.8Ω · 105.4 dB/mW · Easy
See requirements →36Ω · 105.0 dB/mW · Easy
See requirements →30Ω · 104.0 dB · Easy
See requirements →30Ω · 104.0 dB · Easy
See requirements →