The Truthear PURE is 13.8Ω at 105.4 dB/mW; the Truthear ZERO:BLUE2 is 5.8Ω at 97.1 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The ZERO:BLUE2 needs 8.3 dB more than the PURE to reach the same loudness — 1.9 mW against 0.29 mW.
| Specification | PURE | ZERO:BLUE2 |
|---|---|---|
| Impedance | 13.8 Ω | 5.8 Ω |
| Sensitivity | 105.4 dB/mW | 97.1 dB/mW |
| Sensitivity (voltage) | 124.0 dB/V | 119.5 dB/V |
| Power for 100 dB | 0.29 mW | 1.9 mW |
| Voltage for 100 dB | 63 mV | 0.11 V |
| Current for 100 dB | 4.6 mA | 18.3 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.73 Ω | 0.72 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
45 sources are low enough in output impedance for the PURE under the one-eighth rule but not for the ZERO:BLUE2 (FiiO SnowSky Tiny B, FiiO KA13, FiiO KA15, 42 more).
5 sources stay below the audible-hiss threshold with the ZERO:BLUE2 but cross it with the PURE (FiiO BTR11, FiiO K11 R2R, Schiit Valhalla 3, 2 more).
280 of the 280 sources here reach 100 dB on both.
The ZERO:BLUE2 is more demanding than 35% of the 567 non-electrostatic models in this database; the PURE than 18%.
| dB SPL | PURE power | PURE voltage | ZERO:BLUE2 power | ZERO:BLUE2 voltage |
|---|---|---|---|---|
| 80 | 2.9 µW | 6 mV | 0.02 mW | 11 mV |
| 85 | 9.1 µW | 11 mV | 0.06 mW | 19 mV |
| 90 | 0.03 mW | 20 mV | 0.19 mW | 34 mV |
| 95 | 0.09 mW | 35 mV | 0.62 mW | 60 mV |
| 100 | 0.29 mW | 63 mV | 1.9 mW | 0.11 V |
| 105 | 0.91 mW | 0.11 V | 6.2 mW | 0.19 V |
| Source | Price | Headroom, PURE | Headroom, ZERO:BLUE2 | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 16.5 dB | 4.5 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 28.6 dB | 16.6 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 25.5 dB | 13.5 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 40 of them also publish an output impedance low enough for both under the one-eighth rule and a noise figure that stays below the audible-hiss threshold with both.
The cheapest of the 40 is the JadeAudio JA11, at $20. It leaves 16.5 dB of headroom on the PURE and 4.5 dB on the ZERO:BLUE2, its output impedance is 0.5 Ω against a one-eighth limit of 1.73 Ω and 0.72 Ω, and its noise figure puts the hiss floor 11 dB and 16 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| PURE | 7-40kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 | |
| ZERO:BLUE2 | 20-41kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 |
Truthear prints two ranges, “7-40kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the PURE and two ranges, “20-41kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the ZERO:BLUE2.
Both sheets print a tolerance, which is rare enough to be worth pointing at: only 58 of the 490 models with a printed range do. These two ranges can be set against each other, because each of them says how far down the response is allowed to be at the ends.
Not a measurement; maker by maker.
Both have a page of their own. In full: Truthear PURE and Truthear ZERO:BLUE2. Every figure on this page comes from what Truthear published, or is derived from it — what that maker publishes, counted.