The Truthear ZERO:BLUE2 is 5.8Ω at 97.1 dB/mW; the Truthear Zero:RED is 17.5Ω at 99.9 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The ZERO:BLUE2 needs 2.8 dB more than the Zero:RED to reach the same loudness — 1.9 mW against 1.0 mW.
| Specification | ZERO:BLUE2 | Zero:RED |
|---|---|---|
| Impedance | 5.8 Ω | 17.5 Ω |
| Sensitivity | 97.1 dB/mW | 99.9 dB/mW |
| Sensitivity (voltage) | 119.5 dB/V | 117.5 dB/V |
| Power for 100 dB | 1.9 mW | 1.0 mW |
| Voltage for 100 dB | 0.11 V | 0.13 V |
| Current for 100 dB | 18.3 mA | 7.6 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 0.72 Ω | 2.19 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.
49 sources are low enough in output impedance for the Zero:RED under the one-eighth rule but not for the ZERO:BLUE2 (FiiO SnowSky Tiny B, FiiO KA13, FiiO KA15, 46 more).
280 of the 280 sources here reach 100 dB on both.
The Zero:RED is more demanding than 43% of the 567 non-electrostatic models in this database; the ZERO:BLUE2 than 35%.
| dB SPL | ZERO:BLUE2 power | ZERO:BLUE2 voltage | Zero:RED power | Zero:RED voltage |
|---|---|---|---|---|
| 80 | 0.02 mW | 11 mV | 0.01 mW | 13 mV |
| 85 | 0.06 mW | 19 mV | 0.03 mW | 24 mV |
| 90 | 0.19 mW | 34 mV | 0.10 mW | 42 mV |
| 95 | 0.62 mW | 60 mV | 0.32 mW | 75 mV |
| 100 | 1.9 mW | 0.11 V | 1.0 mW | 0.13 V |
| 105 | 6.2 mW | 0.19 V | 3.2 mW | 0.24 V |
| Source | Price | Headroom, ZERO:BLUE2 | Headroom, Zero:RED | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 4.5 dB | 12.1 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 16.6 dB | 23.6 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR11 | $36 | 9.2 dB | 16.2 dB | 0.5 Ω | 8.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 43 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 43 is the JadeAudio JA11, at $20. It leaves 4.5 dB of headroom on the ZERO:BLUE2 and 12.1 dB on the Zero:RED, its output impedance is 0.5 Ω against a one-eighth limit of 0.72 Ω and 2.19 Ω, and its noise figure puts the hiss floor 16 dB and 18 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| ZERO:BLUE2 | 20-41kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 | |
| Zero:RED | 20-40.5kHz (IEC61094, Free Field) | not printed | IEC61094 (free field) |
| 20-20kHz (IEC60318-4, -3dB) | -3 dB | IEC60318-4 |
Truthear prints two ranges, “20-41kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the ZERO:BLUE2 and two ranges, “20-40.5kHz (IEC61094, Free Field)” and “20-20kHz (IEC60318-4, -3dB)”, for the Zero:RED.
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 ZERO:BLUE2 and Truthear Zero:RED. Every figure on this page comes from what Truthear published, or is derived from it — what that maker publishes, counted.