The 64 Audio U18s is 8Ω at 106.0 dB/mW; the 64 Audio Volur is 6.3Ω at 103.0 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The Volur needs 3.0 dB more than the U18s to reach the same loudness — 0.50 mW against 0.25 mW.
| Specification | U18s | Volur |
|---|---|---|
| Impedance | 8 Ω | 6.3 Ω |
| Sensitivity | 106.0 dB/mW | 103.0 dB/mW |
| Sensitivity (voltage) | 127.0 dB/V | 125.0 dB/V |
| Power for 100 dB | 0.25 mW | 0.50 mW |
| Voltage for 100 dB | 45 mV | 56 mV |
| Current for 100 dB | 5.6 mA | 8.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.00 Ω | 0.79 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.
37 sources are low enough in output impedance for the U18s under the one-eighth rule but not for the Volur (FiiO SnowSky Tiny B, FiiO KA15, FiiO BTR15, 34 more).
7 sources stay below the audible-hiss threshold with the Volur but cross it with the U18s (Grace Design m900, FiiO M33 R2R, FiiO K17, 4 more).
280 of the 280 sources here reach 100 dB on both.
The Volur is more demanding than 14% of the 567 non-electrostatic models in this database; the U18s than 9%.
| dB SPL | U18s power | U18s voltage | Volur power | Volur voltage |
|---|---|---|---|---|
| 80 | 2.5 µW | 4 mV | 5.0 µW | 6 mV |
| 85 | 7.9 µW | 8 mV | 0.02 mW | 10 mV |
| 90 | 0.03 mW | 14 mV | 0.05 mW | 18 mV |
| 95 | 0.08 mW | 25 mV | 0.16 mW | 32 mV |
| 100 | 0.25 mW | 45 mV | 0.50 mW | 56 mV |
| 105 | 0.79 mW | 80 mV | 1.6 mW | 100 mV |
| Source | Price | Headroom, U18s | Headroom, Volur | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 14.8 dB | 10.7 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 26.9 dB | 22.8 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 23.8 dB | 19.7 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 32 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 32 is the JadeAudio JA11, at $20. It leaves 14.8 dB of headroom on the U18s and 10.7 dB on the Volur, its output impedance is 0.5 Ω against a one-eighth limit of 1.00 Ω and 0.79 Ω, and its noise figure puts the hiss floor 8 dB and 10 dB below the 20 dB SPL this site treats as the point where a quiet room stops hiding it.
| Model | As printed | Tolerance | Standard |
|---|---|---|---|
| U18s | 10hz – 20kHz | not printed | not printed |
| Volur | 5hz – 22kHz | not printed | not printed |
64 Audio prints 10hz – 20kHz for the U18s and 5hz – 22kHz for the Volur.
Neither range has a tolerance printed beside it, so a wider range on one sheet is not deeper bass or more treble.
Not a measurement; maker by maker.
Both have a page of their own. In full: 64 Audio U18s and 64 Audio Volur. Every figure on this page comes from what 64 Audio published, or is derived from it — what that maker publishes, counted.