The 64 Audio U18s is 8Ω at 106.0 dB/mW; the 64 Audio U6t is 9Ω at 98.0 dB/mW. This page covers what they ask of an amplifier, not how they sound.
The U6t needs 8.0 dB more than the U18s to reach the same loudness — 1.6 mW against 0.25 mW.
| Specification | U18s | U6t |
|---|---|---|
| Impedance | 8 Ω | 9 Ω |
| Sensitivity | 106.0 dB/mW | 98.0 dB/mW |
| Sensitivity (voltage) | 127.0 dB/V | 118.5 dB/V |
| Power for 100 dB | 0.25 mW | 1.6 mW |
| Voltage for 100 dB | 45 mV | 0.12 V |
| Current for 100 dB | 5.6 mA | 13.3 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.00 Ω | 1.12 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.
1 source is low enough in output impedance for the U6t under the one-eighth rule but not for the U18s (Astell&Kern SR35).
16 sources stay below the audible-hiss threshold with the U6t but cross it with the U18s (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 13 more).
280 of the 280 sources here reach 100 dB on both.
The U6t is more demanding than 39% of the 567 non-electrostatic models in this database; the U18s than 9%.
| dB SPL | U18s power | U18s voltage | U6t power | U6t voltage |
|---|---|---|---|---|
| 80 | 2.5 µW | 4 mV | 0.02 mW | 12 mV |
| 85 | 7.9 µW | 8 mV | 0.05 mW | 21 mV |
| 90 | 0.03 mW | 14 mV | 0.16 mW | 38 mV |
| 95 | 0.08 mW | 25 mV | 0.50 mW | 67 mV |
| 100 | 0.25 mW | 45 mV | 1.6 mW | 0.12 V |
| 105 | 0.79 mW | 80 mV | 5.0 mW | 0.21 V |
| Source | Price | Headroom, U18s | Headroom, U6t | Output impedance | Noise |
|---|---|---|---|---|---|
| JadeAudio JA11 | $20 | 14.8 dB | 7.3 dB | 0.5 Ω | 1.7 µV |
| FiiO KA11 | $29 | 26.9 dB | 19.4 dB | 0.7 Ω | 1.7 µV |
| FiiO BTR13 | $59 | 23.8 dB | 16.3 dB | 0.6 Ω | 1.0 µV |
Of the 280 sources here, 280 reach 100 dB on both. 48 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 48 is the JadeAudio JA11, at $20. It leaves 14.8 dB of headroom on the U18s and 7.3 dB on the U6t, its output impedance is 0.5 Ω against a one-eighth limit of 1.00 Ω and 1.12 Ω, and its noise figure puts the hiss floor 8 dB and 17 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 |
| U6t | 20hz – 20kHz | not printed | not printed |
64 Audio prints 10hz – 20kHz for the U18s and 20hz – 20kHz for the U6t.
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 U6t. Every figure on this page comes from what 64 Audio published, or is derived from it — what that maker publishes, counted.