The 64 Audio U18s is 8Ω with a sensitivity of 106.0 dB/mW, which is 127.0 dB/V. To reach 100 dB SPL — genuinely loud, louder than most people listen — it needs 0.25 mW, or 45 mV 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, 280 have at least 10 dB of headroom and another 0 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.
64 Audio publishes this directly as 106 dB/mW (Sensitivity @1kHz @ 1mW (84mV)), per milliwatt, so nothing was converted.
64 Audio prints the impedance as 8Ω Nominal, not as a bare number. Everything on this page is calculated with 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: 64audio.com. How this data was built.
| As it is labelled | As printed | Tolerance | Standard |
|---|---|---|---|
| Frequency Response | 10hz – 20kHz | not printed | not printed |
64 Audio prints 10hz – 20kHz for the 64 Audio U18s, under the heading “Frequency Response”. Source: 64audio.com.
No tolerance is printed with it, so “10hz – 20kHz” says nothing about how loud this headphone actually is at 10 Hz.
Only what the maker printed; maker by maker.
| Level | What it is | Power | Voltage | Current |
|---|---|---|---|---|
| 85 dB SPL | quiet background listening | 0.01 mW | 8 mV | 1.0 mA |
| 95 dB SPL | normal listening | 0.08 mW | 25 mV | 3.2 mA |
| 100 dB SPL | loud listening | 0.25 mW | 45 mV | 5.6 mA |
| 105 dB SPL | very loud | 0.79 mW | 80 mV | 10.0 mA |
| 110 dB SPL | peaks on dynamic music | 2.5 mW | 0.14 V | 17.7 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 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 8Ω | Headroom | Verdict |
|---|---|---|---|---|---|
| FiiO SnowSky Tiny A | USB dongle | $22 | 22 mW | +20 dB | Comfortable |
| FiiO SnowSky Tiny B | USB dongle | $22 | 34 mW | +21 dB | Comfortable |
| Tanchjim Stargate II | USB dongle | $40 | 41 mW | +22 dB | Comfortable |
| ddHiFi TC35AL | USB dongle | $46 | 52 mW | +23 dB | Comfortable |
| ddHiFi TC35Air | USB dongle | $46 | 52 mW | +23 dB | Comfortable |
| Fosi Audio N3 | Bluetooth receiver | $50 | 34 mW | +21 dB | Comfortable |
| Hidizs SD2 | USB dongle | $50 | 18 mW | +18 dB | Comfortable |
| iFi GO link | USB dongle | $59 | 18 mW | +18 dB | Comfortable |
| Kiwi Ears Allegro Pro | USB dongle | $60 | 17 mW | +18 dB | Comfortable |
| ddHiFi TC35Pro (Mountain2) | USB dongle | $66 | 16 mW | +18 dB | Comfortable |
| DUNU DTC 480 | USB dongle | $70 | 16 mW | +18 dB | Comfortable |
| EPZ TP35 Pro | USB dongle | $70 | 28 mW | +20 dB | Comfortable |
| Aiyima A2 Pro | desktop DAC/amp | $75 | 37 mW | +22 dB | Comfortable |
| ddHiFi TC35Pro (Eye2) | USB dongle | $76 | 16 mW | +18 dB | Comfortable |
| ddHiFi TC44 Pro E2 | USB dongle | $99 | 63 mW | +24 dB | Comfortable |
Hiss. At 127.0 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 35 dB SPL in these headphones — clearly audible in quiet passages. Check your own source.
Output impedance. At 8Ω these want a source output impedance below 1.00Ω to satisfy the one-eighth rule; 50 of the 192 sources that publish one miss it. Check yours here.
9Ω · 98.0 dB/mW · Easy
See requirements →9.5Ω · 103.7 dB/mW · Easy
See requirements →6.3Ω · 103.0 dB/mW · Easy
See requirements →40Ω · 113.0 dB · Easy
See requirements →16Ω · 109.0 dB/mW · Easy
See requirements →20Ω · 110.0 dB/mW · Easy
See requirements →