The Sendy Audio Apollo is 16Ω. Its maker prints a sensitivity of 95.0 dB and never says whether that is per milliwatt or per volt, so this page reads it as per milliwatt — on that reading it needs 3.2 mW to reach 100 dB SPL, or 0.22 V across the drivers. If the figure is really per volt, it needs far more.
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, 252 have at least 10 dB of headroom and another 27 have enough. The cheapest portable source that does the job is the Apple USB-C dongle (US) at $9.
This maker printed a decibel figure and no reference unit, so the number above is shown exactly as printed. Everything below reads it as per milliwatt, which is the commoner convention on a sheet that omits the unit — if it is really per volt, this headphone is about 18 dB harder to drive than the rest of this page assumes. The converter explains the difference.
Sendy Audio publishes a sensitivity of 95 dB and does not state whether that is per milliwatt or per volt — the spec sheet simply stops at the number.
Both readings are given here so you can judge for yourself. If that 95 dB is per milliwatt, the figures on this page are right as they stand. If it is per volt, the real sensitivity is 77.0 dB/mW — 18 dB lower at 16Ω — and everything above understates what these need by that much. The per-milliwatt reading is the one shown, because it is the more common convention on a spec sheet that omits the unit; treat it as an indication rather than a specification.
Source: sivgashop.com, underwoodhifi.com. How this data was built.
| As it is labelled | As printed | Tolerance | Standard |
|---|---|---|---|
| Frequency response | 20Hz - 40KHz | not printed | not printed |
Sendy Audio prints 20Hz - 40KHz for the Sendy Audio Apollo, under the heading “Frequency response”. Source: sivgashop.com.
No tolerance is printed with it, so “20Hz - 40KHz” says nothing about how loud this headphone actually is at 20 Hz.
Only what the maker printed; maker by maker.
| Level | What it is | Power | Voltage | Current |
|---|---|---|---|---|
| 85 dB SPL | quiet background listening | 0.10 mW | 40 mV | 2.5 mA |
| 95 dB SPL | normal listening | 1.0 mW | 0.13 V | 7.9 mA |
| 100 dB SPL | loud listening | 3.2 mW | 0.22 V | 14.1 mA |
| 105 dB SPL | very loud | 10 mW | 0.40 V | 25.0 mA |
| 110 dB SPL | peaks on dynamic music | 32 mW | 0.71 V | 44.5 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 16Ω 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 16Ω | Headroom | Verdict |
|---|---|---|---|---|---|
| FiiO SnowSky Tiny A | USB dongle | $22 | 45 mW | +12 dB | Comfortable |
| FiiO SnowSky Tiny B | USB dongle | $22 | 68 mW | +13 dB | Comfortable |
| FiiO KA11 | USB dongle | $29 | 245 mW | +19 dB | Comfortable |
| Tanchjim Stargate II | USB dongle | $40 | 82 mW | +14 dB | Comfortable |
| ddHiFi TC35AL | USB dongle | $46 | 105 mW | +15 dB | Comfortable |
| ddHiFi TC35Air | USB dongle | $46 | 105 mW | +15 dB | Comfortable |
| Fosi Audio N3 | Bluetooth receiver | $50 | 69 mW | +13 dB | Comfortable |
| Hidizs SD2 | USB dongle | $50 | 35 mW | +10 dB | Comfortable |
| FiiO BTR13 | Bluetooth receiver | $59 | 120 mW | +16 dB | Comfortable |
| iFi GO link | USB dongle | $59 | 35 mW | +10 dB | Comfortable |
| Kiwi Ears Allegro Pro | USB dongle | $60 | 34 mW | +10 dB | Comfortable |
| ddHiFi TC35Pro (Mountain2) | USB dongle | $66 | 33 mW | +10 dB | Comfortable |
| iBasso DC03 Pro | USB dongle | $69 | 49 mW | +12 dB | Comfortable |
| DUNU DTC 480 | USB dongle | $70 | 33 mW | +10 dB | Comfortable |
| EPZ TP35 Pro | USB dongle | $70 | 56 mW | +12 dB | Comfortable |
Hiss. At 113.0 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 21 dB SPL in these headphones — clearly audible in quiet passages. Check your own source.
Output impedance. At 16Ω these want a source output impedance below 2.00Ω to satisfy the one-eighth rule; 35 of the 192 sources that publish one miss it. Check yours here.
50Ω · 103.0 dB · Easy
See requirements →32Ω · 98.0 dB · Easy
See requirements →32Ω · 98.0 dB/mW · Easy
See requirements →32Ω · 98.0 dB/mW · Easy
See requirements →32Ω · 98.0 dB · Easy
See requirements →25Ω · 97.0 dB/mW · Easy
See requirements →Compared with its stablemates: vs Peacock.