Sendy Audio Apollo: how much amplifier do you need?

The Sendy Audio Apollo is 16Ω with a sensitivity of 95.0 dB/mW, which is 113.0 dB/V. To reach 100 dB SPL — genuinely loud, louder than most people listen — it needs 3.2 mW, or 0.22 V 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 156 sources in the database, 155 have comfortable headroom. The cheapest portable source that does the job is the Apple USB-C dongle (US) at $9.

Sensitivity here is in dB per milliwatt. Manufacturers often quote dB per volt instead and leave the unit off, which is the single most common reason online calculators give answers that are 10–15 dB wrong. 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.

Most people listen between 75 and 85 dB. The 100 dB row is the one worth planning around: it gives you headroom for dynamic peaks without designing your system for a volume that would damage your hearing in under fifteen minutes. The safe listening calculator puts numbers on that.

Every source in the database, judged at 100 dB SPL into 16Ω. “Headroom” is how much power is left over above what the headphone needs — 10 dB means ten times the required power, which is what you want for dynamic peaks.

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 Vali 2+, would put its hiss at roughly 21 dB SPL in these headphones — clearly audible in quiet passages. The hiss calculator lets you check your own amplifier's noise figure.

Output impedance. At 16Ω these want a source output impedance below 2.00Ω to satisfy the one-eighth rule. 16 of the 156 sources here miss it, the worst being the Bottlehead Crack (OTL kit) at 120.0Ω. Above that threshold the source starts shaping the frequency response. Check yours here.

Or open the comparison tool to put any two models side by side, or browse all 402.