Campfire Audio Astrolith: how much amplifier do you need?

The Campfire Audio Astrolith is 8.2Ω with a sensitivity of 100.1 dB/mW, which is 121.0 dB/V. To reach 100 dB SPL — genuinely loud, louder than most people listen — it needs 0.98 mW, or 90 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 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.

Campfire Audio does something unusual: it publishes 94 dB at SPL: 94db @ 1 kHz- 44.9 mVrms, an SPL at one specific drive voltage rather than per milliwatt or per volt. That is convertible — at 8.2Ω that voltage works out to a known power — and the 100.1 dB/mW above is the result. It is a real figure, just stated in a way nothing else in this database uses.

Campfire Audio prints the impedance as 8.2Ω @ 1kHz, not as a bare number. Everything on this page is calculated with the nominal 8.2Ω, 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: campfireaudio.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 8.2Ω. “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 121.0 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 29 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 8.2Ω these want a source output impedance below 1.02Ω to satisfy the one-eighth rule. 50 of the 280 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 578. Or see every Campfire Audio headphone in the database, and how much of what this site says about them came from Campfire Audio’s own documents.