When I drafted my post on alternatives to masks for infectious aerosols I initially based the air purifier section on the AP-1512. This is a common air purifier that I bought several of on the Wirecutter's recommendation, and I haven't had any trouble with it. When reviewing my post, however, Vivian pointed out that the Airfanta 3Pro was 20% cheaper and produced 72% more clean air. Sounds pretty good!

The design is a lot like a smaller version of a Corsi-Rosenthal Box, with four 6" computer fans instead of a box fan. It was a bit annoying to assemble, but went together well.

A big question with any sort of purifier is noise, and I had a go at a comparison. In each test I used my MacBook Pro with its internal microphone, set to 100%, about five feet from the purifier. I compared:

• AP-1512 on High (~240 CADR):
  (mp3).

• 3Pro on 6/6 (~413 CADR):
  (mp3).

• 3Pro on 4/6 (~270 CADR):
  (mp3).

• 3Pro on 2/4 (~130 CADR):
  (mp3).

• Everything off (0 CADR):
  (mp3).

(CADRs for 4/6 and 2/6 estimated from the numbers in this review.)

For a sense of how loud these are in absolute terms, the AP-1512 is rated 53dB.

Here's the frequency comparison:

You can see that on full power the AP-1512 and the 3Pro make similar amounts of noise, though (a) 3Pro is cleaning a lot more air and (b) the 3Pro has a worse tone per my taste. A better comparison is the 3Pro on 4/6, where it still cleans more air but is both substantially more quiet and reasonably pleasant sounding. And on 2/6 it's essentially indistinguishable from the background while still cleaning a useful amount of air.

The main downside of the 3Pro relative to the AP-1512 is that it can't change it's fan speed based on the level of particles in the air, which is valuable in a cooking (or fire) context. So I'll be keeping my AP-1512s in the kitchen and using 3Pros in the living room and other places where I'm most concerned about infection.

(What I really want is one that combines particle measurement with CO2, as a proxy for aerosol infection risk, and ramps up and down appropriately.)