The Purifier Lab · Air
At what fan speed can you actually sleep — and what does that cost you?
For a given air purifier, what is the measured noise level and the measured PM2.5 decay rate at every fan speed — and how much clean air delivery is given up to reach a level someone can sleep beside?
Results
No results yet. This page publishes the protocol only.
We have written and published the method below, and we have not yet run it. There are no measurements on this page, no charts and no percentage claims, because there is nothing to report.
The protocol is published first deliberately. It means we cannot quietly amend the method once we have seen a result we did not like, and it lets anyone — including manufacturers — tell us the method is wrong before we run it. If you can see a flaw in it, tell us.
The protocol
Measure A-weighted sound pressure at 1 m at every fan speed, in the same session as the PM2.5 decay protocol, and publish decay rate and noise level as a paired figure for each speed.
Instrument
Class 2 sound level meter, A-weighted, slow response; laser particle counter
Model: To be stated on first published run
Calibration: Sound level meter checked with an acoustic calibrator before and after each session. Background room level measured and stated; any session with background above 30 dB(A) is discarded.
What is held constant
- Microphone at 1 m from the unit, at 1 m height, off-axis from the discharge, on a stand rather than handheld.
- Background noise measured immediately before each reading and stated with the result.
- Same room as the decay protocol, with the same sealing, so acoustic conditions are constant.
- Measurements taken at night to keep background level low and constant.
- Every fan speed measured, including the sleep or auto mode, with auto mode's actual selected speed noted.
Steps
- 1
Establish the background
Measure and record the room's background sound level with everything off. If it is above 30 dB(A), the session cannot produce a usable low-speed figure and is rescheduled.
- 2
Measure at every fan speed
Allow the unit 60 seconds to stabilise at each speed, then record a 30-second average. Note the speed label as printed on the unit.
- 3
Pair with decay measurement
Run the PM2.5 decay protocol at the lowest speed, the speed we judge sleepable, and maximum, so each noise figure has a performance figure attached to it.
- 4
Publish the pairing
A table of speed, dB(A) at 1 m, background level, and 30-minute PM2.5 reduction — so a reader can find the row they could sleep next to and see what it delivers.
What this test cannot tell you
Published with the protocol rather than buried after the results. A test whose limits are not stated is a claim, not a measurement.
- A Class 2 sound level meter is adequate for comparative measurement and is not laboratory-grade acoustic testing.
- Perceived loudness is not the same as sound pressure level. A unit with a tonal whine can be more disturbing at 40 dB(A) than a broadband one at 44, and dB(A) does not capture that. We describe the character of the noise in words alongside the number.
- Room acoustics affect the measurement. Figures are comparable between units tested in our room and are not directly comparable to a manufacturer's anechoic-chamber figure.
- What counts as sleepable is a judgement. We state our judgement explicitly and publish every speed's data so a reader can apply their own.
Note