Why fan noise helps you sleep
A fan makes a steady, broadband sound: energy spread across a wide range of frequencies, with no rhythm or words for your brain to follow. That steady bed raises the background level of the room, so short sounds (a door, traffic, a partner snoring) stand out less against it. This effect is called masking, and it is the same reason people use white noise and brown noise for sleep.
A fan is also familiar. Plenty of people grew up sleeping with one on, and its sound has small, slow movements in it (the blades, the head turning) that make it feel less artificial than plain noise. None of this is a treatment; it is simply a comfortable, steady sound that is easy to stop noticing.
How each fan is made
Each preset is built from the same parts in different amounts. The rush of air is a mix of pink, brown and white noise through a band-pass filter: a big box fan is centred low and soft, a desk fan higher and brighter, a bathroom exhaust narrower and boxier, an industrial fan deep and heavy. Under that sits the motor hum, a low tone between 50 and 150 Hz with two or three quieter harmonics. Most fans also get a slight flutter, a dip in level each time a blade passes, which is slow and pronounced on a ceiling fan.
Speed raises the hum pitch and the flutter rate and brightens the air. Oscillation pans the sound slowly from side to side, about once every 5 to 10 seconds depending on speed, and makes it slightly brighter and louder each time the fan faces you, the way a turning fan does. The hum slider sets how much motor you hear, from none at all to a clearly audible drone.
Fan noise vs white noise vs brown noise
| Sound | Character | Good if you |
|---|---|---|
| White noise | Equal energy per hertz, bright and hissy | need the strongest masking of high sounds like voices |
| Fan noise | Soft air rush, low hum, slow movement | grew up with a fan or find plain noise too artificial |
| Brown noise | Energy weighted to the bass, deep rumble | find white noise harsh, or want to cover low traffic rumble |
For every colour of noise in one player, use the noise generator.
Fan noise for babies: keep it far and quiet
The same rules apply as for any sleep machine. Put the phone or speaker at least 2 metres from the cot, never in it or on the rail. Keep the level at or below about 50 dB, roughly a quiet conversation, and use the sleep timer rather than running it all day and night.
A 2014 study in Pediatrics measured 14 infant sleep machines at full volume and found every one louder than 50 dB at 30 cm, with three over 85 dB. A phone at full volume next to a baby can be just as loud, so start low and turn up only as far as you need.