Noise is a problem with air purifiers containing a fan. Air purifiers without a fan are typically much less effective than units with a fan.
Most air purifiers have three or four fan speed settings. There’s typically a large jump in terms of noise emission when you switch a purifier to high fan speed. But 99 percent of the time you’ll run your machine on one of the low or medium settings due to its annoying noise. You must note that the published CADR ratings are tested under full fan speed setting in a lab. It means that running on low or medium settings will supply much less clean air than the published CADR.
The dB(A) scale is logarithmic. That is, it goes up in powers of ten, rather than in single units. Thus an air purifier marked as 60dB(A) is actually ten times noisier than one marked as 50dB(A).
TROMBE Airborne Dust Cleaner provides comfortable sound environment in your bedroom with its proprietary aerodynamic noise control technology. Even it automatically turns off the machine after reaching 10μg/㎥ of PM1.0 concentration while you are in dream.
[Source] Minnesota Pollution Control Agency