What is Quietest noise level in decibels?

Noise in decibels measures how loud a product runs. The lowest figure is the quietest it gets, normally on the lowest fan speed or in night mode, so it is the number that matters for a bedroom or a quiet sitting room. Air Health lists 22 decibels, Airtheeral 22 decibels, Alen Air Purifiers 25 decibels and AirDoctor Europe 39 decibels. AlorAir lists 50 decibels. A lower reading means less background hum while the unit runs.