Available in cool mist, warm mist, and combination models, ultrasonic humidifiers use high-frequency sound waves to vibrate a metal diaphragm until it reaches an ultrasonic frequency. This motion creates micro-fine water droplets that are released into the air as an invisible mist. Ultrasonic units are the quietest of all humidifier types because they emit sound waves at a frequency higher than we can hear. These humidifiers are great choices for your bedroom, child's room, nursery, or any other space where quiet operation is a must. Browse our bestselling ultrasonic humidifiers below.