The quietest portable generator brands are Yamaha, Champion, Westinghouse and Stanley. Quiet factors affect these brands based on environmental elements such as room size, wall barriers and surrounding wilderness.
Yamaha, Champion, Westinghouse and Stanley portable generators have the quietest decibel reading. Generators are quieter when out in the open outdoors, such as a field. When trees or thick forestry, rocks and boulders are considered, generators are in a more confined area and sound louder. Indoor generators sound the loudest when placed against walls, in small rooms or spaces, or against echoing surfaces such as concrete. Large furniture helps buffer noise and reduce echoing.