Flutter Echo

A flutter echo is a rapid series of discrete reflections heard as a buzzing or ringing sound, caused by sound bouncing repeatedly between two parallel reflective surfaces. The repetition rate depends on the surface spacing: for walls 5 m apart, reflections arrive every 29 ms (approximately 34 Hz repetition rate). Flutter echoes are among the most common and easily perceived acoustic defects in rooms and are characterized by a tonal, metallic quality that degrades speech clarity and music quality. They are detected by clapping hands in a room and listening for a rapid "zing" or "brrrt" sound. Treatment options include angling one or both surfaces by at least 5°, applying absorption to one surface, or installing diffusers. Flutter echoes can occur between any parallel reflective surfaces including walls, floor-ceiling, and even large glass panels. They are a particularly common problem in corridors, stairwells, and rooms with large areas of exposed hard surfaces.