Simple Explanation

A quick, high-pitched echo that bounces rapidly between two parallel walls.

Concise Technical Definition

A repetitive acoustic reflection occurring between two parallel, reflective surfaces, typically spaced far enough apart to create discrete echoes below ~15 reflections per second.

Layman-Friendly Analogy

Like a ping-pong ball bouncing back and forth quickly between two walls, but with sound.

Industry Usage Summary

Common in untreated rooms with parallel surfaces; mitigated using diffusers or absorptive materials to break up the reflection path.

Engineering Shortcut

Discrete, high-speed echo between parallel surfaces; not a standing wave.

Full Technical Explanation

Flutter echo is an acoustic phenomenon that occurs when sound waves reflect back and forth between two parallel surfaces, such as untreated walls or ceilings. It manifests as a series of rapid, high-pitched echoes that are perceptibly distinct if the reflections occur fewer than ~15 times per second. This usually happens when walls are more than about 25 feet apart. In contrast, closer surfaces tend to produce standing waves instead. Flutter echo can degrade clarity and intelligibility in a space, especially for speech and music. It is typically addressed with absorptive or diffusive acoustic treatments to disrupt the repetitive reflection path.