RealTraps - Flutter Echo to Distance Chart

Identify the source of flutter echo


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"It can be difficult to identify which pair of surfaces is the main source of flutter echo."

By Ethan Winer

Flutter echo is a pitched "boing" sound you hear when you clap your hands in an empty room, and it's caused by sound waves bouncing back and forth repeatedly between two parallel surfaces. Flutter echo is harmful because its pitched tone is added on top of music played by loudspeakers, or can be picked up by microphones when recording voices or musical instruments.

Even though the fundamental pitch of flutter echo is a fairly low frequency, it consists mostly of higher harmonics at midrange frequencies. So it's easily tamed by placing relatively thin absorbers (or diffusers) on one or both opposing surfaces. However, it can be difficult to identify which pair of surfaces is the main source of flutter echo, especially when the floor is reflective too.

To help determine where acoustic treatment is best applied, the chart below lists the dimensions that correspond to various musical notes. Simply clap your hands, note the pitch on a piano or other musical instrument, and from that you can tell which opposing surfaces will benefit from applying absorbers or diffusers.

Flutter echo is less common across very large distances, but you can still use this chart for wall spacings larger than 20 feet by doubling a listed spacing. For example, a distance of 23 feet yields a G note an octave below the low G shown as 11'6" on the keyboard below.

Flutter to Distance Chart

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