clapper

A clapper is a component inside a bell that produces sound by striking the bell’s interior surface. It is typically a free-swinging metal piece attached to a pivot near the rim of the bell. When the bell is rung, the clapper swings and makes contact with the bell, generating the tone. The clapper’s mass, length, and striking point influence the volume, pitch, and duration of the sound. In large bells, clappers may be operated by ropes, wheels, or motors, and designs vary to balance striking force with durability and tonal quality. Proper adjustment and maintenance are important to prevent uneven wear or damage to the bell.

In filmmaking and video production, the term clapper (or clapperboard) refers to a slate device used to synchronize picture and sound. The top hinged stick, known as the clapper, is snapped shut at the start of a take. The resulting sharp clap is recorded on the audio track and appears on camera, providing a precise cue for alignment of audio and video. The slate typically records scene, take, roll, date, and production metadata. While digital slate systems are common today, the basic purpose remains the same: a distinctive audible and visual marker to aid editing.

The word clapper thus has at least two common meanings: a bell component that initiates sound, and the movable stick on a clapperboard used to synchronize audio and visuals.