swell box

noun
  1. a chamber containing a set of pipes in a pipe organ or of reeds in a reed organ, and having movable slats or shutters that can be opened or closed to increase or diminish tonal volume.

Origin of swell box

First recorded in 1795–1805
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

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Historical Examples of swell box