Expression Pedal - Pipe Organs

Pipe Organs

Beginning in the nineteenth century, it became common for one or more divisions of pipes in a pipe organ to be enclosed in a wooden box, at least one side of which would consist of palettes that open and close in a manner similar to a Venetian blind. A mechanical (later electrical) mechanism connected the box to a pedal that the organist would use to open and close the shutters, adjusting the perceived loudness of the sound. When the box is shut (or closed), less sound is released into the venue. In American and British organs, the enclosed division is usually named the Swell, and the box surrounding the pipes is usually referred to as the swell box. Thus, the expression pedal is sometimes known as the swell pedal or swell shoe. Larger organs may have two or more expression pedals, allowing the volume of different divisions to be individually controlled.

No matter how well a swell box is designed, the sound of the pipes is altered by their enclosure. Even when the shutters are fully opened, the pipes do not speak as clearly into the room as they would if they were otherwise unenclosed.

On pipe organs, the expression pedal should not be confused with the crescendo pedal, which progressively adds stops as it is opened.