Accordion

Overview

An accordion is a portable free-reed instrument that makes its sound from wind, not from struck or bowed strings. The player works the bellows back and forth with the left arm to move air, and presses keys and buttons that decide which reeds that air is allowed to reach. It is effectively two instruments joined by an air pump: a melody keyboard for the right hand and a bass-and-chord button board for the left, each voicing its own bank of reeds.

The instrument splits into the Treble Casework and the Bass Casework, bridged by the Bellows. The right hand plays the Treble Keyboard; the left hand works the Stradella Bass Mechanism. Both ends draw their voices from the Reed Blocks, and Register Switches change the timbre by coupling or muting reed ranks.

How it works

Sound begins at the Steel Reed, a thin spring-steel tongue riveted over a slot in an aluminium Reed Plate. When air is forced across it the tongue is set vibrating at its tuned pitch, chopping the airflow into a tone. Each plate carries two reeds facing opposite ways, one that speaks when the bellows is pressed and one when it is drawn, so the accordion sounds in both directions. A leather Reed Valve Leather valve covers the idle reed on each plate so the moving air is steered through only the reed that should sound, and the plates are sealed into the Reed Block Body with Reed Wax.

Air only reaches a reed if its valve is open. On the melody side, each Piano Key levers open the Pallet Valve that seals its tone hole, uncovering that note's reeds. The Stradella Bass Mechanism does the same job but with leverage: this is the Stradella system, where one Bass Button is linked through Bass Coupling Rods to several pallets at once, so a single press sounds a bass note or a complete major, minor, or seventh chord. The whole instrument is powered by the Bellows, whose pleated folds expand and compress to drive the air; an Air Valve button opens a silent port so the player can reset the bellows without sounding any reed.