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Double action pedal harp
Sebastian Erard's development of the fourchette mechanism and his structural improvements to the harp were generally acclaimed, yet neither harpists nor harpmakers were fully satisfied with the single action pedal harp. In 1811, after several years of experimentation, Erard developed the double action mechanism, with two rows of discs. When a pedal was moved down to the middle notch, all the discs involved rotated, but only the prongs of the upper discs engaged the strings, raising them a semi-tone. When the pedal was moved down to the lower notch the second row of discs engaged the harp strings, raising their pitch another semi-tone, so that the harp could be played in all keys.
Visually, single action and double action harps can be distinguished from each other in two ways:Single Action Harp Double Action Harp On the harp neck there is one On the harp neck there are tworow of forked discs rows of forked discs
On the harp pedestal there e two On the harp pedestal there ar threenotches for each of the seven pedals notches for each of the seven pedals
Roslyn Rensch, Three Centuries of harpmaking, Victor Salvi Foundation
images: Roslyn Rensch, Harps & Harpists