"The square piano is a type of piano that has horizontal strings arranged diagonally across the rectangular case above the hammers and with the keyboard set ...
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in the long side, with the sounding board above a cavity in the short side. It is variously attributed to Silbermann and Frederici and was improved by Petzold and Babcock. The English and Viennese square pianos were built in many different designs, including within the action as well as general appearance, from roughly 1760. Because of the competitive industry and relative youth of the instrument design itself, experimentation ensued in the early years, creating a range of moderators (sound-altering effects) and other technical devices (knee levers; hand stops) not seen today." - (en.wikipedia.org 02.03.2020)
