By the 1820s, the center of piano innovation had shifted to Paris, where the Pleyel firm manufactured pianos used by Frédéric Chopin, and the Érard firm manufactured those used by Franz Liszt. In 1821, Sébastien Érard invented the double escapement action, which incorporated a repetition lever (also called the balancier) that permitted repeating a note even if the key had not return to its resting position. This facilitated rapid playing of repeated notes, a musical device exploited by Liszt. When the invention became public, as revised by Henri Herz, the double escapement action gradually became standard in grand pianos and is still incorporated into all grand pianos currently produced in the 2000s. Other improvements of the mechanism included the use of firm felt hammer coverings instead of layered leather or cotton. Felt, which Jean-Henri Pape was the first to use in pianos in 1826, was a more consistent material, permitting wider dynamic ranges as hammer weights and string tension increased. The sostenuto pedal (see below), invented in 1844 by Jean-Louis Boisselot and copied by the Steinway firm in 1874, allowed for a wider range of effects.One innovation that helped create the powerful sound of the modern piano was the use of a massive, strong, cast iron frame. Also called the "plate", the iron frame sits atop the soundboard, and serves as the primary bulwark against the force of string tension that can exceed 20 tons () in total for a modern grand piano. The single piece cast iron frame for square piano was patented in 1825 in Boston by Alpheus Babcock, combining the metal hitch pin plate (1821, claimed by Broadwood on behalf of Samuel Hervé) and resisting bars (Thom and Allen, 1820, but also claimed by Broadwood and Érard). Babcock later worked for the Chickering & Mackays firm who patented the first full iron frame for grand pianos in 1843. Composite forged metal frames were preferred by many European makers until the American system was fully adopted by the early 20th century. The increased structural integrity of the iron frame allowed the use of thicker, tenser, and more numerous strings. In 1834, the Webster & Horsfal firm of Birmingham brought out a form of piano wire made from cast steel; it was "so superior to the iron wire that the English firm soon had a monopoly." A better steel wire was developed in 1840 by the Viennese firm Martin Miller, and a period of innovation and intense competition ensued, with rival brands of piano wire being tested against one another at international competitions, leading ultimately to the modern form of piano wire.
by the 1820s the center of piano innovation had shifted to paris where the pleyel firm manufactured pianos used by frédéric chopin and the érard firm manufactured those used by franz liszt in 1821 sébastien érard invented the double escapement action which incorporated a repetition lever (also called the balancier) that permitted repeating a note even if the key had not return to its resting position this facilitated rapid playing of repeated notes a musical device exploited by liszt when the invention became public as revised by henri herz the double escapement action gradually became standard in grand pianos and is still incorporated into all grand pianos currently produced in the 2000s other improvements of the mechanism included the use of firm felt hammer coverings instead of layered leather or cotton felt which jean-henri pape was the first to use in pianos in 1826 was a more consistent material permitting wider dynamic ranges as hammer weights and string tension increased the sostenuto pedal (see below) invented in 1844 by jean-louis boisselot and copied by the steinway firm in 1874 allowed for a wider range of effectsone innovation that helped create the powerful sound of the modern piano was the use of a massive strong cast iron frame also called the "plate" the iron frame sits atop the soundboard and serves as the primary bulwark against the force of string tension that can exceed 20 tons () in total for a modern grand piano the single piece cast iron frame for square piano was patented in 1825 in boston by alpheus babcock combining the metal hitch pin plate (1821 claimed by broadwood on behalf of samuel hervé) and resisting bars (thom and allen 1820 but also claimed by broadwood and érard) babcock later worked for the chickering & mackays firm who patented the first full iron frame for grand pianos in 1843 composite forged metal frames were preferred by many european makers until the american system was fully adopted by the early 20th century the increased structural integrity of the iron frame allowed the use of thicker tenser and more numerous strings in 1834 the webster & horsfal firm of birmingham brought out a form of piano wire made from cast steel; it was "so superior to the iron wire that the english firm soon had a monopoly" a better steel wire was developed in 1840 by the viennese firm martin miller and a period of innovation and intense competition ensued with rival brands of piano wire being tested against one another at international competitions leading ultimately to the modern form of piano wire