Development of the modern piano

For more details on this topic, see Innovations in the piano.

In the period lasting from about 1790 to 1860, the Mozart-era piano underwent tremendous changes that led to the modern form of the instrument. This revolution was in response to a consistent preference by composers and pianists for a more powerful, sustained piano sound, and made possible by the ongoing Industrial Revolution with technological resources such as high-quality steel, called piano wire, for strings, and precision casting for the production of iron frames. Over time, the tonal range of the piano was also increased from the five octaves of Mozart's day to the 7⅓ or more octaves found on modern pianos.
Broadwood grand square action
Broadwood grand square action

Early technological progress owed much to the English firm of Broadwood, who already had a reputation for the splendour and powerful tone of its harpsichords. Broadwood constructed instruments that were progressively larger, louder, and more robustly constructed. They sent pianos to both Joseph Haydn and Ludwig van Beethoven, and were the first firm to build pianos with a range of more than five octaves: five octaves and a fifth during the 1790s, six octaves by 1810 (Beethoven used the extra notes in his later works), and seven octaves by 1820. The Viennese makers similarly followed these trends, however the two schools used different piano actions: Broadwoods were more robust, Viennese instruments were more sensitive.
Erard double pilot action
Erard double pilot action

By the 1820s, the center of innovation had shifted to Paris, where the Érard firm manufactured pianos used by Frédéric Chopin and Franz Liszt. In 1821, Sébastien Érard invented the double escapement action, which permitted a note to be repeated even if the key had not yet risen to its maximum vertical position. This facilitated rapid playing. 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.

One of the major technical innovations that helped to create the sound of the modern piano was the use of a strong 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. The increased structural integrity of the iron frame allowed the use of thicker, tenser, and more numerous strings. In a modern grand the total string tension can approach 20 tons. The single piece cast iron frame 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.

Other innovations for the mechanism included the use of felt hammer coverings instead of layered leather hammers. Felt hammers, which were first introduced by Henri Pape in 1826, were 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 improved by the Steinway firm in 1874, allowed a wider range of effects.

Other important technical innovations of this era included changes to the way the piano was strung, such as the use of a "choir" of three strings rather than two for all but the lower notes, and the use of different stringing methods. With the over strung scale, also called "cross-stringing", the strings are placed in a vertically overlapping slanted arrangement, with two heights of bridges on the soundboard instead of just one. This permits larger, but not necessarily longer, strings to fit within the case of the piano. Over stringing was invented by Jean-Henri Pape during the 1820s, and first patented for use in grand pianos in the United States by Henry Steinway Jr. in 1859.
Duplex scaling: Treble strings of a 182 cm. grand piano. From lower left to upper right: dampers, main sounding length of strings, treble bridge, duplex string length, duplex bridge (long bar perpendicular to strings), hitchpins.
Duplex scaling: Treble strings of a 182 cm. grand piano. From lower left to upper right: dampers, main sounding length of strings, treble bridge, duplex string length, duplex bridge (long bar perpendicular to strings), hitchpins.

With duplexes or aliquot scales, which was patented in 1872 by Theodore Steinway, the different components of string vibrations are controlled by tuning their secondary parts in octave relationships with the sounding lengths. Similar systems developed by Blüthner (1872), as well as Taskin (1788), and Collard (1821) used more distinctly ringing undamped vibrations to modify tone.

Some early pianos had shapes and designs that are no longer in use. The square piano had horizontal strings arranged diagonally across the rectangular case above the hammers and with the keyboard set in the long side. This design is variously attributed to Silbermann and Frederici and was improved by Guillaume-Lebrecht Petzold and Alpheus Babcock. Built in quantity through the 1890s (in the United States), Steinways celebrated iron framed over strung squares and were more than two and a half times the size of Zumpe's wood framed instruments that were successful a century before. Their overwhelming popularity was due to inexpensive construction and price, with performance and sonority frequently restricted by simple actions and closely spaced strings.
The mechanism in upright pianos is perpendicular to the keys.
The mechanism in upright pianos is perpendicular to the keys.

The tall, vertically strung upright was arranged with the soundboard and bridges perpendicular to keys, and above them so that the strings did not extend to the floor. Diagonally strung Giraffe, pyramid and lyre pianos employed this principle in more evocatively shaped cases. The term was later revived by many manufacturers for advertising purposes.

The very tall cabinet piano introduced by Southwell in 1806 and built through the 1840s had strings arranged vertically on a continuous frame with bridges extended nearly to the floor, behind the keyboard and very large sticker action. The short cottage upright or pianino with vertical stringing, credited to Robert Wornum around 1815, was built into the 20th century. They are informally called birdcage pianos because of their prominent damper mechanism. Pianinos were distinguished from the oblique, or diagonally strung upright made popular in France by Roller & Blanchet during the late 1820s. The tiny spinet upright was manufactured from the mid-1930s until recent times. The low position of the hammers required the use of a "drop action" to preserve a reasonable keyboard height.

Modern upright and grand pianos attained their present forms by the end of the 19th century. Improvements have been made in manufacturing processes, and many individual details of the instrument continue to receive attention.