Interior of an upright piano, showing the felt-covered hammers. The tuning pins can be seen at upper left. In the treble range shown, each note has three strings.

In the period lasting from about 1790 to 1860, the Mozart-era piano underwent tremendous changes, which 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. It was also a response to the ongoing Industrial Revolution, which made available technological resources like high-quality steel for strings (see piano wire) and precision casting for the production of iron frames.

Over time, piano playing became a more strenuous and muscle-taxing activity, as the force needed to depress the keys, as well as the length of key travel, was increased. The tonal range of the piano was also increased, from the five octaves of Mozart’s day to the 7⅓ (or even more) octaves found on modern pianos.

In the first part of this era, technological progress owed much to the English firm of Broadwood, which already had a strong reputation for the splendour and powerful tone of its harpsichords. Over time, the Broadwood instruments grew progressively larger, louder, and more robustly constructed. The Broadwood firm, which sent pianos to both Haydn and Beethoven, was the first to build pianos with a range of more than five octaves: five octaves and a fifth during the 1790s, six octaves by 1810 (in time for Beethoven to use the extra notes in his later works), and seven octaves by 1820. The Viennese makers followed these trends. The two schools, however, used different piano actions: the Broadwood one more robust, the Viennese more sensitive.

By the 1820s, the center of innovation had shifted to Paris, where the Érard firm manufactured pianos used by Chopin and 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, a great benefit for rapid playing. When the invention became public, and as revised by Henri Herz, the double escapement action gradually became the standard action for grand pianos, and is used in all grand pianos currently produced.

Some other important technical innovations of this era include the following:

        Use of three strings rather than two for all but the lower notes

• The iron frame, also called the “plate”, sits atop the soundboard, and serves as the primary bulwark against the force of string tension. The iron frame was the ultimate solution to the problem of structural integrity as the strings were gradually made thicker, tenser, and more numerous (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 which patented the first full iron frame for grand pianos (1843). Composite forged metal frames were preferred by many European makers until the American system was fully adopted by the early 20th century.
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    • Felt hammer coverings, first introduced by Henri Pape in 1826, gradually replaced skillfully layered leather hammers; the more consistent material permitted wider dynamic ranges as hammer weights and string tensions increased.
    • The sostenuto pedal invented in 1844 by Jean Louis Boisselot and improved by the Steinway firm in 1874.
    • 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, rather than 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.

• Duplexes or aliquot scales; In 1872 Theodore Steinway patented a system to control different components of string vibrations 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.

Today’s upright, grand, and concert 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.

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, it is variously attributed to Silbermann and Frederici and was improved by Petzold and Babcock. Built in quantity through the 1890s (in the United States), Steinway’s celebrated iron framed over strung squares 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 tall vertically strung upright grand 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 about 1810 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. It saved space by using a “drop action” arranged below the level of the keys.

Although there were various crude earlier attempts to make stringed keyboard instruments with struck strings, it is widely considered that the piano was invented by a single individual: Bartolomeo Cristofori of Padua, Italy. It is not known exactly when Cristofori first built a piano, but an inventory made by his employers, the Medici family, indicates the existence of a piano by the year 1700. The three Cristofori pianos that survive today date from the 1720s.

 Like many other inventions, the piano was founded on earlier technological innovations. The mechanisms of keyboard instruments such as the clavichord and the harpsichord were well known. In a clavichord the strings are struck by tangents, while in a harpsichord they are plucked by quills. Centuries of work on the mechanism of the harpsichord in particular had shown the most effective ways to construct the case, soundboard, bridge, and keyboard. Cristofori, himself an expert harpsichord maker, was well acquainted with this body of knowledge.

 Cristofori’s great success was in solving, without any prior example, the fundamental mechanical problem of piano design: the hammers must strike the string, but not remain in contact with the string (as a tangent remains in contact with a clavichord string) because this would damp the sound. Moreover, the hammers must return to their rest position without bouncing violently, and it must be possible to repeat a note rapidly. Cristofori’s piano action served as a model for the many different approaches to piano actions that followed. While Cristofori’s early instruments were made with thin strings and were much quieter than the modern piano, compared to the clavichord (the only previous keyboard instrument capable of minutely controlled dynamic nuance through the keyboard) they were considerably louder and had more sustaining power.

 Cristofori’s new instrument remained relatively unknown until an Italian writer, Scipione Maffei, wrote an enthusiastic article about it (1711), including a diagram of the mechanism. This article was widely distributed, and most of the next generation of piano builders started their work because of reading it. One of these builders was Gottfried Silbermann, better known as an organ builder. Silbermann’s pianos were virtually direct copies of Cristofori’s, with one important addition: Silbermann invented the forerunner of the modern damper pedal, which lifts all the dampers from the strings at once.

Silbermann showed Bach one of his early instruments in the 1730s, but Bach did not like it at that time, claiming that the higher notes were too soft to allow a full dynamic range. Although this earned him some animosity from Silbermann, the criticism was apparently heeded. Bach did approve of a later instrument he saw in 1747, and even served as an agent in selling Silbermann’s pianos.

 Piano-making flourished during the late 18th century in the Viennese school, which included Johann Andreas Stein (who worked in Augsburg, Germany) and the Viennese makers Nannette Stein (daughter of Johann Andreas) and Anton Walter. Viennese-style pianos were built with wood frames, two strings per note, and had leather-covered hammers. It was for such instruments that Mozart composed his concertos and sonatas, and replicas of them are built today for use in authentic-instrument performance of his music. The pianos of Mozart’s day had a softer, clearer tone than today’s pianos, with less sustaining power. The term fortepiano is nowadays often used to distinguish the 18th-century instrument from later pianos.

Piano is the general name given to a musical instrument classified as a keyboard, percussion, or string instrument, depending on the system of classification used. The piano produces sound by striking steel strings with felt hammers that immediately rebound allowing the string to continue vibrating at its resonant frequency. These vibrations are transmitted through the bridges to the soundboard, which amplifies them.

The piano is widely used in western music for solo performance, chamber music, and accompaniment. It is also very popular as an aid to composing and rehearsal. Although not portable and often expensive, the piano’s versatility and ubiquity has made it among the most familiar of musical instruments.

The word piano is a shortened form of the word pianoforte, which is seldom used except in formal language and derived from the original harpsichord with soft and loud). This refers to the ability of the piano to produce notes at different dynamic levels depending on the speed with which a key is depressed.