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 (40000 lbf) in a modern grand piano. 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. 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." But a better steel wire was soon created in 1840 by the Viennese firm of 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.
Early technological progress in the late 1700s owed much to the firm of Broadwood. John Broadwood joined with another Scot, Robert Stodart, and a Dutchman, Americus Backers, to design a piano in the harpsichord case—the origin of the "grand". This was achieved by about 1777. They quickly gained a reputation for the splendour and powerful tone of their instruments, with Broadwood constructing pianos 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 used a more robust action, whereas Viennese instruments were more sensitive.
Several important advances included changes to the way the piano was strung. The use of a "choir" of three strings, rather than two for all but the lowest notes, enhanced the richness and complexity of the treble. The use of a Capo d’Astro bar instead of agraffes in the uppermost treble allowed the hammers to strike the strings in their optimal position, greatly increasing that area’s power. The implementation of over-stringing (also called cross-stringing), in which the strings are placed in two separate planes, each with its own bridge height, allowed greater length to the bass strings and optimized the transition from unwound tenor strings to the iron or copper-wound bass strings. Over-stringing was invented by Pape during the 1820s, and first patented for use in grand pianos in the United States by Henry Steinway Jr. in 1859.
Some piano makers added variations to enhance the tone of each note, such as Pascal Taskin (1788), Collard & Collard (1821), and Julius Blüthner, who developed Aliquot stringing in 1893. These systems were used to strengthen the tone of the highest register of notes on the piano, which up till this time were viewed as being too weak-sounding. Each used more distinctly ringing, undamped vibrations of sympathetically vibrating strings to add to the tone, except the Blüthner Aliquot stringing, which uses an additional fourth string in the upper two treble sections. While the hitchpins of these separately suspended Aliquot strings are raised slightly above the level of the usual tri-choir strings, they are not struck by the hammers but rather are damped by attachments of the usual dampers. Eager to copy these effects, Theodore Steinway invented duplex scaling, which used short lengths of non-speaking wire bridged by the "aliquot" throughout much of upper the range of the piano, always in locations that caused them to vibrate sympathetically in conformity with their respective overtones—typically in doubled octaves and twelfths.
In the period from about 1790 to 1860, the Mozart-era piano underwent tremendous changes that led to the modern structure of the instrument. This revolution was in response to a preference by composers and pianists for a more powerful, sustained piano sound, and made possible by the ongoing Industrial Revolution with resources such as high-quality piano wire for strings, and precision casting for the production of massive iron frames that could withstand the tremendous tension of the strings. Over time, the tonal range of the piano was also increased from the five octaves of Mozart's day to the seven octave (or more) range found on today's pianos.
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 yet risen to its maximum vertical 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 was first introduced by Jean-Henri Pape 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 a wider range of effects.
Pianoteq is a software synthesizer which share some characteristics to a piano module.
Another common form is the stage piano, designed for use with live performances, professional audio, or in a recording studio. This type of digital piano normally makes no attempt to imitate the physical appearance of an acoustic piano, rather resembling a generic synthesizer or music workstation. A distinguishing feature of most stage pianos is a lack of internal loudspeakers and amplification - it is normally assumed that a powerful keyboard amplifier or PA system will be used. However, some stage pianos are equipped with powered speakers.
Alfred Dolge writes of the pedal mechanisms that his uncle, Louis Schone, constructed for both Robert Schumann and Felix Mendelssohn in 1843. Schumann preferred the pedal board to be connected to the upright piano, while Mendelssohn had a pedal mechanism connected to his grand piano. Dolge describes Mendelssohn's pedal mechanism: "The keyboard for pedaling was placed under the keyboard for manual playing, had 29 notes and was connected with an action placed at the back of the piano where a special soundboard, covered with 29 strings, was built into the case".
In addition to using his pedal piano for organ practice, Schumann composed several pieces specifically for the pedal piano. Among these compositions are Six Studies Op. 56, Four Sketches Op. 58, and Six Fugues on Bach Op. 60. Other composers who used pedal pianos were Mozart, Liszt, Alkan and Gounod.
The piano, and specifically the pedal mechanism and stops underwent much experimentation during the formative years of the instrument, before finally arriving at the current pedal configuration. Banowetz states, "These and a good number of other novelty pedal mechanisms eventually faded from existence as the piano grew to maturity in the latter part of the nineteenth century, finally leaving as survivors of this tortuous evolution only today's basic three pedals".
Many digital pianos, especially those that resemble an acoustic piano, have built-in pedals that function much as those on an acoustic piano. In addition, commercially available pedal switches, which are commonly used for regular electronic keyboards, can also be used, especially on portable models. On an acoustic piano the sustain pedal lifts the dampers for all strings, allowing them to resonate naturally with the notes played. Only high-end digital pianos can reproduce this sympathetic resonance effect.
Along with the development of the pedals on the piano came the phenomenon of the pedal piano, a piano with a pedalboard. Some of the early pedal pianos date back to 1815. The pedal piano developed partially for organists to be able to practice pedal keyboard parts away from the pipe organ. In some instances, the pedal piano was actually a special type of piano with a built-in pedal board and a higher keyboard and bench, like an organ. Other times, an independent pedal board and set of strings could be connected to a regular grand piano. Mozart had a pedalboard made for his piano. His father, Leopold, speaks of this pedalboard in a letter: "[the pedal] stands under the instrument and is about two feet longer and extremely heavy".
There are also digital piano modules, which are simply keyboardless sound modules chiefly containing piano samples. One early example of a digital piano module is the Roland MKS-20 Digital Piano.
Some digital piano implementations, like Roland V-Piano, Yamaha MODUS, Casio Celviano Grand Hybrid, and the software-based Pianoteq, use mathematical models based on acoustic pianos to generate sound, which brings the ability to generate sounds that vary more freely depending on how the keys have been struck, in addition to allow a more realistic implementation of the distinctive resonances and acoustical noises of acoustic pianos.
Although the tacks can be removed from the hammers, inserting them causes permanent damage to the felt; for this and other reasons, the use of tacks is generally discouraged by piano technicians.
In general, the sounds produced by a digital piano are based on sampling, by which acoustic piano sound samples are stored in ROM. The samples stored in digital pianos are usually created using high-quality pianos, expensive microphones, and high-quality preamps in a professional recording studio. Usually multiple samples are available for the same keystroke, attempting to reproduce the diversity of sounds observed on an acoustic piano. However, sample-based digital pianos do have limitations on the faithfulness with which they reproduce the sound of an acoustic piano. Because samples are taken for only a limited number of intensity levels, digital pianos usually lack the continuous timbral changes that characterize acoustic pianos. They may also lack the harmonic tones that result when certain combinations of notes are sounded and the natural reverberation that is heard when an acoustic piano is played percussively. They often lack the incidental acoustic noises associated with piano playing, such as the sounds of pedals being depressed and the associated machinery shifting within the piano, which some consider a benefit. These limitations apply to most acoustic instruments and their sampled counterparts, the difference often being described as "visceral".
All of Mozart's mature concertos were concertos for the piano and not the harpsichord. His earliest efforts from the mid-1760s were presumably for the harpsichord, but Broder showed in 1941 that Mozart himself did not use the harpsichord for any concerto from No. 12 (K. 414) onwards. In fact, Mozart's original piano was returned to Vienna in 2012 after a 200-year absence and was used in a concert shortly after its return. This is the same piano that Mozart kept at his home and brought through the streets for use at various concerts.
Moving a piano is a difficult procedure. There is risk to the piano, risk of bodily injury to the person moving the piano and other people and risk of damage to other property. Though moving a piano may seem like a simple procedure, there are hidden factors which compound the procedure. Pianos are difficult to move and should only be moved by a professional who is careful, properly trained, insured, and has the proper equipment.
The wheels attached directly to the piano itself are rarely used for moving, and are used mainly for cosmetic effect. For a studio piano with larger, double wheels, it is only designed for short moves. When moving a studio piano beyond the immediate room or for more than just a few feet, a dolly should still be used.