The piano is a musical instrument played by means of a keyboard. It is one of the most popular instruments in the world. Widely used in classical music for solo performances, ensemble use, chamber music and accompaniment, the piano is also very popular as an aid to composing and rehearsal. Although not portable and often expensive, the piano's versatility and ubiquity have made it one of the world's most familiar musical instruments.
Pressing a key on the piano's keyboard causes a felt-covered hammer to strike steel strings. The hammers rebound, allowing the strings to continue vibrating at their resonant frequency. These vibrations are transmitted through a bridge to a sounding board that more-efficiently couples the acoustic energy to the air. The sound would otherwise be no louder than that directly produced by the strings. When the key is released, a damper stops the string's vibration. See the article on Piano key frequencies for a picture of the piano keyboard and the location of middle-C. In the Hornbostel-Sachs system of instrument classification, pianos are considered chordophones.
The word piano is a shortened form of the word pianoforte, which derives from the originalItalian name for the instrument, clavicembalo [or gravicembalo] col piano e forte (literallyharpsichord capable of playing at the normal level, and more strongly). The musical terms "piano" and "forte" are usually interpreted as "soft" and "loud", but this is not strictly what they mean in Italian. Here, "Piano" means a plane or level, suggesting the normal playing level. "Forte" means a stronger, more powerful level of playing—louder than usual. This refers to the instrument's responsiveness to keyboard touch, which allows the pianist to produce notes at different dynamic levels by controlling the inertia with which the hammers hit the strings.
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Modern pianos come in two basic configurations (with subcategories): the grand piano and the upright piano.
Grand
In grand pianos, the frame and strings are horizontal, with the strings extending away from the keyboard. The action lies beneath the strings, and uses gravity as its means of return to a state of rest.
There are many sizes of grand piano. A rough generalization distinguishes the concert grand(between about 2.2 m and 3 m/9.84 feet long) from the parlor grand or boudoir grand (about 1.7 m to 2.2 m) and the smaller baby grand (around 1.5 m).
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All else being equal, longer pianos with longer strings have larger, richer sound and lowerinharmonicity of the strings. Inharmonicity is the degree to which the frequencies of overtones(known as partials or harmonics) sound sharp relative to whole multiples of the fundamental frequency. This results from the piano's considerable string stiffness; as a struck string decays its harmonics vibrate, not from their termination, but from a point very slightly toward the center (or more flexible part) of the string. The higher the partial, the further sharp it runs. Pianos with shorter and thicker strings, i.e. small pianos with short string scales, have more inharmonicity. The greater the inharmonicity, the more the ear perceives it as harshness of tone.
Inharmonicity requires octaves to be "stretched", or tuned to a lower octave's corresponding sharp overtone rather than to a theoretically correct octave. If octaves are not stretched, single octaves sound in tune, but double—and notably triple—octaves are unacceptably narrow. Stretching a small piano's octaves to match its inherent inharmonicity level creates an imbalance among all the instrument's intervallic relationships, not just its octaves. In a concert grand, however, the octave "stretch" retains harmonic balance, even when aligning treble notes to a harmonic produced from three octaves below. This lets close and widespread octaves sound pure, and produces virtually beatless perfect fifths. This gives the concert grand a brilliant, singing and sustaining tone quality—one of the principal reasons that full-size grands are used in the concert hall. Smaller grands satisfy the space and cost considerations needs of domestic use.
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