The string mass is varied to constrain the frequencies to their proper values. In order to maintain comparable tensions in the strings without inconvenient size for the instrument, the length is not halved with each octave but a ratio between 1.88 and 1.94:1 is used. Working out combinations of lengths, masses and tensions for these strings within a compact instrument is a formidable problem. In the modern piano, the strings are mounted on a cast iron frame to provide the strength to main the required tension in all of these strings (about 30 tons for a grand). The next 18 pitches have two, and the last 60 have three strings each. Generally, the ten lowest pitches have one wirewound string. The grand piano has about 230 strings for the 88 keys. This "7th harmonic problem" can be illustrated by examining the musical intervals formed by a an exact harmonic sequence. The striking point is about 1/7th of the way along the string to discriminate against the 7th harmonic resonance, which is significantly out of tune with the equal tempered scale. Actually, the hammers are in sets for the keys which sound two or three strings. The piano is the standard instrument for the equal tempered scale, yet both the high end and low end of the instrument are tuned so that they depart slightly from equal temperament because the sound has been judged to be more pleasing with that arrangement (see "stretched" tuning discussion below).ĭepressing a key on the piano engages a complex mechanism called the "action" of the piano which causes the hammer to strike the string. There are 52 white keys and 36 black keys (for the chromatic notes), bridging seven and a third octaves with 12 equal semitones per octave. Some grand pianos have on the order of 7000 parts! Their function can be described in terms of six features: the keyboard, the hammers, the dampers, the bridge, the soundboard, and the strings. The right pedal is the damper pedal to dampen the whole keyboard. The center pedal is the sustain or sustenuto pedal which disengages the dampers. It shifts the keyboard beneath the strings so that the hammers strike fewer strings, giving a softer sound. The left pedal is the "soft pedal" or una corda. Three pedals afford the player some control over the sound of the instrument. The soundboard is usually made of spruce.
Energy is coupled from the strings into the soundboard and from it into the air. The soundboard is a crucial element in the sound of the piano.
Held in a heavy cast iron frame, the strings pass over a bridge to a pin block by which the strings are tuned. The strings are sounded by hammer mechanisms which are activated by the keys. The piano has 88 keys which span the frequency range 27.5 Hz (A0) to 4186 Hz (C8). The relatively soft hammer structure, fashioned from pressurized wool, gives a dramatic attack to the tone without sounding harsh. This baby grand is one of several configurations of the piano.