THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

18.9 Strings 535Figure 18.22. Schematic of the mechanism of a grand piano (from Olson, 1967).steel strings stretched on a metal frame. The strings couple through a bridge toa large soundboard. The strings are activated by being struck by hammers thatare connected to keys forming a keyboard. Pressing down on a key actuates thehammer, which, in turn, strikes the string. The conventional piano is equippedwith 88 keys, and the piano covers a wide frequency range of more than sevenoctaves, from A 0 to C 8 (27.5–4186 Hz). The Bosendorfer 244-cm concert grandpiano features 97 keys, but not much music has been written for these extra keys.The extra keys are mainly there because of the additional resonances produced bythe extra strings and the larger soundboard.Figure 18.22 illustrates a schematic of the piano mechanism for a grand piano.The strings stretch from the pin block across the bridge to the hitch-pin rail at theother end. When a key is pressed downward, the damper rises and the hammerimpacts the string, causing it to vibrate. The string’s vibrations are transmitted to thesoundboard through the bridge. The hammer rebounds, remaining about 1.25 cmfrom the string as long as key remains pressed. When the key is depressed, thedamping pad does not engage the string. When the key is released, the dampingpad engages the string to speed up the decay of the sounding note.The largest version of the piano, the concert grand, has 243 strings that varyin length from about 200 cm at the bass end to approximately 5 cm at the trebleend. In this group there are 8 single strings wrapped with one or two layers ofwires, 5 pairs of strings also wrapped, 7 sets of 3 wrapped strings, and 68 setsof 3 unwrapped steel strings. The smaller pianos may contain fewer strings butthey still play the same number of notes. A small grand piano may carry 226strings. The arrangement of the strings is such that the bass strings may overlaythe middle strings, so that they can function nearer the soundboard. The soundboarditself is usually made of spruce and it is up to 1 cm thick; it acts as theprincipal source of radiated sound just as the top plate of a violin does. Becausethe tension forces in the strings are so high, the frames are fabricated of cast