From Academic Kids
A clavichord is a small, very quiet, European keyboard musical instrument. It was invented in about the fourteenth century and continued to be made until the 1840s, and was revived by Arnold Dolmetsch at the end of the 19th century. From the mid-18th century it principally flourished in German-speaking lands, Scandinavia and Iberia. Although most of the instruments built before the 1730s were small (perhaps 4 x 1 x 1/3 feet and four octaves in range), the last instruments built were up to seven feet long with a six octave range.
In the clavichord the strings run transversely from an anchorage at the left-hand end to tuning-pegs on the right; towards the right-hand end they pass over a curved wooden bridge. The action is simple, with the keys being levers with a small brass 'tangent' at the far end which strikes the strings (normally paired) above. The note is sustained as long as the tangent is in contact with the string. The volume of the note can be changed by striking harder or softer, and the pitch can also be varied by varying the force of the tangent against the string, which is known as bebung, and can be used to give a form of vibrato.
Since the string vibrates from the bridge only as far as the tangent, multiple keys with multiple tangents can be assigned to the same string (like a monochord). This is called a fretted clavichord. This technique simplifies the construction since fewer strings are required, but it limits the abilities of the instrument, since only one note can be played at a time on each string. As a result there are rarely more than two notes assigned to each string. They are usually chosen so that notes which are rarely heard together (such as C and C#) are on the one string. In the late 18th century, clavichords were often built unfretted, with a separate pair of strings for each key.
Instruments were built with one or two manuals and pedals, for the practice use of organists. This use was common in the days before the invention of the electric blower, and there is speculation that some practice etudes labelled organ by the composers and now regarded as organ repertoire were in fact more accurately written for the pedal clavichord.
Much of the music written for harpsichord, piano, and organ from the period circa 1400-1800 can be played on the clavichord; however, it is too quiet to use in any but the smallest ensembles. J. S. Bach's son Carl Philipp Emmanuel Bach was a great proponent of the instrument.
There are now numerous clavichord societies around the world, and some 400 recordings of the instrument have been made in the past 70 years. Leading modern exponents of the instrument include Derek Adlam, Christopher Hogwood, Paul Simmonds, Richard Troeger, and Miklos Spanyi, and fine modern copies have been made by makers including Peter Bavington, Martin Kather, Joris Potvleighe, Karin Richter, Ronald Haas, and Thomas Steiner.