Most harpsichords generally have two or more sets of strings, and each set produces different tone qualities. A set of strings at normal pitch is called an 8-foot register. Another set of strings, which sounds an octave higher, is called a 4-foot register. Some modern harpsichords have a 16-foot register, which sounds an octave lower than normal, but this was extremely rare in old harpsichords. Two sets of 8-foot strings may produce different tone qualities because they are plucked at different points or with plectra of different material. Simpler forms of the harpsichord, the virginal and the spinet, have only one string to each note and to each key on the keyboard.

Le terme 8, 16 ou 4 pieds désigne la longueur du tuyau d’orgue, qu’actionne le premier do du clavier. Par extension, un registre de 8 pieds désigne le son fondamental qui est à l’unisson de la plupart des autres instruments. Le registre de 16 pieds sonne une octave plus bas que le 8 pieds, le registre de 4 pieds, une octave plus haut.


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Note added at 2 hrs 17 mins (2005-08-06 18:39:29 GMT)
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Sorry, Orla, forgot all about your text and *en* huit pieds.

Here\'s from the Britannica:
Two-manual harpsichords of this kind were invented at some point before 1620 in Flanders and gradually became known throughout the rest of Europe during the 17th century. These instruments commonly had three sets of strings, two unison sets *at normal pitch* (called *eight-foot pitch* because the low C at this pitch is produced by an organ pipe eight feet long) and a third set of shorter strings tuned an octave higher, or *at four-foot pitch*; this shorter set passed over its own bridge and was fastened to pins driven through the soundboard into a rail fixed to its underside.