135. Keyboard Stringed Instruments.—Throughout the 18th century three main types of stringed instruments with a keyboard were in constant and conspicuous use—the clavichord, the harpsichord and the pianoforte, the first two in more than one form. The clavichord and the harpsichord were inheritances from previous centuries, while the pianoforte was new. So far as the keyboard itself went, the three were not distinguishable. Their mechanical differences lay in the way in which the strings were sounded, and, incidental to this, in the method of stringing. Tonally and artistically they differed considerably. For a time each was felt to have its own special utility, but, as the pianoforte was gradually improved, its superiority became so manifest that finally, at the close of the century, it had practically driven the others from the field.
The clavichord was a keyboard application of the principle of the mediæval
monochord, which was not so much a musical instrument as a device
for the study of intervals. The monochord (as its name shows) had
properly but one string, stretched by a weight over a soundboard, and a
movable bridge by which the string could be divided into parts having
some desired mathematical ratio to each other and hence giving tones in
the corresponding harmonic relation. The essential feature was that the
pitch of the tones was fixed by the placing of the bridge. In the clavichord
each key of the keyboard brought to bear upon some string a
metal (brass) 'tangent,' which was driven against the string and held
there like the monochord bridge, the point of its impact determining
the pitch of the tone. (The vibration of the string took place only on
one side of the tangent, the other part of the string being deadened
by a strip of cloth.) The strings were all of about the same length,
and often two or even three keys operated the same string so far as this
could be managed without interference, thus diminishing the total size
of the instrument and facilitating its tuning. In the earliest clear
references to the clavichord (16th century) the number of keys was
about 20, and in the 18th century the compass seldom exceeded four octaves
(that is, less than 50 keys), but the number of strings might be
much less. In time, however, clavichords were often made with a string
for each key. These were called 'bundfrei' or 'unfretted,' while the
others were 'gebunden' or 'fretted.' The outward shape of the instrument
was that of a simple rectangular box (usually without legs), not too
large to be carried under the arm. The case and inside of the cover
were often ornamented.
The clavichord tone was thin, metallic (since both strings and tangents were made of brass), and never powerful. Since, however, its character was directly dependent upon the pressure of the key, it could be delicately graded as to force, and even be prolonged and given a peculiar wavy effect by rocking or pulsating the finger ('bebung'). Accordingly,
