This is a reprint of the May 2002 Workshop News, in which I described the Swedish clavichord restoration at that time under way
In the last bulletin I mentioned the late eighteenth-century Swedish clavichord, currently occupying a lot of space in my workshop and nearing the end of its restoration. Work to reduce slop in the keys is complete, and strings are being put on to the instrument. It will be some time before it stabilises, since it has not been under tension for some months, but I can already tell what a terrific musical instrument it will be.
Swedish clavichords from the second half of the eighteenth century are closely similar in design. A 'Swedish model' had been developed around 1750, and it worked so well that they kept on making it until well into the 1800's, with very few changes apart from adding extra notes at the top. These instruments are huge - this one is fully 7 ft 6 in long - and they have a correspondingly big sound. I notice already that there will be an excellent singing treble. One reason for this is that the grain of the soundboard runs diagonally, from back right to front left, at an angle of about 25° to the front. In consequence, the treble end of the bridge has only a short length of grain under it which, compared with most clavichords, is closer to the situation that prevails in a harpsichord. I think this makes it easier to 'couple' the string, bridge and soundboard in the treble so as to produce a loud but sustained note.
Treble notes need an area of soundboard that is stiff, but not too heavy. With diagonal grain, the soundboard can be made very thin in the treble and still be stiff enough to match the treble strings. However, with the grain running from end to end, as in most German clavichords for example, the treble end of the bridge has to control a strip of soundboard up to 18 in long. This can only be made stiff enough if it is comparatively thick, but then it is too heavy to be readily moved by the very tiny amount of energy in a treble string.
Or at any rate, that's my current hypothesis! The whole business of soundboard behaviour is still shrouded in mystery and awaits a proper scientific analysis.
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