Domenico Statuto asked:

> I am trying to understand how the position of the tangents in a
> fretted clavichord is to be calculated. Would you please provide a
> brief explanation or point me towards some literature?

The size of each interval - semitone, whole-tone or minor third - in
each fretted group is determined by the *ratio* of the sounding lengths.
So the first thing is to establish what temperament is intended; then
calculate the frequencies for an octave or so of notes; then calculate
the *ratios* between the frequencies of the notes in each fretted group;
then apply these to the sounding lengths.

In practice, it seems highly likely that old makers used traditional
whole-number ratios which are, in several cases, good approximations for
the true ratios. Thus, for example, 23:22 is a good approximation for
the chromatic semitones of quarter-comma mean-tone (e.g. C-C#) and 15:14 
is a good approximation for the diatonic semitones (e.g. C#-D).

I deal with the question of fretting ratios more fully in the reference
section of my book *Clavichord Tuning and Maintenance*, Keyword Press
2007 (currently out of print but will be reprinted later this year).

How did they incorporate these ratios in an actual instrument? It is
easy enough to produce them in a drawing and then transfer the required
lengths from the drawing to the instrument as it is made. But the
evidence is that generally old makers probably did not use drawings. It 
seems likely that in most cases the required ratios were incorporated in 
the *rack* and the tangents were positioned on lines drawn forward from 
the rack. Claas Douwes described the process in a work published in 
1699, and an account of this is given by John Barnes in *De Clavicordio 
[I]* (see 
http://www.musicaanticamagnano.com/index.php?option=com_wrapper&view=wrapper&Itemid=70&lang=en).

Hope this helps. Peter.


-- 
Peter Bavington
Clavichord Maker
291 Sprowston Mews
LONDON
E7 9AE
www.peter-bavington.co.uk

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