Domenico wrote:

> And BTW, the Hubert is doable without overwound strings? it has 7 notes
> - 14 strings - less than the Silbermann in the bass, but it should be
> about the same length, so I guess the Hubert should need about 16-18
> overwound strings? Or am I missing something?

Overwound strings are needed when the sounding length of the string is 
too short for solid wire to sound well. In my opinion, and as a rule of 
thumb, you should consider using them when the frequency multiplied by 
the sounding length *in metres* - the fL as Thomas Donahue calls it - is 
around 105, and they are definitely needed when the fL falls to about 
60. [As an aside, we really need a name for this useful measure, which 
gives us a handle on the scaling of any particular string. The 
dimensions of fL are the same as speed: could we call it 'scaling speed'?]

I had a look at the string lengths on the 1789, as recorded in Koen 
Vermeij's superb study of Hubert's work (*The Hubert Clavichord Data 
Book*, Keyword Press edition 2016). Bottom C has a sounding length of 
1194 mm so if the instrument was tuned to a1=415 the fL would be about 
62. I conclude that it might just be possible to make this instrument 
work with solid strings. You should consider red brass and, for the 
lowest notes, silver wire.

Incidentally, silver for strings needs to be hard-drawn: the wire sold 
for use in jewellery is too soft. Ask for sterling silver (not Brittania 
silver, which is almost pure and, like pure copper, cannot be used for 
strings) and get it drawn as hard as possible.

As a general rule, clavichords of a reasonable size - like this one - 
which go down no lower than 'cello C' can often be made to work with 
solid wire, but they will almost certainly sound better with twined or 
overwound strings. Those that go below bottom C definitely need 
overwound strings.

Hubert himself used them on the 1789 clavichord. He always provided the 
overspun notes with special tangents, forged or bent over so as to 
provide an extra-wide tangent top. On the 1789 instrument (which, 
incidentally, is the latest clavichord by C. G. Hubert to survive, made 
four years before his death in 1793) there are 12 of these special 
tangents, so we can be pretty sure Hubert thought that overwound strings 
were needed for the lowest octave of notes.

Now, I know that the Hass family aparently never used overwound strings, 
even on their five-octave clavichords, though other Hamburg-school 
makers did use them. The bottom bass notes of a typical Hass have an 
unpleasantly squashy feel IMHO and the note is only saved by the 
presence of the 4-foot string. I will stick my neck out and say that the 
Hasses would sound even better than they do now if they were fitted with 
overwound strings in the bass.

> how do you professionals calculate string diameter for clavichords?

The actual mathematical calculations are the same as for harpsichords. 
The final choice of diameters will be the result of trial and error; but 
one must start somewhere, and what I think most of us do is base our 
initial stringing on (1) previous experience; (2) guidance from the old 
makers by way of gauge marks on surviving antique clavichords; and (3) 
calculated tension graphs of the type given in the last section of the 
book by Malcolm Rose and David Law (*A Handbook of Historical Stringing 
Practice for Keyboard Instruments*, available from Malcolm 
[http://www.malcolm-rose.com/Stringing-Practice/stringing-practice.htm] 
and very reasonably priced). The subject is complicated, and both Jean 
Louchet and Thomas Donahue have written at length about it:

Jean Louchet, *The Keyboard Stringing Guide* 2009, available from Lulu

Thomas Donahue, *The Harpsichord Stringing Handbook*, Rowman and 
Littlefield, 2015.

A final word: it is a lot of hard work to make a clavichord. Why 
compromise, and 'spoil the ship for a halfpence of tar'? If it needs 
overwound strings, find a way of getting them.

Hope this is useful, Peter.

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

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