The "Siena-Harpa" Project

Angel with viola a chiavi, Cappella di Palazzo Pubblico, Siena, Italy. Fresco by Taddeo di Bartolo, 1408.


On this site you find images, documents, audio and video recordings dedicated to the Viola a chiavi di Siena (also called Siena-Harpa relating to the Swedish name "nyckelharpa" of this family of musical instruments).

With three instruments inspired by the viola depicted in the fresco by Taddeo di Bartolo in the Cappella di Palazzo Pubblico in Siena, dated 1408, we have recorded some pieces by composers of the same period and the same region, Tuscany, such as Francesco Landini (1325-1397) and Paolo da Firenze (1355-1436).

The project is made by our trio, Marco Ambrosini, Jule Bauer and Didier François, thanks to the research, the advice and the instruments of the luthier Alex Pilz and realised with the support of Hessische Kulturstiftung.

Some pictures of our recording session in November 2021, in the beautiful 14th-century St. John's church of Hatzfeld-Eder (Hesse, Germany).

Measures of the Siena-Harpa by Alex Pilz
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Viola a chiavi di Siena by Alex Pilz.pdf
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The Viola a Chiavi di Siena - by Alex Pilz


What we nowadays call the Viola a chiavi di Siena can be classified to the medieval fiddle. This underscores the fact that the medieval fiddle was one of the most popular instruments of the 15th century. Various body shapes, sizes, number of string, bridge positions, positions of playing the instrument can be identified in preserved sources. In the case of the Viola a chiavi di Siena the fresco by Taddeo di Bartolo reveals many details. In this period it was common to hollow out the body out of a wooden block. The top of the instrument was glued and/or fixed with some wooden nails.

Not many instruments have survived from this period, but those who did let us know what material was used. Spruce for the soundboard and willow, linden, fruit wood, maple etc. for the body. 

The painting gives us many details about the size of the instrument, the vibrating string length, number of strings, number of keys and decorative elements.

On the neck is a box with keys covered by a lid. The strings are fixed on a tailpiece and running over a curved bridge to the pegbox under the lid. The positions of the Cshaped sound holes is in the lower part of the body. The shape is a really common one for the period and draws a conclusion that there exits same body models just with

different neck variety. If we take a closer look at the construction we will come to the point where the question about the soundpost and the position of the bars pops up.

From the view as luthier there are several options to reinforce the soundboard against the string pressure. Three or two bars can be glued across to the string position. A bar can be clued in the middle or on the bass/ treble side following the direction of the strings. Additional in that combination are also small bars in different positions possible

to influence the sound radiation. It is quite possible, that instruments had a soundpost.

As we know from an fresco by L. Signorelli in the Casa Santa, Loreto, Italy. The painting shows a soundpost through the sound holes of an fiddle (Winternitz 1967) before the restoration of the painting. An instrument with a soundpost has a different character. This includes the volume, frequency spectrum and the sound radiation. It also responds different for the player. Furthermore some sound adjustments are possible by changing the soundpost position afterwards.

The construction for the instruments in this project based on the classical way of building and is inspired by the fresco from Taddeo di Bartolo. Measurements and proportions are adjusted as best as possible. The sides, back and neck are made out of maple. The top is spruce. The four row-keyboard is a more complex one as we can find on the painting. The instruments are played with gut strings.

The instrument which is played by Marco Ambrosini is made out of spurce (except the neck) dated back from 1480. 

To understand the character of an instrument and what happens or not while playing it I did some measurements.

The following graphics show two soundboard admittance measurements right after finishing the instrument and after 2 years playing. It is clearly recognizable that some main characteristic peaks moved to the lower register while other didn't. An increase of the amplitude of min. 2.5 dB to max. 6.5 dB on the y-axis. This is the result of two years of playing the instrument and emphasizes the importance of playing a new instrument.


The following graphs compare a Viola and a Viola a chiavi di Siena in a sound radiation measurement set-up.
The frequency response curves representing the instruments and their different character.

The lowest mode which is called the A0 mode is the Helmholtz air resonance. It´s the air movement in the body including the air flow out the sound holes.

The Helmholtz air resonance on a Viola a chiavi di Siena is 215 Hz.


The Helmholtz air resonance A0 on a 40.5 cm long Viola is 230 Hz.

The difference of the two A0 modes is not significant and the rough character of the frequency curves show a similar tendency. Of course we have to pay attention to the different constructions etc. But it suggests that the Viola a chiavi di Siena has a similar sound volume like the Viola. Or the other way around?


Alex Pilz

This project was realised with the support of the Hessische Kulturstiftung