The Crathes Quhissill

The Crathes Quhissill – investigating a puzzling historical flute painting

Studying the original ceiling painting using CAD
Studying the original ceiling painting using CAD

The Crathes Quhissill project had its first public presentation at the 2018 Musica Scotica conference in the Tolbooth, Stirling, on Saturday 21 April 2018.

The project arose at the instigation of Dr Elizabeth Ford and Dr John Purser. Dr Ford summarises it as follows:

"The ceiling of the Muses' Chamber, Crathes Castle, Aberdeenshire, depicts the muses in a consort, each with her associated instrument. Most of the instruments are well represented, but the flute, which ends in a large flared bell, is both baffling and intriguing. Traditional instrument makers tend to argue that such an instrument is impossible to make, and even if it was possible, would not sound like a flute.

It is, however, possible with the use of computer assisted design and 3D printing. This presentation will explore how this technology was used to recreate a playing bell-ended flute, and what the implications are for further study of instruments in art. Acoustical analysis of the recreated flute indicates an expanded range in the flute's high register. This will have implications for sixteenth-century performance practice."

From painted ceiling to 3D-printed flute

Some of the CAD workspaces being used to develop the Quhissill
Some of the CAD workspaces being used to develop the Quhissill

The starting point was a detailed CAD study of the original ceiling painting. Conventional wisdom suggested that an outward bell of the type depicted at Crathes would be of little use on a flute: such a flare is expected to raise the fundamental relative to the second harmonic, narrowing the octave and affecting mainly the lowest note (as with a clarinet bell). Given the different harmonic structure of a flute, even that limited benefit was questioned at the outset.

As work progressed, it became clear that a bell like the one in the painting could have far more significant acoustic effects. Trial-and-error experiments based directly on the painted outline were combined with adaptations of horn formulas to the flute context, leading to two distinct and apparently useful bell geometries.

Two bell designs

  1. Smaller, conservative bell
    The first bell is relatively conservative in proportion and does not significantly alter the octave spacing of D. The lowest note acquires a noticeably warmer tone, and the overall response of the instrument changes:

    • The tone and volume of the finger-hole notes are affected.

    • A model based on a typical renaissance flute (after Martin Wenner, who advised on this model) with this bell added appears mellower throughout its range.

    • The low D's character changes, and differences in intensity between notes are reduced.

  2. Larger bell, based closely on the painting
    The second bell is much larger relative to the flute and follows the painted outline more closely. Its effects are profound and still under study:

    • The lowest harmonics are compressed so that the former 3rd harmonic behaves as the 2nd (the octave).

    • The usual 2nd harmonic is often weakened; in some models it appears around A4 or B4.

    • The tone changes much more markedly, and the role of upper harmonics in the high register shifts.

    • The result behaves effectively like a D flute with upper harmonics more typical of a flute tuned to the G below, potentially offering a usable range perhaps a third higher than a standard renaissance flute.

The exact geometry of this larger bell is critical to the tuning of these harmonics; early prototypes suggest that carefully shaped bells may offer practically exploitable high-register extensions.

Measuring and understanding the effect

Spectrum analysis (using software such as Sonic Visualiser and LAMA) has been used as one tool to study these effects, but it is not fully satisfactory on its own; it provides pointers rather than definitive answers. In future it is hoped that acoustic impedance measurements can be taken from the prototype flutes to identify more clearly what the bells are doing and how these effects might be enhanced and developed.

Typical residual peaks of the scale played on the renaissance flute, no bell, giving an indication of the content of what is being heard
Typical residual peaks of the scale played on the renaissance flute, no bell, giving an indication of the content of what is being heard
Typical residual peaks of the scale played with the use of the smaller bell, showing the typically smaller differences in intensity, and slightly more prominent overtones
Typical residual peaks of the scale played with the use of the smaller bell, showing the typically smaller differences in intensity, and slightly more prominent overtones

Funding for the Crathes Quhissill project has been provided by Dr John Purser, the Hope Scott Trust, the Royal Musical Association, and the Friends of St Cecilia's Hall.