The Crathes Quhissill
The Crathes Quhissill project had its first public presentation at the 2018 Musica Scotica conference in The Tolbooth, Stirling, on Saturday 21st April 2018.
The project arose initially at the instigation of Dr Elizabeth Ford, and Dr John Purser. Dr Ford summarises the project 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."
Studying the original ceiling painting using CAD
Conventional wisdom regarding flutes suggests that an outward flare of the kind depicted in the Crathes painting could have no useful acoustic purpose. An outward flare will naturally tend to raise the fundamental relative to the second harmonic, narrowing the octave, which would seem like a step in the wrong direction. The effect of the bell would be expected to be limited to the lowest note, possibly at best bringing the tone of that note closer to that of the finger hole notes (as with a clarinet bell). Due to the difference in the strength of harmonics in a flute as compared to a clarinet, the value of even this last possibility was questioned prior to the commencement of the project.
As work got underway, it quickly became clear that a bell of the type depicted in the painting could offer much more to the flute than had been expected. Trial and error experimentation based directly on the original painting was augmented by adaptation for the flute, of some formula relating to acoustic horns, leading to the discovery of two distinct and apparently useful bell geometries.
Some of the CAD workspaces being used to develop the Quhissill
The first is relatively conservative in its proportions, and does not significantly alter the octave relationship of D. The tone of the lowest note is audibly different, seeming "warmer". More surprisingly perhaps, the relative volume and the tone of the finger hole notes is affected. A model based on a typical renaissance flute (by Martin Wenner, who kindly provided advice during the development of this model), with the addition of this type of bell, seemed to be "mellowed" throughout its range. The low D took on a noticeably different character, while the differences in volume between notes throughout the range appeared to be reduced (see images on right).
The second bell is much larger, relative to the size of the flute, and most closely follows the outline depicted in the painting. This bell's effects are profound, and are still being studied. The intervals between the lowest harmonics are compressed to the point that the former 3rd harmonic behaves as the 2nd (octave). The 2nd harmonic is often undermined, although in some models it is present sounding around A4 or B4. The tone is altered much more noticeably, and the role of harmonics within the higher reaches of the flute's range changes considerably. Effectively, this appears to be a "D" flute with the upper harmonics that would be expected of a flute tuned to the "G" below that. The possible musical purpose of this is still being explored. The exact geometry of the bell is critical to the tuning of these harmonics, however early prototypes seem to indicate that these more closely spaced upper harmonics might facilitate a range reaching possibly a third higher than in a standard renaissance flute.
It's worth noting here that spectrum analysis is not a particularly satisfactory method of assessing these kind of effects, and is only one of the methods that has been used to evaluate the prototypes created. If used in a very carefully controlled way, software like Sonic Visualiser and LAMA can provide useful pointers, however in future it is hoped that measurements can be taken of the acoustic impedance of the prototype flutes, to identify more clearly what the effects of the bells are, and how these effects could be enhanced and developed.
Funding for the project was provided by Dr John Purser, the Hope Scott Trust, the Royal Musical Association, and the Friends of St Cecilia's Hall.
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.
Quhissill CAD work