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HOW IT'S MADE - Making a cello from carbon

News International-French

2 Dec 2019

As part of a unique partnership between the School of Arts Ghent and Ghent University, and with the support of Research Foundation Flanders (FWO), Tim Duerinck developed, made and tested several composite violins and cellos. Carbon, glass and flax fibres all offer their own unique advantages and result in high quality instruments that can be used in different artistic applications.

Tim Duerinck has developed, made and tested several composite violins and cellos.

Tim Duerinck has developed, made and tested several composite violins and cellos.

Perhaps you’ve already seen a music instrument made of carbon fibre composites? The prices of commercially available carbon violins range from €2380 to €7490. Did you know music instruments can be made from other composite materials as well?

Carbon fibre
Some companies already produce carbon fibre composite instruments. This material is very well suited to violins or guitars due to its high stiffness and low weight. As wooden instruments such as violins have developed over 300 years, composite instruments have some catching up to do in order to reach their full potential. With such a versatile material, research was needed to gain an understanding of the effect of different fibre types, fibre directions, and other attributes related to the sound produced by an instrument.

For this research, the authors combined insights from classically trained violinmakers, musicologists and material scientists to make very high quality prototype instruments and learn more by putting them through relevant scientific tests.
At first, six composite violins were made by the first author, which were identical except for the top plate material.

Three cellos followed, which were made completely from either carbon, glass or flax fibres.

How it's made?
The prototypes were designed based on the dimensions of a conventional instrument but excluded the rather sharp corners to facilitate the mould fabrication. For the sound holes, a simplified modern design was chosen as well, yet the overall dimensions of conventional sound holes were kept for acoustic reasons.

Making a Carbon Cello - Part 1/3 - Pattern making

The back plate, sides and neck were made as one piece. The patterns were handcrafted from medium density polyurethane (PU) foam in a similar way to how a wooden instrument is carved from a block of wood. This process ensured that the knowledge of the age old instrument making craft could be used, for example to give the arching of the soundboards a proper shape.

After crafting, the patterns were coated with a polyester resin to achieve a high gloss surface that could be treated with a release agent. Glass fibre moulds were made to create all the composite parts using the vacuum assisted resin transfer moulding (VARTM) process at Ghent University. The composite parts were acoustically optimized by varying the thickness of the lay up, making the soundboard stiffer in the centre and more flexible towards the edge. This is similar to a conventional wooden soundboard, which is thicker in some regions and thinner in others.

The required thickness was calculated using the classical laminate theory. The composite parts were then assembled in the workshop to finished instruments.

The entire building process of a carbon cello is described in the three videos included here.

Making a Carbon Cello - Part 2/3 - Mould making and infusion (VARTM)

The prototypes were studied through various methods ranging from modal analysis, which was used to study vibrational behaviour revealing signature modes of acoustic importance (Figure 4), acoustic measurements, to how the instruments are perceived by listeners and musicians in double blind tests.

An example of what was learned is that changing the fibre direction in the lay ups has a significant effect on the perceived loudness and tonal colour of a violin.

Thus, by changing the (an)isotropy of the carbon soundboards, the instrument’s sound can be changed to fit the desire of the musician.

Making a Carbon Cello - Part 3/3 - Assembly and Finish

What about flax?
First of all, flax was found to be visually attractive to many musicians, some of them even mistaking it for wood. The material results in a slightly heavier soundboard with more damping, resulting in an instrument that is less loud than its carbon counterpart. The tone colour described as warm, soft and round is much appreciated by listeners and musicians alike, which makes it a favourite for many. The material’s lower ecological footprint is an added benefit.

Many musicians are hesitant towards non natural materials for music instruments, claiming they sound “plastic” or “cold”. Although no evidence of this was found in scientific tests, an instrument made from flax might be more easily accepted in the conservative world of (classical) music instruments.

Tim Duerinck has developed, made and tested several composite violins and cellos.

Tim Duerinck in its laboratory at Gent University.

And sandwich materials?
Luthiers have always sought after the lightest and stiffest wood to make their instruments. They believe it results in an instrument that projects more, or in other words, a louder instrument. A logical next step in the effort to create the most lightweight soundboard and thus, the loudest acoustic music instrument, are sandwich materials.

To investigate this, a violin with a soundboard made from a sandwich material with carbon fibre composite skins and a honeycomb core (Nomex®) was created. The violin was found to be very loud.
One violinmaker who tried the instrument even proclaimed “this is too much; it should be forbidden!”. Perhaps indeed, the team went too far with this one; many professional violin players are already half deaf in their ear closest to the instrument. Yet, the insights gained provide interesting opportunities to tailor the loudness of an instrument to the musician’s desire. More specifically, less loud instruments such as acoustic guitars or ukuleles could benefit from this.

Glass fibre
Finally, a glass fibre cello was also made. To counter the higher weight of the material, the above mentioned sandwich technology was used to create a see through instrument that is impossible to walk by without looking. Especially, more experimental minded cellists are drawn to the instrument for its specific sonic palette. For the instrument’s première in Brussels, cellist Benjamin Glorieux put a spotlight under his chair, illuminating the instrument and adding a visual aspect to a cello solo like never before.

Final cello made from carbon

Final cello made by Tim Duerinck (Left: Final carbon cello - Upper right: Soundholes carbon details - Right mid: The inside of the glass fibre cello before putting in the soundpost - Lower right: Back of the carbon cello)

To conclude
Carbon offers a high quality alternative to wood. By changing the fibre direction and thickness of the soundboards, the sound of the instruments can be changed, which offers great possibilities for the further development of high quality carbon fibre instruments. Violins or cellos made from flax or glass fibre are not yet commercially available, yet the authors’ research shows these materials have great potential in both the sound they produce and their visual appeal to musicians.