3D Printed Acoustic Violin

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Taylor Woodhead, Howard Community College

Mentored by: Alex M. Barr, Ph.D.

Abstract

This paper describes the process of printing, assembling, and testing a playable, 3D printed acoustic violin. Printing considerations such as scaling part sizes, printing orientations that optimize strength, and designing the sound post are discussed as well as methods for securely assembling the violin. Fourier transforms and pressure v. time graphs of A notes played on the 3D printed violin and two wood violins of differing quality are compared. The results indicate that the sound quality of the 3D printed violin is comparable to that of an inexpensive wood violin.

Introduction

The field of 3D printing has seen tremendous growth in the recent years as printers have become more affordable and printing materials become more varied. This has opened the field to tinkerers; leading to websites devoted to at-home 3D printing [1], and community groups/spaces like the Innovation Hub at HCC devoted to 3D printing [2]. I was first introduced to 3D printing my sophomore year of high school and bought my own 3D printer, a Prusa i3 MK2S, around July of last year. I’ve always had a passion and skill for creating things. I’ve also played the violin since kindergarten. I never expected printing a violin to become a physics project, I just thought it would be fun and I was curious if it would work. 3D printing a violin wasn’t nearly as difficult as making a real violin, but not quite as simple as “just hitting the print button”. The project also prompted some interesting questions about the properties of a violin. What is the difference of using plastic in place of wood? How does material impact sound? What other materials have been used to create violins? Why the hour-glass shape of the body? The violin has been around for hundreds of years, but all aspects of what makes a violin a violin is still not understood. Interestingly, traits like the “f” holes were evolved over time through craftsman mistakes and the best instruments were copied [3]. Luthiers (violin makers) consider violin making an art that is passed down rather than science or manufacturing as one might assume. Relatively recently, some luthiers have begun to study violins with newer technology to better understand how they work [4].

Construction

This 3D printed violin is made of PLA (polylactic acid) plastic and was assembled over a period of about three months. The total time spent printing was around 72 hours, with an additional 24 hours of labor.

Figure 1: Overview of various violin parts. The strings are the only part that was not 3D printed.

Computer models for 3D printed violins can be found online. The model used here was obtained from Thingiverse [5]. The original model was closer to a thumb-sized violin and completely unusable. Since all parts are proportional, only one scale value was needed to adjust everything to full-scale. First, a draft neck was printed at approximately what size I thought it should be, then compared it to one of my wood violins. By measuring the lengths of the necks, I used the percent difference to determine the correct the scale, reprinted a new neck, and verified it was the correct size.

Figure 2: Drafted violin neck being compared to the wood violin.

An important consideration to be made prior to printing was how to orient the parts in 3D space. The orientation of a 3D part heavily impacts how strong it will be under certain loads of force. If one looks at any object around them, it can be sliced into 2D shapes. For example if one looks at a soda can, depending on how you slice it, there exist small layers of circles or small layers of rectangles. This is how a 3D printer prints objects. The printer can create a soda can in a vertical orientation by drawing a circular base, then another circle on top, and so on until it has fully created the cylindrical 3D can from 2D layers. This process is illustrated in Figure 3a. Figure 3b shows an alternative orientation in which the can is printed lying down. Although too difficult to see in the rendering since one cannot zoom in, these figures show every single line the printer will print. In Figure 3a, each line represents a 0.35 mm (350 micron) layer. A 123.2 mm (12.32 cm) tall can would thus require 352 individual layers.

Figure 3: a) Digital model of a standing soda can constructed in Slic3r software [6]. b) An alternative slicing of the can showing layers of approximate rectangles instead of circles [7].

These layers give the printed parts a grain effect similar to wood. 3D parts are weaker when stresses are placed in certain orientations along these grains. For example, chopping the can sideways, or vertically pulling the can apart, in Figure 3a would be easy, but crushing or chopping downward would be difficult. Since violins have around 50-80 pounds of tension in the strings, it is important that weak orientations are avoided. If the neck was printed lengthwise, as shown in Figure 4a, it would certainly snap. The neck must be printed in a way that resists the bending force created by the strings.

Figure 4: Digital rendering of the neck piece. The two different orientations show the different possible layer lines. Arrows show the forces placed on the neck piece.

Another factor to consider when printing is overhangs – pieces of a part that hang over open air. Since the printer prints with molten plastic, it must have something to place the plastic onto. If there is air, the plastic just falls. Removable support material that is built up and broken off from overhangs can be used to avoid this problem, but it’s better to avoid doing this when possible since supports create rough patches on the plastic and waste material.

Figure 5: A part (not used for the violin) on the print bed showing support material generation for surfaces that hang too far out. Image by author.

After placing the parts in the optimal orientations, they are ready to be printed. Some parts, such as the violin body, were too large for the print bed, so they were cut in the software and printed as smaller pieces for later assembly into a single larger piece. The body is composed of six separate pieces, and a total of twenty pieces for the entire violin. Most of the assembly was “eyeball approximation” for where pieces should be placed compared to my wooden violin. During the assembly, I noticed two pieces in a normal violin were missing from the Thingiverse files that were important for a functional violin: the sound post and bass bar. The bass bar helps with vibration transfer, but mostly provides strength to the body to support the strings. The sound post transfers vibration from the top of the violin body to the back so that the back vibrates together with the top. 3D models for the sound post and bass bar were created using Autodesk Inventor [8].

The majority of pieces were initially held with super glue then welded at the seams with a soldering iron for more strength [9]. The tail piece (secures the strings at the bottom of the body), bridge (lifts the strings up and transfers vibrations to the body), and sound post are held together by the tension of the strings and friction rather than glue. The placement of a sound post requires special luthier tools, so I modeled and 3D printed my own tools based on pictures online. The first few times tightening the strings caused the tail wire to bust apart, but eventually I found a copper wire that was strong enough.

Testing

How does it sound? It sounds like a plastic violin made by an engineering student. But it looks like a violin, and it makes violin sounds, so that was enough to satisfy my desire to 3D print a violin. It can be hard to judge the quality of a violin unless you have another violin available for comparison. The sound quality of the 3D printed violin was investigated by comparing it to two wood violins of varying quality. Data was collected for Pressure v. Time and Amplitude v. Frequency (Fourier transform) using a microphone and Logger Pro software [10].

Sound is waves of air pressure. An acoustic violin takes the vibrations of the strings, transfers them to the body, creating compressions of air within the body that produce pressure waves, just like a speaker, but without electricity. These compressions happen at the same frequency as the strings. With strings alone and no body, a violin would make very little sound, like a plucked rubber band. Electric violins (same as electric guitars) do not need a body other than to support the strings and provide parts to hold. They electronically measure the vibrations from the strings and amplify them through a speaker. Of the two wood violins, the better violin produced almost double the pressure amplitude of the lesser quality violin when moving the bow with a similar speed and weight. The pressure wave produced by the 3D printed violin was a slightly lower amplitude than that of the lesser quality violin. What can be observed from this is that the better violin was significantly more efficient at transforming string vibrations to audible sound than the other two, and that the 3D printed violin was about as efficient as a lesser quality wood violin.

Fourier transforms indicate which frequencies are strongest in a note and how clean a pitch the violin produces. On a violin, the A string resonates at a frequency of about 440 Hz. When recording the A string being played, it would be expected that this frequency has the largest amplitude in the Fourier transform. This was true for the better wood violin and for the 3D printed violin. Oddly, it was not true for the lesser quality wood violin. Although 440 Hz did produce a large amplitude for the lesser quality violin, a frequency around 1300 Hz produced larger amplitudes on multiple trials. 1300 Hz is close to the frequency of the E string. I hypothesize that energy from the A string goes into the violin body where some gets converted to sound and some energy transfers from the body into the E string. The E string’s vibration then transfers to the body producing the 1300 Hz sound. If true, this would be a sign of poor vibration isolation, which wouldn’t be surprising for a low quality violin. It’s interesting that the 3D printed violin has better vibration transfer to the air than the lesser quality wood violin.

Figure 6: Fourier transform graphs of the A string played on each violin. The A string should produce a dominant peak near 440 Hz with additional peaks being significantly shorter than the 440 Hz peak. Note that the vertical scale on each graph is different.

The 3D printed violin already sounds like a violin to the untrained ear. With more time to completely remake it, it would likely sound significantly better and surpass the low quality wood violin. It’s unlikely well-made plastic violins will ever surpass well-made wood violins.

So what impact do different materials have on a violin? Acoustic violins have been made out of many materials – wood, glass, aluminum, plastic, steel, and carbon fiber – with wood being the primary material [11]. It would be great to be able to compare all these violins, but nearly impossible to collect them all. It’s also hard to compare violins strictly on the basis of material since they are handmade. Every fine detail makes a difference, and every violin is a little different, even if made out of the same material. It seems the plastic 3D printed violin was quieter, like the lesser violin. A luthier will say that a lighter violin will usually sound better than a heavy violin since the inertia of a massive body dampens some of the vibrations. This makes sense since the lesser wood violin sounds softer than the better violin, and is also notably heavier. Another factor that could be affecting the sound is stiffness. The 3D printed violin would be much softer than the other violins and may dampen the vibrations similarly to rubber.

Conclusions

Based on what is known currently by luthiers and the data presented here, the best material to make a violin with would likely be as stiff and least dense as possible. A well-constructed violin made of carbon fiber or graphene would fill this roll. Carbon fiber violins have already been made and have begun to come into contest with wood violins. Arguments can be found on online forums and news sites as to whether the quality of carbon fiber violins is comparable to wood [12]. Carbon fiber violins are definitely starting to gain usage among violinists, promising more potential than any other unconventional material. David Gage, a luthier, claims, “A carbon-fiber instrument may have more point or focus at the front end of the attack, allowing for clearer pitch discrimination. But string players are generally traditionalists. Wood has been used since our instruments’ inception; we trust it and only it to do the job. Also, the durable qualities—not the resonance of carbon-fiber—were what caught instrument makers’ attention” [13]. But this is a claim of opinion. It would be interesting to collect data on a carbon fiber violin.

We know violins are not magic. They are made by humans out of raw materials and operate through observable physics. There must be some set of material properties that optimize the violin. Wood may be that material, but since it is something produced by nature and every tree grows a little different, I think this is unlikely; no two pieces of wood are exactly the same. I expect we can design something “more perfect,” although wood may be the optimal material when considering cost. What’s interesting to note, is that wood itself is carbon and fiber, so there may be some shared properties that make these materials good for violins. Carbon fiber may be the “more perfect” wood. Carbon fiber is usually stiffer and lighter than wood, so I would expect it to produce better sound, but since it’s a relatively new material for making violins, it may still be being improved. Currently, wood violins hold the lead in sound quality. An interesting material to make a violin with in the future would be graphene since it is lighter and stiffer than even carbon fiber.

Future Work

I would like to print a violin bow as well as printing a second violin made of a different plastic for comparison. However, printing and assembling one violin already took three months, so the building portion of this project is done for now. I am currently testing different materials to investigate how efficiently they transfer vibrations. I am using some of the data I already collected as well as new data from tensile and vibration testing.

Acknowledgements

I’d like to thank the luthiers at Gaile’s violin shop for teaching me some things about the violin and giving me advice to improve the construction of my 3D printed violin.

Contact: twwoodhead@hotmail.com

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References

[1] Thingiverse. (2018, March). Retrieved from https://www.thingiverse.com/ (Links to an external site.)

[2] Berkheimer, G. (2016, June 6). HCC unveils new 3D innovation hub. The Business Monthly. Retrieved from https://www.bizmonthly.com/hcc-unveils-new-3d-innovation-hub/ (Links to an external site.)

[3] Jones, J. (2016, January 18). Why violins have f-holes: The science and history of a remarkable renaissance design. Open Culture: The best free cultural & educational media on the web. Retrieved from http://www.openculture.com/2016/01/why-violins-have-f-holes-the-science-history-of-a-remarkable-renaissance-design.html (Links to an external site.)

[4] The Master Studio for Violin Making. (2018, March). Modal analysis animation. Retrieved from http://www.schleske.de/en/research/introduction-violin-acoustics/modal-analysis/animation.html (Links to an external site.)

[5] Cooper, J. (2018, March). Violin. Thingiverse. Retrieved from https://www.thingiverse.com/thing:965261 (Links to an external site.)

[6] Slic3r: G-code generator for 3D printers, http://slic3r.org/ (Links to an external site.)

[7] Thingiverse. (2018, March). Soda Can model. Retrieved from https://www.thingiverse.com/thing:15229 (Links to an external site.)

[8] Autodesk Inventor, https://www.autodesk.com/education/free-software/inventor-professional (Links to an external site.)

[9] A soldering iron is a tool used to melt solder (tin mixed with lead) onto electronics to ensure a secure connection. I used this tool to melt plastic together at the seams for stronger bonds. Safety Warning: Sealed googles and a respirator are required when melting parts joined by super-glue. The glue smoke is harmful to the eyes and lungs.

[10] Vernier Logger Pro software, https://www.vernier.com/products/software/lp/ (Links to an external site.)

[11] I am disregarding electric violins since they use an amplifier and can be made out of almost any material since they do not need an acoustic body.

[12] Boone, M. (2015, March 30). Carbon fiber beats wood at instrument competition. Limelight: Australia’s classical music and arts magazine. Retrieved from https://www.limelightmagazine.com.au/news/carbon-fiber-beats-wood-at-instrument-competition/ (Links to an external site.)

[13] Scott, H. K. (2009, April 12). A buyer’s guide to carbon-fiber instruments. Strings. Retrieved from http://stringsmagazine.com/a-buyers-guide-to-carbon-fiber-instruments/