Table of Contents
An important part of manufacturing musical instruments is the choice of material. Before simply printing out instrument with materials seeming to resemble the traditional material of choice, we should carefully analyze what properties are exhibited by the materials used for musical instruments and choose material for printing with similar or better properties.
Theory of acoustic materials
While the choice material is a matter of tradition and availability for most instrument makers, there is a lot to say on what role materials play in making an effective instrument. There has been a lot of research and experimentation on how materials contribute to tone and how new materials can be used. Most of information presented here comes from The Physics of Musical Instruments by Fletcher and Rossing, (1998).
While discussing materials for musical instruments, there is one important distinction to make. One has to look at the function of a material, is it an:
- The vibrating material
- The resonating material
While one intuitively would assume; a guitar is made of wood so it had wood-like sound properties. But the actual vibrating part is the string, which is made of either nylon or a metal alloy.
In the same way a brass instrument's vibrating material isn't the metal (brass) which makes up the actual instrument, but it's the lips of the player whom vibrate. In fact, it's almost impossible to hear the difference between a brass or wooden trumpet1.
There are a lot of objective measurable qualities of a materials which may indicate whether a material is suited for a certain application or not. For example, when looking for the right kind of wood for a guitar neck, the most important quality is that it should never break under the tension of the strings, tensile strength. As a second quality it should be stiff enough so that the instrument remains in tune, stiffness. This illustrates that the direct sonic qualities of a material are rarely a prime reason for choosing the material.
To make things even more complex, two materials with the same measurable qualities, might sound completely different. This is because internal micro (or even nano) structure plays a huge role in how an object sounds. You can imagine that a symmetric object has a bigger tendency to vibrate, then an randomly distributed material. For this reason guitar and violin makers use book matched wood, so some symmetry remains. But on a micro level this plays as well, a homogeneous crystal structure, like steel, will have less dampening then a less uniform structure like concrete. Because high notes are most easily dampened, this presents itself as metal sound more bright en harsh, the difference between a xylophone and a marimba.
Another complexing factor is that a musical instrument consists of many part, which each play their role. For example, while using a composite material for a violin top might have an effect, it's not as profound as simply increasing string tension on the same instrument. For something like a violin, it's such a complex system, that even the tightness of a screw can have a noticeable impact on the overall sound2.
So while there is a lot to say about the properties of materials used for musical instruments, the choice of material is almost always from a practical standpoint3. This suggest that for my research, I shouldn't be trying to replicate tradition materials, but rather find out what the properties of available materials are, and manufacture something in line with those. (ie. not try to make something resonant, when only damping materials are available)
It's important to note that for most wind instruments the effect of materials is marginal. The most important factors for tone in these instruments are player technique and geometry. For this last factor material plays a role, but only in it's secondary functions; ease of handling for the instrument maker, surface quality and cost. To illustrate this, we can look at organ pipes. Adjusting wall thickness has a bigger impact on the final strength of the pipe, that using another metal barely has any difference. As does geometry, if a square pipe is wanted, one will use wood, while round pipes are made from metal. This not because of matching sonic qualities, but simply because of the fact that wood is easily shaped square, not so easily round, and visa versa for metal.
Even something like surface quality isn't so important, as roughness only becomes an issue, if it varies withing 0.1mm. So it all seems more like a matter of craftmanship, rather then material. Especially considering the difference in tone is influenced by playing style.
Fletcher and Rossing feel like the construction of wind instruments should not be governed by material, but by "ease of fabrication, stability, feel and appearance". So 3d printing could be really useful, as making instruments is labor intensive, with the current state of technique, intensive hand finishing would seem necessary.
Materials of existing instruments
Wood is the material of choice for most musical instruments, it has good acoustic properties, has great strength and looks good. But most importantly, its easy to shape and readily available in most environments.
There is a great deal of variation in different kinds of wood,
lots of room for tweaking
a lot of variations in density and stiffness
problems with some tone-woods becoming endangered
wood has a long cell structure with air pockets. Like a lot of drinking straws aligned to each other. These microscopic air pockets allow it to resonate
wood might be good because of repetetive microstructure and air pockets.
it is said Stradivarius violins are the best because of uniform structure (every year ring the same size) (QUOTE)
due to organic nature, wooden instruments need to be played in. to have it stretched and compressed so often that the material doesn't change anymore.
varnish to seal surface. Else dirt will make it polluted and less good vibration.
for wind instruments you want small cells, so you can work it easily. will not split
usually for cost considerations, plywood (a compsite of multiple glued layers of wood) have been used for student instruments. sometimes with flywood only for nonresonating parts. Top deck of 'real'wood.
for looks often vineered. Greater mechanical strength
anisotripic, more flexible in one direction then the other. for top plates the ratios is 20:1. This is directly relatable to why some woods are more popular then others.
used for strings
used for tabla drums
used for brass
for long, iron hasn't been easy enough to form.
Bronze (lead-tin alloy) and brass (lead-zinc alloy) have been the choises.. becaus you can work with them, while they remain durable for use. (silver and gold not)
either cast, or thin walled to be bendable.
not much difference, for organ pipes they choise the most conveniant metal. Sometime they differ for visual effect, but nearly no change of sound.
zelon/zylon for marimba
for marimba substitute wood for Zylon. Thermal stability, high tensile strengthusualy more control over manufacturing then wood
used as alternative when wood become endangered/more expensive
for drum skins, more uniform then animal gut.
Fiberglass an carbon fiber
not much room for tweaks once it's cast
Haines and Chang (1975) experimented with composie graphite expoxy, worked quite well for guitar tops and violins, but didn't find it's way into the general public.
fiberglass has been used to make reeds, which can't dry out. Opposite you can't adjust them as well
Bones have been used for pipes, mallets and even xylophones
Used for blowing horns, it's no accident that brass instruments have a 'horn', as this is an evolution from ancient instruments made from animal horns.
Large shells are often used as a wind instrument without any modification. With some modification more nuances in tone can be made
Bladder skin has been used extensively for drum skins. And it is no coincidence that the thing on top of a drum is named 'skin.
Also, there has been a lot of use of 'organ skin' like gut, for instrument strings.
Hair can be seen on many instruments, most notably on the bow of a violin or cello.
"Bull kelp is a very long, tubular form of seaweed which dries to form of a curvy conical tube, suitable for making a variety of wind instruments. We have not found a commercial source for dried kelp. If you live on the U.S. west coast, you can go to the beach to gather it yourself.4"
Reed from cane or bamboo
Research showed that exceptionally uniformly dense wood is one of the main causes for the great quality sound of Stradivarius Violins. (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0002554) As 3d printing layers a material it is not uniformly dense by nature. Some processes do this better then others, but in the process used in this process, fact remains that we’re working with a laminated material, which inherently has a poor resonant quality. (is that so??)
Materials available for 3d printing
A strong & tough material with the highest level of dimensional accuracy.
A biodegradable polymer.
Not so durable
A strong and flexible material with a high level of detail. Sandy, granular look, and is slightly porous. Cheap.
A full color material. Brittle.
High detail resin
Able to produce fine details on this photopolymer.
Designed to hold paint
A very smooth material, detailed and “luxurious” to the touch.
A see through material.
Polyamide-like material with aluminum flakes mixed in it. It gives the material an metal-like feel, but only in appearance.
Light and the strongest 3D printing material in the world.
A strong and durable material.
Silver and Gold
Expensive, but good qualities.
Ideal for building material
A powerful laser can fuse common sand to produce glass objects
A 3D printer that can print electrical conductors can make its own circuit boards and other electrical products
There are 3D printers that will print chocolate, cheese and all sorts of organics. Not really interesting for musical instruments
The Physics of Musical Instruments, Fletcher and Rossing, 1998