Violins have a rather beautiful design.
... is such design necessary? Is a violin's natural sound only achieved when it has this specific shape?
I have a particular interest in the f-holes. Are they the way they are because we need it, or is all of this just for aesthetic reasons?
If it is not necessary at all, how differently-shaped could a violin actually be from the normal design?
The sound variance of violins is surely greater than the difference in their optical appearance, so I assume different shapes are possible. Note, that the viola da gamba family, which also has a soprano member (not sounding sooo different) sports C-shaped holes, and baryton has nearly unregular ones so the effect of hole shape seems very minor. I found a nice picture illustrating variance in German wikipedia different forms of viola da gamba. A look-up in a violin makers book (Möckel, Geigenbaukunst) revealed, that of the f-hole the area is important. The violin body mainly needs to support many different resonance frequencies but no overly strong ones. This is most prominently influenced by the thickness of top plate, and (significantly less:) back; the sound post, bridge, type of wood, varnish etc. being less important.
The shape also has to do with structural integrity. A violin would be of no use if it were built in a shape that would not support the high tension of the strings, thus causing the violin body to collapse after being used for some length of time. Instruments in the violin family, among all musical instruments, are notoriously durable; there are individual instruments that are 300 years old that are still being played professionally.
The shape of the violin, and any other musical instrument, evolved over time through the trial and error of musical instrument builders. In the last 150 years or so, there have been various attempts to apply the science of physics to instrument building and to refine the design.
The Luis and Clark company makes re-engineered, futuristic carbon-fiber acoustic violin-family instruments. They have a FAQ with a discussion of some of the elements of their design; you might find it interesting.
I asked your question of a couple of players at the local amateur orchestra I'm in who make their own instruments. I know one was also a member of Cambridge University's Dynamics & Vibration Research Group before he retired. I'm not sure I entirely grasped the answer so this is more of a brain dump than a well structured answer - sorry!
The size of the hole affects the pitch and the quality of the sound. If you tap the front of a violin as you make it the tone changes as the whole size changes. It is generally felt that if the area of the f holes is too small the instrument sounds 'flat' or 'pinched'.
For the given area of hole you want the hole cut so that long curves lie with the grain and short sharp curves lie against the grain of the wood to lessen the probability that the wood will fracture. F holes are good in this respect.
You can think of the front of the violin body as two speakers like in hi-fi speaker stands, a larger one for lower sounds below a smaller diameter one fore higher pitches. The small circle and large circle of the violin body top vibrate in complicated ways: sometimes together, sometimes opposite, and sometimes transverse, i.e. sometimes the top needs to vibrate so that the left-right movement of the smaller section is opposite to the left-right movement of the larger section. But the smaller and the larger circles in a violin top are part of a single piece of wood so something needs to be done to weaken the wood joining the two ends. The f holes successfully do that and are an excellent shape for achieving that decoupling of movement without sacrificing strength overall.
Phew. I hope that helps.
This is an 8 year old dead thread but I had to chime in because all the answers are incorrect. MIT studied this, and holes with more perimeter give more airflow and sound, rather than wide circles (which were used for hundreds of years).
