Spruce Wood and the Acoustics of Violins

Spruce Wood and the Acoustics of Violins

Spruce is a vital raw component of violins. A product of nature, there is great variability that skilled violinmakers understand how to control.

There are countless variables that affect the quality of music created by a skilled violinist and his or her violin. It is the talent, skill, and artistry of the violinist that seems most important. But how the violin is made, and of what materials, matter a great deal as well.

The great names in European violin making – Antonio Stradivari of course, but also Maggini, Stainer, Ruggieri, Amati, Guarneri, and Klotz come to mind – largely had one thing in common when crafting the fine violins produced in their shops: the wood used to craft their instruments. Therefore those woods defined the instrument from the beginning. It was that spruce and maple wood were the most available material to work with.

The argument that these two types of wood, which make up the bulk of any fine instrument, are the be-all to end-all in violin making is almost certainly flawed. The design and crafting of the instrument, as well as how they are played, may have conformed to the natural strengths of spruce and maple. If all a violin maker had available in northern Italy was birch and oak, might violins (as well as cellos, and violas, etc.) look a bit different and sound a bit different – and be considered the norm?

That last question cannot really be answered. Suffice it to say that maple is revered for the soundpost, and spruce (in particular, European spruce or Picea abies) for the soundboard of body of the violin. In technical terms, the highest-grade violin spruce has a low density and what’s described as “a very high specific modulus of elasticity.” This amounts to “a small angle of microfibrils in cell walls, combined with a structure with a majority of axial cells, resulting in a high axial-to-shear and axial-to-transverse anisotropy (different properties that go in opposite directions),” according to a summary of research reported in the Journal of the Acoustical Society of America (“Acoustical properties of wood in string instruments soundboards and tuned idiophones: Biological and cultural diversity,” Iris Brémaud, Vol. 131, January 2012). This anisotropy affects the soundboard (spruce) vibration modes in ways that produce the sound we consider to be most desirable.

The woods used by Stradivari, et al. in the 15th century happened to have had a climate element to them: decades of colder temperatures in Italy, Switzerland and Germany led to slower growth of the spruce trees. In particular, the woods used in Cremonese violins are believed to have superior tonal expressiveness and projection, thanks to the density of the cold-grown spruce trees. It’s the wood’s vibrational efficacy and the effective production of sound that distinguish this rare and highly valued family of violins from others.

There are specialists who know how to identify old spruce trees that will make good violins (too many branches equal too many knots, for example). Finding the right trees is merely the starting point – and to be clear, those trees might be 400 years old – in the long process of creating the music that great violins and violinists give to the world.