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Violins of good acoustical performance have extraordinary quality aspects. These quality attributes, along with some specific variables relating to violin construction are reviewed (reference 1).
Spruce and maple wood selected must be of uniform density (reference 1 and 2). These special density measurements are termed, simulated density values. For best violin performance the values should be narrow in span and be near normal in distribution.
The other key variables; void content, density, flexural modulus, relative speed of sound, hydrodynamic wood expansion, violin plate vibration, violin plate thicknesses, etc. are also important. Considered all together, an assessment of the acoustic quality of the final violin can be predicted.
Maple wood must have the very minimum of seriation defects. Violin wood having cracks or hollow fissures is undesirable. Wood having a tight growth ring pattern with spherical cells touching one another is preferred as it leads to excellent sound transmission.
- Consider changes in violin plate designs by examining photomicrographs of growth ring patterns and cell structure at 100X magnification.
- Measure the vibration response of iron filings on the planks in contact with the Yamaha speaker when special music is played. This allows the first vibration quality of the wood to be assessed and the best area of the plank to be identified.
- Measure the ambient wood density at 0.5% and 1.0% absolute humidity.Maple wood should have a density between 0.55 to 0.72-gm/cc and spruce wood from 0.28 to 0.48-gm/cc. High acoustical quality is associated with wood having a high line slopes on this graph of density versus absolute humidity. Spruce and maple in the lower range of their density span are preferred.
- Measure the plank expansion from ambient humidity to 100% humidity using a hydrodynamic test procedure. These delta readings are identified as simulated density values. Statistical analyses of these data will allow the most uniform area of the plank to be further selected for the violin pattern.
- Measure the longitudinal flexural modulus of the violin wood. Modulus values between 6 to 19-GPa are required. The higher values in this range are preferred, but not much over 19-GPa, as the void content gets too low for efficient sound travel.
- Calculate the speed of sound from the square root of flexural modulus data divided by the density, measured at 1% absolute humidity (reference 1, 3 and 4). Good violin acoustical quality accompanies high values of relative sound speed.
- Measure the void content of the wood using the differences in the density of the wood at 100 % humidity and when water logged divided by water logged density. Spruce wood for the upper plate of the violin should be of high void content (50 to 65% voids) while lower plate of maple should be of low void content (32 to 46% voids). The plate void content plays a key role in defining the violin plate thicknesses.
- Make the violin plates so they match the thin thickness designs used by Stradivarius, the famous Italian luthier (reference 5). Sections in the bout areas of the spruce plate can be as thin as 0.039-in (1.0-mm) thick. The maple plate, relative to the spruce plate will be about double in thicknesses depending on the void ratio of the plates.
- Make the thicknesses of the two plates so the void content in the cross-sectional plate areas is matched at equal distance from the sound post. The void content for each cross-sectional area should increase with increasing distance from the sound post. The void content measured for the planks allow calculation of these plate thicknesses.
- As the plates are finalized, conduct the vibration tests to ascertain and refine acoustic quality. The tests must always be done using the Yamaha speaker, type XW276A0/T93BB with the violin plates in direct contact. Recording and grading the movement of iron flings, or coffee grounds on the wood surfaces as the music or the individual tones of the violin are played accomplish the testing.
- Add an inorganic salt to the violin wood via an aqueous carrier by special means to enhance the acoustics of the violin when used at ambient conditions (reference 1, 6 and 7).
- The following factors elaborate on those above to optimize the violin’s acoustical performance (reference 1):
- 1. Subtle differences in the hydrodynamic statistical data (simulated density) lead to extreme differences in the developed vibration tests of the violin plates. Best vibration performance is realized with distributions of simulated density data are narrow and balanced and where the accompanying vibration response of iron filings on the violin plate is rapid to the music.
- 2. The quality rating is achieved by conducting statistical analyses of simulated density values using the Autoweibull computer program (reference 1). A Weibull analysis is used as it shows distributions of data that range from near normal, to various degrees of skewed curves. Knowing the detailed character of these data distributions is extremely important in violin design.
- 3. The two-sigma span of simulated density (95.45% of the data span) is the best measure of a violin plate’s acoustical performance. The span associated with a poor violin plate may be wide (50 units) while the plate of the perfect violin may have a narrow span less than five units.
The performance of the seven violins constructed is summarized in the following table (reference 1). The Curly Maple (CM-2) bottom plate was removed from failed violin number three, made thinner, and installed in violin number seven where it performed with excellence.
- Ammonium sulfate salt, added to the wood from a water carrier in a special manner so not to debase flexural modulus values.
- 2 Spruce top from 300-year old violin.
- 3 Violin failed because the Wisconsin spruce wood crushed from string tension as the grain structure is too wide (0.5-inch, 1.77-mm) and the flexural modulus of the spruce wood is too low (3.5-GPa).
- 4 Spruce wood 300-years old in violin number one that corresponds to the acoustical quality of a student’s violin.
Of seven violins, the best involved Sitka spruce of density 0.319-gm/cc for the top plate and with curly maple of density 0.615-gm/cc for the bottom plate. The violin plates exhibited good to excellent simulated density uniformity (values of 18 and 19), flexural modulus values of 16.0-and 19.0-GPa and have high values (6.6 and 5.5) for the relative speed of sound.
Rather excellent void trends in the violin plate thicknesses, absence of seriations and thin violin plates also describe the maple and spruce violin plates. Good acoustics allowed this top rated violin to be given a $4,000 monetary rating.
In contrast to this $4,000 rating it is noteworthy that one of the most expensive violins in the world is called “The Lady Blunt” and sold for 15.9-million dollars in 1971 (reference 8). The simulated density values for the plates in this violin, if they could be measured, would no doubt be in a very narrow span.
The highest quality violins will have plates of the following character:
- Have spherical wood cells a tight growth ring structure, particularly in spruce wood.
- Have low density (high void content) and high flexural modulus.
- Have supremely high uniformity in simulated density values.
- Have high relative values for the speed of sound.
- Made precisely to the thin plate dimensions used by Stradivarius.
- Design of the plates is so void content in specific cross-sectional areas matches and increases with distance away from the sound post.
- Have an added salt in the wood to improve the play of the violin.
- 1.) “The Perfect Violin” ISBN: 978-0-578-16046-7, 3/24/2014 by S. K. Randa
- 2.) “Stradivarius” Wikipedia: Theories: X-Ray results of Dutch investigators
- 3.) Internet “Speed of Sound in Materials”
- 4.) “Scientific American” vol. 207 1982 p177 by Carleen Maley Hutchins
- 5.) “Smithsonian” May 2010 p23 by Erica R. Hendry
- 6.) “Science and Technology” Ferbuary 2, 2009 p29
- 7.) “Chem and Chem Eng News” May 23, 1988 p25 by Joseph Nagyvary
- 8.) “Wall Street Journal” April 14-15, 2012
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