Materials

  

The species of wood that you select for your instrument will undoubtedly affect how your guitar will sound, but not nearly so much as you might have been led to believe.  The overall design of the guitar rather than the wood, per se, has a much greater impact.  

The majority of wood selected for guitars is selected purely on visual appearance, with no attempt whatsoever being made to select it on its engineering or acoustical properties.  This fact at the same time accounts for why modern “factory” guitars are rarely either outstandingly good or outstandingly bad.  The quality of the tone produced is primarily a function of the guitar’s design, which for many factory guitars has evolved slowly over many years, yielding trusted products.  These designs are necessarily focused on producing reasonable results from average wood, because the quality of wood in these guitars, from the engineering and acoustical point of view, is unknown.  It is all “average”.  Factory guitars tend to be overbuilt, so as to reduce the number of warranty returns.  So if “good” wood happens along, the resulting instrument is more likely to be worse than average rather than better than average, as the resulting instrument will be even more overbuilt than normal.  So, paradoxically, for factory guitars, better instruments are likely to result from using poorer quality (from the engineering and acoustical view point) materials.  

There is a clear opportunity for custom builders.  Good design and good materials can yield a much better product, and this is how good independent luthiers manage to stay in business.  Even so, few independent builders scientifically measure their wood properties, but some, through long years of experience in remembering what went into their best performing instruments, have learnt what to look for using their visual, tactile and auditory senses.

Important wood properties like density and stiffness (Young's modulus) can vary by up to a factor of two within the same species of wood, and can frequently vary nearly as much in pieces of wood from the same tree.  It is important in achieving a consistent result that the actual pieces of wood that are about to go into a guitar have their material properties measured prior to use.  I test all my top and back wood so that I can determine how thick the plates should be on the guitar to achieve the result I want.  If this isn't done, an awful lot is being left to chance.

The charts to the left show just a couple of parameters I measure.  Details on how these measurements were taken and how they are used can be found in the book.

Long grain Young's modulus

  

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Sound radiation coefficient

  

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