Technical

  

I'm hoping I haven't used too much technical jargon in describing my design techniques!  However, I do get enquiries about technical matters from readers who are interested in these things and can't wait for the book!

  

There follows various down-loadable papers,  articles and technical descriptions/definitions.

  

Acoustical Society of America - Wood for Guitars

  

I was invited to submit a paper to the Acoustical Society of America conference in Seattle, held in May 2011.  Titled "Wood for Guitars", the paper discusses the use of a wide variety of woods used in guitar building and the influence they exert on the guitar's structural and acoustical performance.  The paper was very well received.  Here's the abstract:

  

"Numerous famous luthiers have used low grade salvaged timber and non-wood products to demonstrate that how a guitar is designed to exploit available materials is more important than using prime tonewoods.  The material properties of timber are highly variable and are not the single figures frequently quoted in reference books. Within-species material properties can vary by a factor of two. Consequently, there is significant overlap of the material properties of one species with others, implying that wood species substitution is possible with little acoustical impact if the component is designed and built to acoustical tolerances rather than dimensional tolerances.  However, species selection remains a significant factor in designing guitar components, primarily for structural rather than acoustical reasons.  The woods chosen have to survive long-term loading without excessive distortion over time whilst still allowing the radiating surfaces to vibrate freely.  Important parameters include Young’s modulus, density, stability with humidity variation, heat bendability, and hardness.  The author considers wood for soundboards, braces, backs, sides, necks, fretboards, and bridges. Guitars designed to acoustical criteria (rather than dimensional criteria) where the effects of different stiffnesses and densities of species are minimised, sound very similar."

  

The full text of the 20 page paper can be downloaded from here, or from the ASA Proceedings of Meetings on Acoustics website, via this link.

  

Definition - Monopole mobility

   

Monopole mobility is a measure of the responsiveness of a guitar and is (broadly speaking) a measure of the admittance of the main monopole mode of vibration.  This vibrational mode is generally the most active and is the mode that is responsible for radiating most sound.   The measure is a combination of the effective stiffness K of the mode and its effective mass m.  A good guitar (to my way of thinking) has its mode frequencies in the right place and has high monopole mobility, where monopole mobility is proportional to 1/sqrt(Km).  

  

Sound Spectrum Analysis

  

There is a wide variety of software spectrum analysers available.  One that I use frequently is called Visual Analyser and the directions regarding how I set it up can be downloaded by clicking here.  

  

  

  

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