Last week I attended Trevor Gore's modal tuning class hosted by Robbie O'Brien in Colorado. Despite having twice read the Design volume of his and Gilet's book and have been building based on the books I found the class really insightful and valuable. If anyone interested in a deeper understanding of the working of a guitar ever gets the opprotunity to attend one of his classes I highly recommend it.
The class was well organized covering much of the material in the Design volume. He used a combination of illustrations, software simulations and actual demonstrations to teach how strings and the guitar plates work in a guitar, understanding the different modes of vibration, including the basic theory of modal vibrations and how those modes relate to frequency response curves. The class built on itself each section with review of the relevant content to help avoid leaving any of us behind as he moved the class forward and helped lock in the relevant points from the previous sections.
With that theory the class moved forward to practical uses of the theory presented for example targeting good modal frequencies and avoiding bad ones, the response of typical classical and steel string guitars, static and dynamic requirements of a guitar. The class had some shop work in dynamically and statically determining the attributes of back and top wood and how to use that information while building the guitar to take advantage of the wood that you have. Different bracing patterns were presented and how those patterns can affect the modes of the guitar.
For me an enlightening moment came when he pulled everything together to show how one could address a wolf note on a built guitar, using a tap derived frequency response curve to find the responsible resonance and then using Chaldni patterns to determine the responsible vibrational mode. One could use the visualization of nodes and anti nodes of the mode from the Chaldni pattern to find the best place to suppress the resonance. For example one could place some blue tact putty on the discovered anti node but on or very close to the nodes of the desirable modes.
The three day class was very well structured and a lot of information was presented. Yet somehow Trevor was able to keep a loose interactive feel to the class, accepting questions and moving off on related tangents yet somehow ending every section on time. I truly enjoyed the class and came back with a renewed interest in the topic. Back at my house I took a classical guitar that I had recently built with a top resonance frequency right on G (bad). Using side mass I was able to move the tops 195 Hz resonance to 190 Hz without affecting the other resonances. With the side mass I ended up with a louder good sounding guitar.
Guitar built with mass mounting blocks
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before and after frequency response
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