Innovation

We are developing technology related to guitars constantly. Our first study was related to normal modes of vibration in guitars and how they related to sound production, but our particular interest in acoustic guitars which are amplified. Several research papers have shown the vibration modes of various guitars; we have measured our dreadnaughts and considered several effects to optimize their sound production. If you view the report below for Gibson, Ibanez, and Washburn guitars and consider the plot below for measurements we have made, our instruments can be put into perspective.

http://online.physics.uiuc.edu/courses/phys193/Student_Reports/Fall04/Phillip_Byrne/Phillip_Byrne_P199pom_Fall04_Final_Report.pdf

This is the result of measuring acoustic sound pressure directly below the soundhole while stimulating the guitar from a remote sound source so it might be expected to be slightly different from the results above. This plot shows my favorite Yamaha, a really mellow sweet guitar that I have had for about 15 years. I have another that I've had for over 40 years that has a similar sound, perhaps a little deeper, both are fine for playing around the house but I wanted something with a little deeper bite. Three of our Dreadnaughts are shown, one with a Polyurethane finish  (yellow), one with the soundboard sanded to wood (green) and one with a NC lacquer and our soundhold port (blue - this is an open port ). All are Spruce. Note the port moves the 100 Hz resonance to a lower frequency; this is to be expected since it is closely approximated by a Helmholtz resonance and we have increased the air column length. It also projects sound directly in front of the guitar creating a more directional pattern. Note also that stripping the original Poly coating does not let the guitar "breath" easier, the lower and upper resonance go down, while the middle goes up. Conventional wisdom is that stripping the finish off a guitar soundboard will produce miraculous changes to its sound. This is why we make measurements, conventional wisdom from guitar snobs is a poor excuse for knowledge.

You can correlate the modes with the paper below, note that the closely spaced modes probably appear as one in our measurements since we have a 5Hz resolution. http://www.kettering.edu/physics/drussell/guitars/hummingbird.html

The chart above shows an attempt to measure the slit port that we employ in most acoustic electrics. While we cannot measure the exact port because we cannot get the microphone inside it, we measured a modified version with a larger opening to accommodate the microphone (brown). Note the the lower two resonances are markedly lower, the resonance at 240 Hz is probably lower in the actual slit port, this peak is likely due to the larger opening  used to accommodate measurement. But the trend is clear. Why are we trying to get rid of these peaks, don't they contribute to the guitar's sound? Well, yes and no. Keeping the soundhole clear makes the guitar louder (we're amplifying it anyway) and makes certain notes ring but not how you think. We'll discuss that soon.