Optimization of Acoustic Soundboard through Modal Analysis and Material Selection

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Nicholas, Noah C; Gruber, Cody; Hartman, Nicholas
Acoustic Bodies; Chladni Test; Vibrations; Modal Analysis; Acoustics; Acoustics, Dynamics, and Controls
project description
The purpose of this design project was to determine if it is plausible to design an acoustic top plate assembly made of a non-traditional material which is equivalent in sound quality to that of a standard wooden guitar. Since wood must be crafted by skilled luthiers, the overall cost of producing the completed product is fairly high. To reduce the cost of a finished acoustic guitar, we proposed to alter the material to that of one that is easier to manufacture, such as plastics and composites.Based on our research, our team chose to test both ABS plastic and carbon fiber. In order to test the top plate materials, a test fixture was developed in order to consistently secure the top plate and accurately excite the plate at specific frequencies. To analyze modal shapes of the two materials, we conducted the Chladni Test, which consisted of speakers mounted under the plate producing a range of frequencies. Based on the results of the vibration testing, it was determined that the ABS plate provided inconsistent mode frequencies, so carbon fiber was selected as the best candidate.We adjusted the thickness as well as the bracing on the underside of the faceplate of the two materials due to their different specific stiffnesses. Based on the results of the Chladni test, bracing was placed in locations where maximum deformation of the guitar plate occurred, while also minimizing the amount of bracing. Bracing was chosen for carbon fiber as an X-brace with a top cross support and a flat bridge support, which also provided enough support to hold the tension of the strings.Our team bought a kit with a prebuilt guitar body for assembly. The existing wooden top plate was removed from the guitar kit body, and our newly chosen top plate material, carbon fiber, was installed. Once the guitar was assembled, it was compared against a high-end quality guitar that retailed for $2400. Sound is generally a matter of preference, but we tested qualities such as sustain to provide concrete comparable data. Through this sound quality comparison test, we found that the carbon fiber guitar was very similar to the quality of the higher end wood guitar with some of its tonal qualities even exceeding the reference.