BS in Materials Engineering
Materials Engineering Department
To mitigate the effects of deforestation, man-made alternative materials were analyzed and tested for potential use in the soundboards of acoustic guitars. The materials evaluated included 0.06 in. foamed polycarbonate, 0.12 in. single-ply honeycomb fiberglass, and 0.04 in. epoxy fiberglass. The properties of Sitka spruce, the most common tonewood, were used as a benchmark. The Young’s modulus to density ratio found in Sitka spruce is relatively high, making its properties ideal for soundboard applications. Both Young’s modulus and density were necessary to calculate the acoustic constant of each material that was tested. The samples were subject to the impact of an 8 oz. lead sphere, which struck the center points with a constant force of 0.25N. The collisions resulted in the propagation of sound waves within the structure. Materials were characterized by the resonating frequencies that they displayed between 50Hz and 20,000Hz. The tests were conducted in an anechoic chamber using an MXL 992 large-diaphragm condenser microphone. The microphone was held in a shock absorbent mount placed 12 in. from the center of each sample. The microphone’s built-in 20dB low-pass filter was activated to compensate for near-field-effects. The microphone signals were digitized with a PreSonus FirePod 96k audio interface with 24 bit resolution and 44100 Hz sampling rate. Incorporating Young’s modulus, shear modulus, internal friction, static mechanical properties, and testing results, the most suitable alternative to spruce was determined.