16 ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2023 meter and length of 61 cm and 3 m[3], respectively. This eliminated another 18 species, leaving 29. Six more species were eliminated for sustainability and another eight for producibility, as described above, resulting in the final list of 15 potential soundboard species shown in Table 1. Body (back and sides). The degree to which body woods contribute to the tone profile of acoustic guitars depends on many factors[29]. Therefore, again, we merely endeavored to match key properties of benchmark body tonewoods while supporting producibility and sustainability goals. Analysis was carried out similar to the soundboards, utilizing selection metric values spanning those for Brazilian Rosewood to Honduran Mahogany, since the latter species is also a well-established body tonewood. The ACE value range for the benchmark body tonewoods is shown in Fig. 4 containing 196 species. A second metric was then applied using a standard solution (a pressure sensor) within the Selector[14] to select for species supporting fundamental resonance modes[30] similar to the benchmarks. This metric is termed the Sensitivity to Pressure Difference (SPD) and defined as where σ is the yield strength and E is the Young’s Modulus. The body wood subset was reduced from 196 to 186 after box selection for SPD, per Fig. 5. Further down-selection for acoustic impedance, compressive strength, and volumetric drying shrinkage was carried out sequentially, resulting in 123, 113, and 72 species passing, respectively (figures not shown). These stages were added for the body woods in particular to account for transfer of acoustic energy within the body cavity, and the fabricability demanded by complex forming operations, e.g., during steam-forming the side wall radii. Further down-selection for sustainability and producibility, as described above, resulted in a final list of 14 potential body tonewood species, per Table 1. DISCUSSION The results in Table 1 identify tree species that could serve as soundboards and bodies for acoustic guitars and also meet key producibility and sustainability requirements. In the case of the 15 soundboard species, all are coniferous boreal forest softwoods with the exception of Yellow Poplar. The coniferous species consists of three spruce, four fir, five pine, plus Western Red Cedar (not a true cedar), and Douglas Fir (not a true fir). Various cedar species, including Western Red Cedar, are established soundboard materials Fig. 4 — Acoustic conversion energy box selection for body tonewoods. Fig.5 — Sensitivity to pressure di erence (SPD) box selection for body tonewoods. for classical guitars. Yellow Poplar is utilized for some solid body guitars and organ soundboards, and also as the inexpensive inner layer of some laminated wood panels. The other species are not known to be used commercially for musical instruments. The 14 down selected body species in Table 1 are roughly split between softwoods and hardwoods, which is an interesting result given that production body tonewoods are by and large fabricated from tropical hardwoods. Of the hardwood species shown, four—Ekop, Pilon, Determa, and Angelique—do originate in tropical
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