## 2 Manufacturing Processes of Musical Instruments Made of Composites and Alternative Materials
### Experimental and Numerical Methods for Musical Instrument Vibroacoustic Studies
#### 3.1.2 Vibro-Acoustic Assessments of 3D-printed Musical Instruments
(**a**) The constitutive model is established for modal vibration macroscopically describing the mechanical performance of different filament materials and infill patterns. (**b**) Sequential mode frequencies and shapes are computed, where eigenvector \(U\) indicates mode shape, and eigenvalue \(S=4\pi^{2}f^{2}\) indicates mode vibration frequencies. (**c**) Acoustic radiation is generated by the pairs of surface vibrations, and certain modes are amplified depending on the impact force position, where \(A\) is the sound amplitude at a spatial location, and \(f\) is the frequency. Reprinted from [80] with permission from Elsevier. Copyright 2023 Elsevier. of the violin were created to achieve a 3D-printed version, closely resembling a wooden one. Violins made of PLA or carbon fiber were printed using both vector and mesh models. Upon model testing, it was verified that a 3D-printed violin performs similarly to a wooden violin, with frequencies between the instruments aligning. The total cost to print and build the instrument was found almost 10 times cheaper than a wooden student violin. ODD Guitars [83], founded by [PERSON], Professor of Additive Manufacturing and an experienced design engineer in 3D printing and advanced manufacturing technologies, has been at the forefront of exploring additively manufactured musical instruments, particularly focusing on 3D-printed guitars. [PERSON] and [PERSON] [5] collaborated on a study investigating the production of additively manufactured musical instruments, with a primary emphasis on 3D-printed guitars. ODD Guitars designed multiple guitars using different materials and geometries, aiming to discover the optimal combination for an electric guitar. The instruments were manufactured using Powder Bed Fusion (PBF) technology, specifically PA2200/nylon material. In the process, FEM analysis was employed to simulate the acoustic behavior of the additively manufactured guitars. The analysis revealed a deflection in the body under 100 kg of tension in the first design iteration. Subsequently, a second design iteration was tested, resulting in reduced deflection (Figure 12). After several trials with guitars featuring different designs, they underwent a redesign to address the issue of deflection. The revised design incorporated a wooden core inside the additively manufactured nylon body, as shown in Figure 13, effectively eliminating the deflection problem. ODD Guitars employed additive manufacturing technologies not only for printing electric guitars, but also for acoustic guitars, drums, keyboards, saxophones, whistles, and more. The role of additive manufacturing is rapidly expanding in musical instrument research, enabling the production of instruments in a timely and cost-effective manner. Many research studies on 3D-printed musical instruments focus on wind instruments, leading to numerous works dedicated to developing wind instruments and/or individual components of them. In the study of [PERSON] [44], a flute was designed and printed using two different 3D printing technologies: FDM and Object Polylet technology. The prototypes were based on a standard concert flute. To address mechanical challenges, the  
Figure 12: Finite element analysis showing deflection of 2 nd iteration ODD Guitar body. Used with permission of [Emerald Publishing Limited], from [5]; permission conveyed through Copyright Clearance Center, Inc.  
models underwent variations and changes, evolving through different design iterations in the pursuit of an optimal solution. However, FDM technology proved to be not mature enough to produce sufficient flute keys and proper air pipes. Additionally, Object Polyjet technology exhibited instability over extended periods. After manufacturing, the acoustical behavior of the 3D-printed flutes was tested and found to be like classical metal flutes. [PERSON] et al. [46] investigated the behavior of a 3D-printed titanium flute. A polymer analogue was used to design the titanium flute, transforming its outer surface into lattice patterns.