## 1 Introduction  
Interest in characterizing the elastic and damping properties of composites is increasing as more and more industrial sectors use these materials in very different applications. Among these, the most established sectors include the automotive, aerospace, and renewable energy industries [1; 2; 3; 4; 5]. However, in recent years, this has expanded to include other types of products, such as musical instruments. In this expanding new sector, the modal and transient behavior of different structures has been studied. Commonly, in musical instruments resonances are usually sought to enhance the sound pressure levels obtained for different resonances, modifying the timbre and the qualitative aspects of the resulting sound. Research is particularly extensive in the chordophone family, particularly in the case of classical guitars [6; 7; 8; 9; 10; 11; 12], electric guitars [13; 14], or the string family of instruments [15; 16; 17; 18; 19]. We also find studies linked to percussive chordophones such as the piano [20; 21; 22] and, though scarcer, those dedicated to membranonbones [23; 24; 25]. Figure 1 shows some examples. Composite materials use polymer matrices in their manufacture, so they have viscoelastic behavior. Viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. For the study of this type of material, we express the module in its complex form, as shown by Equation (1) [30]  
\[E^{*}=E^{\prime}+jE^{\prime\prime} \tag{1}\]  
where the real part (\(E^{\prime}\)) is the storage modulus, and the imaginary part (\(E^{\prime\prime}\)) is the loss modulus. The study of the storage module (\(E^{\prime}\)) is a determining factor when characterizing the resonance frequencies of a solid. \(E^{\prime}\) represents the elastic behavior of the material, which is directly linked to the resonance frequencies of any type of solid. Also, for typical resonant elements of musical instruments, such as membranes, plates or shells, we can express their resonances as [31]  
\[f=\alpha\sqrt{\frac{E^{\prime}}{\rho}} \tag{2}\]  
where the square root of the ratio between \(E^{\prime}\) and \(\rho\) is equivalent to the longitudinal speed of sound in the solid, and \(\alpha\) is a parameter defined by the modal and geometric characteristics of the solid. Variations of \(E^{\prime}\) modify the value of each one of the natural frequencies of the system. In turn, the modulus of losses \(E^{\prime\prime}\), is related to the total damping of the system by means of Equation (5) and defines the amount of energy dissipated in each oscillation. The non-elastic or viscous behavior is related to the amount of sound pressure that a resonance will be able to accumulate and the modal decay time. The decay time due to internal damping processes is defined by [32]:  
\[\tau=\frac{1}{\pi f}\ \frac{E^{\prime}}{E^{\prime\prime}} \tag{3}\]  
Figure 1: Some musical instruments made of carbon fiber reinforced with epoxy (CFRE): (**a**) Luis and Clark violoncello [26], (**b**) [PERSON] snare drum [27], (**c**) [PERSON] piano [28], and (**d**) [PERSON] carbon fiber guitar [29]. Because of their configurability, many manufacturers are investigating the use of composite materials for the manufacture of these instruments. The most common are those using Carbon Fiber Reinforced Epoxy (CFRE) [11; 33; 34], but others include those involving bio-composites [35; 36]. These studies relate the mechanical characteristics of the composite to the sound behavior of different musical instruments, but do not contemplate the direct influence of the processing on the elastic and non-elastic behavior of the vibration. Since the vibratory behavior and mechanical properties of the material are closely linked [37; 38; 39; 32], in many cases the processing of the composite offers greater guarantees, such as the laminate of prepregs in an autoclave [40]. But due to the high associated cost, there are numerous studies that propose vacuum bag-only (VBO) processing as an alternative.