## 1 Introduction  
Two dominant types of commercial receiver designs exist for translating electrical signals into acoustic signals: dynamic receivers (also known as moving-coil receivers) [1; 2; 3] and balanced armature (BA) receivers [4; 5]. Products with BA receivers are becoming increasingly popular because of their small size and high sound quality. On account of these advantages, BA receivers have been extensively employed in stethoscopes, hearing aids, earphones, and smartwatches. Therefore, several kinds of research have been done involving analyses of the electromagnetic and acoustic characteristics of BA receivers using the lumped parameter method [6] to set up the equivalent circuit, and finite element method [7] to divide the BA receiver into finite elements. However, no research exists regarding the reliability of BA receiver application. With the increasing demand for high sound quality, an increased number of BA receivers are being used in earphones, which are a popular product. Nonetheless, it is inevitable that earphones are frequently struck by external forces, especially when dropped from a certain height. Compared to dynamic receiver earphones, BA-receiver earphones are more prone to failure because of their smaller size; a gasket is used to protect the BA receiver, but the original gasket (OG) is not sufficient at preventing the BA receiver from being destroyed. Therefore, this article focuses on improving the reliability of BA receiver earphones by designing a novel concept gasket (NCG). To begin, the structures of a BA receiver earphone and the BA receiver are introduced, then the failure of the BA receiver is described using observations from the X-ray photos of the BA receiver before and after the drop impact test. The finite element method used in the dynamic problem [8; 9; 10] was employed to solve the contact problems [11; 12; 13], which often occur in solid mechanics [14]. After this, the governing equations in the updated Lagrangian formulation [15] are presented, and an explicit dynamic analysis [16] is applied to solve the governing equations. Then, the stress tensor is obtained to calculate the von Mises stress [17] on the armature. Based on the simplified model and the analysis method, the first step involved dropping the BA receiver from different directions to determine which direction causes the maximum von Mises stress on the armature and to determine the maximum von Mises stress point. The drop direction was set, and the point was used as a reference for the subsequent analysis. The second step involved the gasket design; the structure and function of the gasket are first mentioned, followed by the main text concerning the design of the shock-absorbing part of the gasket. It is a very new concept to maximize the thickness in the limited internal space, and then to design the shock absorption structure [18; 19] by adding air regions. The solid gasket has nothing more than the elasticity of its material for absorbing shock energy, and is without any additional structural benefits. The air regions inside the gasket provide the internal pressure, which can be treated as added elasticity to absorb more shocks; the other part is the linking component, which connects the gasket and the upper case of the earphone. Subsequently, a gasket based on a novel concept was proposed to perform the drop impact analysis, showing a better shock absorption performance than that of the original gasket. The last step was to complete the experiments to verify the validity of the analysis result, in which the novel concept gasket had a better shock absorption performance. Three experiments were performed; the first was the drop impact test; the second was a collection of the X-ray photos of the BA receivers before and after the drop impact test to check for failure of parts of the BA receiver. If there was not failure occurring on the BA receiver, especially in the armature, this shows the gasket has a good shock absorption performance.