# Analysis and Development of Hybrid Earphone Combining Balanced-Armature and Dynamic Receivers
## 1 Introduction  
Nowadays, earphones are inseparable companions of multimedia devices such as mobile phones, notebook computers, video recorders, dictation devices, personal digital assistants, MP4 players, and personal music systems. The acoustic transducers generally used in these earphones include microelectromechanical system (MEMS) receivers [1; 2], dynamic receivers [3], and balanced-armature (BA) receivers [4; 5]. In this work, the BA receiver and dynamic receiver were combined in a hybrid earphone to improve the sound pressure level (SPL) over a wide range. The hybrid earphone components are depicted in Figure 1. The BA receiver and dynamic receiver were inserted in the front chamber, and both shared the same sound-propagation duct. The hybrid earphone can combine the advantages of the BA and dynamic earphones.  
Some previous works had developed an analytical method to measure the performance of earphones. Because the electromagnetic, mechanical, and acoustic domain characteristics can be described by the second-order partial differential equation, which can be modeled by an equivalent circuit [6; 7], the lumped-parameter method (LPM) was used in the analysis [8; 9]. Based on the LPM, the coupling between the headphone and ear was investigated in artificial ears and models. The influence of the back volume was also considered in the analysis [10]. A model of a dynamic driver in an enclosurewas developed using the lumped-parameter analysis and analogous circuits [11]. Because the LPM model considers every acoustic structure as a circuit unit, such as capacitance or resistance, the acoustic structure should have an ideal regular shape such as a cylinder or rectangular tube. Thus, the LPM has a limitation in that if the acoustic structure is irregular, the LPM will not work. [PERSON] conducted listening tests of various types of earphones to determine the best response curve. Based on his research, the target curve for an insert earphone was defined [12; 13]. To improve the performance of earphones, porous materials were used, and their properties were investigated to check their influence on the SPL of the insert earphone [3].  
The previous works have focused on the analysis of dynamic earphones alone. In this work, the hybrid earphone (a combination of dynamic and BA earphones) is analyzed and designed, for the first time, to achieve full-range improved performance. In this analysis, a combination of LPM in the electromagnetic and mechanical domains and finite-element model (FEM) in the acoustic domain is used to model the irregular acoustic structure.  
The remainder of this paper is organized as follows: first, the analysis tool for the hybrid earphone is explained in terms of the electromagnetic-mechanical LPM and acoustic FEM. The analysis method is verified by the experiment results. Second, based on the analysis tool, an acoustic tube is optimized to reduce the difference between the analyzed earphones and target SPL. Finally, samples with the optimized tube are manufactured and tested. The root-mean-square value of the SPL deviation of the hybrid earphone is considerably smaller than that of the dynamic and BA earphones.