## 1 Introduction  
In terms of acoustic transducers, there are the MEMS receiver [1; 2], the dynamic receiver [3], the speaker box with passive radiator [4], and the balanced armature receiver [5; 6; 7; 8; 9; 10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20]. The Balance armature structure was devized by [PERSON] [5]. Three types of structure are described: the unpolarized armature, the polarized reed, and the polarized balanced armature. A new magnetic circuit balanced armature structure transducer has been developed for use in hearing aids [6; 7]. In the balanced armature structure transducer, the coil is moved outside the magnetic structure. Stationary gaps are located at the two side legs. Based on the proposed polarized balanced armature microactuator, an implantable hearing device was developed [8]. The balanced electromagnetic separation transducer used in a bone-anchored hearing aid is presented in ref. [9]. To minimize harmonic distortions, quadratic distortion forces and static forces are counterbalanced. A closed loop armature is proposed in the structure design of BAR [10; 11].  
Nowadays, the balanced armature receiver (BAR) is widely used in hearing aids and earphones because of its small size and high sensitivity. The BAR is a product that follows the principles of multiphysics. When current is passed through a coil, the flux density in the upper and lower air gap is different, which contributes to the generated force on the armature's end. With the input force, the armature and pin vibrate. The vibration of the pin contributes to the diaphragm's vibration,which leads to sound radiation through the spout. The BAR consists of electromagnetic, mechanical, and acoustic physical domains, which are coupled with each other.  
To construct the electromagnetic mathematic modeling of the BAR, the lumped parameter method (LPM) was proposed in previous research [12; 13] which does not investigate the acoustic domain and cannot predict the SPL result, the key performance criteria of BAR. The multimode of BAR is investigated by using the lumped parameter in refs. [14; 15]. The electromagnetic domain and acoustic domain is not involved. To obtain the SPL result, the acoustic domain is considered [16; 17; 18] while the input electromagnetic parameter (resistance, inductance, force factor) and mechanical parameters (mass, stiffness, force factor) come from experiment, which means the input parameter cannot be obtained in the analysis if there is no sample or experiment.  
This paper is organized in the following structure. In the first part, to predict the SPL and develop a new structure BAR product, LPM is proposed to analyze the performance of the BAR by modeling the electromagnetic, mechanical, and acoustic domains along with their coupling effect according to the modeling dimension and material property, which is defined as the proposed method. Second, BAR is analyzed by FEM (electromagnetic, mechanical domain) and BEM (acoustic domain) which is defined as the previous method [19; 20]. Consequently, the samples were manufactured according to the analyzed modeling. Based on the samples, the SPL experiment result was obtained. Finally, the result shows that LPM was verified by experiment, as the previous method (FEM and BEM). The difference is that the proposed method (LPM) takes 1 hour, while the previous method (FEM and BEM) took 36 hours. In conclusion, the contribution of the paper is that the proposed LPM method makes use of the BAR modeling dimension and material property to predict the SPL result without parameter identification by experiment and is more efficient than the previous method. The proposed LPM method can be used to design a new structure BAR and shorten the development cycle of the BAR. The method detail is listed in Table 1.