###### Abstract  
The generating mechanisms of the mid-high-frequency peaks of a sound pressure level are theoretically investigated in this study with a side-firing front chamber. A mid-frequency peak is caused by the Helmholtz resonance phenomenon of the front chamber, and a high-frequency peak occurs owing to tube resonance. The electromagnetic-mechanical-acoustic coupling method (E-M-A) and resonance equations are used to obtain the sound pressure level and peak frequencies, respectively. Seven side-firing front chambers have been designed with respect to different tube lengths, tube widths and tube heights. Microspeaker samples with different front chamber designs are manufactured to verify the analytical results. The SPL and mid-high peak frequencies comparisons showed good agreement between the analysis and experimental results. acoustic tube; Helmholtz resonator; microspeaker; sound pressure level +
Footnote †: This paper is an extension of work originally presented in the conference on electromagnetic field computation (CEFC), 24 October 2022. Footnote †: This paper is an extension of work originally presented in the conference on electromagnetic field computation (CEFC), 24 October 202. The balanced armature receiver [6; 7] is one of most popular electroacoustic transducers to provide a good acoustic performance, and it has been widely used in hearing aids and earphones because of its small size. The working principle of balanced armature is that, when electric current is passed through the voice, the flux density on the upper surface of the armature is bigger than on the lower surface of the armature. Then, the electromagnetic force is generated on the armature to contribute to the vibration of the pin and diaphragm. Finally, the vibration of the diaphragm causes the sound radiation from the acoustic port. In addition to the above types of microspeakers and the balanced armature receiver, the piezoelectric speaker [8; 9] has been developed and is known as a piezo bender due to its mode of operation. The mechanical motion of a piezoelectric speaker is created by applying a voltage to a piezoelectric material, and this motion is typically converted into sound using diaphragms. However, piezoelectric speakers have serious problems with their vibration material and cost. Among these kinds of electroacoustic transducers, the microspeaker speaker is the most popular type in multimedia devices. The microspeaker is inserted into the microspeaker module and placed inside of a smartphone,; the relationship is depicted in Figure 1a. To ensure that people enjoy multimedia, it is necessary that the microspeaker module provides a good acoustic performance. Owing to the limitations of the inner space of portable electronic devices, the front chamber of a microspeaker module is usually designed as a side-firing type instead of a front-firing type, as shown in Figure 1b. In previous studies, [PERSON] et al. investigated the effect of an enclosure on a microspeaker. The back volume of the enclosure can be treated as the added stiffness of the mechanical system. However, the study did not discuss the effect of the front chamber on the sound pressure level [10]. [PERSON] et al. discussed the acoustic performance of a microspeaker with different enclosure parameters. The main purpose of [PERSON]'s study was to identify the accuracy of the applied methodologies, but there was no discussion of the reason for the peaks around the middle and high frequencies in the side-firing front chamber [11]. In this study, the generating mechanisms of the mid-high frequency peaks of the microspeaker SPL are determined. The 3D electromagnetic-mechanical-acoustic (E-M-A) coupling method is used to obtain the whole sound pressure level of the microspeaker, while the resonance-calculated equations are only for predicting the mid-high peak frequencies. Microspeaker samples with different front chambers have been manufactured to verify the analysis results.