# Design and Analysis of a Novel Microspeaker with Enhanced Low-Frequency SPL and Size Reduction
## 1 Introduction  
With the introduction and development of portable wireless devices, mobile devices have become essential to daily life. As many people use these devices to perform various tasks, the devices serve as a personal computer (PC). Currently, an increasing number of people use these portable wireless devices, especially smartphones, to consume multimedia content. Owing to the increased demand for multimedia content, production of entertainment content such as games, music, and videos has also increased. Sound plays an important role in providing an immersive experience for users, particularly low-frequency sound. Thus, sound is an important consideration for consumers when selecting a smartphone. Usually, a microsp peaker is located at the bottom of the smartphone and is responsible for generating sounds when needed. In the earlier versions of cellular phones, a round microsp peaker was used. [PERSON] et al. introduced and analyzed circular and elliptical microsp peakers [1]. To improve the sound pressure level (SPL), [PERSON] et al. also introduced a microsp peaker with a new magnetic circuit [2]. Instead of using only the outer magnet, they also added a central magnet to increase the magnetic force [2]. To improvethe space utilization in cellular phones, [PERSON] et al. developed a rectangular microspeaker [3]. Furthermore, [PERSON] and [PERSON] developed a rectangular microspeaker in enlarged liquid-crystal displays that has modified structures to improve the acoustic performance, and new structures were added to the yoke to improve the flux density [4]. To develop thinner speakers for cellular phones, [PERSON] et al. proposed a novel magnetic circuit in which the top plate was eliminated [5]. To reduce the thickness, [PERSON] et al. used horizontally magnetized outer magnets instead of vertically magnetized outer magnets [5]. Advances in material research have also prompted engineers to use new materials in microspeakers. A piezoelectric speaker was developed for use in very thin devices [6; 7]. The piezoelectric speaker has a multilayer structure that is thinner than the prototype microspeaker structure. However, this type of speaker is not widely adopted, owing to its high cost and poor acoustic performance at low frequencies. For a smartphone with a bezel-less display, indirect- and direct-vibration actuators were introduced and analyzed [8; 9]. Compared with a microspeaker that generates sound by vibrating the diaphragm attached to the coil, these actuators are attached to the display panel, which generates sound by vibrating the elastic display panel. Microspeakers are widely used in other products. One example is a wearable device called the neckband. A neckband speaker with a passive vibrator was designed and analyzed by [PERSON] et al. using Klippel measurement equipment [10]. The effect of the diaphragm material on the loudspeaker performance was analyzed by [PERSON] et al. for a better frequency response [11]. Diaphrags with micro-corrugations were analyzed by [PERSON] et al. to determine the effects on the acoustic performance [12]. In terms of the sound quality of the speaker module, one study proposed and optimized an L-shaped module [13]. To analyze a speaker system, [PERSON] et al. proposed a method to obtain the nonlinear parameters in the speaker system, such as the force factor. Nonlinear parameters are defined as a function of the voice coil displacement [14]. With the advances in computational power, [PERSON] et al. were able to conduct an analysis of the acoustic performance of a microspeaker using a machine learning algorithm [15]. Previously, devices contained few components, which restricted the size of the microspeakers. In addition, the thicker bezels around the display afforded sufficient space for the microspeaker. However, owing to the demand for larger displays, bezel-less displays were introduced, and many components, such as digital stylus pens, need to be mounted on the smartphone.