Joong-Hak Kwon

Development of Slim Rectangular Microspeaker Used for Minimultimedia Phones

For the recent multimedia capabilities, mobile phones of today need wider and thinner liquid crystal displays (LCDs) and smaller microspeakers with high acoustic performance. For a microspeaker, oval or rectangular configurations are preferable for better space utilization. However, size reduction is often limited by the magnetic circuit. Therefore, in this paper, a new configuration of magnetic circuit is introduced to reduce the widthwise size of the microspeaker. Comparison of magnetic forces between conventional and proposed magnetic circuit is carried out using 3-D finite-element method (FEM) analysis. Simulated results of sound pressure level (SPL) obtained by mechanical and acoustic analysis are also compared with experimental results. In conclusion, the microspeaker proposed in this paper has shorter widthwise length, more competitive price, and higher performance when compared to the conventional type

Design and Analysis of Microspeakers to Improve Sound Characteristics in a Low Frequency Range

The performance of a microspeaker was evaluated according to its sound pressure level (SPL). Generally, it is desirable for a microspeaker to have a constant and high SPL that covers the whole audio frequency range. A microspeaker has a relatively high and even SPL for frequencies higher than the first resonance frequency, but its performance is subpar for frequencies below that first resonance frequency. Many sound sources, including peoples voices, have low frequency ranges; therefore, it is critical to improve the low-range performances of the microspeaker. This paper presents a method to improve the low-range SPL by improving the magnetic circuit structure and changing the diaphragm shape. To improve the electromagnetic force, the existing two-magnet circuit structure was changed to a one-magnet circuit structure, and the magnet volume was maximized in the process. Accordingly, the wire diameter was expanded and more coils can now be used at the same resistance. Therefore, despite the increase in the air gap, the electromagnetic force improved. In addition, the shape and material of the diaphragm were changed, and the vibration system mass was increased. Due to these changes, the first resonance frequency decreased and the low-range characteristics improved. This study analyzed this new microspeaker design through electromagnetic, mechanical and acoustic coupling relations, in addition to conducting verification through pilot product manufacture and experiments.

Application of Response Surface Methodology (RSM) in Microspeaker Design Used in Mobile Phones

This paper proposes a technique for designing magnetic circuits for use in microspeakers, using the finite element method (FEM) and response surface methodology (RSM). RSM is a collection of statistical and mathematical techniques, used to find the best-fit representation of the response of the physical system under investigation. RSM was used to optimize the dimensions of the magnetic circuit. The optimization resulted in the following dimensions: an inner magnet radius (variable A) of 3.595 mm, a yoke thickness (variable B) of 0.4 mm, and a top plate thickness (variable C) of 0.25 mm.

Development of Hi-Fi microspeakers with a woofer and a tweeter used for mobile phones

For mobile phones, high performance microspeakers with broader frequency range are essential parts to realize various multimedia functions such as MP3 playback, speaker phones, and 64 poly-harmonic melody. Noting that the operating frequency range of conventional microspeakers ranges from 900Hzto10kHz, that of 400Hzto10kHz for hi-fi microspeakers is required to meet customer demand in a multimedia era. One possible way of achieving this is to integrate two-way microspeakers (woofer and tweeter) within one device sharing not only magnetic circuit but also vibration space. Noting that the characteristics of the microspeakers are a coupled phenomenon of electromagnetic, mechanical and acoustic system, a systematic analysis must be implemented to fully consider the coupling effects. In this article, a hi-fi microspeaker with a woofer and a tweeter is introduced and the sound pressure level is also calculated and compared with the experimental results. Results show the development can be a successful alternati...

An integrated design of microspeaker module with smaller volume

Microspeaker modules within mobile phones need to be smaller to offer competitive acoustic performance. Generally, a microspeaker module consists of a speaker unit and an enclosure. Typically, microspeaker module design focuses on miniaturization of either the speaker unit or the enclosure individually, using the other part of the module as a design constraint. However, it is difficult to maintain suitable acoustic performance when the total volume (sum of the back volume and the speaker unit) is significantly reduced. We adopted an integrated design method to overcome this issue. The electromagnetic characteristics of microspeaker were analyzed using the finite element method (FEM). According to the FEM, the average axial electromagnetic force per current increased 29%, and the total volume decreased 31% for the integrated design, as compared to the conventional design while maintaining the same perfect acoustic characteristics. The simulation results indicated that the module resonance frequency and sou...

Performance comparison of various magnetic circuits of integrated microspeakers and dynamic receivers used for mobile phones

An integrated device (a microspeaker and dynamic receiver within one structure) has been developed to actualize efficient size reduction. In this article, three magnetic circuit structures of an integrated device are introduced and their characteristics are compared. A systematic analysis of a magnetic field is performed using finite element method analysis. In conclusion, type 1 has the highest electromagnetic force and the best acoustical characteristics.

Study on Acoustic Resonance of Air-conditioner Fan BLDC Motor

Acoustic noises generated during motor operation in mechanical system are from electromagnetic, mechanical, aerodynamic and electrical sources. For identification of mechanical noise origins, misalignment, unbalance, fan shape, resonance, and vibration modes have been extensively considered to describe noise behavior. An experiment-based approach as well as a mathematical approach needs to be adopted for a realistic study into noise and vibration of the motor, because motor noise characteristics differ from type to type due to various noise sources. This paper analyzes noise characteristics of a brushless DC motor for air-conditioner fan, and proves that the test motor noise originates from acoustic modes of airspace in the motor. The motor noise sensitivity analysis by design of experiments reveals that the noise characteristics are closely related to switching frequency and frame thickness.

Development of Combined Permanent Magnet Type Microspeakers Used for Mobile Phones

In mobile phones of multimedia era, microspeakers of high qualify sound are essential parts to generate human voice in speaker phone and MP3 song player. In this paper, two types of microspeakers, outer permanent magnet (PM) and combined PM type, are analyzed using electromagnetic, mechanical and their coupling analysis. For performance comparison, voice coil diameter is chosen as a design parameter to change excitation position and magnet volume for both types. For combined PM type, sound pressure level (SPL) is improved due to increased PM volume compared to outer PM type. Also, with the decreased voice coil diameter for combined PM type, the 1st resonant mode of the diaphragm is more efficiently excited due to concentrative excitation, resulting in lower and broader frequency range. Therefore, it can be said that the combined PM type microspeakers are more advantageous for high performance microspeaker which are essential for multimedia era.

Effect of the Number of Slots on the Acoustic Noise from BLDC Motors

The goal of this study is to examine the effect of the number of slots on the noise from BLDC motors. To this end, the number of poles was fixed to 4 and the number of the slots was set to 6 or 24 before noise was measured. Motors having different numbers of slots showed clear differences in noise. Cogging torque, torque ripple and normal local force were interpreted, analyzed and compared to determine the reason for the differences. To determine the cause of the noise, cogging torque, torque ripple and normal local force were calculated, which are representative noise sources of BLDC motors, and FFT was performed to analyze their frequency components(harmonics). The results show that torque ripple and normal local force were the dominant factors in the noise difference between the 6-slot and 24-pole motors. As the number of the slots increased, the number of harmonics decreased and their amplitude of harmonic were reduced, which was attributed as the reason for the noise differences.

Development of a new magnetic circuit for slim microspeakers

In the minimultimedia market, functional diversity, high performance, and design are given top priority. Lightweight mobile phones of unique design especially attract customer interest and are usually considered to be highly competitive items in the marketplace. Therefore, mobile phones need wider and thinner liquid crystal displays and smaller microspeakers with high acoustic performance. There are two main directions for development of slim microspeakers. One is reducing the thickness, and the other is reducing the width. In the case of reducing the width, the total magnet volume is maintained through extending the length of the magnet circuit [S. M. Hwang et al., IEEE Trans. Magn. 39, 2003 (2003)]. In contrast, reducing the thickness results in a reduction in total magnet volume unless width is increased, which causes many difficulties in the manufacturing process. In this paper, we introduce a new magnetic circuit for slim microspeakers. This new magnetic circuit, which excludes the top plate, makes i...