Mesoporous Silica Microspheres Composited with SBA-15s for Resonance Frequency Reduction in a Miniature Loudspeaker
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doi: 10.1007/s40242-020-0028-z
Article
Mesoporous Silica Microspheres Composited with SBA-15s for Resonance Frequency Reduction in a Miniature Loudspeaker ZHANG Xinyue and CHE Shunai* School of Chemistry and Chemical Engineering, State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, P. R. China Abstract Microspheres composited with mesoporous SBA-15 particles and silica were investigated as fillers in miniature loudspeakers to study the factors influencing the resonance frequency offsets(RFOs). Mesoporous silica microspheres(MSMs) were prepared by self-assembling SBA-15 mesoporous silica in a microemulsion synthesis system. The formation process involved the fabrication of a stable O/W microemulsion of tetrabutyl orthosil icate(TBOS) and hexadecyltrimethylammonium bromide(C 16TAB) and encapsulation of SBA-15s. The RFO increased and then decreased with increasing particle size(in the length range of 0.7―5.5 μm and in the width range of 0.2―0.45 μm), increased with increasing pore size(in the range of 7.0―9.4 nm) of SBA-15s, and increased with decreasing particle size(105―900 μm) of MSMs. Keywords Mesoporous silica microsphere; Microemulsion; SBA-15; Resonance frequency offset
1 Introduction The loudspeaker system[1] consists of an energy-generating device(driver) and a cabinet volume that has walls with a floor, ceiling, and side walls. The International Engineering Commission(IEC) takes the resonance frequency of a driver as the starting point of the effective low frequency range[2], which is the lowest vibration frequency that a loudspeaker system can achieve. It is well known that loudspeaker systems composed of a driver and a closing box possess a greater resonance frequency than individual driver units because the stiffness of the enclosed air inside the cabinet is added to the stiffness of the whole loudspeaker system[3]. Mobile phones, laptops and other electronic devices that have built-in speakers are becoming increasingly popular in our daily lives and have become lighter and smaller[4] while providing consumers with high-quality listening enjoyment. A small cabinet volume often has a higher resonance frequency that can interfere with the output of the low-frequency sound signal. To maintain high-quality bass output, the resonance frequency of the loudspeaker system must be reduced. One of the methods for reducing the resonance frequency in a small and constant volume is to fill the interior cabinet with sound-absorbing materials[1]. Currently, there are two main mechanisms to interpret sound-absorbing behavior. First, it has been considered that the sound energy can dissipate through viscous dissipation near the solid-gas interface or heat conduction of solids according to the transformation of adiabatic to isothermal compression with filling of the sound-absorbing materials, which was mainly determined from
the sound-absorbing performance of materials with centimetre-level structures[5]. Obviously, this mechanism cannot fully explain the hundred microns or s
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