Development of New Diaphragm Materials for Loudspeakers

扬声器的声学特性在很大程度上受振膜材料的物理性质的影响。频带与比模量E/rho成正比，谐波失真随损耗角正切η值的增大而减小。通过增大E/rho和η值来改善扬声器的声再现特性，本研究旨在开发聚合物-无机物或聚合物-金属复合材料扬声器用新型振膜材料。采用聚合法、聚合物乳液法和轻金属阳极氧化法制备了复合材料。在无机、金属或有机粉末的存在下，在水介质中使用各种引发剂进行乙烯基单体的聚合，并且容易获得用聚合物包封的粉末。利用聚合物末端离子基团与填料表面的静电吸引力，将聚甲基丙烯酸甲酯乳液粒子紧密地沉积在云母、石墨、碳纤维、木粉等填料上。这些复合材料可以直接成型并精确地形成任何形状。另一方面，采用电解氧化法对铝薄板进行氧化，阳极氧化膜与各种聚合物结合。这些复合材料表现出高的E/rho和η值，特别是在云母、膨胀石墨和铝的氧化膜中。结果表明，用膨胀石墨/聚甲基丙烯酸甲酯复合膜制成的扬声器振膜在高频范围内频率响应特性平坦，谐波失真小，是一种优良的Hi-Fi扬声器振膜新材料。

Acoustic characteristics of loudspeakers are largely influenced by physical properties of diaphragm materials. The frequency band is in proportion to specific modulus E/rho and the harmonic distortion decrease with increasing loss tangent eta value. Acoustic reproduction characteristics of loudspeaker is improved by enlargement of E/rho and eta value.The purpose of this investigation is development of new diaphragm materials for loudspeakers made of polymer-inorganic substance or polymer-metal composite materials. These composites were prepared by means of polymerization method, polymer emulsion method and anode oxidation method of light metal. Polymerization of vinyl monomers was carried out in the presence of inorganic, metal or organic powders in aqueous medium using various initiators, and powders encapsulated with polymer were readily obtained. Furthermore, polymethyl methacrylate emulsion particles was tightly deposited onto various fillers such as mica, graphites, carbon fiber, wood powder etc. by considering electrostatic attraction between filler surface and terminal ionic groups of polymer. These composite materials could be directly molded and accurately formed into any shape. On the other hand, aluminum thin plate was oxidized by the electrolytic oxidation and oxide film on anode was combined with various polymers. These composite materials showed a high E/rho and eta value, especially in mica, expanded graphite and oxide film of aluminum. Frequency response characteristics of speakers using a diaphragm made of the expanded graphite polymethyl methacrylate composite film was flat and harmonic distortion was lower in the high frequency range.From results, these composite materials were found out to be excellent new diaphragm materials for Hi-Fi loudspeakers.