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物理特性的影响。频带与特定模量E/rho成正比，谐波失真随损耗正切值的增加而减小。通过增大E/rho和eta值来改善扬声器的声音再现特性。本研究的目的是开发聚合物-无机材料或聚合物-金属复合材料的新型扬声器膜片材料。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、金属或有机粉末存在的情况下，用不同的引发剂在水介质中进行乙烯基单体聚合，得到包覆聚合物的粉末。利用填料表面与聚合物末端离子基之间的静电吸引力，将聚甲基丙烯酸甲酯乳液颗粒紧密沉积在云母、石墨、碳纤维、木粉等多种填料上。这些复合材料可以直接成型并精确成型成任何形状。另一方面，采用电解氧化法对铝薄板进行氧化，并在阳极上结合各种聚合物形成氧化膜。复合材料表现出较高的E/rho和eta值，特别是在云母、膨胀石墨和铝氧化膜中。膨胀石墨聚甲基丙烯酸甲酯复合薄膜制成的扬声器膜片在高频范围内频率响应特性平坦，谐波失真较小。结果表明，这些复合材料是一种优良的新型高保真扬声器振膜材料。

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.