![]() ![]() ![]() The resulting diaphragms formed from variable thickness films not only vary in weight and - a far more serious result-the formed-edge compliance is not uniform.ĭr. PET is a commodity material and high-speed processes are used with resulting film thickness variations typically exceeding 10%. The main message is that as with all cheap materials, it is handled as such. In this article, we will discuss the importance of precision extrusion processing for resins in the production of films. Yet even in products with modest audio expectations, if exposed to high temperatures, a product’s diaphragm is going to melt. Because of all of this, PET should be limited to entry-level products. The melting point Tm is 250☌ (482☏) and while it is appealing to diaphragm forming factories to have such a low Tg and high melting point, this wide tolerance enables fast sloppy forming. And, PET loses its mechanical integrity or Tg (glass transition) early on at about 78☌ (172☏). The problem is that as with all thermoplastic resins, it softens when it gets hot. Because it is a cheap and a workable material, it has omnipotence in audio. First synthesized in the 1940s, PET was invented independently by both DuPont (Mylar) and ICI Films (Melinex). There are a half-dozen plastics that can be used as polymer films for diaphragms used in earphones, headphones, soundbars, smart speakers, laptops/tablets, and esoteric components such as ribbon planar drivers and air motion transformers (AMT). As PET (polyesters) requires higher weight than PEEK to achieve shape integrity, PET diaphragms have a lot of unnecessary additives. This is the lower end of plastics and while it works, it is no match for better products. for PET (bottle plastic), which dominates most earphone and headphone diaphragm applications. The cost for extruded polymer films start at less than $4/lb. The diaphragm material and shape are the most significant contributors to speaker sound quality. After forming to the net shape, the polymer film becomes glassy again upon cooling below Tg. Thermoplastic films, from polyethylene terephthalate (PET) to PEEK, can be formed when the temperature of the plastic reaches above its glass transition temperature (Tg), changing from a glassy to a rubbery state-becoming pliable and moldable. ![]() PEEK granules, film and actual speaker diaphragms. ![]()
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