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ATE’s speaker cone.
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A combination of properties make the material especially suitable for speaker applications such as diaphragms, domes, and voice coil bobbins. APTIV films from Victrex (www.victrex.com) are based on the supplier’s PEEK polymer technology. John Getz, APTIV film commercial leader at Victrex, said the films meet the long-term fatigue performance required for a speaker diaphragm. “The semicrystalline nature…of the polymer provides a relatively high modulus from the crystalline phase as well as a degree of damping from the amorphous phase.”
Speaker diaphragms can be made in different thicknesses, lending more flexibility in the design process. Where metal foils are replaced, the lower density of the film allows a faster response and less mass of inertia in the entire speaker system. This is of particular interest in compression driver applications. Many of the latest generation mobile phones have higher-power speakers, which increases the operating temperature of the voice coil and diaphragm. This rules out the lower temperature films used in previous generations.
“OEMs are increasingly pushing for a lighter-weight, high-performance solution to facilitate meeting demands for reduced systems cost and improved product performance, including durability, reliability, miniaturization, increased functionality, and eco-friendly application design,” Getz tells APPLIANCE magazine. He says the new film grades can be manufactured up to 1.5 meters wide, making it the widest PEEK film available, and thicknesses can range from 6 to 750 µm, adding to design flexibility.
Cutting End-Product Costs
A key advantage of the film is that it can facilitate customers and end-user systems-cost reductions. “Systems cost takes into account a variety of factors beyond material price,” Getz explains. These include extended part life due to the film’s durability, improved manufacturing yields, improved manufacturing cycle times, and reduced part weight through use of thinner films or the lower specific gravity of the film. The film enabled one customer to cut thermoforming cycle time by 50%. Another customer eliminated adhesives by heat bonding the film directly to the metal substrate of the part.
Audio Technology Engineering (ATE; Burgau, Germany; www.a-t-e.de) is one audio equipment OEM that has made use of the black film to enhance the design process of its P2C speaker cone. The film enabled free surface design capabilities and allowed parts to be thermoformed with intricate details. The P2C sandwich cone made with the black film is said to be recognized as an excellent technology solution for cones used in speakers of all types. The design offers a number of acoustic properties, including lower distortion and ringing, no break-up modes, very simple crossovers, and a flatter frequency response in comparison with cones made from conventional materials such as polypropylene, paper, and aluminum.
According to Norman Gerkinsmeyer, general manager of ATE, the film enhanced the cone’s design process by enabling free surface design capabilities. “The ability to thermoform APTIV film into intricate details in the speaker cone design means that the manufacturing process is fast and efficient, allowing it to be used in high volume and cost-competitive applications,” he said.
The film has been used in microphone spacer films. “Microphones are produced using surface mounted device (SMD) methods where they are attached to a board while going through solder reflow,” Getz explains. “However, polyester terephthalate (PET), the current spacer material, has low heat resistance, causing the microphones to melt or be deformed.” Victrex film was selected for its high temperature capabilities as well as electrical reliability, chemical resistance, and physical properties.
The film has also been specified in cell phone speaker diaphragms. “These diaphragms must be able to manage extremely high power inputs and high temperatures while producing excellent sound quality in a very small package,” Getz tells APPLIANCE. “APTIV film has the ability to survive temperatures in excess of 230°C (446°F) combined with outstanding fatigue properties, and yet it is easily thermoformable with short cycle times on standard equipment.”
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