The Development of a Porous Metal Cone Loudspeaker
The paper describes the deficiencies encountered with bass drivers using conventional pulp paper cones with regard to sub-harmonic resonances resulting from non-rigid piston action of the cone. Prior attempts of improvements with the addition of certain fibers to the cone pulp material have been made. The development of a cone is described, explaining the reasons for selecting a double-layer construction with nickel of a certain porosity as cone material plus the addition of aluminum foil to achieve high bending stiffness (with high Young's modulus) and still low weight for a high upper usable frequency limit. Comparative measurements are shown plus photos visualizing holographically cone vibration patterns by the time-average technique. Using this double-layer construction, the onset of harmful resonances could be considerably moved up in frequency to extend the useful change of the driver.
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