A technique is described whereby the mechanical damping factor Qm of a woofer can be controlled using ferrofluid in the voice coil gap region. This provides the engineer with flexibility to choose form a much wider variety of basic woofer designs to achieve a desired system bass response. The thermal conductivity advantage of ferrofluid over air is shown to increase the heat sinking capabilities of the driver and thus offers additional design benefit. Basic woofer design with ferrofluid is discussed with emphasis on the effects of differential pressures produced by voice coil excursions.
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