In Pursuit of Increasingly Linear Loudspeaker Motors

In this paper, analytical calculations are used to study existing loudspeaker motors totally made of permanent magnets. When the iron is removed from a loudspeaker, Eddy currents and reluctant effects are also removed, improving the linearity of the loudspeaker. Performances of each proposed magnetic motor structures are compared, from the intensity of their created induction to their ability to respond as an accurate image of the driving current. For a given structure, the authorized excursion length on which the loudspeaker motor is linear is a criterion for limiting its frequency range. The good understanding of the behavior of any magnets assemblies lead to a so-called ldquolinear structure,rdquo whose volume is optimized and able to create a very uniform induction, along a distance range that can be chosen. When this is achieved, the force that makes the moving part of the loudspeaker oscillate becomes proportional to the current running through its voice coil. Thus, this loudspeaker motor is linear as well as using a reduced magnets volume, and can be applied to all frequency ranges.