### Author Topic: Speaker magnet and coil geometry how it works  (Read 126 times)

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#### Mike Jung

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##### Speaker magnet and coil geometry how it works
« on: April 15, 2021, 07:36:19 am »
I am trying to understand how a speaker REALLY works and in particular the reason for the geometry of the magnet and coil. I do not understand why they are shaped like that and how the coil repels / attracts the concentric magnets.

I wonder if somebody knows an explanation on the Web or maybe some book where this is discussed more in depth than the elementary way in most electrical texts.

#### Kleinstein

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##### Re: Speaker magnet and coil geometry how it works
« Reply #1 on: April 15, 2021, 07:55:09 am »
The round coil is conventient for production and symetry, so it is the obvious choice. To ease on heat transfer the coil is reltively thin (often just 1 layer or wire). The magent is formed to produce a relatiely homogenous and strong  magentic flied at the coil. As an alternative form one could have a relatively long coild that extends beyound the magentic field, so that all the field goes through the coild - this way also gives a linear response (constant force for a given current independent from the position). This is a radial field to have an axial force from the current through the coil.

To get the flux to the inside it needs a cetain size inside, so that the coil diameter can not be very small. Some suitable steel plate are usially used to concentrate the magentic flied from the relaticely large area magents at the outside (at least for the classic form with ferrite magents). Often the magent itself is just on the outside with axial magnetization.

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