On this episode of Ask The Expert, Otto Jørgensen talks all things voice coil magnets – how the are made and how we magnetise them.
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Today we are going to talk about how we glue the metal pieces of a loudspeaker driver together, but before we go into how we glue things, let's discuss why we have these three metal pieces in the first place.
Every loudspeaker essentially functions by sending a current into the voice coil. This creates a magnetic field with a specific polarity around the coil itself. The voice coil is then put inside a fixed magnet, and the variations in the current being sent to the voice coil cause it to move relative to its surrounding magnet.
The problem is the polarity of the magnet is different than the polarity of the voice coil. Enter the extra pieces of metal we mentioned earlier... One of these we are using what's called a yoke. A yoke guides the magnetic flux from the bottom of the magnet to the inside of the voice coil.
The other part is a top plate, which takes magentic flux from the other side of the magnet and guides that to the outside of the voice coil.
Finally, we need to make the magnet a magnet. What starts as a piece of is glued to the iron yoke and top plate and placed in a magnetiser.
By using this yoke and top plate construction, we ensure that we have a very precise magnet gap, allowing us full control over the strength of the neodymium magnets.
And that's how we manufacture the magnet system of a loudspeaker driver.