Neodymium Speaker Magnets

A neodymium ring magnet in a loudspeaker is a sintered Neodymium (NdFeB) annulus magnetised through its thickness and clamped between a steel back plate and a top plate, so that its field is directed into the narrow air gap where the voice coil hangs. These neodymium speaker magnets are selected for their ability to provide strong magnetic flux in a compact motor assembly. The ring shape is not decorative, because the bore accommodates the central pole structure around which the voice coil moves, which is why a speaker magnet is bought to an outside diameter and a hole rather than to a holding force.

Sizes follow the driver. A headphone or a small sensor-scale motor may use a ring of a few millimetres across, a portable speaker may use one around twenty to thirty-five millimetres, and a car door or PA driver often requires a larger magnetic assembly. Material is N42 or N45 as standard and N52 where a more compact design requires higher magnetic performance, provided the operating conditions are suitable. The alloy can also be specified without terbium or dysprosium when a customer needs that stated on the drawing.

The comparison in the table is the one buyers ask us to price against. Neodymium magnets offer higher magnetic energy density than ferrite, allowing speaker designers to achieve the required air-gap flux with a smaller magnet volume. The actual gap flux density depends on the complete magnetic circuit, not the magnet material alone. That difference is one reason compact speakers can use smaller motor assemblies, and it is also why a factory moving from ferrite to neodymium usually redesigns the steel around the magnet rather than dropping a smaller ring into the old yoke and hoping.

Where the field goes matters more than how much of it there is. The voice coil sits in a narrow magnetic gap, and the force on that coil depends on the flux density at its position, which is why we ask for the plate drawing alongside the magnet outline rather than the magnet outline alone. Charging is through the thickness with the poles on the two broad faces, and when a design wants the field concentrated in the gap, it is the low-carbon steel that is shaped to do it, not the magnet alone.

Rings for drivers are pressed, sintered and then ground on both faces, on the outside and on the bore, because a loudspeaker gap will not forgive an out-of-round part or a burr on the inner edge. Tolerance holds to about ±0.1 mm, the edges are chamfered to reduce chipping and coating damage during assembly, and nickel-copper-nickel is standard since the ring is glued and clamped in place rather than handled afterwards. If a motor needs a neodymium ring magnet, send the outside diameter, the bore, the height and the gap from the plate drawing, and we will confirm grade, coating and magnetising before quoting.

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