Overhung & Underhung Coils
The image above shows two ways in which the voice coil is immersed in the magnetic field. The most common method is the overhung design where the height of the voice coil is greater than the magnetic gap's height. The underhung design which is used mostly in high-end speakers has the coil's height smaller than the gap's. The differences, advantages and disadvantages of both methods are given in the table below.
| Overhung coil | Underhung coil | ||
| • | Coil height is greater than the gap's height. | • | Gap's height is greater than the coil's height. |
| • | This method keeps the number of windings within the magnetic field (or flux) constant over the coil's normal excursion range. | • | This method keeps the magnetic flux that the coil experiences, constant over the coil's normal excursion range. |
| • | Higher coil mass, sensitivity medium to high.‡ | • | Low coil mass, sensitivity low to medium.‡ |
| • | Soft non-linearity as the coil exceeds limits. | • | Hard non-linearity as the coil exceeds limits. |
Both topologies attempt the same goal: linear force acting on the coil, for a driver that reproduces the applied signal faithfully.
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