Magnets in moving-coil speakers

The moving coil is the most widely known and used structure of speakers. The moving coil speaker performs well and is relatively easy to design and produce. In our daily lives, most speakers are using this form.

The moving coil speaker is composed of a magnetic circuit system, a vibration system and a supporting frame. The magnetic circuit system mainly consists of a magnet and an iron core. These two components are sticked to a plate generating a stable magnetic field.

The vibrational system mainly includes voice coil, vibrating diaphragm and other components. As the current flows through the voice coil, the changing current causes the voice coil to produce a changing magnetic field. The magnetic field generated by the voice coil interacts with the stable magnetic field generated by the magnet, causing the vibrating diaphragm driven by the voice coil to vibrate, and finial causing the sound.

Under the same conditions, the stronger of the available magnetic field is, the greater the kinetic energy generated by the current, which means the speaker is easily driven under strong magnetic field. But when the magnetic field force exceeds a certain range, the lower frequency signal might be ignored, which might cause the loss of low frequencies.

To sum up, the moving coil speaker need to choose the right magnet. The greater the magnetic force the magnet has, the more sensitive the speaker is. But when magnetic force is too strong, it will cause the loss of details.

There are two types of moving coil speakers: internal magnetic type and external magnetic type. The magnet of the inner magnetic type is wrapped in the shell, it is not easy to leak magnetic field so the volume of the speaker is relatively small. At the same time, due to the magnet is wrapped in the housing, there is no space to place a big magnet. In order to generate stronger magnetic field in limited space, neodymium magnet is the best choice of this speaker. Since the magnet of the outer magnetic type is not limited by volume, ferrite is usually used.


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