Speaker is a device that converts an electricalsignal into an acoustic signal. Speaker consists of mainly three parts: 1) Apermanent magnet, 2) A diaphragm, 3) A coil of wire/voice coil. Speaker workson a principle of electromagnetism and motor effect.
The sound emits by aspeaker is due to movement of a diaphragm, which compresses and expand of airsurrounding to it. This movement of a diaphragm is due to electromagnetattached to it. An electromagnet is a magnet which is created by currentcarrying coil often known as a solenoid. In the speaker, a permanent magnet isplaced inside the coil.
When current passes through the coil, it creates amagnetic field around the coil. This magnetic field has north and south polaritysame as a permanent magnet. Electromagnet feels the force due to a permanentmagnet and this force makes electromagnet and diaphragm move. Back and forthmovement of a diaphragm according to a different range of frequencies, itproduces sound. According to Motor effect, “when an electric currentflow through a wrapped coil that is placed in an electric field, the coil willexperience a force and move.
” The movement of diaphragm depends upon thedirection of current flow through the coil. This can be shown by two cases: 1)as shown in fig-1 when current flows in the upward direction and according toright-hand rule, it creates a clockwise magnetic field around the coil anddirection of the force is in the direction of thumb means a direction of thecurrent. The direction of a magnetic field by a coil is opposite to thedirection of a magnetic field by a permanent magnet.
This cause repulsionbetween these two magnets, so coil move right attached to a diaphragm. 2)asshown in fig-2 when current flows in a downward direction and according toright-hand rule, it creates an anti-clockwise magnetic field around the coiland direction of the force is in the direction of thumb means the direction ofthe current. The direction of a magnetic field by a coil is in the direction ofa magnetic field by a permanent magnet. This cause attraction between these twomagnets, so coil move left attached to a diaphragm. As applying alternating current to the coil, the diaphragm moves back and forthaccording to the direction of current and at a specific frequency of theapplied alternate current.