The outer cone is known as the diaphragm and it is attached via a supporting frame to a conducting coil through which current can pass. This coil is wrapped axially around a cylindrical magnet. When current is passed through the coil, the latter behaves as an inductor and generates a magnetic field. Since there was no magnetic field produced by the coil in the absence of current, this change in the magnetic field (due to the coil acting as an electromagnet) is repelled by the cylindrical bar magnet due to lenz’s law. Therefore, the attached diaphragm also moves accordingly.

If a steadily time-varying current (sinusoidal) is applied to the coil, the resulting vibratory motion of the coil and the diaphragm will also be sinusoidal at the same frequency. The vibrating cone therefore results in a sound wave at that frequency (since a sound wave is essentially longitudinally vibrating air pressure fronts). Certain qualities differentiating good speakers from bad ones would be good casing, large driver (magnet) size, (neodymium magnets for a stronger field), matching impedance of the coils to the signal source, etc.

That's all🙂