A light voice coil is mounted so that it can move freely inside the magnetic field of a strong permanent magnet. The speaker cone is attached to the voice coil and attached with a flexible mounting to the outer ring of the speaker support. Because there is a definite "home" or equilibrium position for the speaker cone and there is elasticity of the mounting structure, there is inevitably a free cone resonant frequency like that of a mass on a spring. The frequency can be determined by adjusting the mass and stiffness of the cone and voice coil, and it can be damped and broadened by the nature of the construction, but that natural mechanical frequency of vibration is always there and enhances the frequencies in the frequency range near resonance. Part of the role of a good enclosure is to minimize the impact of this resonant frequency.

Sound is essentially waves of air at high and low pressure. A speaker cone generates sound by moving back and forth (oscillating). As it moves forward, the air pressure in front of it increases slightly. As it moves backward, the air pressure decreases slightly. A mechanism consisting of a coil of wire (called the 'voice coil') and a permanent magnet is attached to the speaker cone. This mechanism makes the cone move. When an electric current flows through the voice coil, it becomes an electromagnet. Depending upon the polarity of the electromagnet, the permanent magnet will either attract the voice coil (moving the cone backward) or repel it (moving the cone forward). By varying the strength and frequency of the electric current in the voice coil, the frequency (low, midrange, high) and the amplitude (sound volume) generated by the speaker cone can be controlled. Low-frequency sounds require large pressure waves, so a low-frequency speaker (woofer or subwoofer) needs to be large and requires a lot of electrical power. Conversely, high frequency sounds involve small pressure waves, so the speaker can be small and does not require much power. I hope this helps.

electricity is passed through a coil centered inside of a magnet... when it flows through in oscillating directions it causes E=mc2 "of sorts" to turn electricity into mechanical energy pushing airmass back and forth with frequencies audible an inaudible to the human ear.