A typical speaker has several parts. The part that vibrates to make the sound is called a cone or diaphragm. It's a flexible surface that can be pushed out or pulled inward by the rest of the speaker mechanism. It's the diaphragm that creates the changes in atmospheric pressure that we perceive as sound.
An electromagnet called a voice coil attaches to the center of the cone. A permanent magnet -- a magnet that keeps its magnetic field without electricity -- sits behind the voice coil on the other side of the cone. This means that a speaker uses two different types of magnets, which is what gives speakers the power to push and pull against the atmosphere rapidly.
Electromagnets take advantage of the relationship between electricity and magnetic fields. As electricity flows through a wire, it generates a magnetic field. Coiling electrical wire around a core -- like an iron nail -- creates a magnet when the current is on. Turning off the electricity causes the magnetic field to dissipate.
Magnets have two poles -- a north pole and a south pole. Permanent magnets always have the same north and south poles. But an electromagnet's poles can switch depending upon the flow of electricity. Forcing the flow of electricity to reverse also reverses the position of the electromagnet's poles.
This is important because with magnets, similar poles repel one another and opposite poles attract. By altering the flow of electricity through the voice coil's electromagnet, the permanent magnet's magnetic field will either push or pull on the voice coil. Since the voice coil attaches to the diaphragm, this will cause the diaphragm to pull inward or push outward.
Speakers alter the flow of electricity within a voice coil thousands of times per second, creating the precise vibrations necessary to create sounds ranging from deep booming bass notes to the high pitch of a piccolo.
In traditional speakers, electricity flows from an amplifier within the source -- such as a stereo system -- to the speaker over two wires. This allows the source to alternate the flow of electricity to the speakers, which causes the electromagnet's poles to switch. Wireless speakers have to create the same effect without the benefit of wires. But how do they do that?