At its most basic level, sound is one way we perceive vibrations. When an object inside the Earth's atmosphere vibrates, it pushes against and pulls on surrounding air molecules. In turn, they affect surrounding air molecules. It becomes a chain reaction.
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Imagine a bell. When it rings, its surface actually flexes inwards and outwards. When the bell's surface flexes inwards, it pulls air molecules toward the surface of the bell. They pull on other molecules around them, and those pull on even more molecules. We call this area of decreasing air pressure rarefaction.
Extending outward from the vibrating object is a wave of air pressure fluctuations. If you happen to be within range of the wave -- the energy dissipates over distance -- your eardrum vibrates in reaction to the changes in pressure. Your eardrum is connected to tiny bones in your middle ear. These bones connect the eardrum to the cochlea in your inner ear. The cochlea is filled with fluid and tiny little hairs. As the bones vibrate the cochlea, fluid flows against the hairs, which triggers nerve signals that move from the ear to the brain. Your brain then interprets these signals as sound.
Sound can travel through solids, liquids and gases. If you put your ear down against a table and have someone gently scratch upon it, you'll hear it loud and clear. That's because sound generally travels more efficiently through solids than gases. This is also why sound doesn't travel in the vacuum of space -- there aren't enough particles to collide with each other to propagate sound.
The nature of the sound depends upon how forcefully and frequently the molecules bump into each other. Molecules that really bash into each other create louder sounds -- a large mallet striking a huge gong is going to make molecules collide more forcefully than a tiny bell would. Faster fluctuations in the atmosphere create sounds with a higher pitch than those that have slower fluctuations. The gong's sound won't just be louder than the tiny bell, but also deeper in pitch -- the bell creates faster fluctuations in air pressure than the gong does.
Speakers -- wireless and wired alike -- create sound through vibrations. All it takes is a little electricity and magnetism.