Here's How Speakers Make Multiple Sounds At Once

In our daily lives, there are many miraculous scientific and technological concepts we take for granted. For example, your favorite Bluetooth speaker from a major brand on your desk is able to play the full scope of a 100-piece symphony for your listening pleasure, but how can one audio source accurately replicate 100 different instruments playing over each other? The answer lies in the mechanics of sound and speaker technology, and their ability to merge multiple composite soundwaves into a single, comprehensive source.

While you could, in theory, have a dedicated speaker for every single instrument in that hypothetical symphony, it wouldn't sound any different from having all of those instruments relayed through a single speaker. This is because, rather than beaming multiple individual waves into our ears, a speaker's job is to find the single point of commonality between disparate waves and merge them into a comprehensive sound that our ears can parse. It sounds more complicated than it actually is, pun unintended. You just need to understand how sound moves, and how a speaker moves it.

A soundwave is often depicted as a sine wave, a single, wavy line, bouncing and dipping with changes in volume, pitch, and other miscellaneous factors. While this is a convenient abstraction, it's not the most accurate one. Rather than a single line, sound has more of a conical shape, blasting outwards in a 3D pattern with that line at the center.

Sound, as a physical phenomenon, is the result of air particles being vibrated by minute frequencies. The human ear intercepts these vibrated particles: the outer ear collects them, the eardrum vibrates at the same frequency, the small bones in your ear wiggle, and the fluid and hair in your cochlea transform the sound into an electrical signal your brain can parse. This is why it hurts if you listen to music too loudly; the vibrations are too violent, injuring the components of your ears.

When there are many sounds overlapping each other, your ear can't catch all of them simultaneously, so it simplifies by looking for common threads. This is why music sounds like a single, cohesive sound, because your brain is automatically simplifying all of the different instrument sounds into a single wave. It's within this particular human function that speakers are able to work their magic.

A speaker is kind of like an inversion of the human ear. Rather than receiving sound vibrations, the speaker itself vibrates using a magnetic coil, blasting sound waves out and vibrating the air in front of it. The speaker is just moving the air in front of it at a particular frequency, which your ears can pick up.

In the same way that your ear simplifies sounds, so too does a speaker. Every instrument in a song produces its own unique waveform, which a speaker unites into a single, unified waveform of immense complexity. For example, if you played the sounds of a guitar and a piano over each other, the speaker would create a unified wave, matching the points where their soundwaves are identical, while leaving the disparate portions still audible. This is why you can still pick out the individual instruments of a song if you listen carefully.

The human ear can parse sound frequencies between 20 and 20,000 Hz, so even if the overall waveform is complex, as long as it's within that range, you can hear it. Theoretically speaking, if you could produce a completely identical soundwave to the one your speaker is producing, it would sound exactly the same, even if it's coming from a different source. A speaker doesn't "make" music or sound; they just relay it in a simplified manner. Of course, wireless audiophile-grade speakers are able to perform that relay without sacrificing portions of the soundwave, while a cheap pair of headphones may sound blurred or muffled.