From sound waves to brain waves: the basics of acoustic science

Sound fills our lives with meaning, yet not that many of us actually understand how it comes to be. So here’s a look at exactly what happens when sound is created, and the process it takes to get into our brains.

So, what is sound?
Sound is the energy created when a material or object vibrates. The bang of a drum. The clap of your hands. The vibration of your throat as you speak. This vibration causes surrounding air molecules to vibrate as well, carrying the energy outwards from the source in the form of longitudinal waves. Eventually the sound waves hit the air in your ear and vibrates your eardrum. Your brain then converts the incoming sound energy into the sensations we perceive as noise, speech and music.

Sound travels, but it needs a way to get there.
Like light, sound comes from a single source. But unlike light, sound cannot travel through a vacuum. Sound waves always need a medium to travel through – be it air, liquid or gas – because without adjacent molecules to vibrate against, the ripple effect of the sound wave dies out. Sound’s need for a medium was discovered by an English scientist named Robert Boyle (1627-1691). He placed a ringing alarm clock inside a large glass jar and then sucked all the air out with a pump. As the air disappeared, the sound extinguished too, as there were no surrounding atoms or molecules to carry the oscillation outwards.

We’re all on different wavelengths.
From the shrill ringing of your alarm to the distant rumble of thunder, the slamming of a car door to a mother hushing her baby – all of these sound waves operate in the same manner, and yet each is entirely different and creates its own distinct pattern.

The pattern of a fundamental sound wave can be broken down into amplitude and frequency. Amplitude is the distance between the peaks and troughs of a sound wave, and represents the volume of a sound. A big sound wave with high amplitude is heard as a louder sound. Frequency is the number of peaks and troughs produced in a certain amount of time. A sound wave with increased frequency is heard as higher pitched.

On top of the fundamental wave, there are lots of higher-pitched sounds called harmonics. Harmonics and fundamentals work together to give sound a unique shape. This is why different instruments, including the human voice, all sound so singular – even when producing sound waves of the same amplitude and frequency.

If a tree falls in the forest…
While it takes a physical process to start sound energy and send it oscillating through the air – take a tree falling in the forest, for example – it also takes a psychological process to convert the incoming energy into an interpretation of sound. So, then, the answer to the age-old question is no. If there is no one around to hear it, the falling tree does not make a sound. (From an acoustic science point of view, anyway.)

For more information regarding the science of sound, please contact your local clinic.

NHC blog is our place to explore ideas and themes of interest. For professional audiology advice, please contact your local clinic for a consultation.