How the evolution of our ears has to shape design
Our sense of hearing has developed over millions of years. This lengthy process has made humans expert listeners, but it’s also left us with ancient relics of the way our ancestors once heard. Professor Trevor Cox is Britain’s leading expert in all things auditory and has been dubbed “the David Attenborough of the acoustical realm”. Here he explains how our ears work and why we can still mistake the revving of a V8 muscle car with the roar of a hungry lion.
Sound plays a crucial role in shaping whether we think a product is well-designed, and some of our reactions have surprisingly ancient roots.
Mammalian hearing evolved a long time before speech and music appeared, when our ancestors were small creatures scurrying around the undergrowth hunting insects and trying to avoid being eaten by dinosaurs. The need to hunt and avoid becoming someone else’s lunch explains why we have two ears. By comparing the sound between the two ears, we can work out where it is coming from. It also helps to explain why we have exquisitely sensitive hearing, because picking up a faint snap of a twig is vital when it comes to avoiding becoming a predator’s prey.
We still have these ancient structures in our brains that form our sonic early warning system, hence why we can still be startled by the sudden noise made by machines, even though there’s no real danger.
If a product emits more low frequencies, has more bass, it tends to sound more powerful. This is picking up on ancient associations between the frequencies in a sound and the size and power of what created the noise. After all, giant dinosaurs would have roared a bass rumble while our ancestral mammals would presumably have emitted a high pitched squeak.
While learning such associations is vital for survival, it is unlikely that this is ‘hard-wired’ into the brain from birth. It is much more likely that we pick this up as infants. Some of what we experientially learn about sound happens in the womb, as from the third trimester a foetus can hear. One study showed that neonates of mothers who liked Eastenders first learnt to recognize the theme tune in the womb!
It is not known exactly when speech and language evolved, with estimates ranging from about 70,000 to 700,000 years ago. Before then our ancestors would have been vocalising — maybe we sounded similar to chimpanzees? Like other social animals, we would have been calling to attract mates, protect territory and warn others of danger.
A distress call like a scream is particularly loud because it contains a lot of power at frequencies where the ear is most sensitive. The most potent screams also have a ‘roughness’ to the sound — a sound also favoured by lead singers of heavy metal bands. For distressed screams, the harshness is caused by the uncontrolled vibrations of the vocal folds when someone is so frightened that they let rip uninhibited.
This high-pitched rough sound has similar acoustic characteristics to the sound of scraping fingernails down the blackboard. Our response to that archetypal horrible sound, seems to be our brain mistaking the scraping for a distress call. It is certainly something you’d want to avoid when designing the sound of a product!
Trevor Cox is Professor of Acoustic Engineering at the University of Salford. He is author of Sonic Wonderland. His next popular science book, Now You’re Talking, comes out in May 2018.
