Making sense of sound

It’s easy to take hearing for granted as most of us know nothing about how the delicate ear interprets sound waves, writes Abré J Steyn.

Making sense of sound
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Everything we perceive, andmost of what we can’t, travels in waves – light, sound, heat, radio, micro waves and cosmic waves, to name a few. Each is a different form of energy that can vary in wavelength or frequency. The ear converts sound-wave energy into electrical energy that can be detected by the brain.When you’re in the bush, every sound has a meaning. I recently had a practical display of the importance of sound in nature.

Importance of sound in nature
While friends of mine visited, guests of another kind stopped by too. Hearing us talk and laugh, a group of francolin appeared on the stoep and as usual, walked around the house as if it belonged to them. One flew onto my lap to see if I had a few pips of grain hidden in my hand. One bird, still outside, must have suddenly spotted the resident African hawk eagle doing its rounds and made a soft, purring alarm call.

Most primates, like this chimpanzee, have smallish, immovable ears, very similar to those of humans.

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Every francolin froze like a statue, without blinking an eye – even those that couldn’t see the sky. The soft-sounding alarm was understood by all, even across species barriers. After we watched them in amazement for a few minutes, I gave a reassuring tongue-click and like magic they all relaxed and continued scrutinising the house.

Superior and inferior ears
Mammals have the best hearing of all animals. I recently read an interesting book, Into the thorns, by Wayne Michael Grant – one of our readers – who was a professional leopard hunter in Zimbabwe for many years. He stressed leopards’ acute hearing-sense and said that, at night, a leopard at a bait can hear the soft coughing, sneezing or even wind-letting of a hunter in a blind 100m to 150m away.

But I lost Wayne’s contact details and so I ask that he contact me again. All diurnal primates, including humans, lost out in the ears department. Relying more on superior sight, all primates – except primitive, gnome-like nocturnal primates such as bushbabies – have quite weak hearing, compared to the astonishing auditory ability of other mammals. The typical primate ear is relatively small with limited frequency sensitivity or mobility.

But the less superior human ear was crucial in making us the most intelligent, powerful species to walk the earth. It’s part of a sensory system without which speech, language and the written word would never have come about. Without it, I wouldn’t have been able to write these words. This is the medium through which we store knowledge and how we communicate around the globe.

Protect your hearing
Becoming deaf is no joke, and we should protect this essential sense. The ear’s basic functioning is quite well understood, but most of us don’t appreciate the wonderful delicateness of this marvellous organ, until we go deaf or lose some of its efficiency.

The author’s hunting cap, with the ear-plugs that automatically close when a sound is too loud. He uses these when hunting.

After this hunting season, a new group of hunters will have “hunter’s ears” – an irritating high-pitched ringing or buzzing in the ears – because they didn’t protect their ears from the harmful effect of gunshot noise. The condition, called tinnitus, is irreversible. I know, because for the last 30 years, I’ve suffered from it. It gets worse with age and at times it drives me almost insane. Sound waves striking your eardrum (or tympanum) are transmitted by the three auditory bones (malleus, incus and stapes), which set up vibrations in the fluid of the spiral-shell-shaped cochlea in the inner-ear.

It’s internally lined by nerve cells with minute hair-like projections that are stimulated by these vibrations to transmit electrical impulses through the auditory nerve to the brain. High-frequency vibrations, which don’t travel far through the fluid in the tube, are recorded closest to the cochlea’s entrance, while low-pitched sound is recorded deep down inside. When sounds are too loud, the vibrations are so violent that they amputate the hairs that record high-frequencies. The resulting lesions cause a perpetual high-pitched “ziiing” and a reduced ability to hear high notes, like certain bird calls.

To me this was a great loss, one that could’ve been prevented. Now that it’s too late, I never shoot without proper ear protection. Even when I’m hunting, I use special ear plugs, fitted with valves, which close whenever a sound is too loud. They don’t impede hearing of speech or normal sounds, but shut down instantly when a shot is fired. I bought them several years ago, but I’m not sure where they can be bought today – maybe firearm dealers that stock them could let me know.

I’m sure that other excessive noises, like over-loud music, the noise of power tools, or the ear-splitting blearing of vuvuzelas close to one’s ears can have the same effect as gunshot-noise in causing tinnitus. Affordable and readily-available user-friendly ear protection should be promoted more enthusiastically. The days when my brother Hennie and I used to lie down in the stillness of the Namib Desert, listening to the silence, are just distant memories. Today, there’s a non-stop swarm of noisy cicadas buzzing in my ears. It’s horrible. Don’t let it happen to you.