As humans, we can hear the rumble of distant thunder but can’t hear the crack of lightning unless it strikes close by. We hear the bass but not the treble because powerful low-frequency sound travels long distances well. But the bass humans hear cuts off at about 20 Hz – below that, you can only feel the sound at close range as it vibrates your chest. If we were capable of hearing bass frequencies lower than 20Hz, we would be able to hear our own muscles moving.
In comparison, there are many animals who appear to hear and produce sounds well below our range, known as infrasound. These include:
- Guinea fowl
Sound consists of waves of high and low air pressure. When they reach the eardrum the waves push it in and pull it out, creating a vibration transmitted through the middle ear bones to the cochlea, where specialized cells produce nerve impulses and our brains interpret these as sound. The waves we hear best range from a fraction of an inch to about a metre, whereas infrasound waves range from tens of metres to miles.