How we hear sound can be described in terms of loudness and pitch. The loudness level is the volume you hear the sound. Pitch equates to whether the sound has a high sounding tone or a low sounding tone.

The human ear has the ability to hear sounds between 20Hz and 20,000Hz, providing us the ability to hear conversation, music. Sounds below the human hearing range are called infrasounds and those above the hearing range are called ultrasonic. We look at sounds that the human ear cannot hear even with no hearing loss. 

 

Animal Communication

Many animals can hear beyond the hearing range of human beings. The size of the animal is a usual factor in sound being produced. One of the largest animals on the planet, the blue whale communicates at a range of 10 to 30Hz at a volume of over 180dB. This sound is transmitted hundred of miles underwater, which is a large bellow of a noise yet as human beings we stuggle to hear this being below our hearing range. Blue whales are solitary creatures, generally swimming alone however being able to vocalise such distances allows them to communicate to other blue whales when needed. Another larger than life animal on the planet creating unaudible sounds is the elephant. Elephants produce and hear sounds at a low pitchs of around 10-30Hz. It is still not quite clear how these sounds are produced but it is related to the large size of the elephant's larynx. Using infrasounds means that similar to blue whales, even thought they do not have the added bonus of sound travelling faster underwater, they too have the ability to communicate long distances without being heard by human beings. A very unsual candidate that also produces sounds in the infrasound regiong is the Koala. A male koala uses a mating call around 10Hz. They are able to do this as they have an extra set of vocal cords that produce a series of continuous sounds on inhalation and exhalation.

On the other end of the spectrum, there are a few animals that communicate using ultrasound. Bats inparticular are well documented and reported on their communication and hearing ability at high frequencies around 12-160Khz. A bat dectector device is often used to be able translate bat calls to audible sounds that we can hear, a device often used to detect the presence of bat. Bats have poor eyesight and therefore rely heavily on their hearing. Hearing through their lower jawbone,  dolphins and porpoise also hear sounds that are ultrasound.  With an ability to hear the same as the human hearing range plus up to 150KHz, there is nothing we can hide from a dolphin. In comparison to other marine mammals such as whales mentioned previously, dolphin sounds cannot transmit vocalise as far. Both bats and dolphins also use their ultrasound volcalisations for echo location. This means high pitch clicks are used to detect distance from and presence of particular objects.

 

Earth Noises

 There are a number of sounds produced by the earth that are inaudible because they are infrasound noises. A volcano errupting can produce a tone of 2Hz and then volcano thunder produces a level just over 20Hz. However with technology able to detect such sounds at over 250km away.  Sounds produced via earth quakes underground also known as seismic noises are recorded at below 1Hz.

Storms

 

Volcanoes

 

Machine Noises

Wind turbines

 

 

Friction Sounds

 

 

https://link.springer.com/article/10.1007/BF00679906

https://link.springer.com/referenceworkentry/10.1007%2F978-90-481-8702-7_146