The definition of a sound in physical terms is a type of energy made by vibrations, this can then propagate in the form of an acoustic wave and is very often transmitted via a medium such as air, liquid or a solid.

In human terms the reception of sound waves are limited to frequencies of around 20Hz to 20KHz, usually anything above or below this range is said not to be audible by humans. They are of course variables between individuals and the sensitivity can deteriorate with age especially at higher frequencies.

There are many species that can hear way beyond the human range, as an example Bats and Dolphins have evolved with very sensitive hearing and are able to hear higher frequencies above 100kHz, elephants are able to hear lower frequencies at around 14hz, while common pets such as dogs can hear frequencies around 67hz to 45Khz depending on age and breed.

Cats can have pretty sensitive hearing and our feline friends can hear higher frequencies than some dogs with a typical range of around 55hz to 79Khz, this makes their hearing one of the best in mammal kingdom.

So what is sound?

The sound you hear has travelled from its original source which then vibrates your ear drums to reproduce the sound.

This sound itself is caused by an energy source which makes vibrations for example, think of a drum, when you hit the drum (the energy) the skin of the drum vibrates, the harder you hit the drum the louder it sounds and the larger the vibrations.

As the skin vibrates it causes air particles surrounding it to vibrate as well and it is these vibrating particles that makes the sound wave.

Sound waves travel at 343 m/s through the air, known as the "Speed of Sound" this can also equate to 761mph or 1100 feet per second.

Sound can travel though other mediums other than air such as liquids or solids, this is providing there are particles to bounce off of. In the vacuum of space for example there are no particles and therefore no sound can travel.

British Sound Archives
An Extensive library of unique sound recordings from all over the world which covers the entire range of sound from Music to Wildlife. All freely available at the British Sound Archives.

BBC Sound Effects Archive
From animals to Zeppelins from across the world from the past 100 years. There's over 33,000 clips including effects made by the famous BBC Radiophonic Workshop as well as effects made for BBC TV and Radio productions. The BBC Sound Effects Archive.