The world's loudest animal might surprise you

There are many ways to measure loudness, so the loudest animal on Earth may not be what you expect

The blue whale is not the loudest animal on Earth, despite what you may have learned in school. While its calls are claimed to be louder than a jet engine at take-off, clocking in at an impressive 188 decibels (dB), the sperm whale is actually louder: its communicative clicks have been measured at 230 dB.

Looked at side by side, the numbers seem pretty conclusive, but decibels, which measure sound pressure, are not the only way to measure loudness.

In fact, loudness is subjective, dependent on how humans perceive it. This means there are many other factors to consider in any discussion of loudness.

"From a human-centred perspective, you have to consider the hearing threshold depends on frequency," says Magnus Wahlberg of the University of Southern Denmark.

To understand how humans hear, we first have to understand something about the nature of sound.

Hertz (Hz) is a measure of sound frequency. For instance, each note of a musical instrument comes to our ears at a different frequency: the higher the note, the higher the Hz.

Humans can hear a wide range of frequencies, from 20 Hz to 20,000 Hz (20 kHz). Many sounds lie within this range, from a blue whale's low-pitched songs to a rat's high-pitched distress calls.

But we do not hear all these sounds equally. Instead, our hearing threshold is different for sounds of different frequencies.

"Blue whales call at 20 Hz and sperm whales at around 10 kHz," says Wahlberg. For us to hear blue whale calls, they must be made at an intensity of 70 dB or more. But for sperm whale clicks, the human hearing threshold is around 15 dB.

Read the full story here