Decoding the mysterious knocking sound in a Finnish cave

Finland's Pirunkirkko Cave , which means "Devil's Cathedral" in English, is located in Koli National Park and is famous for its intermittent knocking-like sound.

Decoding the mysterious knocking sound in a Finnish cave

A knocking sound is coming from Pirunkirkko Cave. Video : University of Helsinki

A research team from the University of Eastern Finland has found the cause of the strange noise in Pirunkirkko Cave, Mail reported on November 27. According to researchers Riitta Rainio and Elina Hytonen-Ng, it is due to a special resonance.

Pirunkirkko is a 34-meter-long, Z-shaped cave where, according to legend, sages met to communicate with the spirit world. In a new study, scientists explored whether the cave’s acoustic characteristics could help explain the legend associated with it. Analysis of the cave revealed a unique resonance phenomenon that both magnifies and prolongs sounds at specific frequencies.

The researchers believe the phenomenon is caused by standing waves between the smooth parallel walls of the cave. This creates a tone at the cave's natural frequency of 231 Hz, which can be heard for a second after sounds such as clapping, drumming or pounding.

The team also interviewed and recorded a modern-day witch doctor who used the cave for rituals. They found that the sounds he made were amplified by the cave at its natural frequency.

While common in buildings, resonance is rare in natural environments, largely due to the lack of parallel solid surfaces. For this reason, the team suggests that the resonant sounds in caves may make visitors feel as though they are being visited by spirits.

An Khang (According to Mail )

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