Stonehenge was Built to Amplify Sound During Ancient Rituals

A new study by acoustics engineers at the University of Salford suggests that the ancient pagan religious site of Stonehenge may have been designed to amplify sound in very specific ways. 

Constructing a 1:12 scale model of the site, with missing stones also represented, the engineers tested the sound properties of the structure they called "Minihenge." Speakers and microphones were placed in and around it, and then ultrasonic sounds 12 times their normal frequency were used to account for the difference in scale.

The results of their research have been published in the Journal of Archaeological Science.

“Constructing and testing the model was very time consuming, a labor of love, but it has given the most accurate insight into the prehistoric acoustics to date,” Trevor Cox, the project’s lead researcher, said in a statement. “With so many stones missing or displaced, the modern acoustic of Stonehenge is very different to that in prehistory.”

The study found that noises from inside the monument would have reverberated without much echo against the massive standing stones, increasing the volume inside, while decreasing exterior noise. This would have made it easier for those inside and harder for those outside the structure to hear what was going on inside. The study indicates that the stones were capable of amplifying the human voice by more than four decibels.

“You’d think that the sound would just disappear to the heavens, but there are enough stones horizontally that the sound keeps bouncing back and forth,” Cox told the New Scientist. “It’s quite magical that you could feel what it would have sounded like to have been in that space.”

One inference drawn from this is that the religious rituals held at Stonehenge were "intimate" events limited to a small group of participants, even though the site’s construction would have required a huge amount of manpower. This suggests a highly hierarchic society, although it should be stressed that this is a major assumption.

Plan for the Stonehenge scale model and the placement of speakers and microphones. Image courtesy of the Acoustics Research Centre/University of Salford, Manchester.

While the sound properties the team at Salford are clearly important, they don't cancel out or exclude the importance of the astrological alignment of the stones that is generally believed to have been the primary factor in the placement of the stones. 

In 2014 Cox also speculated that some of the smaller stones used in the ancient site’s construction may have been chosen for their musical qualities, as they make sounds much like a metallic gong when struck. That theory was tested in a 2013 study conducted by researchers from the Royal College of Art in London, who were able to “play” Stonehenge’s ringing stones like a giant xylophone in a unique form of “rock” music.

Looks like Spinal Tap were right, after all.