It may be 5,000 years old and missing a few pieces, but we pretty much know what Stonehenge looked like when the final stone was placed into position on Salisbury Plain in Wiltshire, England. While its true and full purpose is still a mystery, many have suspected there was an acoustic aspect to the placement of the stones, creating sounds or amplifications to those standing inside the circle. An acoustic engineer recently led a team that created a scale model of the original and used architectural acoustics to recreate what those people may have heard, even with no roof to hold it in. The results were astounding.
“We expected to lose a lot of sound vertically, because there’s no roof. But what we found instead was thousands upon thousands of reflections as the sound waves bounced around horizontally.”
In an interview with Smithsonian Magazine about his recent study published in the Journal of Archaeological Science, Trevor Cox, lead author from the Acoustics Research Centre at the University of Salford, tells how he noticed that all of the previous acoustic studies of Stonehenge were done using the current partial structure, so he decided to find out what it sounded like when first built somewhere around 2200 BCE.
To build an eight-foot-wide, scaled-down model of the original in an acoustics-testing chamber, he 3-D-printed 27 of the stones, used them to make silicon molds and then cast the other 130 stones. Some were cast solid in a plaster-polymer mix while others were hollow and filled with an aggregate and plaster mix. They were then sealed with a cellulose car spray paint to prevent sound from being absorbed. Cox then placed microphones inside the model and began creating sounds in the chamber.
“It was found that the stone reflections create an average mid-frequency reverberation time of (0.64 ± 0.03) seconds and an amplification of (4.3 ± 0.9) dB for speech. The model has a more accurate representation of the prehistoric geometry, giving a reverberation time that is significantly greater than that measured in the current ruin and a full-size concrete replica at Maryhill, USA.”
Not only did the sounds reverberate vertically between the stones, it was amplified to four decibels. In addition, the sounds were found to linger far longer than expected and definitely longer than they do in the current partial structure. While it’s would be really impressive if this was intentional, Cox thinks the sound amplification and reverberation was a surprise to the builders and first users.
What’s next? Cox plans to put plastic people in the model to test their effect. He’d also like to recreate voices, perhaps chanting or singing, plus musical instruments of the era playing to come closer to experiencing what the early ceremonial users might have heard. The research is not just for fun either – the reverberation he discovered is of interest to modern musicians who want to tune their music to sound like it was played inside Stonehenge in 2200 BCE.
We knew about the Stonehenge rocks. Now we know that Stonehenge rocked!