The ‘Stonehenge Lego’ model reveals the unique soundscape of the pagan monument
Scientists built a model of Stonehenge, the famous megalithic structure of the stones in Wiltshire, England, and used it to recreate how sound would have been reflected off the surfaces of the stones. They found that the arrangement of the stones would probably have amplified the speech and improved the music, but only if one were in the circle, according to a recent study in the Journal of Archaeological Science.
Nicknamed “Stonehenge Lego”, the scale model is the work of acoustic engineer Trevor Cox of the University of Salford in England and several colleagues. (Fun fact: in 2007/2008 Cox led a one-year study to identify the top 10 worst sounds. The sound of someone vomiting was at the top of the list, followed by feedback from the microphone, babies crying, and a train scratching along the tracks.) This latest article builds on their preliminary findings from the last year. Since then, they have been working to test the acoustics of different stone configurations that would have existed at different times in the monument’s long history.
Recreating historic “soundscapes” is part of a relatively young field known as acoustic (or archaeoacoustic) archeology. For example, researchers sought to understand how acoustics may have influenced the result of key Civil War battles, such as the Battle of Seven Pines on May 31, 1862. Another effect of interest to acoustic archaeologists is the chirping– reminiscent of the call of the quetzal, a brightly colored exotic bird native to the region – as you clap at the bottom of one of the massive stairs at the Mayan Temple of Kukulkan in Chichen Itza, central Mexico.
These soundscapes can have practical applications. Concrete example: last year, the famous Notre-Dame cathedral in Paris was badly damaged by fire. Fortunately, French acousticians had made detailed measurements of Notre-Dame’s âsoundscapeâ in recent years. Another scientist, Andrew Tallon, had used laser scanning to create detailed maps with precision from inside and out. All of this data will help to help architects integrate acoustics into their reconstruction plans, in the hope of preserving the cathedral’s unique soundscape.
Stonehenge is also known to exhibit unusual acoustic effects; it buzzes in strong winds, for example. And in 2017, researchers at the Royal College of Art in London found that its igneous blue stones make a thud when struck, which those who built the monument may have associated with mystical or healing powers. This could explain why some of these stones were transported such long distances; most were probably quarried in a Welsh town called Maenclochog (translation: “ringing rock”). Apparently, the townspeople used the blue stones as church bells until the 18th century.
The acousticians measured the properties of the monument as it exists today, but “the sound is very different from the past because so many stones are now missing or out of place”, Cox et al. written in their last article. There is in fact a large-scale model of Stonehenge in Maryhill, Washington, which is closer to its prehistoric formation, and scientists have also measured its acoustic properties. But Cox et al. believe their model more accurately reflects the shape and size of actual stones.
“The problem with the other models we have is that the stones aren’t quite the right shape and size, and how the the sound interacts with the stones mainly depends on the shapes, ” Cox told The Guardian last year. “These blocks from Maryhill are all very rectangular, whereas the real Stonehenge, when you look at them, they are all a little more amorphous because they are made of stones that have been chiseled by hand.”
Coxswain et al. relied on laser scans of the site itself, as well as existing archaeological evidence, to build their model, which is 1/12 the size of the real thing – a replica as large as the acoustic chamber of the university could accommodate. The outer circle of standing sarsen stones was probably 30 originally. Today, there are five standing sarsen stones included in a total of 63 complete stones, as well as 12 fragmented stones. Archaeologists have estimated that a total of 157 stones were placed at the site approximately 4,200 years ago.
To make their model, Cox and his colleagues 3D printed 27 stones of different shapes and sizes. “You 3D print them, then you make silicone molds of them, then you throw them in a plaster-polymer mixture, then you paint them with car paint”, Cox told the Guardian. “I ruined the floor of my dining room.” Then, they placed the model in the sound chamber to take their measurements.
As we stated earlier, there is a definitive relationship between the quality of acoustics in a room, the size of the room, and the amount of absorption surfaces present. This is captured in a well-known formula for the calculation reverberation time, always the critical factor to assess the acoustic quality of a space. Reverb is not the same as an echo, which happens when a sound is repeated. Reverb is what happens indoors when sound cannot travel a sufficient distance to produce these echoing delays. Instead, you get a continuous ring that gradually âdisintegratesâ (fades).
Acoustic engineers typically measure ‘impulse responses’ on site and store them digitally for later use. Clap your hands in an empty concert hall or church. It is the impulse. (A starting gun or bursting balloon are also good impulses.) The sound reflections you hear are the building’s response. Record both the impulse and the response, then compare the acoustic profile with a recording of the impulse only for reference, and you can extract a pattern of the reverberations in the room.
This is essentially what Cox et al. did with their model of Stonehenge. They placed several microphones and speakers throughout the structure, both inside the circle and just outside of it. Then they played high and low frequency chirping sounds through the speakers, and the reflections of the sounds off the model stones were captured and recorded by the microphones.
They found that the reverberation time was around 0.6 seconds inside the circle for mid-frequency sounds – ideal for amplifying human speech or the sounds of musical instruments like drums. (For comparison, your living room probably has a reverberation of around 0.4 seconds. A large concert hall typically has a reverberation time of around two seconds, while a cathedral like Notre Dame has a very long reverberation time. reverberation for about eight seconds.) But these sounds were not projected beyond the circle into the surrounding area, and there were no echoes, since the internal groups of stones served to scramble and disperse the sounds reflected on the outer circle.
Cox and his co-authors are careful to point out that the acoustic properties of Stonehenge were not necessarily the main driver behind the monument’s unique design. âIt seems unlikely that sound was a major driver of the design and arrangement of the stones at Stonehenge,â they wrote. “Other considerations were more likely to be important, including the astronomical alignments, the incorporation of two different groups of stones, the replication of similar wooden monuments, and the creation of an awe-inspiring and awe-inspiring architectural structure.”
This last study “shows that the sound was quite well contained in the monument and, by implication, [Stonehenge] was pretty well isolated from the sounds coming in, âarchaeologist Timothy Darvill of the University of Bournemouth in England – who is not affiliated with the new research –said Science News, adding that the unique acoustic properties “must have been one of Stonehenge’s fundamental experiences.”
DOI: Journal of Archaeological Science, 2020. 10.1016 / j.jas.2020.105218 (About DOIs).