Acoustic studies carried out on a 3D-printed replica of the enigmatic Stonehenge revealed a curious property of the ancient monument — its structure was capable of amplifying the sounds produced inside and muffling the sounds outside. In other words, it would be the perfect place to make speeches and run secret rituals, preventing outsiders from listening, participating, or spying on the inner circle.
Built around 5,000 years ago, the mysterious stone circle structure was erected in rural Wiltshire, southwest England. There are other similar stone monuments, but the most famous is also the most sophisticated, which perhaps explains its fame. Adding to the curiosity is the fact that we don’t know who built Stonehenge or why, although the latest research is already yielding some clues.
According to Trevor Cox, who is leading the current efforts, the acoustics of places influence how they are used. Understanding the sounds of a prehistoric site is an important part of archeology, which led him to apply such methods at Stonehenge. Theories surrounding the building say it could be a burial ground, place of healing or even a celestial calendar, given that the outer stone ring’s spaces line up exactly with the summer and winter solstice.
The Sounds of Stonehenge
Taking about 10 years, Cox’s research found that the monument was a huge echo chamber, leading to the belief that it was used as a place for rituals, in which only the elite of the people of the time participated. The researcher noticed that the acoustic scale modeling technique had never been applied in prehistoric sites, which led him to consider that Stonehenge could have some different property.
To find out, he created a 1:12 scale replica, small enough that it could be tested in the semi-anechoic chamber at the University of Salford (an almost soundproof room, with geometric foam on every surface except the floor).
Cox was able to obtain a computer model of the monument from English Heritage, helping to understand what it looked like 4,000 years ago, when it would have been built. Many stones are currently missing or have fallen away, with the arrangement changing greatly from 2000 BC to the present day. To recreate the ancient look, 157 stones were 3D printed, taking 6 months. After being painted gray and arranged properly, the acoustic tests began.
As the size is 1/12 of the original, the sounds had to have their frequency multiplied by 12. Loudspeakers placed around the room played the frequencies the scientists were looking for, and microphones picked up the results. A computer model created by Cox simulated voices and music, distorting them and simulating the properties of prehistoric construction.
Acoustics since prehistory
Surprising the researchers, Stonehenge — which has no ceiling or floor — bounces sound between spaces in the stones, keeping it within the circle. The voice, like the music, would have sounded more powerful and impactful in the center of the structure. The directionality of the voice is one of the most interesting aspects of the research, since on a hill with normal grass, without stones, a person with their back turned would only have their speeches heard ⅓ of the time, on average.
The sound reflection of the stones amplifies the voice by 4 decibels, however, which increases the speech understood rate to 100%. Ceremonies or rituals performed within the circle would be private, excluding anyone outside. Research has already indicated that Stonehenge’s surroundings could have cultivated hedges (grass or tree fences), also visually hiding the site from anyone who could not participate.
Cox likens building acoustics to the difference between standing in an empty movie theater and a cathedral—although it doesn’t seem that different to us, accustomed to moving in and out of enclosed spaces, a Late Neolithic person, unfamiliar with the acoustics of a building. walls, would have found the effect mesmerizing.
The first results of the research were published in the scientific journal Journal of Archaeological Science in 2020, but Cox and his team are continuing to study the venue’s acoustics further, exploring, for example, how people in the stone circle might have changed the reverberation of the sound.
Recently, with miniaturized models of up to 100 people inside the mini Stonehenge, new measurements were made. As our bodies absorb sounds, changes in acoustics during ceremonies certainly happened.
Changes according to the position of the listener are also being verified, as this changes depending on whether we are facing or sideways to the source of the sound. Reflecting sounds laterally improves the quality of music in concert halls, for example. Human ceremonies usually involve speech, chanting, or other forms of sound, which would likely have been important to the people who lifted the stones at Stonehenge, although we don’t know who they were.
Definitive conclusions about these mysterious prehistoric humans are impossible, but more hints about what they were doing in the stone circle will be published after further analysis of the data by Cox’s team later this year.
Source: Journal of Archaeological Science, BBC
