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Jan 25th 2021

Stonehenge Sound Science Offers Acoustic Addition to Monumental Methodology

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Hearing the name “Stonehenge” creates a common set of mental images featuring massive and monolithic minerals towering above Salisbury skies. It also raises a host of questions around who built the structure, why and how they accomplished such a feat. Now, researchers from the University of Salford have added their own audio appellation: What did Stonehenge sound like?

Henge-ing Your Bets

Despite its place in human history and regular appearance in television, movies and novels, the history of this henge — a circular ditch and bank — aren’t exactly set in stone. While it’s likely the site was used as a burial ground and took millennia to fully construct, the mandate and methodology behind this prodigious project remain shrouded in myth.

Consider the second phase of the building process, which historians typically date to around 2,800 BCE. Approximately 80 bluestones were lifted into standing positions and placed in a circular formation. Not only were these stones massive, but they were also likely located at least 200 miles from the Stonehenge landscape, meaning ancient builders needed to both ship and stand these stones without the aid of any modern technology — including the wheel.

The site’s purpose is also uncertain. Many scholars believe it may have been used as a ceremonial site or pilgrimage destination, while other researchers suggest it functioned as an astronomical calendar. More recent discoveries also indicate its potential as a place of healing.

Now, there’s a new entry making noise in the field of Stonehenge science: acoustic archaeology.

Acoustic Advantages: The Science of Sound

As Ars Technica notes, acoustic archaeology — also called archaeoacoustics — focuses on the role of sound during historical events or in specific locations. For example, acoustic archeologists have examined the role of “acoustic shadows” in the loss of critical Civil War battles and the sound of a chirping bird produced when visitors clap their hands at the bottom of the Mayan Temple of Kukulkan at Chichen Itza.

The Stonehenge landscape has long been known for strange sounds. For example, the arrangement of stones creates peculiar echoes and produces humming noises in strong winds. Acoustical engineer Trevor Cox and his team at the University of Salford decided to explore these auditory oddities further by creating “Stonehenge Lego,” a 1/12 scale model made of 3D-printed and painted blocks standing in for the real standing stones, which produced a structural soundscape capable of both amplifying speech and enhancing music. Cox and his team explain, “It seems improbable that sound was a primary driver in the design and arrangement of the stones at Stonehenge,” but the acoustical advantages would certainly have garnered attention. Archeologist Timothy Darvill of Bournemouth University also notes that these structural sounds “must have been one of the fundamental experiences of Stonehenge.”

Can You Hear Me Now?

Work by the University of Salford team turned up two salient soundscape insights: Audio signals inside the stone circle were amplified, while those outside were dampened. As a result, participants within the monument could better hear music or speaking, while those passing by were largely unable to listen in.

To measure the acoustic properties of a structure, acousticians use what’s known as “impulse responses” — the time between initial sound input (impulse) and any sound reflections (response) off any surfaces. For the Stonehenge Lego model, Cox and his team used four-directional speakers in five locations producing sounds at twelve times normal frequency to account for the 1/12 structure scale. They found that sound inside the circle reverberated for at least 0.6 seconds in most cases and up to 0.8 seconds for lower-frequency impulses.

For comparison, larger spaces such as cathedrals may have reverb times up to 8 seconds, while your average living room comes in at around 0.4 seconds, making the 0.6-0.8 second range ideal to slightly amplify sound without causing significant interference or echo.

Rock n’ Role

Much like the pyramids, the stones of Salisbury Plain stand as a testament to human ingenuity and engineering— and provide an endless source of speculation for historians, astronomers and archaeoacoustic adherents alike. Yet, while the exact role of this mammoth monolith may never be fully revealed, one thing is certain: There’s beauty in the sound of science.

Check out Northrop Grumman career opportunities to see how you can participate in this fascinating time of discovery in science, technology, and engineering.

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