Some archaeologists argue that sound effects were an important, perhaps even decisive, factor in how early humans chose and built their dwellings and sacred places. However, assessing the claims of 'acoustic archaeology' encounters a fundamental problem: sound is ephemeral. We do not even know what our ancestors were thinking - or often a clear idea of the original layout and acoustic properties of the structures we are interpreting.
     "We are visually very sophisticated, but acoustically very primitive," says UK archaeologist Paul Devereux, an advocate of the claims of acoustic archaeology. Our ancestors, by contrast, would have been "acoustically more calm and attentive in a much quieter world", he says. Without artificial light, listening intently would have been imperative to ward off night-time predators. In a time before writing, moreover, information was principally communicated orally. It seems reasonable that prehistoric humans would have paid more attention to their acoustic landscapes than we do today. "Senses as a whole were more fused," says Julian Thomas, an archaeologist at the University of Manchester, UK. "There wasn't the separation of vision from the other senses as there has been over the last few centuries. Nowadays we tend to prioritise vision."
     We also know that our ancestors appreciated their ability to exploit their environment to make sound early on. The discovery of three flutes in 2009 in a cave in south-west Germany pushes the origins of music back to the middle Palaeolithic era, 40,000 years ago. Lithophones or rock gongs - stones that create a tone when hit - are found around the world. A cave at Fieux à Miers in the Midi-Pyrénées region of the south of France contains a 2-metre-tall feature which resonates like a gong when struck. Recalcified fractures on the lithophone indicating where it was struck can be dated back to the upper Palaeolithic, around 20,000 years ago. Outdoor examples include Kupgal Hill in Karnataka state, southern India, where an outcrop of dolerite boulders emits loud ringing tones when hit with granite stones.
     Iegor Reznikoff of Nanterre University, Paris, has examined the caves of Rouffignac in the south of France and showed that paintings are located where the most interesting sound effects are heard. But systematic analyses of such sites are few and far between. It is one thing to show that our ancestors were aware of their acoustic environment. It is quite another to prove that they intentionally designed their surroundings with acoustics in mind.
     One focus of this debate lies with enclosed spaces such as burial mounds, underground temples and burial chambers dug out of rock and earth. In the 1990s, Devereux and his colleagues measured the acoustics of six sites in the UK and Ireland dating from around 3500 BCE to 400 BCE, and found that all of them have resonant frequencies between 95 and 120 hertz, within the range of a male voice. Chant in a drone at the right frequency and you can map out the shape of the acoustic resonance, hearing the sound loud in one place and hardly at all in another - a dramatic and impressive sound effect. Devereux thinks this is no coincidence: the spaces were tuned to maximise the acoustic impact of ritual chanting.
     Not everyone is convinced. Matthew Wright, an acoustics researcher at the University of Southampton, UK, is scathing in his commentary. "If you are going to conclude that particular burial mounds were designed for chanting, then you have to also conclude that my bathroom was made for singing," he says. Devereux accept that acoustic intent in the design of burial mounds is far from proved, and it will be difficult to do so conclusively.
     And what about Stonehenge? With no roof on the monument, any sound made within it might be expected to scatter vertically and be lost to the atmosphere, either directly or after reflecting from the ground. Yet the stones of the monument are oddly two-faced: while the sides facing outwards are roughly hewn, the interior surfaces have been chipped away at laboriously to provide a surprisingly smooth, slightly convex form that is ideal for high-frequency reflection.
     In 2009, Rupert Till, a musicologist from the University of Huddersfield, UK and Bruno Fazenda at the University of Salford, UK, measured Stonehenge's acoustic signature by bursting balloons to map out the reflections within it. What Till and Fazenda measured was impressive. "It's actually like walking into an enclosed space with a lively acoustic," Till says. "It is a really good space for speech because reflections from the stones mean you can be heard everywhere within it, even if you're hidden behind a stone." Clap your hands in the space and the sound reverberates around the monument as it reflects from stone to stone. The reverberation takes about 1.2 seconds to die down - typical for an opera house or school hall but astoundingly long for a space with no ceiling.
     Accident or design? Till suggests that our ancestors might have learned that such smoothly shaped surfaces gave off stronger echoes by observing the properties of other standing stones. Fazenda is more sceptical, suggesting it is more likely that Stonehenge was built for religious purposes, and that our ancestors exploited the lively acoustic they had created to support speech.
     Here as elsewhere, perhaps we shall never know for certain whether our ancestors built with acoustics in mind. "There may never be 100 per cent proof of acoustic intentionality," Till says. "That uncertainty just adds to the interest, mystery and aura of the ancient sites."

Source: NewScientist (27 August 2010)