The Acoustic properties of chambered cairns

Dr Aaron Watson at work in the entrance to Maeshowe

Were the acoustic properties of Orkney’s chambered cairns as important to the builders as their role of housing the dead?

From recent research on the subject, it certainly appears they could have been.

Dr Aaron Watson, an Honorary Fellow at the University of Exeter, has spent a number of years investigating the effect of sound at some of the county’s best-known prehistoric sites.

After repeated visits to measure and record audio data, Dr Watson is of the opinion that sound played an integral part in the rituals and ceremonies surrounding sites such as Maeshowe and the Ring of Brodgar.

His research shows that certain prehistoric monuments exhibit specific sonic effects – effects that would have been impossible for Neolithic man to explain. As such, were they interpreted as having an “otherworldly” source?

At Maeshowe, for example, specific pitches of vocal chant, as well as drumming, inside the cairn produced specific, unsettling, effects in those present.

In the chamber, the behaviour of sound was seen to be considerably different from that of the outside world, with the ancient stone walls amplifying noise to create a variety of audio effects.

Standing Waves

One of these effects is the phenomenon known as "standing waves". These produce distinct areas of high and low intensity as the sound waves interact – either cancelling each other out, or combining to enhance, the sound.

This effect means that by moving through the chamber, the listener experiences areas of high and low volume that appear to have no relationship to the source of the sound.

Practical experiments with chanting in the cairn saw the volume and intensity of the voices enhanced, with the noise filling the interior so completely that it became difficult to determine the source.

So, imagine a Neolithic drummer, or chanter, in Maeshowe. In the stone chamber, the drummer could have appeared to be surrounded by silence, while the sounds they created were emphasised in other, apparently unrelated, areas. In Maeshowe, for example, the loudest areas were found to concentrate around the tomb’s side chambers, perhaps giving the impression of otherworldy sound emanating from the realm of the dead.

Infrasound

But perhaps more incredible is the idea that infrasound – sound below the ability of humans to hear – generated in the cairns could alter the mental states of those participating in ceremonies.

The principle of "Helmholtz Resonance" - the phenomenon of air resonance in a cavity – was found to apply to a number of prehistoric cairns.

The most commonly-used example of this phenomenon is the noise created when blowing across the neck of a bottle. Maeshowe, for example, shares the same basic structure as a bottle - an air filled chamber connected to the outside world by a long, narrow neck.

To create this effect, the users of the cairn had to create a sound that was at the correct frequency for the dimensions, and design, of the chamber. The larger the chamber, the lower the pitch required to create the effect and, therefore, the slower the required drumbeat.

In Maeshowe, a drum was used and the researchers discovered that the correct frequency was 2 hz. This is an "infrasonic frequency" which means that, although inaudible to humans, it can be felt as distinct physical, or psychological, sensation.

Test subjects reported the feeling that sounds were emerging from inside their head and body. They experienced feelings of dizziness, nausea, headaches, flying sensations and also that their pulse-rate was being affected.

Dr Watson suggests that prolonged exposure to these "sounds" could have had a profound effect - an effect that Neolithic man could only ascribe to the supernatural.

So were the tombs built with these scientific phenomena in mind?

Probably not – at least not initially.

Instead, Dr Watson thinks their acoustic properties were co-incidental – a “by-product” - that came to be exploited and added to the sites’ significance to the Neolithic users.

He is convinced that these acoustic effects, once “discovered” marked the cairns as spiritually significant - a place where Stone Age man was closest to his gods, or ancestors.

He said: "These monuments from the distant past were not the remote and silent places we visit today; they may best be understood as gateways through which people of the Neolithic period passed to gain access to dimensions far beyond the reality of their everyday lives."

It is clear from archaeological remains found in and around many of Orkney's cairns that the activities carried out were ritualistic.

For many years, historians have been fairly certain that the cairns were not mere repositories for the dead but an active part of the community’s religious practices. As such, various activities probably took place inside the chambers and these could well have been grand, theatrical events involving singing, chanting and music.

But were these effects deliberately exploited by those who officiated over the rituals and ceremonies? Or were these "priests" as in awe as those who witnessed them?

In an earlier article for British Archaeology, Aaron Watson expands on this idea: "Perhaps we can envisage entering the darkened environment of the chamber where the stale air, peculiar smells and presence of the dead would heighten the sense to any sounds being made. Combined with echoes and possibly resonance, these elements could have amounted to a remarkable and affecting experience.”

He wrote: "We cannot know for certain if these acoustics properties were exploited thousands of years ago but it seems highly likely. We know these sites were visited repeatedly for generations. Even today, reproductions of the sounds of the monuments are stirring and vaguely disturbing.”

Brodgar's echoes

Sound may also have played a part at the nearby Ring of Brodgar.

Although only 27 of the ring’s estimated 60 megaliths remain, Dr Watson recorded distinct echoes across the interior.

Sound created at the edge of the circle, for example, produced indistinct echoes, reflected from the other stones. Sounds made at the centre, however, echoed back and appeared to envelop the listener. Using handclaps or drumbeats, the delayed echo also made it appear as though the stone were producing a separate sound themselves.

With the completion of the acoustic experiments, the next stage was to see how the data could apply to the “real world” of Neolithic Orkney.

Although the work is ongoing, one thing is very clear. Neolithic Orkney was not a silent place.

Instead of the romantic vision of peace and quiet that pervades the sites today, imagine a scene where the ancient Orcadians chanted, danced and beat their drums – the only way they knew how to reach the state that allowed communication with the spirits of their ancestors.

Life in recent centuries was by no means sombre and silent, so perhaps we shouldn’t assume it was in prehistory.