Camster Round passage tomb.

Acoustics at the Grey Cairns of Camster

There are two early Neolithic cairns at the Grey Cairns of Camster in Caithness, a long cairn with two chambers and a round cairn. Both have been excavated and partially reconstructed. Since 1996, Camster Round has been a focus for archaeoacoustic research because it was restored using original materials.

Camster Round has a stone-built passage and chamber buried within a circular cairn. This creates a dramatic juxtaposition between the inside and outside that is emphasised by the claustrophobic passageway.

Listening and recording within the confined passage of Camster Round.

Sounds generated inside Camster Round appear loud and enhanced because they are contained by the confined stone walls. In contrast, sound does not travel easily along the passage, so a listener outside will hear a distorted impression. Higher frequencies are lost, emphasising sounds such as drumming.

Moving away from the passage to the sides of the cairn, higher frequency sounds become even more filtered. Around the back of the cairn, bass sounds created by drumming in the chamber sounded like they were emerging from beneath the ground rather than from inside the cairn.

Intriguingly, the sound of a drum being played within the chamber of Camster Round could be distantly heard from within the chambers of nearby Camster Long. These monuments are 200 metres apart, and the sound could not be detected in the open air between them. One explanation is that these sounds are being transmitted through the ground. It is also possible that the silence in the chambers makes it possible to hear sounds that were otherwise obscured by natural noises in the outside world.

Camster Round in the foreground, with Camster Long visible on the skyline.

Standing waves at Camster Round

The enclosed chamber of Camster Round is suited to the creation of standing waves, distinctive resonances that result from the interaction of sound waves reflecting between walls. Standing waves are easy to make, requiring only a constant tone from the voice or a musical instrument. By varying the pitch it is possible to ‘tune’ into the space. At Camster Round there are a variety of standing wave resonances, some rather more distinct than others.

When a standing wave was generated the sound appeared to develop a life of its own, expanding to fill the space and behaving in extraordinary ways. This included unexpected changes in volume as the listener moved around, and even subtle shifts in pitch. Counter intuitively, it could become quieter nearer to the source, or suddenly appear to change completely. Standing waves could also distort the voice in unusual ways, as well as resonating with parts of the body to create some unnerving sensations.

The chamber inside Camster Round.

Interpreting the acoustics of Camster Round

Camster Round can create a variety of dynamic sound experiences. The filtering of sound between the inside and outside creates contrasting experiences between people inside the chamber and those outside. Whatever events were taking place there, it is only possible for a small group to share the confined chamber. This might suggest that some people were excluded entirely.

An audience outside could not have seen what was taking place in the chamber, and the sounds that they heard would have been highly distorted. Perhaps the monument was understood to have special properties that could transform place and people; such effects could not have been reproduced outside of these monuments. They may have been the voices of spirits, ancestors or other forces.

While passage tombs often contain the remains of the dead, this need not imply that this was their only purpose. A structure such as Camster Round may have been a place where people could also engage directly with unusual powers. These extraordinary sounds may therefore have accompanied journeys by both the living and the dead.

Further reading

Watson, A. and Keating, D. 1999. Architecture and sound: an acoustic analysis of megalithic monuments in prehistoric Britain. Antiquity 73, 325-36.