Aaron Watson Archaeology Research
Maeshowe
Maeshowe is the largest surviving chambered mound in Orkney, and one of the most spectacular Neolithic buildings in Britain. The dry stone walling in the chamber and passageway is extraordinarily precise, and the entrance is aligned to allow a beam of light to illuminate the chamber at the midwinter sunset. Abstract patterns and lines were scratched onto the walls in the Neolithic.
A large circular mound of clay covers the chamber and passage, and this is surrounded by a wide open platform where people might have congregated. Outside this is a ditch and external wall. To gain access to the central chamber it was necessary cross these features and move through the restricted passageway. Intriguingly, a balanced stone block can be pivoted into place, effectively sealing the entrance.
Passage grave chambers are enclosed stone-lined spaces, causing sounds to be contained and echoed. This is especially true at Maeshowe, where the precise joins in the stone walling creates a near unbroken surface for sound reflections. This also makes the interior ideal for standing waves, an acoustic phenomenon caused by the interference between sound waves as they reflect between walls. When a standing wave is generated the nature of the sound becomes expansive, and behaves in rather unusual ways. Standing waves can also seriously distort speech.
It is also possible that sounds could have been introduced into Maeshowe from the outside. The blocking stone does not entirely seal the passage, allowing the possibility for communication with the interior. Interestingly, there is an open slot above the passage entrance at Newgrange in Ireland that could have been used in similar ways.
Similar to Camster Round, sounds generated within Maeshowe’s chamber are poorly transmitted down the passageway. Furthermore, the mound covering Maeshowe is sealed with clay so very little sound emerges except through the passage entrance. Even here, listeners will only gain a very distorted impression of events inside. It is possible that distorted sounds emerging from the passage entrance might have taken on a magical quality.
Infrasound
Many societies communicate with ancestors or spirit worlds through altered states of consciousness. Altered states can be achieved in many different ways, and often involve sound. At Maeshowe it is possible that people inside inadvertently generated infrasonic sounds that could exert a physiological or psychological influence upon. This results from the phenomenon of Helmholtz Resonance.
Helmholtz Resonance is caused by the repeated oscillation of sound waves between an enclosed chamber and the outside world along a confined passageway. Under certain conditions a single frequency can be powerfully amplified to levels that far exceed the original source. Intriguingly, the format of a passage grave like Maeshowe is very similar to that of the classic Helmholtz Resonator.
Testing Infrasound
The presence of Helmholtz Resonance at Maeshowe was tested with the assistance of acoustician Dr. David Keating. We tried a number of methods to incite the movement of sound pressure waves through the monument, including walking along the passage (thereby generating a pressure wave) and beating a drum. Intrguingly, we recorded a 2 Hertz resonance at 120 decibels caused by walking around the interior, while a single drum played at 2 beats per second (the frequency necessary to incite resonance) registered a 2 Hertz resonance at over 110 decibels. While these sounds are below the threshold of human hearing, they can still have effects.
Wider studies have shown that 2 Hertz frequencies can induce a variety of sensations. At levels similar to those recorded inside Maeshowe, these can range from pressure and headaches through to dizziness and disorientation. The results cannot be too specific, as the impact of infrasound is difficult to measure, and also influences people in varying ways. Another potential problem is that the sound of loud percussion can itself have effects upon listeners.
Was infrasound deliberate?
It seems unlikely that Maeshowe was intentionally constructed to create infrasound. Helmholtz Resonance is most likely an accidental by-product of the passage grave format, and enhanced by the precision of the stone walling. Because there are few cavities, these walls reflect sound energy that might othewise be absorbed. While Helmholtz Resonance should be possible at most passage graves, tests have yet to demonstrate its presence at other sites.
Helmholtz Resonance need not have been a deliberate feature of the design of Maeshowe for it to be significant. These tests have shown that people would not have needed to understand the phenomenon as infrasound can result from people moving through the interior. Perhaps any effects on those inside contributed to the otherworldly or special qualities of Maeshowe in prehistory.
Interpreting the acoustics of Maeshowe
A significant characteristic of passage graves is the way in which their architecture unavoidably guides the movement of people. While it is possible to accommodate more than 20 people within the chamber at Maeshowe, this leaves very little room for any kind of performance. It also becomes difficult to see images upon the walls, or to view the sunset along the passage at midwinter. Limited space might have divided an audience between those who were accommodated within, and those who were not. The visual and audible experiences of these two groups would have been very different.