Maeshowe — Dr AARON WATSON

The exterior of Maeshowe.

Acoustics at Maeshowe

Maeshowe is the largest chambered mound in Orkney, and one of the most remarkable Neolithic structures in Britain. The dry stone walling in the chamber and passageway is remarkably precise, and the entrance is aligned so that a beam of sunlight illuminates the chamber at the midwinter sunset. Abstract patterns and lines were incised upon the walls in the Neolithic.

A circular mound of clay covers the chamber and passage, and this is surrounded by a broad level platform where people might have congregated. The margins of the platform are defined by a ditch and external wall. To gain access to the central chamber it was necessary to cross these features before negotiating the low passageway. At the passage entrance is a carefully shaped stone block that can be pivoted into place, effectively blocking access to the interior.

Three views of the chamber inside Maeshowe.

I first conducted archaeoacoustics research here with David Keating in 1998. One of the first things we noted was that the stone walls at Maeshowe contain sound very efficiently. Very precise construction techniques minimised gaps between the stone blocks to create an almost unbroken surface upon which sound can reflect. This is further enhanced by the use of large stones within the walls so that sections of the passage and side cells are effectively solid stone.

Maeshowe's interior is very conducive to standing wave resonance, an acoustic phenomenon caused by the interference between sound waves as reflect between solid walls. We found the most effective standing waves resulted from tones such as humming or chanting, and that their impact was very noticeable. At a resonant frequency, the sound becomes expansive and begins to behave in unusual ways. Some sounds appeared to move around while the source remained still, and others appeared louder with increasing distance from their source. Standing waves can also distort speech, and the resulting resonances within the speakers voice box were sometimes uncomfortable.

Aaron Watson (standing) and David Keating measuring standing waves inside Maeshowe in 1998.

Similar to the smaller passage grave of Camster Round in Caithness, sounds generated within Maeshowe’s chamber are poorly transmitted along the passageway. The clay mound covering Maeshowe also serves to isolate the interior so that very little sound emerges except through the passage entrance. Even here, listeners will only gain a very distorted impression of events inside. To people who did not have share our scientific understanding of acoustics, it is possible that such unusual sounds might even have been understood to have special properties.

We also considered the possibility that sounds might have been introduced into Maeshowe's chamber by people outside. Even when the passage entrance was sealed by the blocking stone, a narrow gap remains between the top of this stone and the passage ceiling. Interestingly, an open slot above the passage entrance at Newgrange in Ireland that could have been used in a similar way.

Infrasound

Ethnographic accounts suggest that there are many societies, in both the past and present, that communicate with ancestral, or spirit worlds, through altered states of consciousness. These states can be achieved in different ways, and some may involve unusual kinds of sound. At Maeshowe, it is possible that people inside may have inadvertently generated infrasound that could exert a physiological and psychological influence. This results from a phenomenon known as 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 tomb like Maeshowe is very similar to that of the classic Helmholtz Resonator.

Testing for infrasound at Maeshowe

The presence of Helmholtz Resonance at Maeshowe was explored in detail. 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. Intriguingly, 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 technically below the threshold of human hearing, they may still have effects upon the mind.

Wider studies have shown that 2 Hertz frequencies can induce a variety of sensations. At levels similar to those recorded inside Maeshowe, these can include a sensation of pressure or headaches, dizziness and disorientation. We cannot be too specific, as the physiological impact of infrasound remains difficult to measure, and can influences people in various ways. If drumming is used as the source, we also have to take into account the possibility that loud percussion can itself have an impact upon listeners.

Measuring equipment installed inside Maeshowe in 1998. In the foreground is an omni-directional dodecahedron loudspeaker and bass. To the right are oscilloscopes and sine wave generators, while the microphone on the tripod was extremely sensitive and able to detect very low frequency sounds.

Was infrasound deliberate?

While we were able to demonstrate the presence of infrasound inside Maeshowe using sensitive equipment, it seems unlikely that this monument was intentionally constructed for this purpose. My thinking is that Helmholtz Resonance is an accidental by-product of the passage grave format, and that at Maeshowe it is further exaggerated by the precise stone walling. Because there are so few cavities, energy is reflected rather than absorbed. While Helmholtz Resonance is theoretically possible at other passage graves, comparable fieldwork at Newgrange did not detect infrasound. Here, large cavities in the walls seem to prevent the effect from occurring.

Although Helmholtz Resonance may not have been a deliberate result of the design of Maeshowe, this does not mean it is insignificant. Our tests showed that the effect does not have to be understood to be triggered - this can happen even when people are moving around the interior. The phenomena did not have to be understood for unusual effects to potentially occur upon people, and these may have contributed to the otherworldly or special qualities of Maeshowe in the Neolithic.

Interpreting the acoustics of Maeshowe

A significant characteristic of passage graves is the way in which the format of their architecture guides the movement of people. While it is possible to accommodate more than 20 individuals within the chamber at Maeshowe, this leaves rather little room for any kind of performance. It also becomes difficult to see carved images upon the walls, or to view the effects of the sunset at midwinter. Indeed, this 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 audiences would have been very different.

Thanks...

Many thanks to Historic Scotland for permission to conduct fieldwork at Maeshowe, and to the site staff for their support.