This project emphasises the unique character and construction of Mousa broch, questions the model of Mousa broch as a roofed home (an interpretation adopted by Historic Scotland in 2002) and considers the way in which sound and light informs our understanding of the spaces contained within its structure. Underpinning the approach to data collection was the architectural concept of aural space. The author attempts to convey an impression of aural space inside Mousa broch by the creation of an audio-visual record supported by acoustic analysis, archaeological discussion, and an architectural breakdown of the spaces within the broch structure. Audio recordings, sound samples, photographs and movies were made on Mousa island and inside Mousa broch during the period of the Summer solstice of 2009.
The results of the analysis of reverberation times for selected spaces are unambiguous. Spaces inside the broch walls created by galleries, cells and the staircase of Mousa broch demonstrate short reverberation times. Acoustic analysis of audio samples support the conclusion that the broch's sonic character can be universally characterised as very dry or 'dead'. The thickness of the dry stone wall construction and the diffusing effect of its fractured surfaces on incoming sound waves influence the sonic character of the aural space. Inside Mousa broch, sounds of at least 1000 Hz and upwards are not reflected but scattered, diffused by the edge surfaces and gaps between the stones in the walls. The author concludes that the influence of what could be called 'dry stone diffusion' found at Mousa broch will occur in all dry stone constructions, including other prehistoric brochs, roundhouses and monastic beehive cells. The identification of a characteristically 'dry' acoustic associated with dry stone construction allows us some insight into the acoustic environment shared by our ancestors in Atlantic Scotland. Photographs and video recordings of the action of sunlight around the walls inside Mousa broch during the solstice period suggest that the broch may perform the function of an interface between ground and sky, a construction in which vertical void sets and stairs are component parts of a solar/celestial measuring device (this possibility remains to be investigated).
This article is Open Access, made possible by the generous support of Historic Scotland.
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