This project attempts to convey some impression of the aural space inside Mousa broch by the creation of an audio-visual record of the broch captured during the period of the 2009 summer solstice. The audio-visual record is supported by archaeological discussion and an architectural breakdown of the spaces in the broch. Sound sources/instruments were chosen for their sonic characteristics, weight and portability. It was the author's intention that although the sounds created by iron bars, drum and whistle might not have been heard within the broch by its builders/occupants, they would have been sounds recognisable to them (Hickmann et al. 2001; see Section 4.1). The approach was informed by the methodology and recommendations of the Acoustics and Music of British Prehistory Research Network.
Audio recordings, photographs and movies were collected by the author (assisted by PhD student Justin Vitello) on Mousa island in the Shetlands from 19th–22nd June 2009. These files are accessed via a cross-sectional drawing of the inner wall of the structure, divided into selected areas deemed significant for their ability to influence aural space. In the creation of this project, the remote location of Mousa island and the location of Mousa broch (approximately 1 mile (1.6km) across rough ground) were important logistical considerations. Air freight limitations restricted the weight of audio-visual recording equipment to a maximum of 30kg, which shaped the final approach (see section 4). The creation of an archive of high amplitude sinusoidal sweeps recorded inside the broch would have been ideal but was beyond the scope of the field trip. Sinusoidal sweeps would assist in acoustic analysis, facilitate the investigation of potential acoustic phenomena (echoes and standing waves) and could be used to create convolution reverb samples for selected spaces. In all parts of the broch, the irregular shape and surface of the walls are difficult to model and this makes accurate acoustic prediction of the behaviour of sound waves against their surfaces difficult.
For over 150 years, the archaeological community has investigated the origins and possible functions for the brochs of Scotland. In 2002, the model of Mousa broch as a roofed structure was adopted by Historic Scotland. In contrast, this project emphasises the unique character and construction of Mousa broch (see Fojut 1981) and questions the model of the broch as a roofed home and considers the way in which sound informs our understanding of the spaces contained within its structure.
There is no standard definition of aural space and little agreement on the limit of its meaning. An increasing awareness of the importance of environmental sound (Begbie 2000) and innovative architectural approaches have informed the development of what some regard as a nebulous concept and others (including the author) see as a powerful tool. Begbie's statement that there is no neat distinction between a place and its occupant, that 'Aural space opens up a space which is not that of a discrete location and which is for want of a better word the space of omnipresence' (Begbie 2000, 75), represents an extreme interpretation of the concept. The current project is based on the idea that aural space is linked to our perception of sound (noise) in the world around us and that it is influenced by sound both at audible levels and at frequencies beyond the threshold of human hearing. Campbell and Greated (1994, 276) point out that the sounds we hear are influenced by our perception of source broadening and envelopment and are not dependent on their source direction. Sound has the ability to flow through openings and influence the moods of those that occupy the space. Blesser and Salter's description of navigational spatiality, our ability to '…hear spatial attributes, such as a wall or open window… [and] to use our ears to supplement vision' (Blesser and Salter 2009, 75), highlights subtle, subliminal aspects of aural perception often taken for granted. Based on these insights, it can be argued that the concept of aural space involves aural perception and that the laws of acoustics are relevant to and can describe aspects of its complex character. We can examine the environment in which aural space exists and we can investigate ways in which we may perceive that space, but we can never completely describe its nature. The concept of aural space is important because in part it helps us to describe and better understand the space that surrounds us and may inform our knowledge of how that space is or was used. Various resources, a scale model of the broch (Figure 1), architectural plans and illustrations, laser scans, photographs, audio samples, video clips and soundscapes, acoustic analysis and archaeological discussion contribute towards the portrayal of aural space. In every area of Mousa broch, sounds surround, fill and occupy the structure. The interaction between sound and the broch wall surfaces contribute to its character. In order to understand these interactions more fully, a breakdown of the structure of the broch follows, detailing the position and structure of the voidsets and highlighting some of the architectural anomalies.
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