158 THE BUILDING CONSERVATION DIRECTORY 2025 CATHEDRAL COMMUNICATIONS building, while another section is located in a poorly insulated projecting structure or in front of south windows and exposed to direct sunlight, the two will be subject to different levels of influence from external conditions, thereby resulting in different air temperatures and acoustic performance. A further acoustic issue results from the linear expansivity of the materials from which different types of pipes are constructed. Metal flue and reed pipes expand and contract at different rates, resulting in organs being out of tune with themselves following temperature changes. Flues change by approximately 0.8Hz per 1°C. Reed pipes, which change by less than this, are made using a variety of materials which can result in individual pipes losing their tuning by a significant degree. Loss of tuning stability may be short-term while variations persist, but regular and large temperature fluctuations sometimes encourage organ tuners to attempt to rectify the differential by ‘cone tuning’ flue pipes. Regular intrusive tuning of this type can result in dimensional response, causing small but semi-permanent distortion of the materials (pipe tops, collapsing mouths and toes, damage to reed tuning wires and resonators), hastening the need for extensive restoration work. BUILDING ENVELOPE AND CONDITION The building envelope provides a buffer between the internal and external environmental conditions. A wellconstructed church, with substantial walls and limited glazing, should provide a high level of both thermal and hygral buffering. In other words, large fluctuations in external weather will be reflected by far smaller variations in the internal microclimate. As organs ideally require a stable microclimate, both for optimal acoustic performance and conservation, a well-constructed and well-maintained church has the potential to provide benign conditions. This passive buffering is undermined by weak architectural elements or poorly maintained structures which allow air leakage to the exterior, as well as by simple management measures including leaving doors and windows open for ventilation. The condition of the building is also a significant influence on the conditions to which the organ is exposed. If the building envelope and the rainwater disposal system are in poor condition, water will accumulate in the ground or in the walls, evaporating to the interior which will increase the relative humidity and the risks of condensation. This type of deterioration doesn’t tend to be evenly spread and will often be found in enclosed spaces, behind or beneath organs, where moisture levels can build up to the extent that pests, such as beetles or microbiological growth are encouraged and, in the worst instances, both dry rot and wet rot can occur. LOCATION WITHIN THE BUILDING The building microclimate to which the organ is exposed is affected both by the characteristics of the building envelope and the way in which the air within the building is changed, either by patterns of use or by heating and ventilation. An organ located in a small church or chapel with substantial areas of glazing will be exposed to greater thermal instability than an instrument in a large, early medieval cathedral. In the same way, an organ located by a door which is often left open will undergo a greater level of instability than one set within the building away from any external openings. Heating use can also have a significant impact on the stability of the microclimate and thus on the conditions for the organ. The locations of the pipework within the instrument and of the different keyboard and pedal divisions, affect the instrument’s performance. If the pipework of a keyboard or manual division is located in a part of the building with uninsulated roofs, such as a cathedral triforium, there will be far more heat gain and loss. This results in fluctuations of both temperature and relative humidity, which might not be the case if the main sections of pipework were located elsewhere, Images showing the large pedal 32 ft Open Wood pipes of the Great Organ at Canterbury Cathedral under the roof of the north triforium gallery. The roof is uninsulated (right), exposing it to huge fluctuations in temperature and humidity. St John’s College Chapel, Cambridge and (right) chart showing the location of the organ chamber Sugar of lead (lead acetate) is caused by the corrosion of lead pipework. Splits in a soundboard table: although difficult to see they can easily be heard.
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