INTERIORS 5 157 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 PIPE ORGANS and the building environment TOBIT CURTEIS and WILLIAM McVICKER MOST CHURCHES and other places of worship are heated intermittently. For the congregation, cranking up the heating in the winter months helps to take the edge off the cold. For the fabric of the building, and its often centuries-old furnishings and fittings, rapid changes in temperature and humidity before and after each service causes stress. Church organs are particularly vulnerable as the environmental conditions affect both their conservation and their acoustic performance. As a result, organs often lose their tuning or suffer physical deterioration which can sometimes be irreversible. With many custodians of church buildings now focusing on their approach to net zero carbon emissions, a further factor has been introduced which increases the potential for negative effects. Although there is extensive research into the environmental performance of church buildings and an increasing body of information about the effects of decarbonisation measures, the effect of the church environment on organs is little studied1. This short paper is intended to provide an introduction to some of the important environmental factors affecting them, in order to enable practical steps to be taken to avoid negative consequences for both conservation and acoustic performance. PHYSICAL DETERIORATION An organ’s microclimate affects its performance in a number of ways. Variations in relative humidity (RH), caused either by changes in ambient temperature (AT) or in air moisture content (absolute humidity or AH), can cause the working parts of the organ to become physically distorted or corroded, resulting in their poor performance. For instance, elevated RH can cause sensitive organic elements, such as timber soundboards or stop mechanisms, to swell, resulting in restricted movement of the stops (whose on/off mode is controlled by sliders in the soundboards), or cause condensation in lead pipes leading to lead acetate corrosion, sometimes known as sugar of lead2. This white crystalline compound is said to have a sweetish taste, hence the phrase ‘sugar of lead’; it is water-soluble and one of the most bioavailable forms of this metal. Similar to other lead compounds, it is poisonous Long-term and large fluctuations in RH can cause expansion and contraction in other organic elements, such as the console components, pipes and soundboards, causing them to warp or split. In leather reservoirs (bellows), concussion valves or pneumatic key-action motors, RH fluctuations result in the leather stiffening or cracking. TUNING AND ACOUSTIC PERFORMANCE Air temperature also affects the acoustic performance of musical instruments. A variation in air temperature of 1°C can cause a change in pitch of approximately 1Hz (often the metric 2°F/1Hz is used) because the denser cold air results in greater resistance to the transmission of sound vibrations3. Therefore, if an organ is tuned for a particular temperature profile and the ambient temperature in the building changes significantly, this can cause considerable acoustic distortion. This is further complicated in organs where the various pipe-sections are located in different parts of a large building or at different levels within the organ case. They may be subjected to A college chapel and, below, a thermal image showing solar gain through its uninsulated roof varying temperature instability, resulting in diverse pitch alterations in different sections. For example, if one pipe-section is located centrally in a well-insulated
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