INTERIORS 5 159 CATHEDRAL COMMUNICATIONS THE BUILDING CONSERVATION DIRECTORY 2025 such as on the pulpitum in the centre of the cathedral. If sections are located in both uninsulated north and south triforium galleries, they will vary from the central section but, on either side, in different ways and at different rates. This is often exacerbated by the fact that, with so much equipment to fit into often relatively small areas, little space is generally left between the organ pipes and external roofs, resulting in a far greater influence of external conditions than would otherwise be the case. This will affect pipes in different ways with contraction and expansion of large pipes, which speak in the range of 16 to 32Hz, undergoing very little change of pitch, while smaller metal pipes are much more prone to changes in temperature, affecting their resulting pitch far more. Projecting organ extensions often have less substantial walls and roofs than the main building, giving them more unstable internal environmental conditions due to radiant heat gain or loss. Organ extensions often have awkward roof junctions and are vulnerable to water ingress from roof defects or failing rainwater disposal systems. To counter the effects of different organ sections located in different microclimates, insulated enclosures are sometimes constructed. This provides protection for the environmentally sensitive elements of the instrument housed in thermally inefficient parts of the building. In certain forms of organ-building this is sometimes achieved by constructing an insulated timber case within the area of the building where the pipes are located. This is open to the main building on one side (sometimes known as tone cabinets), thereby allowing the box to be ventilated with the main cathedral air and thus heated and cooled in the same way as other parts of the instrument located elsewhere. In principle this is a sensible approach but it relies on the enclosure being a substantial construction that is genuinely able to provide thermal buffering both in summer and winter, avoiding the local effect of external weather variations. It is also based on the assumption, which is often erroneous, that the conditions throughout the rest of the building are homogeneous so that the air mixing with the ambient air and organ case will provide the same conditions for the enclosed pipes as those elsewhere in the building. The observations of organists who have experienced uneven tuning failure in different sections, which is backed up by environmental monitoring data gathered in a number of projects, has demonstrated that, in fact, the microclimatic variations across a large and complex building, such as a cathedral, are often so great that they limit the effect of many insulated enclosures. Organs are sometimes built with their keyboard divisions stacked vertically within the organ’s casework (known as a Werkprinzip design), so that sections of pipework located at the top of an Data showing conditions in the main organ case on the pulpitum (the screen separating the choir from the nave) and in the cased pipes in the nave north tower behind the Minstrels’ Gallery at Exeter Cathedral Details of the organ enclosure for the section of the instrument behind the Minstrels’ Gallery at Exeter Cathedral The Minstrels' Gallery at Exeter Cathedral with the organ enclosure behind instrument’s structure can be subject to different temperatures as heat rises within a building envelope, or heat gain or loss occurs through the uninsulated roof. Just as with sections in different parts of the building, this can result in an organ being out of tune with itself. If any section of the organ is located close to large windows, it could be subjected to solar gain when the sun is out and radiant heat loss, in addition to cooling at night and during the cold parts of the year. It is not unusual for some or all of these factors to form part of any organ installation, both on a diurnal as well as seasonal basis. Organs constructed on
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