A study of mechanical pipe organ actions and how they influence musical performance

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The action of a pipe organ is the link from the key moved by the finger to the valves (pallets) that admit air to the pipes. There is a widespread belief among organists that mechanical actions are desirable because the direct link from key to pallet allows the player some control over the movement of the pallet, and thus over the starting and ending transients of the pipes. These transients (the way that the sound builds up and diminishes) are critical to the recognition of different sounds.One of the characteristics of mechanical actions is 'pluck'. This is an initial resistance to the movement of the key as the pressure difference across the pallet valve is overcome. It has been likened to pushing your finger though a thin layer of ice. It is very difficult to control the finger immediately after the pluck point, and thus to control the motion of the pallet. In addition, there is some flexibility in even the most rigid action, and there is some movement of the key before the pallet opens. As soon as the pallet does start opening, the tension in the rest of the action is released, causing the pallet to spring open; this further reduces the possibility of controlling the subsequent motion of the pallet.Experiments carried out so far show clear evidence that players make rhythmic variations in order to make expressive changes when they believe that they are varying the key movement. There are also clear variations in the key movement before the pluck point depending on how players think that they are moving the key. This variation is not evident in the critical post-pluck movement during which the pallet is opening. One of the main goals of this project is to test the hypothesis that expression is achieved primarily through subtle control of inter-note timing, rather than through modification of the initial transient of the note. The motion of keys and other parts of the organ action during playing will be measured, together with recordings of the sound output. A number of professional players will be involved in the tests, which will be carried out on a wide range of organs including a specially built laboratory instrument. In large mechanical action organs there has to be a compromise between repetition rate, key force and flexibility, often leading to an uncomfortably heavy action. Some recent large organs have been provided with alternative electric actions, and there is evidence that the electric action is almost exclusively used in preference to the mechanical action. This duplication can lead to undesirable compromises in either or both actions as well as significant additional cost. Another goal of this project is to develop software capable of accurate simulation of the characteristics of an organ mechanical action, in collaboration with colleagues in Stuttgart. The aim is to provide organ manufacturers with a reliable means of predicting the touch characteristics of a planned mechanical action organ. Organ windchests follow the same essential form that they have had for several centuries, and the design of pallet valves lacks a scientific foundation. Laser-based techniques will be used to obtain a detailed analysis of the airflow around the pallet valve, in order to obtain a deeper understanding of the effects of pallet design on the touch and sound of mechanical action organs.