On Dynamic Behaviour of Wind Systems for Pipe Organs

Doktorsavhandling, 2002

The wind system sets the operational conditions for the organ pipes. The pipe foot pressure is by nature very unsteady and is a result of the wind system response to the activities of the organ player. Changing flows create propagating pressure waves. These are spread in the wind system, interact with each other and are reflected at the system boundaries. This investigation is in many aspects related to the newly reconstructed baroque organ in Örgryte Nya Kyrka, Göteborg, Sweden. The dynamic behaviour of the wind system was studied by means of measurements and numerical simulations. The full scale laboratory test rig was used to illustrate component characteristics as well as system performance. Among the many results achieved, the very strong influence of the wind trunk length on the pallet box pressure is to be pointed out. Unlike pallet box pressures, transient pressures in the tone channel can easily be affected by the organ player by means of sensitive fingering at key attack and release. Computer simulations as well as test rig measurements confirm this behaviour and illustrate the impacts of several design parameters. By means of section valves, different wind system layouts were created and tested in Örgryte. The flexible system in Örgryte offers a certain amount of freedom to tune the wind system to suit the type of music played. Furthermore, the influence of the type of wind supply (blower/bellows) was studied. The new arrangement with a speed controlled blower performed very well. All tests and simulations point out the dominant role of the wind trunks on the dynamic behaviour of the wind system and the importance of the system layout. The numerical simulations proved to be most informative and principally correct. The wind system research - creating the background of this report - is done within the research programme of Göteborg Organ Art Center (GOArt) covering a much wider field of the organ art.