Seite - 22 - in Proceedings of the OAGM&ARW Joint Workshop - Vision, Automation and Robotics

Development of a fully Automated tuning system for organ pipes* Clemens Sulz1 and Markus Trenker2 Abstract—Many pipe organs consist of thousands of pipes, divided basically into two different types: flue pipes and reed pipes. Because of the fact, that the principle of sound generation differs, reed pipes must be tuned by hand periodically, which is a time-consuming and thus expensive process. The aim of this project was to do a feasibility study, to determine if this tuning process can be automated and to build up several prototypes for extensive testing. Thereby different actuator technologies were examined and evaluated. Finally a very cheap and compact actuator solution was developed. Appropriate software for controlling the system was programmed and the required drive electronics were developed. Tests with the prototypes have shown that the system is able to perform the tuning process in much shorter time than a human being with satisfying precision. I. INTRODUCTION The pipe organ, called the king of instruments, has fasci- nated people for hundreds of years. It is the only instrument, which is played by feet and hands simultaneously, produces a huge range of tone colors and covers the whole frequency spectrum of the human hearing. Pressing a key causes air to stream into specific pipes, whereby each pipe produces one tone with a determined tone pitch and timbre. There can be thousands of pipes in a single pipe organ, with each pipe producing a unique sound. Basically, two types of pipes are used in pipe organs: flue pipes and reed pipes (left side of Fig. 1). The sound of the flue pipes is generated in the same way as in a real flute. The air stream strikes against the lip and begins oscillating with a specific frequency. The result is a standing wave or vibrating column of air inside the pipe body. These are the facade pipes a beholder can generally see in a church and which represent the majority of the pipe stock. The pipes of the other type, reed pipes, work in a completely different way and are hidden inside the organ. Within the pipe foot there is a metal tongue, which begins to oscillate, if air flows through the pipe (right side of Fig. 1). The so-called tuning spring is used to adjust the pitch of the reed pipe, because it defines the oscillatory length of the tongue. The tone color of reed pipes allows imitating trumpets, clarinets, oboes or other wind instruments. *This work was supported by Rieger Orgelbau GmbH, Schwarzach 1Clemens Sulz, MSc wrote his Master Thesis about this topic and got his degree as MSc in Engineering at University of Applied Sciences, FH Technikum Wien, Vienna in 2016clemenssulz@yahoo.de 2DI Dr. Markus Trenker supervised this Master Thesis and lectures at the Institute for Advanced Engineering at University of Applied Sciences, FH Technikum Wien, 1200 Vienna markus.trenker@technikum-wien.at Fig. 1. Left picture: both types of organ pipes (reed pipe and flue pipe); Right picture: inner parts of reed pipe (tuning spring is moved to tune the pipe) II. PROBLEM DESCRIPTION The pitch of flue pipes depends directly on the velocity of sound, which in turn depends on air temperature. So the pitch is lowered, if the temperature is decreased and vice versa. Because of the fact, that in reed pipes the tongue oscillates and not the air, the pitch of these pipes stays almost constant. A temperature change of just 1-2°C causes an audible detuning of the organ. Not least because of the lower number of reed pipes and their easier tunability, the pitch of the reeds is tuned to the pitch of the flue pipes. To tune the pipes the tuning spring has to be moved up or down for each single pipe. Generally this tuning process requires two people (one sitting at the keyboard pressing down the keys and one tuning the pipes) and takes between a few hours and several days for big organs. Because of the associated expense, the reed pipes often are not in tune and are not used by the organist. The aim of this project was to develop a system, which can tune reed pipes automatically. Refined, the aim was to determine whether a technical system is basically able to tune the reed pipes with satisfying precision in an acceptable amount of time. Furthermore, because of the number of reed pipes (usually a few hundred) the solution should be very cost-effective. Especially the little reed pipes were a challenging object of research due to the high sensibility of the tuning spring. Thereby movements of less than a micrometre are required to adjust the pitch exactly enough. The final stage of the project was to build a few prototypes to test and demonstrate the abilities of the system. 22