Authentic organ sound through modern technology

For the restoration of the 18th-century mechanical organ in the village church of Woubrugge, organ builder Elbertse & Van Vulpen took a special decision: instead of using an air pump to generate wind, an ingenious solution was devised that authentically creates wind through the original bellows. In a collaboration with Festo and ERIKS, the idea was translated into a technical solution in which a servo-driven spindle guide, sensors and controls in a custom-built control box take over the work of the ‘calcants’, the organ pedals.

organ pipes

When the organist presses a key or pedal, they mechanically open a valve, allowing air to flow into the respective organ pipe. When it hits the labium (the flue pipe which produces sound through the vibration of air molecules), it eventually creates the characteristic sound of an organ. This air is called 'wind' in organ terminology and comes from one or more large bellows that were filled by so-called organ pedals or 'calcants'. They did this by stepping on a lever mounted on each of the bellows; after stepping on it (and filling the bellows), the bellows collapsed by their own weight, thereby forcing the wind towards the organ. Operating these levers was a tiring job that required a whole team to produce sufficient wind in large organs with many bellows. Even then, many organists were troubled by the fact that even with so many people it is not always easy to create the required constant wind pressure.

Electric drive

These problems were solved when technology allowed organ ‘wind’ to be generated using a ‘wind’ machine or electric blower: a combination of electrically driven pumps and fans that produce constant and relatively quiet ‘wind’. A blessing: no more people needed and always a constant ‘wind’ pressure. Marijn Slappendel is employed by Elbertse & Van Vulpen Orgelmakers and knows: 'A blessing in terms of labour and consistancy of air pressure but the new solution also brought new problems. For example, the electric wind generator produces noise that can disturb soft organ music. In addition, this way of generating wind causes 'restlessness in the sound of the organ'. This is a difficult aspect to define not easy to measure, but for organists and connoisseurs an unmissable limitation of an electric wind generator.

Elbertse & Van Vulpen together with colleague Martin de Deyne

Elbertse & Van Vulpen together with colleague Martin de Deyne

Village church Woubrugge

As an organ builder, Elbertse & Van Vulpen specialises in both building new organs and (increasingly) restoring old organs. There was a long-standing desire to eliminate the aforementioned 'restlessness' by lifting the bellows in the 'old' way instead of filling them with wind using fans. 'Obviously it was not the intention to breathe new life into the calcants either,' Marijn points out, 'But somewhere it had to be possible to find a technical solution that fills the bellows with air as if by a calcant.'

Marijn was given an idea when he read an article describing how Festo had used a servo motor in combination with a controller to automatically open the bellows of a small Italian organ at the conservatory in Regensburg. "The solution in this form was not suitable for larger organs, but it did indicate that there were possibilities," Marijn believes.

With this in mind, he contacted Festo when the organ maker was commissioned to restore the Mitterreither organ from the Dorpskerk in Woubrugge. This late 18th-century organ (1794) with over a thousand organ pipes was in dire need of restoration including an organ case full of cracks and crevices, damaged and soiled pipes and leaking wind chests. 'We wanted to give this organ back its authentic sound and came up with a construction in which a shaft with a carrier would push up the bellows from below so that it could fill with air. By lowering the shaft back down faster than the bellows themselves, the latter can sink back down completely on its own weight and thus produce wind for the organ in an authentic way.'

Van Vulpen 2

The solution

As simple as it sounds, so many questions came up during the development and realisation phase. Among them were the controls: what should they look like and how could they be best and most compactly housed? For example, the organ works with three bellows of which at least one must always be filled with wind in order to provide the organ with wind at all times. In all cases, the controls must therefore prevent all three bellows from being empty at the same time. In addition, Marijn looked for a method to easily measure how far a shaft is extended so that the position of the bellows is known at all times. Moreover, the movement pattern of the shaft - and thus the bellows - had to be completely controlled and the shaft had to be able to retract quickly enough for the bellows to collapse under their own weight.


In cooperation with Festo and ERIKS, a servo-driven spindle actuator was finally chosen for the project. This consists of the Festo ELGA-BS ball screw guide in combination with an EMMS servo motor, a CMMT servo drive and the CPX-E automation system. The sensor to measure the position of the axis was the SIEH proximity sensor. Marijn: "This sensor is attached to the bellows and moves along an element with a hole in it. Every time the sensor passes a hole it counts a step so that the controller knows exactly where the bellows are.'

In the final solution, the controller constantly checks each of the three bellows to see if they still contain air or are completely closed. In the latter case, the controller will give the shaft a start signal to run out. The movement pattern is such that the actuator first moves slowly upward until the carriage feels that it encounters the bellows. At that point, the actuator accelerates and then continues at a preset speed until it is almost at the end of the stroke. In the final stretch, it slows down again until the bellows reaches its desired end position. Then the actuator pulls back relatively quickly, allowing the bellows to drop down on its own weight and let the wind into the organ.

Control cabinet

The hardware component of the control - the CPX-E PLC - is built into a separate control cabinet designed by ERIKS. An important part in this project that was able to meet all the organ builder's requirements. Marijn: "Festo chose ERIKS Precision Motion & Control in Schoonhoven as the partner company for their knowledge, experience and flexibility to fulfill motion requests as required.

He continues: "Moreover, their knowledge and experience complemented Festo seamlessly, enabling us to jointly translate our vision for the future into a scalable solution. The cabinet is now such that in the future we can easily choose the required number of modules to suit the number of bellows a specific organ uses. So for the organ of Woubrugge we have a cabinet with the controls for three drive systems, but we can easily make five or eight of them. The software is also modular in such a way that we can reuse large parts in a subsequent organ '

Marijn quickly mastered programming the control system after two days of training from Festo. 'It is a nice idea for me as an organist and restorer, with little experience in mechanical engineering, that I know and master the controls. After all, it means that I am not dependent on others when there is a malfunction and, moreover, am able to do the programming work completely independently for the next organ.' He concludes, "In the meantime, I have already partially embarked on that path with the independent fine tuning of the design for this organ in order to get the most out of it. Everything we are now perfecting in this first organ will provide benefits for any organ that follows. Truly a solution that has music in it.

November 2023