Zimbelstern

All self-respecting Central European baroque organs had a zimbelstern (or cymbal star). It’s a special sound effect in many smaller as well as larger organs, and was used both as an effect to accentuate a triumphant climax or as an celestial accompaniment to e.g. a christmas hymn.

Instrument status: First version finished, but needs reconstruction

DESIGN

There are many, many ways to make a zimbelstern, but basically it’s a (usually pneumatic) motor driving one or more mallets, beaters or pendulums to strike a number of bells or chimes. The effect is an unpitched (or at least of undetermined pitch) cacophony or celestial sound (depending on the zimbelstern).

Original design sketch

We decided on using 7 tuned bells in combination with some small brass bells. Originally we intended to make a dual zimbelstern, with two pneumatic motors driving two concentric rotating shafts, one for the tuned bells and the other for the small brass bells.

The outer shaft for the (lower) tuned bells were a piece of 12 mm brass tube, mounted in two pillow block ball bearings and connected to the upper pneumatic motor.

 

Building the dual pneumatic motors

The inner shaft for the (upper) brass bells were a 5 mm brass rod, fixed with a ball bearing at the bottom of the motor box. The top anchor point was a flanged ball bearing placed into the top of the 12 mm outer shaft/tube. Our hope was that this setup didn’t transfer too much rotation from one motor to the other.

In reality, we did indeed observe some transfer of rotation, but not enough to make the other bells sound off.

 

Building the motor blades

The motors were very simple constructions. We milled grooves into a central core mounted to the rotating shaft, and placed pieces of thin, light wood in the grooves, constantly taking care that the motor fan were well-balanced.

The two motor fans were in separate compartments, divided by a sheet of acrylic glass. At the back of the motor box, there were two air inlets, one for each motor compartment.

The plan is to use the two spare, auxillary output valves in the PipeDream61 organ. Here is a test of the lower tuned bells, though with the shaft turned by hand, not by air:

Is seen in the video, we actually built the double-bladed motor, but had to realize that our cheap ball-bearings simply weren’t good enough. Specifically the 12 mm pillow block ball bearings had too much friction for the relatively low air flow from the organ to move the motor fan.

The finished (but not working) zimbelstern

What now? Well, the lower motor/inner shaft/upper bells works perfectly, because the 5 mm ball bearings have much less friction. So what we’ll do is re-calibrate our ambitions and make it into a single zimbelstern instead of a dual-action monster. That means replacing the two motor fans with a single large fan, mounted on a 5 mm shaft in low-friction ball bearings. That also means that activating the zimbelstern will make both the tuned bells and the small brass bells sound off. That’s OK. Very baroque.

STATUS

[June 2018]
Our focus is presently on the PipeMare projects, but if we get the time, it would be relatively simple to remake the zimbelstern. We have the materials, and we know how to do it. One thing is for certain: It has to be finished by christmas!


Next: Read about the PipeMare triple-organ project

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