The Armin Strom Mirrored Force Resonance Fire is one of the most ingenious and interesting watches we’ve had in the office in quite a while. It’s a new take on a resonance watch – one that takes a very clever, but also technically extremely difficult, approach to getting two balances to beat in sync with each other.
We had an opportunity to take a look at a working prototype of the Mirrored Force Resonance with Claude Greisler, Armin Strom’s Director. According to Greisler, the development of the resonance system for the Mirrored Force Resonance was undertaken with research support from the École polytechnique fédérale de Lausanne (the Swiss Federal Institute of Technology Lausanne) and involved a considerable amount of trial and error.
The basic idea is simple. A resonance watch is based on the phenomenon of resonance between two oscillators that have the same natural frequency. Natural frequency just means the frequency at which any oscillator (a pendulum, a guitar string, a balance with spring) “wants” to beat (for instance, a pendulum slightly less than a meter long, swinging in normal gravity, is going to make one full oscillation once per second). If two oscillators – in the case of watches and clocks, two balances or two pendulums – are somehow able to influence each other mechanically, they’ll tend to start beating in sync with each other; this is the resonance effect. Two resonating balances should offer better stability of rate and higher precision, since the two oscillators will tend to reinforce each other.
We discussed some of the physics, and some earlier examples of (very rare) resonance watches and clocks in our introductory coverage of the Mirrored Force Resonance, and Greisler told us that early experiments led him and his research team to conclude that for the balances in modern watches, a great deal of the mechanical coupling is due to aerodynamic interaction of the balance rims. We also talked about Breguet’s assertion (in his own notes from two centuries ago on resonance watches) that aerodynamic coupling was not a factor, and Greisler speculates that for balances of different masses and running at different frequencies, either mechanical coupling or aerodynamic coupling may predominate.
As with the Breguet resonance pocket watches, and the resonance chronometers of F. P. Journe, there are basically two complete going trains in the Mirrored Force Resonance Fire. However, in the Mirrored Force, the balances are coupled to each other via an extremely elaborately shaped steel spring that’s attached to the terminal outer curve of both balance springs, transmitting force from one to the other. The back of the watch is largely taken up by the plate and mainspring barrels (one each, for each train) with the real action happening up front.
The two separate seconds hands, for convenience, can be re-set to the zero position simultaneously, without interfering with the coupled oscillation of the balances. This is done via a pusher on the case flank, which when pressed, activates a hammer and heart-piece system identical to that used for chronograph re-set. It’s a nice addition to a resonance watch and one that allows for easy synchronization with a time signal or other time standard (and a great touch insofar as the resonance system is all about rate stability). In the image below, in the seconds subdial to the right, you can see the flat face of the re-set hammer adjacent to the number 20, and the heart-piece on the central axis of the three-pronged minute hand.
The action of the spring is a ton of fun to watch – seeing it in motion gives you a direct grasp of how the shape of the spring allows the two balance springs to influence each other, while at the same time minimizing lateral force on the balance pivots (which would tend to amplify positional variations in rate) as you can see in the video below.
It’s quite a show, and one that, for sure, you’re not going to get anywhere else. Making a resonance watch is something that’s happened only a few times in the entire history of wristwatches, and it hasn’t happened that much more often in the entire history of watch and clockmaking, and while this is certainly about as niche as it gets, it’s also great to see active research going on in the field – as well as to see a watch that really illustrates in a beautiful and unmistakeable fashion, some of the fundamental physics of horology.
The Armin Strom Mirrored Force Resonance Fire is priced at $ 67,000, and is limited to just 50 pieces; expect availability around the end of November. For more, visit Armin Strom online.
Movement, caliber ARF15, 36.60mm x 7.70mm, 48-hour power reserve, running in 43 jewels at 25,200 vph. Case, 18k rose gold, 43.40mm x 13mm; 50 meters water resistance.
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