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THE PETITE SONNERIE

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1. Definition and principle

Petite sonnerie is a striking complication belonging to the family of passing strikes. Unlike the Grande sonnerie, it does not repeat the value of the hours at each quarter. Instead, it strikes the hours only when each full hour passes. For the three intermediate quarters, it merely indicates the number of quarters elapsed. This economy of striking is precisely the main advantage of this complication. Indeed, Petite sonnerie consumes less energy than a Grande sonnerie. It thus represents a balanced compromise between sound information and energy Autonomy.

2. Position within the family of strikes

Petite sonnerie belongs to passing strikes, whose Release is entirely Automatic. In this respect, it is fundamentally different from the Minute repeater, which strikes only on demand. Moreover, within passing strikes, two levels coexist. On one hand, the grande sonnerie repeats the hours at every quarter hour. On the other hand, the petite sonnerie only strikes them on the full hour. This distinction directly affects the mechanism’s energy consumption. Indeed, the grande sonnerie strikes the hours four times per hour, compared to just once for the petite sonnerie. The latter therefore offers significantly greater autonomy, while still retaining useful time information.

3. The striking sequence

The petite sonnerie organizes its sound signal according to two distinct phases. First, at the passing of each full hour, it strikes the hour value on the low-pitched gong. Then, at the first, second, and third quarters, it strikes only the number of quarters on the high-pitched gong. For example, at 10:00, the watch strikes ten low-pitched chimes. At 10:15, it strikes one high-pitched chime; at 10:30, two high-pitched chimes; at 10:45, three high-pitched chimes. Thus, the listener clearly identifies the full hour, then follows the progression of the quarters. However, to decode the time accurately, they must remember the last low-pitched chime heard.

4. Release and power source

Unlike the Minute repeater, the Petite sonnerie triggers automatically at every quarter hour. This automatic Release implies that energy must be stored in advance in the striking Barrel. This is why the Crown is generally wound in both directions of rotation. In one direction, it winds the mainspring of the Movement; in the other, that of the striking Barrel. Moreover, when the Minute repeater is combined with the Petite sonnerie, the Release of the repeater is carried out by a Pusher. This Pusher then replaces the slide (or latch) specific to the repeater alone. Indeed, since the striking Barrel is pre-wound, no additional Winding is required upon activation.

5. Reading the time: snail cams and racks

To determine the number of strikes to be struck, the mechanism relies on stepped cams called snails. Each snail (the hour snail and the quarter snail) is connected to a component of the motion work and features several steps. Opposite each snail, a rack positions its feeler on a step. The height of this step determines how many teeth engage, and therefore how many strikes will be struck. For the petite sonnerie, two snails suffice: the hour snail and the quarter snail. Thus, at each quarter hour, the mechanism automatically reads the position of these two cams. This system of cams and toothed sectors forms the heart of the counting mechanism in many mechanical striking watches.

6. Gongs, hammers and sound

The sound relies on two gongstuned to different pitches. The low tone signals the hours; the high tone, the quarters. These two tones are struck by hammers actuated by the striking train. In modern constructions, the tones often take the form of metal wires wound around the Movement. This architecture maximizes the vibrating Length and, consequently, the quality of the sound produced. Furthermore, the Material and shape of the Case significantly influence the final acoustic rendering. Thus, fine-tuning the sound of a Petite sonnerie requires care comparable to that of a Minute repeater.

7. Speed regulation

Without regulation, the striking train would unwind in a fraction of a second. Two technical solutions make it possible to impose a regular pace on the strikes.

The flywheel (or regulator flywheel) is a rotating component whose wings, subjected to air resistance, brake the rotation of the striking Train (wheel train) and impose a regular cadence. The wings of the flywheel move according to the energy received from the striking Barrel under the effect of centrifugal force. At the start of the strike, when the Barrel’s energy is greatest, the flywheel’s wings move away from the flywheel’s Axis, further braking the striking Train (wheel train). Conversely, when the Barrel’s energy weakens, the flywheel’s wings move closer to the center and accelerate the rotation of the striking Train (wheel train). Proper Regulation / Adjustment of the flywheel ensures a constant rhythm of the struck blows throughout the striking process.

The Pallets (lever)-Regulator is composed of a Pallets (lever) with two pallets alternately engaging a wheel. This system produces a slight characteristic noise and is more sensitive to the wearing position.

8. The Switch: slide and Pusher

For obvious comfort reasons — particularly at night — any striking mechanism must be able to be deactivated. Two solutions are commonly used for this purpose. The sliding latch is a sliding lever, usually positioned on the Case middle or on the Case back. By sliding it, the user locks the release lever, thus preventing the striking train from being released.

The Pusher performs the same function in a smaller space, often integrated into the case middle next to the crown. In some versions, a small Hand or a window on the Dial visually indicates the position of the Switch — chime mode or silent mode —, thus avoiding any uncertainty.

9. Association with the minute repeater

In some cases, a petite sonnerie watch is associated with a Minute repeater. This association allows the user to obtain the exact time to the minute, on demand. Indeed, the Passing strike automatically informs at every quarter hour. The Minute repeater, for its part, completes this information at the simple press of the Pusher or its slide. However, their coexistence on the same Movement imposes specific technical constraints. Notably, the two mechanisms often share the same gongs and hammers, thus simplifying the construction. These pieces, combining Passing strike and repeater, are among the most ambitious achievements in mechanical high watchmaking.