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THE WESTMINSTER CHIME

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1. Definition and principle

The Westminster chime is a striking complication that reproduces a melody every quarter hour. Unlike conventional strikes, it does not strike simple repeated blows to indicate a numerical value. Instead, it plays a musical phrase composed of four notes of different pitches. This melodic sequence is characteristic of the Westminster chime in London, from which it takes its name. Like the Grande sonnerie and the Petite sonnerie, the Westminster chime belongs to the family of passing strikes. It is triggered automatically every quarter hour, without user intervention. However, it uses four distinct gongs instead of two, which considerably increases the complexity of the mechanism.

2. Position within the family of strikes

The Westminster chime belongs to the passing strikes, which are triggered automatically without user intervention. However, it differs clearly from conventional strikes with repeated blows. Indeed, the Grande sonnerie and the Petite sonnerie strike several identical strokes on one or two gongs. The Westminster chime, on the other hand, plays a melodic phrase on four tuned gongs. This musical nature implies a radically different Release logic. Whereas the Snail (cam) determines a number of strokes, the chime requires triggering four gongs in a precise order. Furthermore, like the Grande sonnerie, the Westminster chime signals both the quarters and the hours. At each quarter, it plays a musical phrase; on the full hour, it plays the complete melody, then strikes the hour value.

3. The musical sequence

The Westminster chime unfolds its melody across four tuned bells according to a specific scale. At each quarter hour, the sequence lengthens by a phrase of four notes. Thus, at the first quarter, only one phrase is played. At the second quarter, two successive phrases are performed. At the third quarter, three phrases follow one another. At the full hour, finally, the four complete phrases resound, followed by the striking of the hours on a low-pitched bell. This progression ensures increasing temporal information throughout the hour. Furthermore, the sequence gradually lengthens, so that each quarter is characterized by a distinct listening duration. Consequently, a listener familiar with the melody can identify the elapsed quarter by ear alone. This wealth of sound information constitutes the major advantage of the Westminster chime over other passing strikes.

4. Release and energy source

Like any passing strike, the Westminster chime requires a striking Barrel independent of the mainspring. This Barrel is generally wound by rotation of the crown in a specific direction. Energy consumption is particularly high, as the four phrases at the full hour mobilize a large number of strikes. With each strike, a hammer activates a gong, resulting in an energy expenditure proportional to the number of notes. In addition, the striking of the hours is added to the melody, prolonging the operation of the striking train. Some movements include a large-capacity barrel to compensate for this increased consumption. This architecture ensures a sufficient power reserve to power the mechanism for several days.

5. The chime program cam

The central technical element of the Westminster chime is the cam chime program cam, sometimes called the program wheel. This Cam drives the hammers in the precise order of the melody, phrase after phrase. It is fixed to the striking Train (wheel train) and completes one full cycle every hour. On its periphery, raised fingers or stops trigger each hammer at the right moment. The arrangement of these elements is precisely calculated to faithfully reproduce the melodic sequence. This system differs fundamentally from the Snail (cam) used in conventional striking mechanisms and the Minute repeater. Indeed, the Snail (cam) determines a number of strikes; the Cam imposes a triggering order among four hammers. The design of this Cam is the most delicate operation and the most specific to the Westminster chime.

6. Gongs and hammers

The sound production of the Westminster chime relies on four tuned bells according to the melody’s scale. Each bell is struck by a specific hammer, driven by the chime’s program cam. The four bells must be precisely tuned to faithfully reproduce the characteristic melody. In watches and clocks, they usually take the form of wire springs coiled around the movement. The length and diameter of each wire determine its resonance frequency, and thus its pitch. Adjusting the tuning is a delicate operation. Furthermore, the material and shape of the case directly influence the quality of the final acoustic rendering.

7. Speed regulation

Without a Regulating organ, the striking Train (wheel train) would perform the melody at an uncontrollable speed. Two technical solutions make it possible to impose a regular cadence on the hammers. The inertia flywheel slows the rotation of the Train (wheel train) through air resistance; it is silent, but not very adjustable. The regulating Pallets (lever), on the other hand, offers precise cadence adjustment thanks to its Eccentric Screw. For a Westminster chime, cadence regulation is particularly important. Indeed, each note must resonate long enough before the next one is struck, so that the rhythm of the music is respected. If the cadence is too fast, the notes overlap and the melody becomes unintelligible. The musical quality of the chime therefore depends as much on the Regulator as on the tuning of the gongs.

8. The mode selector

The Westminster chime is generally associated with a selector allowing the chime to be activated or deactivated. In its simplest version, this selector offers two positions: chime active and silent. Some more elaborate movements offer a third position that only strikes the hours. In the silent position, all striking is suspended, thus preserving the power reserve of the barrel. In the chime active position, the mechanism is triggered automatically at each quarter hour. This selector is essential for adapting the piece to the context of use. Indeed, the Westminster chime, due to its musical nature, is more recognizable than a conventional strike.

9. Association with the minute repeater

The Westminster chime can be associated with the Minute repeater on particularly complex movements. In this case, the minute repeater strikes the time on demand at the simple press of the pusher, down to the exact minute. This combination offers complete audible information: the automatic melody at each quarter and the repeater on demand. Technically, the two complications share the same four gongs and hammers, simplifying construction. Nevertheless, the Minute repeater must also incorporate a minute snail (cam) to complete the information. The combination of a program cam and a minute snail (cam) on the same movement represents a considerable challenge. These pieces are among the most complex achievements in mechanical haute horlogerie.