Chopard

Delving deeply into the Chopard L.U.C Full Strike Minute Repeater part 2 of 3 - Technology (incl. videos!)

 

With the L.U.C Full Strike, Chopard has created one of the most advanced and accomplished minute repeaters currently on the market, in both musicality, technology as well as user-friendlyness. With this article, part 2 of a series on this watch (part 1 - intro & manufacture, can be found here ), I'd like to revisit the immense technological mastery Chopard demonstrated with their first repeater:



Chopard endowed the Full Strike with ingenious and very practical solutions which make this watch such a fascinatingly complete minute repeater. And this despite the fact that the tune is downright classical for this complication:



The movement is essentially made of 533 parts, a staggering number, which Chopard some 15,000 hours of development time for the movement which bears 3 patents.



What the Chopard Cal. L.U.C 08.01-L brings to the table to outstand its (not so numerous) peers is its musicality, its elegance in operation, and the effortlessliness it affords to the owner. Please allow me to recapitulate its main outstanding features, which I shall tackle one after the other:

1. Crystal clear sound: World's first sapphire gongs, as integral part of the watch glass. Thus, sound source and amplifier form one single unit
2. Consummate cadence: Perfect musicality with defined intervals between notes
3. Indefatigable power: Reserve for 12 full sets of 32 gong strikes at 12:59 and 60-hours of separate timing autonomy. COSC certification
4. Unmitigated security: Built-in safeguards against user error breaking strike mechanism, with water resistance to boot

In the following, I would like to examine each of the points in detail.

1) Superior sound quality and volume thanks to a unique integration of a sapphire gongs and crystal:
When devising the quality of sound one goal is to find a most pleasant range in the combination between sound frequency and intensity. That is a complicated task given the intricacies of the human sense of hearing. What we 'hear' is in fact the information originating from vibrations, electronically processed by our brains, ie. our hearing 'constructs' sounds. We have to keep in mind that human hearing is essentially a sense to facilitate our survival by enabling communications amongst our peers, signalling danger, etc., but much less so deriving pleasure. That was a luxury afforded later.


With the above, a few notes should be taken:

• Human hearing is optimised for recognising human voice, e.g. between 80 to 260 Hertz, and above up to the sound babies make when crying, i.e. up to around 3,500-4,000 Hz.
  
• Acoustic information processing by our brain favours higher frequencies over lower, thus, we recognise a higher frequency as louder compared to a lower one produced at the very same intensity of a sound.
  

The sound of a minute repeater gong should be in the higher range of the human voice frequency range, but still well centered in the area of perception, which singled out a (theoretical) sweet spot between 1000 and 3000 Hertz (thus within the preferred range, but above human voice and a lower than a baby's cry) at an intensity between 50 and 70 dB:



While many repeater chime within this range, it is the volume of the sound which represents on of the most eminent Achille's heels. If measured according to the ISO 3745 norm (distance between the watch and the recording device being 1m), most wristwatch minute repeaters's sounds fall within a range between 36dB and 40dB. With the gongs attached to the movement, which itself is housed in a closed case, the changes for the repeater sound to leave the watch case are limited.

Many efforts have been made to increase the audibility of chiming watches, amongst there larger gongs, different case materials (e.g. steel or titanium), alternative mountings for the gongs (e.g., in the case, such as Blancpain), or implementing specific sound amplificating devices such as membranes (AP Royal Oak Concept Supersonnerie). While these efforts brought about tangible advances, with the AP leading the group with a loudness of about 55 dB, there is still ample room for improvement, as the present accomplishments still do not reach the sweet spot mentioned above.



Further improvement, so it turned out, needed a thorough outside-the-box thinking, and the solution developed together with the UNIVERSITY provided for a radical change of the game. The gongs are to be crafted together with the watch's crystal as a monobloc from a solid piece of sapphire:



I had the chance to see this impressive feat of engineering - and really love to show you the pictures:



As you can see, it is indeed a single piece of sapphire which was used to carve our the crystal and the gongs.



Both gongs originate from the same anchor post, and turn in opposite directions just like with a conventional minute repeater. I don't want to imagine what care is needed to polish the crystal and the handling issues that came with the direct print of the minute track of the dial section:



For fine tuning, the designers and watchmakers have essentially three degrees of freedom:

1. thickness of the crystal
2. thickness of the gongs
3. length of the gongs

In the end, Chopard hit precisely the predicted sweet spot:



The sapphire monoblock construction has one significant additional benefit that impinges heavily on the economics as well as on the consistency of production: Once the 'magic formula' for the best sound quality has been found, the result is reproducible without the need for fine-tuning of individual pieces. With the specific conception of the Full Strike, this even applies accross different case materials as the sound is directly produced and amplified with the sapphire gongs/crystal element, and not, as for conventional instances, from the gongs through the case.But please list yourself:



2) Well defined and constant cadence: ensuring perfect musicality with defined intervals between types of notes
One under-appreciated but in fact really noticable characteristic of conventional repeater mechanisms is the variation in the length of the intervals between the different types of chimes, e.g. between the hours and the quarters chimes, once less then the full sequence (12:59h) is activated. When contemplating over various repeating watches we usually don't notice as - for maximum listening pleasure - we usually set a repeater to the mentioned time.

However, the lower the number of events to strike for the higher units, the longer the silent period is before the next lower units are chimed. The reason s are twofold: (i) the repeating mechanism transmits its information to the gongs almost in real time, with no 'information buffer' in betwee, (ii) the activation lever also provides the energy for the chimes, and therefore needs full activation pass.

Thus, the entire mechanism goes through a full activation course. When, e.g. at 01:26h, the first and only hour is stroke, the full hours sequence until 12 will run, albeit silently after the first hours gong.

(A conventional minute repeater mechanism. Image source: US Patent US7773463B2)

Chopard's Cal. L.U.C 08.01-L is quite different in this regards and breaks new grounds in several ways.



First, the striking function gauges the time information traditionally from its respective calipers, however, the information is not directly transmitted to the gong system as it is read, but instead stored intermittendly on a rack system, collected and processed, and only then passed onwards by the racks' teeth to the striking hammers.



This intermediary information buffer, comparable to RAM or a fast cache drive in a computer, could be called a 'mechanical memory'. It collects hours and quarters on concentric disks. The quarters rack is aligned relative to the hours rack and locked into 4 possible positions. The degree of which the entire assenble then turns records the hours number.



The hours rack, you clearly see the 12 outer teeth which drive the hours hammer, as well as the 4 inner notches which define the quarters chimes:



The hours are read by a beak from the constantly turning hours snail and then fed on the hours rack, and from there driving the hours hammer.



The quarters are controlled by a large quarters snail who will lock the quarters rack into position. Note that this rack activates both the hours as well as the minutes hammers ('ding-dong'; you can see this nicely on the top right graph).



Finally, the minutes are gauged by a classical four-armed minutes snail which defines the angle of movement of the minutes rack.



The system is as much techncially advanced as it is aesthetically beautiful. No wonder Chopard chose to display it prominently!



As a a result, the chimes follow each other at precisely defined intervals, regardless whether a full strike (at 12:59) or a partial strike (at 01:20) is required: there is no period of silence in between:



A second critical component for a pleasant sound its the speed of its notes. The govenor is responsible for regulating the speed of the chimes, which has a most critical impact on the tonal qualities of the watch. Traditionally, two concepts have been used: the anchor governor, essentially an escapement system, and more recently the centrifugal govenor, which uses friction of tiny springs bent outwards against its housing through centrifugal forces. This is the system Chopard chose as well.



On the govenor train, a spindle holds two arms each arrying a gold weight and a friction spring. Both arms are connected by a third spring which counteracts the centrifugal forces in a defined, centripetal, way. The faster the spindle turns, the stronger the centrifugal forces are and the more the arm extends outwards towards the housing. At some speed the arms extend that much that the two friction springs reach the housing, thereby creating friction that increases with spindle speed.



This is essentially how the speed of the repeater chimes is defined through the interplay of centrifugal, centripetal and friction forces. The assembly itself is a delight to behold and a mechanical microcosm in its own right. Again, a feast for the eyes:



3) Power reserve for many strikes because you might want to listen again and again...
Just like with the considerably more complex Grand Sonnerie constructions, the chiming mechanism draws its energy not from the actuation of the sliding lever, but from its own dedicated repeater spring barrel.



The reason for this is that (i) the case construction is simpler, and the case can be made reasonably watertight, and (ii) to ease operation of the chime - something any owner will appreciate. The spring system of the repeater is actually one of the simpler details of the Full Strike movement. The crown discharges energy depending on direction, clockwise into the going train, counterclockwise into the repeater barrel. A differential is responsible for the distribution task.



The barrel is connected via an intermediate wheel to the striking mechanism.



This setup however has implications on the sequence of actions once the repeater pusher is pressed. Chopard opted to separate the energy from the information gathering activities in order to let the latter be completed securely and also in order to save mainspring energy (with conventional repeating mechanism the governor already starts before the time information is entirely read. For a conventional solution this might not have immediate and customer-critical implications, but for implementations with an own barrel, such as Chopard's, its crucial that sping energy is used carefully).

The separation is managed by a clutch mechanism similar to a horizontal clutch in classical chronographs (look at the red gear connecting mainspring barrel and repeater mechanisms as well as the green gear and its supporting lever which can be pivoted in and out of the gear train, top image below). If you look at the images from top left to bottom left in a clockwise direction, the sequence of actions becomes clear:



In a normal state the repeater barrel is in-line with its repsective mechanism (middle left), coupled with a rocker wheel (middle right). The activation lever (dark grey, 'smiling' shape) is connected with the crown pusher,and intermittendly moves the green gear out of the train as long as the crown is pushed (bottom right). At that time, the repeater reads and stores the time information off the hour, quarter, minutes on each respective snail. Afterwards (once crown pusher released again), it falls back into its original position and both the green and the red gears are in contact again (bottom left). The power train from the mainspring is intact again and thus can drive the parts of the striking mechanism and “play the time”.

4) Built-in safeguards against user error
Integrated into the entire gearworks are a number of security mechanisms, preventing damage to the complicated and costly movement, and also adding to the overall superb user experience of this watch. Standard ones found in most minute repeater are (i) an all-or-nothing trigger (watch chimes only if actuator fully pushed) amd (ii) a mechanism preventing operation of the repeater in case the owner has the crown in time-setting position.

A thrid mechanism is unique to this watch, and comes in handy since the repeater has its own source of power: Since triggering the repeater mechanism is uncoupled from infusing energy into the system, the construction engineers at Chopard needed to make sure that the watch only then strikes the time when sufficient energy for a complete sequence is stored in the repeater barrel. Furthermore, by implementing the activator as a pusher coaxially located in the crown (similar to a rattrapante), Chopard could guarantee a water resistancy of 30m.

The following video illustrates the safeguards properly:



The problem of low energy is particularly important to this watch. Chopard realised that as a combination of a power reserve indication with a blocking device, a concept that is known from other Chopard watch such as the Ferdinand Berthoud FB-1 (ok, that's not a Chopard in the narrow sense of the definition) or IWC's 5000-calibre family, where the watch is stopped although the mainspring would provide power for an additional few hours, however, at reduced precision.

In the schematics below the functionality of the mechanism is illustrated. On the top part, sufficient power is still avialable, an the pusher in the crown can activate the repeater lever. On the bottom image, the power reseve has run down to the point that the red lever blocks the green one and thus prevents the trigger.



Overall, the technical refinements makes one forget that this is the first minute repeater from Chopard. The details are impressive, and the problems identified and subsequently addressed speak volume about the thoroughness the Genevan manufacture applied on this timepiece.This is nothing like a 'me too' or a beginners project.

The Chopard L.U.C Full Strike is a mature, sonically superb and technically thoroughbred minute repeater. It stands on its own merits at the very apex of the already lofty realm of chiming watches. Well done, Chopard!

In an upcoming article I will revisit the aesthetic details of this watch - stay tuned!

Best and thanks for reading, Magnus

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