Refining tones
The same techniques used hundreds of years ago in pocket watches are still used today in the fine tuning of gongs on a wristwatch repeater.
Images from the deconstruction of a Pocket Patek Philippe Perpetual Calendar, Moonphase, Minute-repeater, full hunter pocket watch (circa 1880).
The foot of the two gongs found either side, upon which the hammers of the repeater mechanism hit in order to sound the time.
The foot, like the gongs are made from hardened and tempered steel.
Where the gongs enter the foot they are then filed, (see the flat section on the gong). This allows the gongs to resonate when the hammers hit them which is close to the foot section of the assembly. The tonality of the gongs is adjusted by the filing of the gongs as they enter the foot, and their lengths.
The gongs are driven into the rectangular ends of the foot.
In the centre of the foot is a filed out groove that allows the foot when screwed to the main-plate of the movement to be solidly fixed in place, even if there are slight variations in flatness on the underside of the foot or the surface it sits upon.
The loudness of the gongs when struck by the hammers is dictated by the strength upon which the hammers impact them, this in turn is dictated by the strength of the springs the arm the hammers, their weight and the distance the hammers travel before hitting the gongs.
Afterwards the type of case the watch sits in, design, material and the physical size of the repeater all effect the final sound.