In the Yearbook EIGHT/2 (2011), Jaeger-LeCoultre wrote:
A small hammer strikes the gong-ring suspended inside the watch case-back 80 times a second. With each impact, the sound is propagated inside the case at over 18,000 km per hour; making the latter resonate like a music instrument.”
Of course, it is the Memovox they were writing about.
Jaeger-LeCoultre choose to visualise sound as a wave. A great way to transfer sound in a printed page.
Shown above is the reference E 877 a.k.a. the Snowdrop with one of the pages from the Yearbook 2011 as a backdrop.
The description do not fit perfectly for the Snowdrop since in the older models of the Memovox there is no gong-ring suspended inside the watch case-back.
Instead there is a pin on the inside of the case back on which the hammer strikes making the case itself the “gong”. This is the reason for Memovox Calibre 916 and earlier Calibres have a sharper more cricket like sound than the later Memovox Calibres 914, 918 and 956.
The sound of the modern Calibres are more similar to a school bell, but much nicer!
This technical difference, which is closer to the Minute Repeater, you get a better sound but you lose some of the vibrations transferred to the wrist, which can be a handy feature in a noisy environment or while diving when the sound can be hard to hear clearly.