The minute repeater is the most challenging acoustic complication to create in watchmaking, and the reason is straightforward: it's not enough that it works, it must sound good. The mechanism is activated via a lateral slider — or in some cases a pusher — that winds a spring and triggers a sequence of hammers striking harmonic gongs: first the hour chimes, then the quarter chimes, and finally the remaining minute chimes. A watch showing 3:47 therefore produces three strikes for the hours, three doubles for the quarters, and two singles for the minutes remaining until the next quarter. Eight beats in total, produced in just a few seconds.
I have held minute repeaters from many different manufacturers, and the difference in sound between a good example and a mediocre one is immediately apparent. What matters is the harmony between the two gongs, the duration of the note, the depth of the tone, and the absence of background noise during activation. Vacheron Constantin introduced the so-called silent strike regulator in 2007 precisely to isolate the mechanical noise of the internal rack wheel from the pure chimes — a problem anyone who has activated a minute repeater in a silent room knows well.
The choice of case material directly impacts sound quality. Titanium, thanks to its low density and high rigidity, does not absorb sound waves the way gold and platinum do. Some manufacturers — I think of Urban Jürgensen's Cosmic Rain, but not only them — hollow out the case to create a resonance chamber. It's a detail you don't see but you certainly hear.
The minute repeater is one of three pillars of the grand complication alongside the chronograph and the perpetual calendar. It's not a written rule, but it is the recognized benchmark of the industry. It requires extremely small parts, extremely tight tolerances, and a number of hours of final regulation that no other complication demands to the same extent. For this reason it remains the exclusive province of very few manufactures capable of completing the entire process in-house.