Sound in watchmaking is not a side effect: it's the primary objective of an entire family of complications, and its quality depends on a chain of mechanical choices that begins with the gong material and ends with the case geometry. From the workbench I've learned that two minute repeaters with nearly identical calibers can sound radically different, and the difference almost always lies in the case's acoustics, not the movement.
The most representative complication is the minute repetition, called by many the queen of complications. When you activate the lateral slide, a mechanism of hammers strikes one or more tuned gongs, translating the exact hours, quarters, and minutes into sound sequences. Acoustic legibility depends on three parameters: rhythm of the strikes, timbral clarity, and absence of background noise — that buzzing of the fly-back regulator that betrays imprecise adjustment. Traditional gongs are tempered steel, wrapped around the movement; cathedral gongs wrap almost twice, producing a richer sound with a longer vibration tail. Chopard in the L.U.C Full Strike worked gongs carved from sapphire crystal from a single block — tuned to C# and F — achieving a crystalline timbre impossible with metal. Patek Philippe in caliber 5750 used platinum hammers: their greater density compared to steel prolongs the sound decay, that final fade that distinguishes a well-struck gong from one that cuts off abruptly.
The case is an acoustic instrument as much as the gong. The soundbox — the resonance chamber between movement and case — amplifies or dampens everything. Audemars Piguet developed the Supersonnerie over eight years: the gongs are mounted on a 0.6 mm sapphire sound board, the caseback works as an amplifier, a silencer regulator eliminates the buzz. Ulysse Nardin with Devialet took another path: a 0.3 mm DLC titanium membrane connected to the gong via a torsion bar, which vibrates like a loudspeaker diaphragm and brings the sound to 85 dB at 100 mm distance. Gramophone principle applied to the wristwatch.
The carillon adds a third hammer compared to the classical repeater, achieving chords instead of simple intervals. The super-compressor case, born for underwater applications, finds an acoustic use in Memovox: the double sealed case creates resonance and amplifies the alarm gong. The telemetric scale on chronograph dials instead exploits the opposite principle — the difference in speed between light and sound — to measure distances: start the chronograph at the flash, stop at the thunder, read the distance in kilometers on the outer scale.
I have no direct experience with the double bellows of cuckoo watches beyond basic mechanics: for those movements I defer to those who restore them professionally.