Mixo horns were used by many marques, including Rover/BL/MG... right through from the 1960s.
PSA had them on BX, XM and likely good few others.
They were originally made with a metal (cast aluminium) body, but later changed to plastic.
There were actually three in the range: Basso, Midi and Alto. Rarely fitted as a trio; even P5 only got two.
They produce a splendid sound, if properly mounted (jokes will surely follow) and given some decent wiring.
Somewhere, I might still have a pair of these Windtone horns, by Lucas. They came off a 1956 S1 Hillman Minx.
Weighing a couple of kilo each, and with spring-steel mounting flanges, these beauties could actually remove pedestrians from crossings. As a pair (again Hi & Lo note) they would draw a good 30amp when the horn ring was pressed, causing the ammeter to plunge.
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