François Boucher, Renaud et Armide, 1734. Paris, Musée du Louvre. Via Wikimedia Commons (public domain).
Paris, 15 February 1686, Théâtre du Palais-Royal. The Académie royale de musique gives Lully’s Armide for the first time, before the Grand Dauphin, with sets by Jean Bérain. In the second act the knight Renaud arrives at an enchanted place, sings of the beauty of the landscape and falls asleep on the grass, beside a river: so says the stage direction in the libretto. For that sleep Lully asks the violins to put on their mutes, and the piece has gone down in history under a title that is an orchestral instruction, Les sourdines. It is one of the first documented cases of muted strings written into a score, and the transcriptions for harpsichord and for lute that circulated still carry that name.
Since then the wording has not changed. On the stand you find con sordino, or the abbreviation con sord., and further on senza sordino. The violinist takes a small comb and slips it onto the bridge, the thin maple bridge on which the strings rest. It can be ebony, metal, rubber, even leather; the most recent orchestral models stay threaded on the strings behind the bridge and slide forward in an instant when the part calls for it. It does not touch the strings where they are played, does not close the body, does not plug the f-holes. It merely weighs.
And the weight is enough. The strings alone make very little noise: it is the bridge that picks up their vibration and passes it to the top plate, and in the passage it acts as a filter. Jim Woodhouse, who for years studied violin acoustics at Cambridge, has described in good instruments a broad hill of response between 2,000 and 4,000 hertz, which acousticians call the bridge hill. It falls exactly in the region where the human ear is most sensitive. Adding mass to the bridge shifts its resonances downward and flattens that hill. The sound becomes darker and less brilliant, because the mute damps above all the high vibrations of the bridge. The muted violin, before it even plays more softly, loses the band of frequencies the ear hears best.
In the seventeenth and eighteenth centuries this distinction was not at all obvious. Deirdre Loughridge, in a study published in 2016 in Early Music, reconstructed the debate: musicians did not agree on whether the accessory really changed the timbre of the instrument or merely lowered its volume, and the very concept of modifying timbre was not yet familiar. One detail demolishes the cliché of the piece of wood: for most of that period, Loughridge writes, musicians preferred metal mutes to wooden ones. And the meaning was not always what we take for granted today. We say ethereal, otherworldly; they more often heard in it water murmuring, a plaintive character, an effect that the scene suggested case by case. The river beside which Renaud sleeps, in this sense, is already written into the timbre.
Physics has vindicated those who heard a colour and not a volume, but the numbers say the two go together. A study published in 2025 in Acta Acustica measured the effect of different mutes, from the lightest to the heaviest, and confirmed the mechanism: the added mass shifts the resonances of the bridge and reshuffles the balance between low and high. The light orchestral mutes, the ones that slide on the strings, take away about 23 per cent of the sound’s intensity. The classic ebony mute takes away 28.5. Heavy practice mutes, the metal ones designed for playing in a flat without disturbing the neighbours, take away between 70 and 81 per cent.