Aliquot stringing is the use of extra unstruck strings in the piano for the purpose of enriching the tone.
As currently implemented, the Blüthner aliquot stringing system uses a fourth aliquot string in each note of the top three octaves. This string is raised slightly with respect to the other three strings, so that it is not struck by the hammer. Whenever the hammer strikes the three non-aliquot strings, the aliquot string vibrates sympathetically, adding to the richness of the tone. This same string resonance effect occurs, on a more limited scale, when other notes on the piano are played that are harmonically related to the pitch of an aliquot string.
The Blüthner piano is widely considered to be among the top rank of pianos being built today. Other premier piano makers also enrich the tone of the piano through sympathetic vibration, but they use a different method known as duplex scaling. For discussion, see piano. Confusingly, the portions of the strings used in duplex scaling are sometimes called the "aliquot strings," and the contact points used in duplex scaling are called aliquots.
Aliquot stringing and the duplex scale are not equivalent. An aliquot string vibrates out of phase with the main strings of its note. This configuration dissipates the tonal energy through the soundboard more slowly, which in principle could create a more sustained singing tone. Opinions differ on whether this actually happens in Blüthner pianos. The noted piano authority Larry Fine says of Blüthner pianos "the sustain is good, but at a low level of volume, giving the tone a refined, delicate character." On the other hand, the Blüthner company claims that the effect of aliquot stringing is apparent only in loud playing.
In the construction of other string instruments sometimes aliquot parts of the scale length are used to enhance the timbre of musical instruments. Examples are the Japanese koto and non-Western traditional instruments with sympathetic strings. The aliquot position (1/7th of the scale length) of the bridge on a violin is also important for the sound of the instrument.
The word "aliquot" comes ultimately from the Latin word meaning "some, several". In mathematics "aliquot" means "an exact part or divisor", reflecting the fact that the length of an aliquot string forms an exact division of the length of longer strings with which it vibrates sympathetically.