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The Undertone series, also commonly called the subharmonic series is a series of pitches with mathematical relationships to one another that are a naturally occurring sequence the can be represented by divisions or additions of equal measured parts. The series is an inversion of the overtone series, which can be described through equal divisions of string length, the undertone series can be described by equal additions of string length.
Methods to play an undertone series
Acute bowed force, as to interrupt the natural vibration of a material
This is only possible on instruments with large wound strings that are very long such as the cello and double bass. The method involves bowing the string strongly, in such a manner that causes the string to vibrate as though it had a longer overall length than is typical, shifting pitch following the undertone series as the firmness of the bowing is increased. This type of bowing should be considered a form of regulation. Typically the three notes in the series can be generated on a bowed contrabass
Reduction of air on invert reeds
Brass instruments can be 'underblown' by the reduction of air into the instrument paired with a loose embouchure. This technique is most commonly possible on instruments such as the didgeridoo, contrabass trombone and tuba. This series also follows the typical sequence of the undertone series, but may be somewhat out of tune as the pitches are lowered. On a didgeridoo of reasonable length the first 8 pitches in the undertone sequence can be generated.
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Didgeridoo, Large strings, Forced vibration instruments, savarts wheel, terpodione
