Algol was originally written in the summer of 2008 as a duet for my wife, cellist Emily DuFour, and I, with the accompaniment of an electronic drone. The title refers to a binary star (also known as the Demon Star) in the Perseus constellation, representing the eye of Medusa, whose gaze would turn anyone who beheld it to stone. As an eclipsing binary star, Algol contains two stars orbiting their common center of mass in such a way that each eclipses the other roughly every 3 days.
A periodic cancellation also occurs with musical tones, when two pitches are very close together. In the case of Algol, the electronic drone comprises two harmonic series separated by a syntonic comma, an interval with the ratio of 81:80. The two fundamentals create cancellations, or beats, roughly every 2.4 seconds, the second harmonics beat twice as fast, and so on up to the 20th harmonic, which beats about 8 times per second. The syntonic comma is created in the quartet by stacking justly-tuned perfect fifths from the open C of the cello up to the open E of the violins, and adding the slightly lower E tuned as the simpler 5:4 just major third from the same C.
Over the course of the piece, the quartet explores the two harmonic series and the relationship between them. The quartet begins with notes from the lower harmonic series, gradually shifts to the upper series via fifths, and introduces the seventh (cello) and eleventh (second violin) harmonics. After returning to the lower series, the cello introduces the thirteenth harmonic, and the "Medusa eye" of the syntonic comma is gradually revealed between the first violin and viola. The cello pulls the pitch up to the upper series, and the viola introduces the seventeeth harmonic, followed by the nineteenth in the first violin. Then the quartet descends to the lower register, and very gradually slides into the lower series once more. Finally, the quartet stacks fifths again, reaching the E of the upper series on top, and viola slides the width of the syntonic comma down to the E of the lower series.