Their vocal tract can be shaped to resonate at frequencies associated with the tone being produced. Most gadgets overblow at two times the speed of the fundamental frequency the octave, but as the clarinet acts as a closed pipe system, the reed cannot vibrate at twice its common speed because it would be creating a 'puff' of air at the time the old 'puff' is returning as a rarefaction. This means it can't be bolstered and so would die away. The chalumeau sign up plays basics, whereas the clarion sign up, aided by the sign in key, plays third harmonics a perfect 12th higher than the fundamentals. The first a couple of notes of the altissimo range, aided by the sign up key and venting with the first left hand hole, play fifth harmonics a major 17th, a perfect twelfth plus an enormous sixth, above the fundamentals. The clarinet is therefore said to overblow at the twelfth and, when moving to the altissimo register, seventeenth. By assessment, nearly all other woodwind devices overblow at the octave or just like the ocarina and tonette do not overblow at all. This overblowing behavior explains the clarinet's great range and sophisticated fingering system. The fifth and seventh harmonics also are accessible, sounding a further sixth and fourth a flat, faded fifth higher respectively; these are the notes of the altissimo register. This is also why the interior "waist" size is so important to these harmonic frequencies. Clarinet bodies have been crafted from various components adding wood, plastic, hard rubber, metal, resin, and ivory.