result. In the generation of its tones, a reed organ is similar to an accordion or concertina, but not in its installation, as an accordion is held in both hands whereas a reed organ is usually positioned on the floor in a wooden casing (which might make it mistakable for a piano at the very first glimpse). Reed organs are operated either with pressure or with suction bellows. Pressure bellows permit a wider range to modify the volume, depending on whether the pedaling of the bellows is faster or slower. In North America and the United Kingdom, a reed organ with pressure bellows is referred to as a harmonium, whereas in continental Europe, any reed organ is called a harmonium regardless of whether it has pressure or suction bellows. As reed organs with pressure bellows were more difficult to produce and therefore more expensive, North American and British reed organs and melodeons generally use suction bellows and operate on vacuum. Reed organ frequencies depend on the blowing pressure; the fundamental frequency decreases with medium pressure compared to low pressure, but it increases again at high pressures by several hertz for the bass notes measured. American reed organ measurements showed a sinusoidal oscillation with sharp pressure transitions when the reed bends above and below its frame. The fundamental itself is nearly the mechanical resonance frequency of the reed. The overtones of the instrument are harmonics of the fundamental, rather than inharmonic, although a weak inharmonic overtone (6.27f) was reported too. The fundamental frequency comes from a transverse mode, whereas weaker higher transverse and torsional modes were measured too. Any torsional modes are excited because of a slight asymmetry in the reed's construction. During attack, it was shown that the reed produces most strongly the fundamental, along with a second transverse or torsional mode, which are transient. Radiation patterns and coupling effects between the sound box and the reeds on the timbre appear not to have been studied to date. The unusual reed-vibration physics have a direct effect on harmonium playing, as the control of its dynamics in playing is restricted and subtle. The free reed of the harmonium is riveted from a metal frame and is subjected to airflow, which is pumped from the bellows through the reservoir, pushing the reed and bringing it to self-exciting oscillation and to sound production in the direction of airflow. This particular aerodynamics is nonlinear