Definitions

free reeds

Free reed aerophone

A free reed aerophone is a musical instrument where sound is produced as air flows past a vibrating reed in a frame. Air pressure is typically generated by breath or with a bellows.

Operation

The following illustrations depict the type of reed typical of harmonicas, pitch pipes, accordions and reed organs as it goes through a cycle of vibration. One side of the reed frame is omitted from the images for clarity; in actuality, the frame surrounds the reed on four sides and cuts the space in an upper and under reed area. As soon in the area under the reed a negative pressure is created, the reed will start to move. See at Bernoulli's principle for entire explanation.

A reed is fixed by one end in a close-fitting frame. The loose end has a slight rising bend.
Air depression is applied under the reed; the reed prevents air flow, except for a small, high-velocity flow at the tip.
The reed is sucked through the opening, allowing the air to pass.
The elasticity of the reed forces it back through the frame.
Each time the reed passes through the frame, it interrupts air flow. These rapid, periodic interruptions of the air flow create the audible vibrations perceived by the listener.

In a free-reed instrument, it is the physical characteristics of the reed itself, such as mass, length, cross-sectional area, and stiffness, which primarily determine the pitch (frequency) of the musical note produced. Of secondary importance to the pitch are the physical dimensions of the chamber in which the reed is fitted, and of the air flow.

History

Various free reed instruments appear to have been invented since antiquity, but were unknown in the West until comparatively recently. Among the ancient instruments, the khene of Laos, the shêng of China and the shō of Japan have survived to modern times. It has been claimed that the shêng was brought to Saint Petersburg, Russia near the end of the 18th century, inspiring a series of inventions in the early 19th century that were the foundation of the development of the modern free reeds; Cyrill Demian's (see below) patent of 1829 however states that the reeds in his instrument "were known for more than 200 years as Regale, Zungen, Schnarrwerk, in organs."

Some notable free reed instruments:

Other examples

Related instruments

In the related woodwind instruments, a vibrating reed is used to set a column of air in vibration within the instrument. In such instruments, the pitch is primarily determined by the effective length of that column of air. Although the Chinese sheng, Japanese sho and Laotian khene have pipes, the pipes do not determine the pitch. In these instruments, the pipes serve as resonating chambers.

External links

References

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