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. Airflow over one side of the reed creates an area of low pressure on that side (see the Bernoulli's principle article for details), causing the reed to flex towards the low-pressure side. The reed frame is constructed so that the flexing of the reed obstructs the airflow, which reduces or eliminates the low pressure area and allows the reed to flex back.

	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 shēng of China and the shō of Japan have survived to modern times. It has been claimed that the shēng 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:

• The Chinese hulusi and bawu
• Querhammerflügel with Aoline, circa 1810, made by Johann Kasper Schlimbach at Königshofen Bayern, using steel reeds and frames made in one part.
• The hand-aeoline, by Christian Buschmann, 1822.
• The accordion, patented in 1829 by Cyrill Demian.
• The concertina, patented in two forms (perhaps independently):
  • Sir Charles Wheatstone, 1844.
  • Carl Friedrich Uhlig, 1834.

Other examples

• The harmonica.
• The harmonium.
• The melodica.
• The bandoneón.
• The hulusi.

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

• What Is A Free Reed?
• The Classical Free Reed, Inc. website
• Reeds World Musical Instrument Gallery

References