A free reed aerophone
is a musical instrument
is produced as air flows past a vibrating reed
in a frame. Air pressure is typically generated by breath
or with a bellows
The following illustrations depict the type of reed typical of harmonicas
, pitch pipes
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.
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:
- 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):
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.