The reeds of an early 20th century
button accordion, with closeup.
A free reed aerophone
is a musical instrument
is produced as air flows past a vibrating reed
frame. Air pressure is typically generated by breath
or with a bellows
The following illustrations depict the type of reed typical of
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
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
||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
||The elasticity of the reed forces it back through the
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
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
- The concertina, patented in two forms
In the related woodwind
, 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.