Some people are mystified by the term "Free Reed Instrument" but all it really means is what it says on the label!
A free reed is simply one that is free to vibrate within a frame when deflected, normally by air.
The reed consists of a "springy" metal blade with one end fixed to a metal plate, above a vent of the same profile. Ideally the blade should prevent air flow except at its very tip.
In slow motion, air passing the tip draws the blade into the vent until it interrupts the airflow and then its elasticity causes it to return. It is this sequence repeated at speed and the repeated "chopping" of the air-flow that sets up audible waves.
The pitch or frequency is determined by the size and rigidity of the the blade and is not governed by the amount of air.
With some exceptions the reeds are mounted in pairs to either side of a single plate, opposite a flapper valve that prevents air from leaking in the wrong direction.
This arrangement means that each reed sounds either on the suck or
blow, the plate would be described as unisonic if both give the same note, bisonic if they differ .
Generally speaking reeds do not sound alone, but together with another set or sets tuned to a slightly different pitch. The resulting differences in frequency give rise to interference waves and produce a tremolo effect, thus giving a "happier" sound to the music.
FREE REEDS (An explanation, not an offer!)
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5 March 2008
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