In MMD 000418 Johan Liljencrants wrote:

> The frequency is quite a lot higher than the natural one for the reed
> (as determined only from its mass and elasticity) because it does not
> oscillate in a sinusoidal fashion like a free reed.  It rather goes
> in a sequence of half-periods -- when trying to enter the 'negative'
> half-period it bangs into the shallot and immediately bounces back to
> start another 'positive' half-period.

The _real_ art of reed voicing is to prevent the tongue "banging"
against the shallot.  It should roll down the shallot face,
progressively closing the opening, until it is fully closed, then roll
back.  If the curve is not right the tongue may bang against the
shallot, resulting a metallic clanging, spoiling the intended tone.

The technical term for this phenomenon is that the tongue has a "flat".
The test for flats is to hold the tongue/shallot assembly up to the
light and, observing the light passing through the space between tongue
and shallot, slowly pull down the free end of the tongue with a finger
nail.  The point at which the gap disappears should steadily move along
the shallot.  If it jumps any distance suddenly, or opens up again
further back, there is a "flat", and the curve has to be redone.

The curve of a clarinet or oboe is simple in that the point of light
closure moves at a steady pace from one end to the other, given a
steady movement of the free end.

On the other hand, a trumpet tongue displays a more complex movement.
The point of light closure should appear to move slowly at first,
increasing speed at the centre and decreasing again towards the free
end (or "tip").  This is termed an increased "tip curve" and helps to
promote the characteristic trumpet tone, aided by its tapered
resonator.

John Page, UK