Klarinet Archive - Posting 000465.txt from 2001/06

From: MVinquist@-----.com
Subj: [kl] Re: open tube v. closed tube
Date: Sat, 16 Jun 2001 12:57:18 -0400

Further to Dee's comments on flute -

The flute is of course open at the bottom. In fact, in his book, Boehm says
that his goal was to make tone hoes are so large that the flute is
effectively only as long as the highest open hole.

The top of the head joint is closed, but the embouchure hole is open, making
the flute open at both ends. When you blow, you make an airstream from your
lips to the far upper edge of the embouchure hole, splitting into two
streams, one going down into the hole and the other going above the edge.

The part of the air stream going down increases the pressure inside the tube.
The part of the air stream going up decreases the pressure inside the tube
(in the same way that an airplane wing produces lift), making it lower than
the outside air pressure.

One or the other of these effects initially predominates. If the pressure
inside the tube is higher, the downward airstream it gets pushed out, above
the edge of the embouchure hole. If the airstream is above the edge, higher
air pressure there pushes the stream back down below the edge, which
increases the pressure inside, which pushes the airstream above the edge, and
so forth. This vibration of the airstream is the equivalent of the clarinet
reed and is what makes the sound on a flute.

This is the principal mechanism, although there are other physical and
acoustical phenomena that have an effect, such as the reflection of vibration
back from the bottom end of the tube and the fact that modern flutes have a
decrease in tube diameter in a parabolic curve at the upper end of the head
joint.

In any event, the embouchure hole is acoustically "open" so that the flute
acts as an open pipe.

Best regards.

Ken Shaw

---------------------------------------------------------------------
Unsubscribe from Klarinet, e-mail: klarinet-unsubscribe@-----.org
Subscribe to the Digest: klarinet-digest-subscribe@-----.org
Additional commands: klarinet-help@-----.org
Other problems: klarinet-owner@-----.org