6-4 Initiating Vibrations In An Air Column

1) Edge Tones

Edge tones occur when the air pressure inside the column is more than the air pressure outside the column. The actual sound is initiated when air is blown into the column. The energy of the jet stream is transferred into sound as it hits the edges of the column. Furthermore, air will stream out of any slits or holes in the columns, which changes the frequencies and pitch of the notes (which is why the pitch changes on a clarinet by using your fingers to cover the holes/ leakage of air).

What is the relationship between frequency and velocity?

As the velocity of the jet stream increases, the frequency also increases. Occasionally, this increase consists of a frequency "jump" to a higher level frequency.

What is frequency proportional to?

    Frequency is proportional to 1/n
    Frequency is proportional to v
    Frequency is proportional to v/n

2. Reed Tones

A reed is a thin strip of metal, cane, or plastic that is placed on an instrument to control the sound waves. A metal reed is used in harmonicas and pipe organs and is noted for oscillating at only one frequency. Cane and plastic reeds are softer and more flexible. For this discussion we will be focusing on cane reeds (such as those found on clarinets, saxophones, oboes, bassoons, and English horns). A cane reed is carefully shaped and clamped to a well designed mouthpiece which gives it enough space to vibrate fully.

What affects the reed?

The difference between the pressure of the reed in the musician's mouth and the pressure inside the mouthpiece.

How does a reed work?

When air is blown into a mouthpiece the reed begins to close, causing the air moving into the mouthpiece to decrease. The air that does get through the hole is moving rapidly. However, it is the initial air flow which starts the oscillations. In this instance, the reed and mouthpiece act like a closed end cylindrical tube.

Continue: #REDIRECT 6-5 Initiating Vibrations On A Membrane

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