6-3 Initiating Vibrations On A String

1) Plucking the String

One way to initiate sound on a string is to pluck the string with your finger (known as pizzicato to string players).

Here is a violin player plucking the strings to produce sound: Pizzicato Polka

When the violin is plucked in the midpoint in produces the following initial shape:

To determine the frequencies present in the resulting vibrations determine which harmonics, when superimposed, will add together to form the initial shape.

How can you determine which harmonic frequencies will be present?

Look at the harmonic waves in the following diagram. To see which frequencies will be present see where the node of the initial shape matches the harmonic's node.

In this diagram we can see that the initial shape of the string plucked and the first harmonic has the same node. Therefore, this frequency will be present when plucking the string. The rest of the odd harmonics have maximum nodes in the same position as the initial shape. So we can assume that these harmonics will also be present when the original string is plucked.

What happens to the relative intensity when a string is plucked?

The relative intensity decreases as the harmonics increase. This is shown in the diagram below (click to enlarge):

Also, the closer you pluck to the end of the string, the richer the harmonic content of the resulting vibrations.

2. Striking the String

When a string is struck there is tremendous force and vigor. (For example, when a key is pressed on the piano, it causes a hammer to strike the string inside the piano.)

Here is the inside of a piano with the hammer hitting the strings as it is being played:Hammers & Strings Inside A Piano

To have the maximum amount of energy transferred, the hammer should break contact with the string before the wave has been reflected back. This ensures that the hammer does not damper any of the sound waves that are being reflected.

What happens to the relative intensity when a string is struck?

The intensity of the harmonics diminish slower than if the string had been plucked.

    Proportion: 1/n

3. Bowing the String

When bowing a string there is continuous energy being placed on the string. This allows the performer to have more control over the sound.

Here is a cello player bowing the strings to produce sound: The Swan

As the musician bows the string, the string is alternating sticking to the bow and sliding against it. During the sticking portion, the string moves with the bow. When it slides, the string moves in the opposite direction of the bow.

This diagram shows that the harmonics present depends on the string's shape.

Continue: #REDIRECT 6-4 Initiating Vibrations In An Air Column

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