Vibrations into Sounds
Sound is caused when objects vibrate. An action causes an object to vibrate, and these vibrations, in turn, set off waves and patterns of vibrations in the air.
As the sides of the object move back and forth they push and pull the nearby air molecules.
The push and pull of surrounding air molecules creates a wave in the air, rippling out from the vibrating object.
We can see the same process happening in the bath or the sink.
If we place our hand in to the water and move it back and forth (like the vibrations of the object) we create waves within the water. This is exactly the same physical process that happens in the creation of sound, only the ripples are formed within the air.
Our ears can detect soundwave vibrations as they cause the ear drum (and other parts of the ear) to move. The brain then converts this motion in the ear drum, into the sound that we hear.
Sound vibrations in the air can also be felt by the rest of our body, when an aeroplane or train passes we can sometime feel the vibrations in our chest. The same is true of drums in a loud rock concert.
All objects vibrate in different ways, this is the reason that different objects have different sound qualities.
Different Objects = Different Vibrations = Different Sounds
All objects vibrate in their own individual way. Some objects are just not very good vibrators at all (for example a rock), while others are especially good (for example a tight string).
The way that an object vibrates when struck directly relates to the sound that it produces.
Listen to the sound and compare it with the picture of the glass above. What characteristics of the glass give rise to the sound that we hear?
Smaller and more flexible objects can produce more high frequency waves (they vibrate back and forwards at a faster rate), while larger and inflexible objects tend to produce low frequency waves (they vibrate back and forwards at a slower rate).
How would you describe this sound? How might the shape and size of the object relate to its sound?
Pitched vs. Non-Pitched Sounds
When a string is plucked, the vibration energy is focussed up and down the string and so the sound wave pattern created in the air is also more controlled and focussed.
When a cymbal is hit, the vibration energy travels erratically through the object, leading to an erratic and noisy wave pattern in the surrounding air
Describing How Objects Sound
With experience, we can learn to predict the type of sounds that an object will make. This can be really useful in helping us to decide which sounding objects to pick and use within a composition.
There are many words that we can use to describe sounds and many of these words can also be used to describe things that we see. Below are a list of possible descriptive words, can you match these words to sounds that you have heard?
- High pitched
- Low pitched
Which words from the list would you use to describe the sounds in this clip? How many sounds are there? What might be causing the sound?
Ping Your Ruler
Take a ruler and hold it firmly down onto the desk with the palm of your hand, but making sure that one end is hanging over the edge of the desk.
Then ‘ping it’ (push down and let go the end hanging over the edge of the desk) and you should hear a sound. This sound is created by the back and forth vibrations of the ruler.
- How does the sound that you hear change as you move the ruler?
- What happens to the sound when more or less of it hangs over the edge?
- What if you move the ruler dynamically (while it is wobbling)?