There are four basic types of soundwaves generated by oscillators, and each of these waves have a different sound quality.
Let’s examine each wave type in detail:
Sine Wave
What does it look like?
A smooth flowing signal that moves between extremes.
What does it sound like?
A very smooth and rounded sound.
Extra
A sine wave is the purest type of sound wave, all the energy is focused at a fundamental frequency
Square Wave
What does it look like?
A signal that switches abruptly between extremes in an alternating fashion.
What does it sound like?
A brighter more assertive sound, which is a little harsh (looks square in shape).
Extra
The square wave is made up of a series of sine tones. BUT, it contains only odd harmonics (3,5,7,9… etc.). These harmonics decrease in loudness as they get further from the fundamental (they are inversely proportional).
Triangle Wave
What does it look like?
An angular signal that moves in straight lines between extremes (looks triangular when viewed).
What does it sound like?
We hear the triangle wave as a more rounded sound (closer in character to the sine wave than the square wave).
Extra
The triangle wave is made up of many individual sine waves. Like the square wave, the triangle wave contains only odd harmonics, but these decrease in amplitude much faster than in the square wave (they are inversely proportional to the square of the harmonic frequency).
Sawtooth Wave
What does it look like?
A jagged wave that ramps up slowly, and then suddenly drops back (looks like the cutting edge of a saw).
What does it sound like?
Extra
The sawtooth wave is made up of individual sine tones and contains all harmonics of the fundamental frequency. The amplitude of these harmonics decreases at exactly the same rate as that of the square wave.
Frequency and Amplitude
Soundwaves are produced when an object vibrates back and forth, setting off a pattern of vibrations in the air (see also – Where do Sounds Come From). These vibrations can be measured and viewed by using an oscilloscope. We can then observe how changes in the properties of the soundwave affect what we hear.
Pitch = Frequency
The faster an object vibrates back and forth, the higher its frequency of vibration. Frequency is a measure of the number of back and forth motions (cycles) that take place in each second. The higher the frequency of vibration, the higher the pitch that we hear.
Watch how the frequency of the waves increases as the pitch rises:
Watch how the frequency of the waves increases as the pitch falls:
Fact
When we play low frequency sounds on a loudspeaker, we can sometimes see the cone of the loudspeaker moving. This is because the loudspeaker is creating a low frequency sound and is vibrating at a low speed. When the loudspeaker is reproducing a high frequency sound, it moves so quickly that we are no longer able to see the vibrations.
Loudness = Amplitude
The further an object vibrates back and forth, the greater the amplitude. The greater the amplitude of a soundwave, the louder it seems to be.
Fact
The quietest sounds move the cone of a loudspeaker only a little bit, while the loudest sounds move the cone of a loudspeaker a lot.
Watch how the amplitude of the waves increases as the sound fades in:
Watch how the amplitude of the waves decreases as the sound fades out:
TAKE CARE: LOUD SOUNDS CAN DAMAGE YOUR HEARING PERMANENTLY!!!
Activity
Next time there is a thunderstorm, listen out for the sound of the thunder and count the number of seconds between the flash of lightening and the roll of thunder. Can you work out how far away the storm is from you?
Extra
The Speed of Sound
Sometimes people think that high and low sounds travel at different speeds. This is WRONG. All sounds travel at a fixed speed (343m/s in air (768mph)). It is important to note that the speed of sound is different from the frequency, the rate at which the sound wave oscillates (moves back and forth). A high frequency sound and a low frequency sound will travel at the same speed. BUT, the high frequency sound will contain far more wave cycles than the low frequency sound. Light travels a lot faster than sound (299,792,458 m/s (670,616,629 mph)). The speed of light is so fast that our human eyes simply see it as an instant. The difference between the speed of sound and the speed of light, is the reason why you can often see things that are a long way away before you can hear them. Lightening and thunder are a great example of this.
Lightening and Thunder = Sound and Light
When lightening and thunder happen at the same time, then you know that the storm is above you. When there is a delay between the flash of the lightening and the roll of thunder reaching you, you know that the storm is further away from you. Sound travels 343 metres every second. So, if there is a one second delay between the lightning flash and thunder roll, we know that the storm is 343 metres away from us (1s x 343m = 343m/s). If there is a two second delay, we know that the storm is 686 metres away from us (2s x 343m = 686m/s) and if there is a ten second delay, we know that the storm is 3430 metres away from us (10s x 343m = 3430m/s).
