Pitch and Loudness


Sound travels as a longitudinal wave where particles vibrate back and forth as they pass energy on to neighbouring particles. It is useful to visualise sound as a transverse wave when exploring the properties of sound. Two common properties are pitch and loudness. Pitch is often referred to as how high or low a note is, whilst loudness refers to well, how loud it is or how much sound energy it has.

Pitch and loudness can be analysed by looking at the amplitude and wavelength of a transverse wave that represents the sound wave. An oscilloscope can be used to observe sound wave patterns as transverse waves. An audio generator can be used to generate a sound that is played through a speaker. A microphone connected to an oscilloscope can be used to detect the sound wave, whilst the oscilloscope will display the sound wave as a transverse wave pattern on a screen.

The pitch of a sound is related to frequency, which is related to the wavelength of a wave. The higher the frequency (shorter wavelength), the higher the pitch. The loudness of a sound wave is related to the amplitude. A bigger amplitude results in a louder sound.

The diagram below illustrates the properties loudness and pitch in terms of amplitude and frequency:


Example 1:

Using the wave below, draw two more sound waves:

a) same pitch, softer

b) higher pitch, louder

 

a) is in orange, b) is in blue


Example 2:

a) A sound wave has a frequency of 1000Hz and an amplitude of 5cm. If the sound is altered to have a pitch twice as high and it is also twice as loud, how does this impact the frequency and amplitude?

Frequency = 2000Hz

Amplitude = 10cm

b) What is the wavelength of the new sound wave?

Using v=f\lambda

v=340{ m }/{ s }

f=2000Hz

\lambda =\cfrac { v }{ f }

\lambda =\cfrac { 340 }{ 2000 }

\lambda =0.17m

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