Chapter 8.3

Chapter 8.3 Loudness and Decibel

Learning goals

5.3 Loudness and the decidbel scale

• • Name the unit of sound intensity.
  
• • Explain which two factors influence the amount of decibel measured.
  
• • Explain how the deicbel scale works and be able to do simple calcualtions with it.
  
• • Name three ways of reducing the risk of loud noises.  

Four wave properties

1. Amplitude

2. Frequency 

3. Speed

Amplitude: how hard or intensive a sound is

3) Which of these two waves has a higher amplitude? Explain.

Image 1

Image 2

4) Listen to these two sounds. Of which does the sound wave have a higher amplitude?

Sound A

Sound B

• Make sure to be in presentation mode.
• Click the icon to play the sound.
  
• Make sure to keep the volume of your computer the same!

4) Listen to these two sounds. Of which does the sound wave have a higher amplitude?

Sound A

Sound B

• Make sure to be in presentation mode.
• Click the icon to play the sound.
  
• Make sure to keep the volume of your computer the same!

The soundwaves of sound B have a higher amplitude, because the sound is louder.

The decibel-scale

The decibel (abbreviated dB) is the unit used to measure the intensity (loudness) of a sound.

• The unit of Loudness: decibel (dB)
• If you double the number of the sound source, the loudness increases by 3 decibles 

• you measure the sound intensity with a decibel meter

If you double the number of the sound source, the loudness increases by 3 decibles 

dB(A)

You will often see noise levels given in dBA instead of dB. Measurements in dBA, or dB(A) are decibel scale readings that have been adjusted in to the varying sensitivity of the human ear. 

Threshhold of hearing

Is when you start hearing the sound. 

Threshhold hearing for adults is 0 dB ( very soft sound)

Assignment 

In a football stadium the loudness is measured at the centre of the pitch. If 1000 people cheer the loudness is 80 dB. What will the loudness be if 100.000 people cheer?

– 1000 mensen: 80 dB

– 2000 mensen: 80 + 3 = 83 dB;

– 4000 mensen: 83 + 3 = 86 dB;

– 8000 mensen: 86 + 3 = 89 dB;

– 16 000 mensen: 89 + 3 = 92 dB;

– 32 000 mensen: 92 + 3 = 95 dB;

– 64 000 mensen: 95 + 3 = 98 dB;

– 128 000 mensen: 98 + 3 = 101 dB.

Loudness(sound intensity) of 100 000 is about 100 dB