Sound power and the decibel

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Sound power and the decibel
Introduction to Acoustics

• University of Salford
• Acoustics Audio and Video Group

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Learning Outcomes

• Define sound power and sound power level
• Give examples of sound power levels
• Convert from sound power to sound power level and
  back again

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Sound power

• Sound sources create sound energy
• The sound energy per second produced by the
  source is the sound power
• Sound power has units of watts (joules/second)

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Some sound powers
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Sound power level

• Sound power level is denoted by LP or LW
• W0 is the reference power, 10-12 watts
• dB means decibel

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Sound power vs sound power level
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Ratio of sound powers in dB

• The ratio of any two sound powers can be
  expressed in decibels
• Relative level in decibels is given by
• W1 and W2 are the two sound powers

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Some sound power ratios
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From dB to ratio of sound powers

• The ratio of the two sound powers

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Sound power level to sound power

• Sound power W is given by

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Conclusions

• Sound power is a property (strength) of a sound
  source
• Sound power level is the decibel form of sound
  power
• decibels are always a ratio (they must have a
  reference value)