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Loses intensitydue to

Sound travelling through a material

Attenuation

• Sound beam comparable

to a torch beam

•Reduction differs for small

and large reflectors

• Energy losses due to

material

•Made up of absorption

and scatter 

Beam Spread

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Scatter 

• The bigger the grainsize the worse the

problem

• The higher the

frequency of theprobe the worse the

problem

M!z " M!z

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#eam Spread

The sound beam

spread out and the

intensity decreases

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#eam spread and $ttenuation combined

%&'(S!

)&'

(S!

*o attenuation+only beam

spread, -d# reduction

%&'

(S!

.-'

(S!

 $ttenuation and beamspread, -d#/ reduction

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Sound 0ntensity

1omparing the intensity of 2 signals

1

0

1

0

 P 

 P 

 I 

 I =

Electrical power proportional to the

square of the voltage produced

2

1

2

0

1

0

)(

)(

V 

V 

 P 

 P =

2

1

2

0

1

0

)(

)(

V 

V 

 I 

 I =!ence

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Sound 0ntensity

2

1

2

0

1

0

)()(

V V 

 I  I  = 3ill lead to large ratios

21

2

0

10..1

0

10.. )(

)(

V 

V  Log 

 I 

 I  Log    =Therefore

dB

V 

V  Log 

 I 

 I  Log 

1

0

10..

1

0

10..  20=

 BELS 

V 

V  Log 

 I 

 I  Log 

1

0

10..

1

0

10..  2=

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1

0

10..20

 H 

 H  Log dB   =

2 signals at 2&' and )&' (S!,

3hat is the difference between them in d#4s5

2..2020

4020

1010..  Log  Log dB   ==

3010.020×=dB

dBdB  6=

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1

0

10..20

 H 

 H  Log dB   =

2 signals at &' and &&' (S!,

3hat is the difference between them in d#4s5

10..2010

10020

1010..  Log  Log dB   ==

120×=dB

dBdB  20=

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 $mplitude ratios in decibels

• 2 6 7 -d#

• ) 6 7 2d#

• " 6 7 )d#• & 6 7 2&d#

• && 6 7 )&d#