Sound Intensity

Intensity definition Changes with distance Intensity scale - decibels

Which wave is has higher energy?

a)

b)

Sound Intensity

Higher energy = higher amplitude. In terms of sound, this means it is louder!

Higher amplitude = Higher volume

Intensity Changes with Distance

Peanut butter on bread, as you spread it out, the thickness of the peanut butter decreases, but the total amount of peanut butter does not.

Intensity Changes with Distance

The total energy of the sound wave does not change, it just spreads out.

Geometric Proof

r

R

2r = RSet up a ratio

Area of small circleArea of large circle

4r2

4R2

r2

R2=

r2

(2r)2= r2

4r2=

1

4

Main Point

Double the distanceIntensity decreases by 4 times

Inverse Square Law!

2

1

dI

Intensity = volume

Create your own analogy…

Intensity Source10,000,000,000,000 Jackhammer, gun

1,000,000,000,000 Siren, rock concert100,000,000,000  

10,000,000,000 Subway, lawn mower1,000,000,000  

100,000,000 Busy traffic10,000,000 Vacuum cleaner

1,000,000  100,000 Normal Conversation

10,000 Mosquito buzzing1,000 Whisper

100  10 Rustling leaves

1 Threshold of hearing

The human ear is AMAZINGThis is a huge range of

intensities. Also, it is an inconvenient

scale.

Intensity Source dB10,000,000,000,000 Jackhammer, gun 130

1,000,000,000,000 Siren, rock concert 120100,000,000,000   110

10,000,000,000 Subway, lawn mower 1001,000,000,000   90

100,000,000 Busy traffic 8010,000,000 Vacuum cleaner 70

1,000,000   60100,000 Normal Conversation 50

10,000 Mosquito buzzing 401,000 Whisper 30

100   2010 Rustling leaves 10

1 Threshold of hearing 0

Source dBJackhammer, gun 130Siren, rock concert 120

  110Subway, lawn mower 100

  90Busy traffic 80

Vacuum cleaner 70  60

Normal Conversation 50Mosquito buzzing 40

Whisper 30  20

Rustling leaves 10Threshold of hearing 0

Main Point

Decibel scale is used to measure sound intensity (volume)

+10 dB = 10 times the volume

+20 dB = 100 times the volume

USA Today – ipod article

Extra Credit assignment

Write a 500 word report (NO COPY PASTE!)

On hearing loss and ear bud use.

Use sources USA Today article OSHA Other?

Must cite your sources ( www.bibme.com )

The Threshold of hearing is strongly dependent on frequency

Which is the easiest frequency to hear?

~ 3300 Hz

When the sound is loud (top curve, threshold of pain) all frequencies can be heard equally well.

Frequency Response Curves