4 • Measurement of Sound Energy

Define Sound Intensity (I)

The rate at which energy passes a unit area perpendicular to the direction in which the sound is travelling

Define the SI Unit for Sound Intensity

Wm-2

Define The Bel (B)

The human ear responds to relative increases in sound intensity rather than actual increases

Label This Formula

Number of Bels

I2 - second intensity

I1 - first intensity

Define Sound Intensity Level / The Decibel Scale

The sound intensity of a source of sound expressed relative to the threshold of hearing

What happens when the Sound Level doubles?

The Sound Intensity Level increases by 3dB

Define the SI Unit for Intensity Level

Decibels

dB

Define Threshold of Hearing

The minimum sound intensity value that the human ear can detect

Define the value of Threshold of Hearing

1 ×10 -12 Wm-2

Name an instrument that measures sound levels

Sound Level Meter

Demonstrate how a sound level meter works

1. Microphone works on the same principal as the ear

2. Diaphragm vibrates in a similar way to ear drum

3. Scale adapted to ears frequency range

Name a use of the Sound Level Meter

Noise Reduction