MEASURING SOUND LEVELSAnd Determining If Its Harmful To Our Hearing

Physics 101

What is a sound wave?

1. A sound wave is a longitudinal wave.a. Note: Molecules in a medium for a longitudinal wave move parallel to

the direction of the wave.2. In a sound wave, it has compressions and rarefactions, which are areas of

high pressure and low pressure when it is propagating.

Shaded= Compressions Rarefactions= Spaces in between

3. Sounds waves are calculated in decibels (dB)a. Decibels are a commonly used unit for logarithmic comparisons of

power or intensity.

How do you calculate Decibels (dB)?

Key Formula: β(I) = 0 dB +10 log10 (I/Io)

Where: I stands for sound intensity in W/m2

Io stands for the sound intensity level (10-12 W/m2) at 0 dBβ stands for sound intensity level in dB

Problem! At a nightclub with your friends, it is determined that the sound intensity measures 2.50 W/m2. According to 85 dB is considered harmful, would the sound intensity at the nightclub be harmful?

Solution!

Using the sound intensity given in W/m2, it is possible to determine the dB using the formula:

β(I) = 0 dB +10 log10 (I/Io)β= 0 dB + 10 log ( 2.5 W / m2 / 10-12 W / m2 )

β= 113.98 dB

If the nightclub is playing music at 113.98 dB, then it is considered harmful to your hearing!