lo 1 (corrected)
TRANSCRIPT
Measuring Sound
Introduction
Everyone is familiar with sound, we have ears to detect it after all!
But what is sound? Sound is a mechanical wave which is
created by a vibrating object. But how do we measure it?
Instrument
Sound Level Meter
Common Sound Intensity Levels
http://windchimes.co.za/photos/sound_intensity_levels.gif
Unit of measuring sound
Unit: Decibel (dB) Reference sound intensity level of 0
dB is an intensity of: I0=10-12 W/m2 (the quietest sound a human ear can detect)
All other sound intensities are measured in reference to this threshold hearing intensity.
Sound Intensity Level
When comparing a specific sound intensity to the reference intensity (Io), it’s known as sound intensity level.
Equation:
Where B= “bel” I= specific sound intensity I0 reference intensity (I0=10-12 W/m2 )
Question #1 :
A) You are at the Mariners soccer game where you are told the sound intensity is 10^-20
W/m2. What is the sound intensity level?
b) Is this level lower or higher than the threshold of human hearing?
*Hint*: What are you trying to find?*
Solution #1:
A) Since you know sound intensity level corresponds to “B”, you would use the equation below and simply plug in the values you know.
I= specific sound intensity= 10^-20 W/m2
I0= reference intensity= 10^-12 W/m2
B= what you are trying to find. Calculate! Answer: -80 dB b) Since the answer is negative it’s indicating that the sound is below the threshold level for human hearing (because the threhold for human hearing is 0 dB).
Question #2
You are at the Thunderbird Stadium watching a basketball game, where you find out the sound intensity level is 100 dB. What is the sound intensity in W/m2?
Solution #2
You will need to rearrange the sound intensity level equation, to find sound intensity (I) inside the Thunderbird stadium.
Solution continued...
Plug in known values:
Divide by 10:
Solution continued…
Since it’s log base 10, everything can be written in base 10:
Isolate for I0=
Final Answer: 10-22 W/m2
*To check*: Just plug back into original equation
Thank You!