1. Sound and Hearing it

2. Sound waves are… What type of waves are sound waves? Mechanical waves
What does that mean?
They have to move through a medium.
More specifically, they are longitudinal waves
They are made of compressions and rarefactions and cause the medium to vibrate in the same direction as the wave

3. Speed of sound Sound speed varies, depending on medium
Travel fastest in solids, slowest in gases
Speed of sound = 342 m/s (in air)
THAT’S 765 mph!
In water speed of sound = 1798 m/s
Travels fastest in the most dense media
Why??
Because the particles are closest together so they easily bump into each other passing the energy along

4. Intensity is measured in decibels (db)
Intensity: the rate at which a wave’s energy flows through an area
Sound intensity depends on:
Amplitude – density of compressions
A greater amplitude (closer compression) means more energy is passing through the wave
Distance from source - closer to source the more intense the vibrations
This is why you can “feel” the bass when close to a speaker
Intensity is measured in decibels (db)

6. Many people consider intensity and loudness to be the same thing, however….
Loudness is Subjective!
This means it depends on the person who is hearing it
It varies from person to person
What is loud and obnoxious music to your parents may be just the perfect listening loudness for you

7. Frequency
Frequency of a wave in general means how many waves appear in a given amount of time
Frequency of a sound wave depends on how fast the source of the sound is vibrating
The faster the source causes vibrations, the higher the frequency

8. Pitch How high or low a sound seems to be
Depends on frequency (& therefore on wavelength)
…high frequency (low l) sounds are high pitched
…low frequency (high l) sounds are low pitched.
Human ears hear sounds between 20 and 20,000 Hz.
We hear best between 440 & 7000 Hz

9. The Doppler Effect (of sound waves)
Doppler Effect: a change in sound frequency (pitch) caused by the motion of the sound source, the listener, or both.
Why do we observe this?
Note: The sound is still being produced at the same frequency at its source, the air compressions change frequency by movement of the source.