2) physically- a series of disturbances of molecules
Vibration
the principle prerequisite for sound
vibration is affected by
the transmitting medium and sound source.
the medium most have mass and elasticity
elasticity
the ability of an object to resist changes in shape or volume. The more densely packed molecules the more springier.
Tuning fork Pitch
Pitch is consistent when striking a tuning fork. The only variables that change are the vibrations(amplitude) and the loudness.
- mass and elasticity dictates how the fork osscilates
Tuning fork motion
At rest the tuning fork has kinetic energy
at the centre and beyond resting the tuning fork has potential energy
Pure tones
the simplest of all sound waves
sine waves
allow us to represent a sound wave mathematically
sine waves described in 3 ways
1)phase
2)amplitude
3)frequency
Phase as a circle
used to describe the starting position of the sound or the phase relationship between 2 or more sounds. Can have the same amplitude and frequency but different phases
We use phase for
Localization
constructive interference
two sine waves add together
destructive interference
is when two sine waves cancel each other out resulting in no signal. This happens when sine waves start at opposite phases
amplitude
measures of strength and magnitude of sound wave. Measures in sound pressure. It relates to the force being applied to the source
peak to peak
maximum peak to maximum trough measurement
root mean square amplitude
the average of many points on a sine wave
Frequency
the rate at which a sine waves repeats itself over time. How much does it vibrate per second? f=1/T T=1/F
Hearing ranges for normal hearing
20 hz to 20,000 but our best hearing is 1000-4000 Hz. Hearing tests show sensitivities from 250 Hz to 8000 Hz
Speed of sound
-influenced by the temperature and how dense the medium is. The tighter the molecules are packed the faster sound can travel.
-not related to hertz
wavelength and frequency
inverse relationship. When wavelength increases freq decreases and when freq increases wavelength decreases
-as speed of sound increases the wave length increases
The longer the wavelength of a sound wave
the thicker a walls needs to be to attenuate it. When we test normal hearing at 20Hz we need to be in a room with thick walls.
stationary source
the frequency does not change so we hear the same pitch
moving source
as it approaches you the pitch gets higher then lower as it passes you (doppler affect)