Acoustics Flashcards
elasticity
Elasticity (internal stiffness) of the mass returns the mass back to its resting position (equilibrium)
inertia
Due to inertia, the mass moves beyond its rest position
Mass Spring Oscillator
The spring-mass oscillator consists of a spring (fixed at one end) that is attached to a mass which is resting on a special low-friction surface.
When not vibrating (at rest), the system is at equilibrium
Simple Periodic Signal
Always a sinusoidal waveform. Basically a pure tone. The waveform will repeat in equal periods.
What’s a waveform?
Change in some quantity over time. (Amplitude versus time)
What will determine the frequency of vibration?
the mass of the object &
the stiffness or elasticity of the object
Reduce Mass
Increases Frequency
Increasing Frequency
Reduces Mass
Are stiffness and frequency directly or inversely related?
Stiffness and Frequency have a direct relationship.
Are mass and frequency directly or inversely related?
Mass and Frequency have an inverse relationship.
What two properties determine the frequency of the spring-mass oscillator?
The spring-mass oscillator will vibrate at a frequency that is determined by its mass and stiffness
Period
the time it takes for one complete cycle of periodic vibration to occur
What is the x-axis of a wave form?
time
Frequency (f) and Period (T) are reciprocally related: (formula)
f (Hz) = 1/T (s) and T (s) = 1/f (Hz)
ex. If T = .01
1/.01 = 100 = F=100Hz
1000 milliseconds
1 second
50 milliseconds
.05 second
5 ms
.005 second
What determines the amplitude of vibration?
Magnitude of the force and degree of energy loss (damping)
damping
reduction of amplitude over time. (Energy Loss) The amplitude of vibration will gradually decrease because of energy losses in the system (friction)
For a lightly damped wave, amplitude decays slowly
For a heavily damped wave, amplitude decays rapidly
peak to peak amplitude
Distance between a waveforms peak and trough
peak to trough
peak amplitude
Distance between zero (equilibrium) and the waveform’s peak or trough
Propagation of a Sound Wave
Air particles, like the spring-mass oscillator, move in place around their rest position
How does a sound wave travel in air?
When air particles are disturbed, they behave like small masses connected to one another by springs. (Air, an elastic medium)
Simple sound waves in air
When a tuning fork is struck, air particles will move in place about their theoretical rest positions