Lecture 1- Nature of Sounds, Signals, & Sine Waves Flashcards
Define sound and its characteristics (What controls the characteristics of sound?)
- Frequency (pitch)
- Amplitude (volume)
- Phase
- Sound in air (the medium)
- Speed (wavelength)
What are signals and systems?
Signal: something that needs a source; something that conveys information
- a signal has meaning and contains what we are trying to perceive or listen to
System: any process that produces an output signal in response to an input signal
E.g. Speech goes into the microphone and then an electrical signal comes from the microphone
E.g. The middle ear is a system
What is a sound? More specifically, where does a sound come from and how does it transmit?
- Sound requires a source
- A source of sound must be able to vibrate
- To vibrate, a source must have two properties (mass (m) and Elasticity (E))
- To transmit sound, a medium must be capable of being set into vibration
Define Newton’s First and Third Laws
First Law of Motion- Inertia
- The property addressed is called inertia
- All bodies remain at rest or in a state of uniform motion unless another force acts in opposition
- Magnitude of inertia is directly proportional to the mass
- Thus, mass is a measure of inertia
Third Law of Motion: Reaction forces
- With every force there must be an equal and opposite reaction force
- Vibration: elasticity is the reaction force to inertia
- Vibration continues without reapplication of external force (vibration sustained by opposing forces)
Describe the vibratory motion of a spring
- System engages in simple, harmonic, or sinusoidal motion
- Spring can be compressed
- Elasticity (restoring force) opposes deformation force
- Hooke’s Law: magnitude of restoring force (F) is directly proportional to magnitude of displacement (x)
- As spring is compressed, greater force required for additional compression
Define the vibratory motion of a pendulum
- Restoring force is gravity, not elasticity
- Potential energy is greatest at the maximum points of displacement
- Kinetic energy is greatest at equilibrium
Define compression and rarefraction
Compression: density increases (peak)
Rarefraction: density decreases (trough)
Describe the movement of sound through a medium
- alternate regions of compression and rarefaction move through the medium
- Medium is not displaced over a great distance
- Sound is characterized by propagation of density changes through elastic medium
- Air particles move over a very small distance
- Two events that occur at some rate:
- Rate (frequency) of vibratory movement
- Rate (speed) of wave propagation
- Sound is oscillation of air pressure (pressure wave)
- Air molecules do NOT travel through space to carry sound
What are the two types of wave motion? Define them.
Longitudinal wave
- Spring-mass system
- Direction of particle movement is parallel to wave movement
- Elements of spring move back and forth
- Wave moves in same plane
- Not compressions and rarefactions
Transverse Wave
- Stretched rope or string
- Vibration of medium is 90 degrees re: direction of wave propagation
- Elements of rope move up and down
- Wave moves at right angles
- Note peaks and valleys
Describe the speed of sound. What is the speed of sound governed by?
- speed of wave propagation is governed by properties of the medium
- speed increases as temperature increases
What are the properties of the medium?
- Mass
- Density: the mass per unit volume
- Density varies with height above sea level - Elasticity
- Property that enables recovery from distortion of shape or volume
- The tendency of air volume is to return to its former volume after compression (in other words, density is restored)
What are some measurements of amplitude?
- Instantaneous measures are always linear
- Average measures can be linear or logarithmic
- Peak amplitude
- Peak to peak amplitude
- Root mean square
What makes a vibrating system stop?
- Motion ceases due to frictional resistance
- Kinetic energy transformed to thermal energy
- Result is damping, or damped vibration
