Exam 2 Flashcards
What is sound?
- Vibrations that travel through the air or another medium
What is the source of sound?
- The back and forth motion of a mechanical object around its equilibrium positon
What is the back-and-forth motion called?
- oscillation or vibration
What is the Doppler Effect?
- A change in volume sound!
1) Static sound source: stationary frequency
2) Moving sound source: Sound properties change; depending on where you are, you can have a low frequency or higher frequency
What is oscillation?
- Back and forth movement—>DUE TO GRAVITY
- Pendulum
- Lunar Tide
What is Vibration?
- Back and forth movement—> DUE TO ELASTICITY
-Mass and Spring System - Tuning fork
What is Pendulum Motion?
- Oscillates back and forth between two states ( Swings)
- Helps us understand how motion works
Why does the pendulum swing back and forth?
-Because of the interaction between inertia and the restoring force of gravity
- When the pendulum moves, energy distribution changes potential–>Kinetic Energy
Why does the pendulum eventually stop?
- Potential Energy—> Kinetic Energy
- Because of the force of friction
What is a sine function?
- Oscillation made by a pendulum
- Called a sinusoidal motion( moving back and forth at regular intervals)
What is periodic motion?
- Motion that repeats itself in regular intervals until it is stopped by friction
What is simple harmonic motion?
- Acceleration! The more you pull it one way, the more it will wan tot stay in the other direction
What is waveform?
- A function that represents changes of any physical quantity as a function of time
What is a Cycle?
- a cycle is one full repetition of periodic motion
What is a waveform?
- Number of cycles per second
- Unit for frequency is hertz( Hz)
Frequency( f) = Number of Cycles/ Time
What is period?
Period(T) is time required for the completion of one cycle of a periodic motion
What is amplitude?
- describes the size of pressure variations ( Distance from equilibrium to the top/bottom of the crest)
- Measured on the Y axis
- Related to loudness
How do sound waves move?
They move through a medium( Like air) via particle-to-particle interaction
What is the particle-to-particle interaction?
1) Particles in space resting
2) Particles create a change of events when they hit each other
3) Creates vibration and transfers energy
4) Energy overtime gets smaller and smaller
What is compression?
- Area where air molecules are bundled up (high pressure)
What are Rarefactions?
- Area where air molecules are more spread apart ( Low pressure )
What is a phase?
- Location of a cycle in wavelength
- Measured in degrees
- Max positive magnitude is 90 degrees
- Max negative magnitude is 270 degrees
What if 2 waves are the same? Different?
1)the same—>Amplifies it!
2) Different—> cancel each other out!
What is a phase relationship?
- The difference between phases of two periodic waveforms as they cycle through time
- Involves in phase/out phase
What is in phase?
What is out phase?
What does magnitude mean?
- The amount or quantity of something
- Magnitude of a waveform at at any given moment of time is called the instantaneous magnitude
What is the average magnitude for simple harmonic motion?
Zero!
What is a resonance curve?
- Shows the amplitude of vibration as a function of frequency of the driving force
What are the characteristics of a sound wave?
- rarefaction
- Condensation/compression
- Wavelength
- Period
- Frequency
-Crest
-Trough?
-Amplitude
-Cycle
-Phase
true/false: Sound needs a medium to travel
True!
What are the different types of mediums?
Vacuum, Gas,Liquid,Solid
What do speed and sound depend on?
Density and Stiffness( of the medium)
What affects the density and stiffness of the medium?
Temperature
True/False: The GREATER the STIFFNESS and the LOWER the DENSITY, the faster the speed of sound
TRUE
What does greater stiffness equal?
- Greater stiffness=returns to resting position quickly
What happens as the temperature increases?
The density of air decreases
What happens to the speed of sound when temperatures are higher?
Sound is faster
What is friction?
- A transfer of energy
What is damped friction?
- Overtime/displacement
-Gets lower across time: energy decipates really fast
What is a Standing wave?
- A wave that has its reflection come back: Increase of areas enhance, areas cancel out
- Combination of two waves moving in opposite directions, each having the same amplitude and frequency
-Vibrations being produced - Inhancemnets= louder/more displacement
What is a node?
- Middle point if wave
What is an antinode?
- Greasted amplitude of wave
What creates resonance?
- Standing Wave
How does resonance relate to the ear canal?
- Having its own frequency( Natural frequency)
- WHen driving frequency matches natural frequency
Thus creating an enhancement of sounds
What systems only have one resonance frequency?
- Pendulum
- Mass and spring
True/False, Most vibrating systems have more than one resonance
True!
What is the resonance curve?
- Shows the amplitude of vibrations as a function of the frequency of the driving force
- Enhancement in magnitude
- moving/displacing of a specific frequency
- Vibration force matches natural frequency
- Being further away=not as much enhancement
What are complex vibrations?
- Combination of two or more sinusoidal
- Objects commonly vibrate with s complex vibration
What is simple sinusoidal vibration?
- Rarely present in nature
- Pure tones—> 1 frequency component
What is the Fourier Theorem?
- Any complex vibration is the sum of various sinusoidal motions of varying amplitude, frequency, and phase
- Complex vibration that you separate/break down
- Simple waves with frequency
What is periodic vibration?
- Complex waves
- Shows rhythm and pattern
What is Aperiodic vibration?
- Complex waves
- No rhythm is shown
-lots of frequency
-no pattern - Motion is random( This is called noise)
What is a fundamental period?
- The duration of one cycle
- Pitch we perceive
: Number of harmonics that can be divided by
What is waveform synthesis?
- Combination of several individual sinusoidal motions into a complex waveform
What does being harmonically related mean?
- When components of a complex wave form are whole number multiples of the f0
- Components are called harmonics
What are harmonics?
A mode of vibration is the specific vibration pattern of a vibrating system associated with each resonance frequency of the system
First mode of vibration?
First harmonic!
Second mode of vibration?
- Second harmonic!
- Equal to two times the fundamental
Third mode of vibration?
- Third harmonic!
- Equal tp three times the fundamental
Where can you find the most displacement?
- In the antinode
Where can you find the point of destruction?
Node
- Waves cancel out
What is a common factor?
- An integer that can be divided into a number with no remainder
What is the greatest common factor?
- the largest of the common factors
- Number that can be divided evenly, no fractions
What is an octave?
The doubling of frequency
What is a missing fundamental?
When the fundamental frequency is not equal to the frequency of its lowest component
What is a complex periodic wave?
When frequency components are harmonically related( all components are whole number multiples of f0)
What is waveform analysis?
Breaking down complex waveforms and determining its components
Shows us the frequency domain of the vibration
Spectral Components are displayed as verticle lines
What is a spectrum?
- A graph used to show the amplitude of the components
- X-axis: Frequency ( Hz)
- Y axis: Amplitude
What is a complex aperiodic vibration?
- No pattern to waveform
- many different components that do not appear as separate lines on the spectrum
what is a line spectrum?
- Consisting of one or more separate verticle lines
What is a continuous spectrum?
When a spectrum has many spectral components
Where would sound travel the fastest?
In a Solid
What does stiffness mean?
In acoustics, it is elasticity; the ability of vibrating objects to return to its original position
What are the two most common types of modulus of elasticity?
- The bulk module of elasticity for fluids and gases
- Young’s modulus of elasticity for solids
What does sound pressure indicate?
- Indicates how compressed or rarefied the particles are
What does sound intensity indicate?
- Indicates how much sound power is transferred from the sound source to the surrounding area
Infrasound?
- Sounds of very low frequency that cannot be hear( typically below 20Hz)
Sound( audible sound)
- Sounds of frequencies that can be heard( typically in 20Hz to 20,000 Hz range for humans)
Ultrasound?
Sounds of very high frequencies that cannot be heard( Typically above 20kHz)
What is impulse noise?
- Single brief event caused by a sudden change in a sound source
EXAMPLE: Delay and decay—> a gunshot can cause hearing loss if you are too close to the sound
What is impulse noise?
- Single brief event caused by a sudden change in a sound source
EXAMPLE: Delay and decay—> a gunshot can cause hearing loss if you are too close to the sound
What is continuous noise?
- Continues for a period of time and is made up of a large number of random acoustic events connected together
- Can be divided into two categories:
1) Nonstationary Noise
2) Stationary Noise
What is a power spectrum density function?
The average amount of sound power across all of the frequencies of the sound
Absorption:
- feature that sound engineers/musicians think about
- Absorbed because of the characteristics of the wall, ceiling, floor, etc.
- Volume can be different because some sound is absorbed and sound can be reflected back
Absorption Example:
- Think about an ocean wave;
ocean waves can be observed by the dirt
reflected back means it won’t have the same energy as before
Does the absorption coefficient vary?
- Varies from 0 to 1
- Depends on the frequency of the sound wave ( high? or low? between?)
- Depends on the properties of the boundary( wall?)
What absorbs more sound energy?
- Soft material!
Ex: carpet, drapes, upholstered furniture)
Absorption coefficient:
- usually increases with sound frequency
- Sometimes absorption is higher for low frequency sounds
Absorption coefficient:
- usually increases with sound frequency
- Sometimes absorption is higher for low frequency sounds
What is the reflection coefficient?
- reflected property of a boundary
- Varies from 0-1
Depends on:
1) frequency of the arriving sound wave
2)properties of the boundary medium
What happens to all of the energy arriving at a boundary?
- It is either absorbed or reflected so that the total sound intensity must equal the sum of the two
Sound absorption and reflection are important for the construction of:
- Concert halls
- Classrooms
- Hospitals
- Libraries
What happens during refraction?
As sound enters a new medium:
1) frequency remains the same BUT
2) the wavelength and direction change because the speed of sound changes
What is sound refraction?
- The bending of sound waves ( change in direction) when the sound enters a medium with a different density or stiffness
Sound refraction in the air?
- Since the speed of sound in warmer air is greater than the speed of sound in cooler air, sound waves bend towards the cooler air
- Sound arrives from different angles/directions( reflected/refracted)*
What is Reverberation?
- When you hear a sound persist after the sound is gone( sound is continuing to play)
- Large space+highly reflective walls= a lot of reverberation
- Small Spaces+absorbing material= very little reverberation
What is reverberation time?
- The time it takes for a brief sound to decrease in sound pressure by 60dB
- Depends on the volume size of the room and the absorption provided by the boundaries of the room
What is diffraction?
Sound waves bending around objects and through openings in boundaries
Sound bending through energy
What is an acoustic shadow?
- An area in which sound waves do not enter or in which the sound intensity is decreased ( or does not exist)
What are beats?
- Changes in waves caused when two sine waves that are very close in frequency interfere with one another
- They occur because of the periodically changing phase relationship between two pure tones
What is the Doppler effect?
- When the sound source moves toward the listener, the wavelength of sound in the medium is affected and it gets shorter
What does the absolute difference tell us?
- Tells us how much greater one measurement is than another. This involves subtraction
EXAMPLE: My child has grown 4” in the past month
What does the relative difference tell us?
Tells us how many times greater one measurement is than another
EXAMPLE: Mississippi is twice as large as west Virginia
Treu/False: An octave is a doubling in frequency
true! 200Hz? next octave will be 400Hz
Why do we use a logarithmic scale?
it compresses a large range of power magnitudes into a much smaller range
- easier range/reasonable
Why is the decibel scale used?
- Correlates with human perception
- Compresses a large range of values to a much smaller/manageable range
-Supports decimal notation by using the base 10 logarithm
Clicker Question: What is the sound pressure level of a balloon popped at your ear?
155 dB SPL
