sound test
sound
a longitudinal wave caused by a vibration (that travels at around 343 m/s)
loudness
the amplitude
decibels
a dimensionless unit that describes the ratio of two intensities of sound
resonance
the phenomenon that occurs when the frequency of a force applied to a system matches the natural frequency of vibration of a system
Doppler effect
an observed change in freq when there is relative motion between the source of sound and a listener
Intensity
the rate of energy flow through a given area
Harmonics
positive integer multiple of the fundamental frequency of a periodic wave;
Harmonic frequencies
the frequencies of these standing waves are integer multiples of the fundamental frequency F1
Harmonic wavelengths
the wavelengths of these standing waves are integer multiples of the fundamental wavelength
harmonic series
infinite series of positive fractions and numbers
beats
sound waves of slightly different freq produce beats; differences between frequencies=number of beats per second
how does sound begin
a vibrating object pushes the air molecules against each other which squeezes the molecules closer together (compression). When the object moves in the opposite direction the molecules spread apart (rarefaction). the object continues to vibrate and creates a series of compression and rarefractions.
what freq can humans hear?
20Hz-20,000Hz
Infrasonic waves
less than 20Hz
Ultrasonic waves
more than 20,000Hz
Frequency
waves per second
How are pitch and frequency related?
The higher the frequency, the higher the pitch
factors that play into pitch
background noise and loudness
decibel equation
dB=10log ( I/1*10E-12)
What does the speed of sound depend on?
the medium
list mediums that sound waves travel through from slowest to fastest
gases, liquids, then solids
why does sound travel fastest through solids?
the molecules are closest together so they can vibrate into each other much faster
the formula for the distance sound travels
V= distance/time
Intensity Formula
i = P/ 4 (pie) r (squared)
What kind of wave is sound emitted as?
Spherical wave
I
Intesity
What is intensity measured in?
watts/m (squared)
P
power
What is power measured in?
watts
r
radius/distance from source
What is r measured in?
meters
What are wavelengths measured in?
meters
What does intensity determine?
loudness
What happens to the brain if the intensity is doubled?
the brain doesn't perceive the sound as twice as loud
What is the sensation of loudness approximately?
logarithmic
How can you change the intensity to effect the loudness?
increase the intensity by 10x
What is the decibel scale used for?
to describe a sound's relative loudness as perceived by the brain
What does plucking a string instrument create?
standing waves that are the superposition of various wavelengths
what are the ends of the strings always?
nodes
with fixed ends of the strings,
the standing waves are only able to occur at specific frequencies
What are the specific frequencies of string instruments called?
harmonic series
What happens when you jump an octave?
The higher note has twice the frequency of the lower note (higher pitch)
What does fingering the strings do?
shortens the length of the vibrating portion of the string creating new wavelengths and frequencies for standing waves
What is the longest wavelength of a standing wave when both ends of a pipes are open?
double it's length or 2L
What is the longest wavelength of a standing wave when one end of a pipe is closed?
it's length times 4 or 4L
The equation for the fundamental frequency of a pipe with both ends open?
Fn= nv / 2L
The equation for the fundamental frequency of a pipe with one end closed?
Fn= nv / 4L
Harmonic frequencies of a pipe with one closed-end
only odd harmonics
Why do chords on the piano have more than one note?
there are more harmonics
Doppler effect: What happens to the pitch as the sound source approaches you?
the pitch goes up
Doppler effect: What happens to the frequency of the sound source as it approaches you?
the freq goes up
Doppler Effect: what happens to the pitch as the sound source goes past and moves away from you?
the pitch goes down
Doppler Effect: what happens to the freq as the sound source goes past and moves away from you?
the freq goes down
Fundamental freq for open pipe
1V / 2L
Fundamental freq for one end closed pipe
1V / 4L
What does pitch depend on?
freq
Which was to sound waves travel?
in all directions
Doppler Effect: why is the pitch higher when coming towards vs away?
the waves arrive more frequently
How is a sound wave created?
As an object vibrates, it bumps the molecules around it setting off a chain reaction of molecules vibrating and bumping into each other creating a series of compressions (particles closest together) and rarefactions that travel creating a sound wave.
What does the intensity depend on?
power
If the distance is divided by 2 what happens to the intensity?
divides by 4
Resonance occurs when a force causes an object to vibrate at?
it's natural freq
Why do people wear ear protection when working with loud machines?
even though when you hear a loud machine it doesn't physically hurt, the vibrations can cause damage to your hearing.
Fundamental freq
the lowest freq of vibration a sound source can produce (F1)
What happens the the Fund freq when the length doubles?
the fund freq cuts in half
How do you calculate the rest of the harmonics based on the fund freq?
you multiply the fun freq by the harmonic number
How did the Tacoma bridge collapse?
Eddies the wind blowing past the bridge caused periodic upward gusting. The gusting was near the bridge's natural freq so the amp increased greatly. The increased amp was too much for the bridge and it collapsed.
Why do soldiers not march in cadence when going across a bridge?
the cadence could be the same as the bridge which could cause a harmonic motion with a large amp.
What is the difference between air and string instruments?
- vibrations of air can't be changed like strings can