Transcript Sound Powerpoint

Sound
Sound
• DEF: A pressure variation that is
transmitted through matter.
Link to pic of bell animation
• Collisions are high pressure / compressions.
• Pulls are low pressure / rarefacation.
• Have same properties as waves in general
– Reflection (Echo)
– Interference (Beats, noise canceling)
Sound Speed Dependent Upon:
• Medium traveling through.
(Ear on train tracks)
• Temperature of medium
• Pressure of medium.
– Sound will not propagate in a vacuum (no pressure)
• Accepted Speed of sound at STP (Standard Temp. and
Pressure)
– 20 degrees Celcius (68 deg F) and 1 Atm of pressure (14.69 psi)
V
Sound
= 343 m/s (1125 ft/s)
Speed of sound in various Media
Media
Temperature (C)
Speed (m/s)
Air
0
331
Air
20
343
Water
25
1493
Salt Water
25
1533
Rubber
25
1550
Iron
25
5130
You are at home and you see lightning followed
by a clap of thunder. They are 15 seconds
apart. How far away is the storm?
Loudness
Loudness is amplitude of sound wave.
Human ear is fearfully and wonderfully made.
– Can detect a change in pressure of 1 billionth of an Atm.
• (Why your ears pop driving, flying, and swimming)
Hearing occurs over a huge spectrum of pressures: a logarithmic scale
is used.
Decibels (dB) Sound level measuring scale.
The Ear
Link to ‘How Hearing Works’
Decibel Scale
Decibels (dB)
Pressure (Atm) Example
0
20
40
2 × 10-10
2 × 10-9
2 × 10-8
Threshold of hearing
60
80
100
120
140
2 × 10-7
2 × 10-6
2 × 10-5
2 × 10-4
2 × 10-3
Normal Conversation
Whisper at 1 meter
Study Hall
Busy Traffic
Fire engine siren
Rock concert
Jet on carrier deck
Prolonged exposure can cause moderate to permanent hearing loss.
Pitch
• Pitch is known as frequency.
• Human range of hearing:
20 Hz - 16,000 Hz
• Average person over 70 has lost the ability to
hear frequencies above 8000 Hz. Which is why
speech is hard to decipher for older people.
• Ultrasonic – Frequencies above audible range
– Bats, ultrasound, dog whistles, cleaning
• Infrasonic – Frequencies below audible range
– Earthquakes, elephants
NOTE
Freq (Hz)
C
261.63
C#
277.13
D
293.66
Eb
311.13
E
329.63
F
349.23
F#
369.99
G
392.00
G#
415.30
A
440.00
Bb
466.16
B
493.88
C
523.25
A = 440 Hz is used as the standard, and the interval between each note is 21/12 = 1.05946
How’s Your Hearing
Turn Your Speakers Up, and Click on the Speaker Icons below to find your Ringtone!!
8.0 KHz
16.7 KHz
10.0 KHz
17.7 KHz
12.0 KHz
18.8 KHz
14.1 KHz
19.9 KHz
14.9 KHz
21.1 KHz
15.8 KHz
22.4 KHz
Frequency vs. Musical Note Value
600
2
500
Frequency (Hz)
A
Bb
493.88
G#
466.16
G
440
415.3
369.99
349.23
329.63
293.66
277.13
261.63
200
311.13
300
392
400
523.25
y = 0.623x + 12.949x + 248.8
R2 = 1
100
0
C
C#
D
Eb
E
F
F#
B
C
The Doppler Shift
• The Doppler Effect is experienced whenever there is relative
motion between a source of waves and an observer.
• Occurs in all waves (mechanical and electromagnetic)
– Uses: Weather radar, police radar, ultrasounds,
astronomy, NASCAR
• Toward – Higher Frequency
• Away – Lower Frequency
Doppler Shift Animation
Why Jets are never where they ‘seem’
Breaking the Sound Barrier
Breaking the Sound Barrier
Breaking the Sound Barrier
Breaking the Sound Barrier
Sonic Boom
A Sonic Boom is heard
when something breaks the
sound barrier.
343 m/s (767 mph) = Mach 1
Sonic Boom scientifically known
as a Shockwave
Bull whips and jets are other
examples of supersonic
speed; speed faster than
sound.
Ultimately, the farther a sniper can be from his target and still
remain accurate the more effective he is and the less likely he
is to be discovered. Using a 7.62mm round, snipers can shoot
nearly silently as long as they're shooting from over 600
meters. A bullet leaves the rifle barrel faster than the speed of
sound. The cracking sound a bullet makes is a tiny sonic boom.
Even if a target doesn’t hear the rifle shot, he will hear the bullet
fly by. But the drag created by wind resistance on a 7.62mm
round as it travels through the air slows the bullet down to subsonic speeds at around 600 meters. So at ranges over 600
meters, the bullet no longer makes that distinct cracking sound.
Army Ranger Sniper tells us, "If you're shooting at a target 800
or 1,000 meters out, you could be shooting at that person all
day long and they don't even know they are being shot at."
Speed Slang
•
•
•
•
•
Mach 1: 1 x the speed of sound (343 m/s)
Mach 2: 2 x the speed of sound (686 m/s)
Subsonic: All speeds under Mach 1
Supersonic: All speeds over Mach 1
Hypersonic: All speeds over Mach 5 (3800 mph)
•
Sources
of
Sound
Sound has to be produced by a vibrating object.
–
–
–
–
–
Percussion: surface vibrates
Brass instruments: lips vibrate
Woodwind instruments: Reed vibrates
Stringed instruments: Strings Vibrate
Piped instruments: Column of air vibrates.
Open Tube Resonator
Resonance in Air Columns
• Length of tube dictates pitch (frequency).
– Shorter = higher frequency
2 Types
Open Pipe / Tube: Both ends open.
Ex: Flute, Clarinet, Trumpet, Pipe organ
Closed Pipe / Tube: One end closed.
Ex: Soda bottle, bell
Open Tube Resonators
If the end is open, the elements of the air have complete freedom of
movement and an antinode exists
Link to animation of Open Tube Resonance.
Open Tube Resonators
• In a pipe open at both ends, the natural
frequency of vibration forms a series whose
harmonics are equal to integral multiples of the
fundamental frequency
v
ƒn  n
 nƒ1
2L
n  1, 2, 3,
Closed Tube Resonators
• If one end of the air column is closed, a node must exist at this end
since the movement of the air is restricted
Link to animation of Closed Tube Resonance.
Closed Tube Resonators
• The closed end must be a node
• The open end is an antinode
v
fn  n
 nƒ1
4L
n  1, 3, 5,
• There are no even multiples of the fundamental
harmonic
Example Problem
When a tuning fork with a frequency of 392 Hz is used with a closed pipe
resonator, the loudest sound is heard when the column is 21 cm and next at
65.3 cm. The air temp. is 27 deg Celcius. What is the speed of sound at this
temperature?
Sound Quality
All 3 waves have same amplitude, period and
frequency, but they have a different shape.
Shape is Timbre or tone color / tone quality
Consonance: When 2 notes sound ‘good’
C Major Chord: C – E – G
For past 2500 years, accepted as ‘Sweetest’ 3 note chord
Dissonance: When 2 notes sound ‘bad’
Octave: When 2 notes have a frequency of 1:2
Beats
• Beats are alternations in loudness, due to interference
•
Waves have slightly different frequencies and the time between constructive
and destructive interference alternates
•
The beat frequency equals the difference in frequency between the two
sources:
ƒb  ƒ2  ƒ1