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)

VSound = 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) Example0 2 × 10-10 Threshold of hearing

20 2 × 10-9 Whisper at 1 meter

40 2 × 10-8 Study Hall

60 2 × 10-7 Normal Conversation

80 2 × 10-6 Busy Traffic

100 2 × 10-5 Fire engine siren

120 2 × 10-4 Rock concert

140 2 × 10-3 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 Hearing8.0 KHz

10.0 KHz

12.0 KHz

14.1 KHz

14.9 KHz

15.8 KHz

16.7 KHz

17.7 KHz

18.8 KHz

19.9 KHz

21.1 KHz

22.4 KHz

Turn Your Speakers Up, and Click on the Speaker Icons below to find your Ringtone!!

Frequency vs. Musical Note Value

261.63

277.13

293.66

311.13

329.63

349.23

369.99

392

415.3

440

466.16

493.88

523.25

y = 0.623x2 + 12.949x + 248.8

R2 = 1

0

100

200

300

400

500

600

C C# D Eb E F F# G G# A Bb B C

Fre

qu

ency

(H

z)

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 sub-sonic 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

Link to animation of Open Tube Resonance.

If the end is open, the elements of the air have complete freedom of movement and an antinode exists

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

1ƒ ƒ 1, 2, 3,2n

vn n n

L

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

• There are no even multiples of the fundamental harmonic

1ƒ 1, 3, 5,4n

vf n n n

L

Example ProblemWhen 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 QualityAll 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: 2 1ƒ ƒ ƒb