Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I A 2. If A doubles I...

33
Sound

Transcript of Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I A 2. If A doubles I...

Page 1: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Sound

Page 2: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Loudness and Pitch

• frequency = pitch

• Amplitude = volume or intensity

• I A2.

• If A doubles I increase by 22 or 4.

Page 3: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Standing Wave & Resonance

pattern that results when 2 waves, of same f, & A travel in opposite directions.

Often formed from pulses reflect off a boundary. Waves interfere constructively (antinodes) & destructively (nodes) at fixed points.

Page 4: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Standing waves have no net transfer of energy – no direction propagation of energy.

Page 5: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Standing Waves form at natural frequencies of the material. Occur when material is at resonance.

When system is disturbed it vibrates at many frequencies. Standing wave patterns continue. Other frequencies to die out.

Since there is resonance, the amplitude of particular wavelengths/frequencies will be amplified.

Page 6: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Relation of Wavelength to String Length for Standing Waves L = 1/2.

Page 7: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

= L.

Page 8: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

= L

Page 9: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

General expression relating wavelength to string length for standing waves:

• n ( ½ ) = L

• n is a whole number

• A whole number of half ’s must fit.

Page 10: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Although we would perceive a string vibrating as a whole,

it vibrates in a pattern that appears erratic producing many different overtone pitches. What results are particular tone colors or timbres of instruments and voices.

Page 11: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Each standing wave pattern on a string can produce a harmonic.

Harmonics

Page 12: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

The lowest possible frequency at which a string could vibrate to form a standing wave pattern is known as the fundamental frequency or the first harmonic.

Page 13: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

2nd Harmonic

Page 14: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Which One??

Page 15: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

String Length L, & Harmonics

Standing waves can form on a string of length L, when the can = ½ L, or 2/2 L, or 3/2L etc.

Standing waves are the overtones or harmonics.

L = nn. n = 1, 2, 3, 4 whole number harmonics. 2

Page 16: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

FrequenciesSince standing wave forms where ½ can fit the string exactly, we can calculate f:

L

nvf

2

f

vfv

2

nL

Substitute v/f for .

f

nvL

2

Must know speed in material.

n = harmonic

Page 17: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

1st standing wave forms when = 2LFirst harmonic frequency is when n = 1 as below.

L

nvf

21

When n = 1, f = v/ . This is fundamental frequency or 1st harmonic.First harmonic has largest amplitude.

Page 18: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

L

nvf

22 For second harmonic n = 2.

f2 = v/L

Other standing waves with smaller wavelengths form other frequencies that ring out along with the fundamental.

Page 19: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

In general,

The harmonic frequencies can be found where n = 1,2,3… and n corresponds to the harmonic. v is the velocity of the wave on the string. L is the string length.

L

nvfn 2

Page 20: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Pipes and Air Columns

Page 21: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

A resonant air column isA resonant air column issimply a standing simply a standing

longitudinallongitudinalwave system, much likewave system, much like

standing waves on a standing waves on a string.string. closed-pipe resonatorclosed-pipe resonator tube in which one end is tube in which one end is

openopenand the other end is closedand the other end is closed

open-pipe resonatoropen-pipe resonatortube in which both endstube in which both ends

are openare open

Page 22: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Pipes – the open end has antinode.

Page 23: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Standing Waves in Open PipeBoth ends must be antinodes.

How much of the wavelength is the fundamental?

Page 24: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

The 1st harmonic or fundamental can fit ½ into the tube.

Just like the string L = n 2

fn = nv2L

Where n, the harmonic is an integer.

Page 25: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Closed Pipe Resonator

Page 26: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Closed pipes must have a node at closed end and an antinode at the open end.

How many wavelengths? L = 4

Page 27: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Here is the next harmonic.How many ’s?

L = 34

Page 28: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

There are only odd harmonics possible – n = odd number only.

L = 1/4.L = 3/4.L = 5/4

fn = nv where n = 1,3,5 … 4L

Page 29: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Application: When waves propagate through a tall building, the building resonates like a tube open at two ends.

• What is the equation that relates frequency to wave velocity and building height?

L

nvf

21

Page 30: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

The building is 360 m tall and allows waves to travel through it at 2400 m/s, what frequency wave will cause the most damage to it? Explain why.(Hint: What is the resonant frequency)?

• 3.3 Hz

Page 31: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.
Page 32: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Holt read 13 - 3

pg 509 38 - 39, 41, 44 46, 47 pg 499 #1 – 4

Start in class finish for hwk.

Page 33: Sound. Loudness and Pitch frequency = pitch Amplitude = volume or intensity I  A 2. If A doubles I increase by 2 2 or 4.

Hwk read 491 – 503

do 499 and 503