The production of soundWaves always begin with

A vibrating object.

This vibration causes the Molecules around it (usually

Air molecules) to move.

This movement is a wave pattern.

Compression is the region of aLongitudinal wave in which the

Density and pressure are Greater than normal.

Rarefaction is the region of a Longitudinal wave in which

The density and pressure areLess than normal.

So these two definitions show That sound waves are

Longitudinal.

The average person’s hearing Range is about 20 and

20 000 Hz.

Sound frequencies less than 20 HzAre called infrasonic and

Frequencies above 20 000 Hz are called ultrasonic.

The frequency of a sound Determines its pitch.

Pitch is how high or low we Perceive a sound to be.

Ultrasonic waves can produce Images of objects.

The speed of sound depends On the medium in which

The sound moves.

The speed of sound in room Temperature air is about 346 m/s,And is about 1490 m/s in water.

Sound waves propagate in All three dimensions.

It works the same was a A radiating black body.

This leads to the Doppler Effect.

Relative motion creates A change in frequency.

The Doppler Effect is a Frequency shift that is the result

Of relative motion betweenThe source of waves and

An observer.

You have experienced the Doppler Effect in most Everyday of your life.

It is most easily noticedWhen you hear an ambulanceComing and going past you.

You can find the change inThe frequency due to the

Doppler Effect by a formula…

f`` = f v v0 v vs+-

+-

f ` is the new frequencyv0 is the observers speed

vs is the speed of sound source

The frequency perceived by a Detector is equal to the velocityOf the detector relative to the

Velocity of the wave, divided byThe velocity of the source

Relative to the wave, multipliedBy the wave’s frequency.

A trumpet is played at 524 Hz whileTraveling in a convertible at 24.6

m/s. If the car is coming toward youWhat frequency would you hear?

564 Hz

Intensity is the rate at whichEnergy flows through a unitArea perpendicular to theDirection of wave motion.

Intensity = Parea

P = PowerArea = 4πr2

So the SI unit for intensity Is W/m2

What is the intensity of the soundProduced by a trumpet at a

Distance of 3.2 m when the powerOutput of the trumpet is 0.2 W?

Intensity = 1.6 X 10-3

Intensity and frequency Determines which sounds

Are audible.

Relative intensity is Measured in decibels.

Decibel level is the relative Intensity, determined by

Relating the intensity of a sound Wave to the intensity at the

Threshold of hearing.

When measuring decibels, everyStep of 10 is double the

Intensity.

So sounds at the threshold ofPain are 4096 times as loud as

Sounds at the threshold of hearing.

10 Rustling leaves

50 Normal Conservation

130 Machine Gun

The fundamental frequencyIs the lowest frequency

Of vibration of a standing wave.

The harmonic series is a Series of frequencies that Includes the fundamental Frequency and integral

Multiples of the fundamentalFrequency.

Harmonic series of standingWaves on a string…

fn = nv2L

n = harmonic number

L = length of vibrating string

v = speed of waves on the string

Harmonic series of a Pipe open at both ends…

fn = nv2L

v = speed of sound in the pipe

L = length of vibrating air column

Harmonic series of a Pipe closed at one end…

fn = nv4L

v = speed of sound in the pipe

L = length of vibrating air column

n = harmonic number (odd only)

What are the first 3 harmonics in A 2.45 m long pipe that is open at

Both ends? What are the first 3Harmonics of this pipe when one

End of the pipe is closed? The speed of sound is 345 m/s.

Open : 70.4, 141, 211Closed: 35.2, 106, 176

Harmonics account for The sound quality, or timbre.

Timbre is the quality of a Steady musical sound that is

The result of a mixture of Harmonics present at Different intensities.

The fundamental frequencyDetermines pitch.

A beat is the interference of Waves of slightly different Frequencies traveling in theSame direction, perceivedAs a variation in loudness.

A forced vibration at the Natural frequency

Produces resonance.

Resonance is a condition that Exists when the frequency of A force applied to a system

Matches the natural frequency Of vibration of the system.

Dissonance is an unpleasant Set of pitches.

Consonance is a pleasant Set of pitches.

Two music notes with frequenciesRelated by the ratio 1:2 are Said to differ by an octave.