Experimental Phonetics

Session 1- Sound WavesGolnaz Modarresi Ghavami

What is sound?

• A disturbance of the positions of particles within a substance.

No sound in a vaccum! Why?

• Because sound presupposes an elastic medium!

Sound Propagation

• A sound is produced by a momentary disturbance of air particles that move back & forth.

Sound propagation in an elastic medium

Compression

Rarefaction

Sound Waves

Definitions

• Compression: The movement of air particles closer together causing an increase in pressure at a point. Regions of compressed air are called peaks.

• Rarefaction: When air molecules move further apart than their normal “resting” position, an expansion of the inter-molecule and hence a decrease of pressure occurs. Regions of rarified air is known as valleys.

Note: There is no movement of matter!

Air particles move only locally around their rest positions

Speed of sound 1129 feet/sec 340 m/sec

(350 m/sec in VT)

770 mph

Speed of breath stream

1 foot/sec 1 mph

What Body of air is Disturbed in Speech?

1. Voice Source

• Disturbance of air in

glottis →vocal tract → outside

• E.g. Vowels, nasals, approximants

2. Noise SourceDisturbance of air in a constricted area

a) Flow of air forms a jet and turbulent fluctuations in air velocity observed downstream.

b) Creation of turbulence by the rapid flow of air against an obstacle or a surface.

Case b produces much stronger sound intensities: Voiceless Sibilants: [, , t,]Voiceless Non-sibilants: [f, ]

3. Transient Source

• Disturbance of air at the release.

• E.g. Voiceless Stops

What about other sounds?

Voicing + Noise

Voicing + Transient

Transient + noise

Transient + noise + voicing

Voiced fricatives

Voiced Stops

Voiceless Affricates

Voiced Affricates

Objects that move like air particles

The Period of a Pendulum

• Pendulum: A suspended object (bob).

• Period (t): The time taken to complete a back & forth movement.

• The period of a pendulum depends only upon the length of the pendulum.

• The longer the length, the longer the period.

len

gth

Period (t) or Cycle

Question

• If two pendula have the same length, but one has a 2 pound weight on its end while the other has only a 1 pound weight, which will have the longer period?

Answer

• If two pendula have the same length, but one has a 2 pound weight on its end while the other has only a 1 pound weight, which will have the longer period?

• They will have the same period.

Frequency of a Pendulum

• The frequency of a pendulum is the number of cycles (periods) completed in a unit of time.

• f =1/t• f = frequency t =period

Question

• The period of a grandfather clock pendulum is 2 seconds.

• How many cycles per second?

• How many cycles per minute?

Answer• The period of a grandfather

clock pendulum is 2 seconds.• How many cycles per second?• f= 1/t f=1/2 cycle per

sec

• How many cycles per minute? • 1min=60 sec

• 1 ½• 60 x

• 60 * ½ /1= 30 cycles per min

Amplitude of a Pendulum

• Amplitude of a pendulum: The distance from the center, rest position to the point of maximum displacement.le

ng

th

amplitude

Amplitude of a Wave

• Amplitude of a wave: The distance from the center, rest position of the wave to the point of maximum displacement.

amplitude

Speed of a Wave

• Speed of a wave: The distance traveled divided by the time of travel.

Wavelength

• Wave length: The distance between two consecutive corresponding points on the wave.

Relationship between the Variables

• v =λf• Velocity (speed) = wavelength * frequency

Question

• If 30 waves pass under your boat per minute and the length of each wave is 2 meters, what is the speed of the waves?

Answer

• If 30 waves pass under your boat per minute and the length of each wave is 2 meters, what is the speed of the waves?

• v=λf• v=2meters * 30 waves/min.• v=60 meters/min

Transverse Waves

• Waves that travel in a direction perpendicular to the direction of the waves.

Longitudinal Waves

• Waves that travel parallel to the direction of the wave.

• Sound waves are longitudinal waves.

• Longitudinal waves are composed of rarefaction & compression.

1. Simple Harmonic Motion

• A motion that repeats itself at a fixed number of times in a second, i.e. it has only one frequency of vibration.

• E.g.

1. Swing of a pendulum

2. Swing of a swing

Simple Harmonic Motion

Sine wave/Periodic Wave

Compression

rarefaction

Periodic Wave/Sine Wave

• Periodic Wave: A wave in which the same exact pattern of air pressure variation is repeated exactly over and over.

• Sine Wave: A periodic wave that has a smooth and symmetrical curve connecting the points of maximum and minimum pressure.

Sounds made by simple harmonic motion of an elastic medium

• Pure Tones: Simplest of all sound patterns. Has only one frequency of vibration. It is the result of a vibration that repeats itself at a constant number of cycles per second.

• E.g. a sound made by:1. A tuning fork2. The pluck of a guitar

string3. Vibration of the sides of

a glass when tapped

Aperiodic Waves

• Aperiodic waves do not repeat themselves as a function of time.

• E.g. static on radio, sudden explosion,• and fricatives, white noise (sounds like the

hissing of a radiator

2. Complex Movement

• Any motion that has more than one frequency of movement.

Sounds Made by such Movements

• Almost all sound in the real world are the result of complex movements.

Complex Waves

• Almost all sounds in nature are complex, i.e. they have more than one frequency of vibration.

Periodic Complex Wave

Why these terms? periodic

e.g., vowel aperiodic

e.g., white noise

see she

periodic + + - -

complex + - + -

e.g.,vowels

’pure tone’ voicelessfricatives

non-existant

voiced fricatives

Classification of Speech Sound Waves

Damping

• Vibration of actual objects are always affected by damping forces (friction & internal resistance to bending) affecting the amplitude of motion.

• The resulting wave is called a “damped oscillation”.

No Damping

Damping