Hearing & Speech Science Midterm Slides

What is Acoustics?

A branch of physics concerned with the study of sound

• Production, transmission, reception, and effects of sound waves

What are Transverse Waves?

Particles in the medium move perpendicular to the direction in wave travels

• Waves moving along a string

What are Longitudinal Waves?

Waves in which the particles move parallel to the direction in which the wave travels

• Oscillation of air particles

What is Sound?

A particle vibration within an elastic medium

What is Vibration?

The back-and-forth motion of an object or particle around an equilibrium point

What is Compression?

Particles closer together than at rest

What is Rarefaction?

Particles farther apart than at rest

What is Inertia?

A fundamental property of all matter. The resistance an object has to change in its state of motion

What is Mass?

A quantitative measure of Inertia. The resistance that a body of matter offers to a change in speed of position upon application of a force

What is Elasticity?

The ability of the object or particle to return to its starting position (or shape) after the forces deforming them have been removed

What is Restoring Force?

(Usually gravity or elasticity): Returns object to resting position (equilibrium point)

• Elasticity is the restoring force that returns air particles to resting position

What is Displacement?

How much each particle in a wave moves, usually back and forth (positive and negative displacement) around an equilibrium point

What is Distance?

How far the wave (or sound) travels through space

• Speed of Propagation = 344 m/s at standard conditions

What is Amplitude?

The maximum excursion from equilibrium

• Can be expressed in displacement, velocity, or pressure

• The max amplitude is the change from the zero line to the max positive peak

What is Maximum Displacement?

When particles are farthest from equilibrium

Maximum pressure occurs when

particles are most bunched together (compression)

• happens when their displacement is crossing zero

• Not when displacement is at its maximum

• Creates a quarter-cycle (90degrees) phase lag between displacement & pressure

Displacement lags behind _______ & ________

Particle velocity & pressure

When a wave is Periodic, it ___________

repeats itself over time

When a wave is Aperiodic, it ______________

does not repeat itself over time

What does Phase indicate?

a particular time in the cycle of motion using the angles from a circle as the unit of measure

Starting phase refers to __________

the phase at time = 0

What is Instantaneous phase?

Refers to the phase at any given moment in time

What is Maximum positive amplitude?

ALWAYS corresponds to 90degrees

What is Maximum negative amplitude?

ALWAYS corresponds to 270degrees

Phase relationship - Positive ______, negative _______

leads, lags

What is Period (T)?

the amount of time it takes to complete one repetition of the wave

• Seconds/cycles

What is Frequency (f)?

the number of cycles a wave completes in one second

• f = cycles/second

_______ & _______ are reciprocals of each other

Frequency & period

What is Wavelength?

distance between two consecutive points that share the same phase in a wave (crest-to-crest)

• Determined by propagation velocity (c) & frequency (f)

What are the physical properties of air (slower sound)?

Mass, density, & pressure

What are the physical properties of air (Faster sound)?

Temperature & elasticity

Big Mass =

low frequency

Small mass =

high frequency

High altitude: air is _____

thin

• Less mass = faster sound

Could tundra: air is _______

dense

• More density = slower sound

Humid beach: _____ density = ______ sound

Less density = faster sound

Warm air: Faster-moving molecules

quicker collisions → faster sound

Cold air: slower-moving molecules

Fewer/slow collisions → slower sound

What is Sound Intensity?

Rate of sound energy flow

If medium is ______, particles move less, leading to _______________

denser, lower intensity

If medium is _______, particles move more, leading to ____________

less dense, higher intensity

When the distance from the source increases, the intensity will ________

decrease

When the distance from the source decreases, the intensity will _________

increase

When a sound encounters an object or new medium (Hit the object)

Absorption, refraction, reflection

When a sound encounters an object or new medium (Avoid the object or curve around)

Diffraction

What is Absorption?

Energy is transmitted

What is Refraction?

Energy changes direction during absorption

What is Reflection?

Energy bounces back

What is Diffraction?

Energy bends around objects & through openings

What is Wave Interference?

When 2+ waves propagate in the same medium

• Travel independently, can pass through each other

What is Constructive Interference?

Waves partially or completely in phase

• Resulting in wave with larger amplitude than either wave alone

What is Destructive Interference?

Waves partially or completely out of phase

• Results in a wave with smaller in amplitude than at least one of the waves

What is a Decibel?

measures how much larger or smaller a sound is compared to something else - a ratio

What is value?

quietest sound an average healthy human can hear

The average threshold of human hearing for each frequency

0 dB HL: Hearing level

dB SL: used for ____________

Speech testing.

• How well a person can perceive speech when it is a certain number of their hearing thresholds

What is Impedance (Z)?

Opposition to the flow of energy through a system

• Impedance increases, sound intensity (amplitude) decreases

What are the three main components of Impedance?

1. Resistance (R): friction - comes from the outside the system

2. Mass Reactance: comes from inside the system

3. Stiffness Reactance: comes from the inside the system

What is Damping?

Loss of energy due to resistance

What is Mass Reactance?

Opposition to energy flow due to mass (inertia) of the system

Higher mass =

• Higher impedance at higher frequencies

• Greater vibration at lower frequencies

• Large and low

Lower mass =

• Higher impedance at lower frequencies

• Greater vibration at higher frequencies

• Small and high

What is Stiffness Reactance?

Opposition to energy flow due to stiffness of the object/vibrating system

Greater stiffness =

• Greater impedance at lower frequencies

• Greater vibration at higher frequencies

• Stiff and squeaky

Less stiffness =

• Greater impedance at higher frequencies

• Greater vibration at lower frequencies

• Lose and low

Resonance is determined by which two physical properties of an object?

1. Mass Reactance

2. Stiffness Reactance

What is Free Vibration?

Vibration where, once started, no additional energy is added

• Frequency of vibration is resonance frequency

Reactance equals zero - mass & stiffness cancel each other out

What is Forced Vibration?

Vibration where an external force is continuously or periodically applied

• Driving frequency: frequency of external force

What are Nodes?

Points where displacement remains zero

What are Antinodes?

Points of greatest vibration magnitude

What are Acoustic systems?

Masses of medium that vibrate

What are the three basic types of tubes?

1. Closed at both ends

2. Open at 1 end, closed at other

3. Open at both ends

Closed end is

node

Open end is

antinode

What is a Standing Wave?

When sound bounces between 2 parallel surfaces

• Generated by the resonant frequency of a system

Rules for matched rules:

• Waves on strings that have both ends tied

• Waves in tubes that have both ends closed or both ends open

Rules for unmatched ends:

• Waves on strings that have one end tied and one lose

• Waves in tubes that have one end open and one closed

Displacement nodes =

pressure antinodes

Pressure nodes =

displacement antinodes

Periodic sounds are

1. Pure tones

2. Complex tones

Must repeat over time

Quasi-Periodic sound =

speech

Some parts of the signal repeat, others don’t

More than one frequency = complex

Aperiodic sound =

noise

More than one frequency = complex

Impulse sound =

Click or pop

Mostly quasi-periodic or aperiodic

More than one frequency = complex

Sinusoids =

pure tones & just one frequency

Complex tones =

Has a pitch but sounds “richer”

More than one frequency = complex

A wave is ________ if it repeats itself over time

periodic

A wave is _________ if it does not repeat itself over time

aperiodic

A wave is called _________ when there are components that clearly repeat and components that clearly do not

quasi-periodic

A wave is _________ if it can be described by a sinusoidal equation

simple

A wave is _______ if it is made up of many individual sinusoids combined - has more than one frequency component

complex

What is the Fourier Theorem?

A complex wave is the sum of simple waves

What is Waveform synthesis?

Process of combining several individual sinusoidal motions into a complex waveform

What is Fourier analysis?

Taking a complex acoustic signal and splitting it into its component sinusoids (pure tones)

A sinusoidal waveform appears as a _____________ on the spectral display because it represents only one component

single vertical line

A complex periodic vibration with three components has a spectrum with ____________

three vertical lines

When the spectrum has a few, discrete frequency components called a __________

line spectrum

____________ has all the spectral components in a certain frequency range

Continuous spectrum

What is a Spectrogram used for?

Used to show amplitude, time, and frequency all at once

X-axis = time

Y-axis = frequency

Darkness/color = intensity or amplitude

What are Harmonics?

whole numbers that are multiples of fundamental frequency

What are the 2 main reasons that explain all complex periodic sounds have harmonics?

1. Must be more than one component in order to be complex

2. The components must be harmonically related to create s sound that repeats over time (that is periodic)