ALL Physics 167

Period

The time required to complete one cycle of oscillating motion

Frequency

The number of cycles occurring in one second (in Hz)

Damping

resistance that causes periodic motion to gradually decrease

When will acoustic intensity decrease?

when one gets farther away from the object creating the acoustic intensity

Natural mode of vibration

specific vibration pattern in which a pattern moves repeatedly

Does a 1st mode system have a high or low natural frequency?

it has the lowest natural frequency

What does moving in phase mean?

moving together

What does moving out of phase mean?

moving in opposite directions

Node

points that are at equilibrium on a mode

Anti-node

the highest and lowest points on a mode

Simple harmonic motion

oscillatory motion under a restoring force proportional to the amount of displacement from an equilibrium position

Wave

disturbance traveling through a medium

Longitudinal wave

molecules move parallel to the wave motion

can move through any medium

Transverse wave

molecules move perpendicular to the wave motion

can move through solids

What type of waves are sound waves?

longitudinal waves

wavelength

distance before a wave will repeat

What medium does sound waves travel faster in?

solids

Why can’t transverse waves travel through fluids?

molecules in fluids are not strongly bound together; they do not have sufficient restoring force to return to their original positions

What happens to the wave speed if the tension of a string is doubled?

the wave speed will increase

What happens to the wave speed if the linear density of the string is doubled?

the wave speed will decrease

Condensation

positive acoustic pressure

Rarefaction

negative acoustic pressure

What and where is equilibrium?

Equilibrium is between condensation and refraction. The pressure is neither negative nor positive

Reflection

When waves change direction due to a change in the medium

Absorption

The attenuation of energy of a wave. Absorption of sound wave occurs when a wave travels over a long distance or travels through a fibrous or porous medium

Refraction

The bending of a wave toward a region of lower sound speed. This occurs when the wave speed changes in a medium or when changing medium

Diffraction

The bending of waves around obstacles

Doppler Effect

A change in apparent frequency due to a moving sound source or moving receiver

Effect of reflections of a curved surface

Reflections off of curved surfaces can focus wave energy to only a certain region

Effect of reflection of a rough surface

Diffuse reflections (or scattering) occur when the reflecting surface is rough

Where will waves bend naturally during refraction?

towards the slower wavespeed (colder air)

Effect of frequency of waves in amount of diffraction

low frequency waves bend a lot

high frequency waves bend a little

When a sound source is approaching a listener how will the perceived frequency be?

the perceived frequency will be higher

When a sound source is moving away from a listener how will the perceived frequency be?

the perceived frequency will be lower

How do sound wavelengths compare to light wavelengths?

sound has longer wavelengths then light

Superposition

When two waves exist at the same place and time, they add together

Constructive Interference

The waves are in phase and thus increase in amplitude as they add together

Destructive Interference

The waves are in out of phase and thus decrease in amplitude as they add together

Beating

two periodic waves with nearly the same frequencies

f = |f2 - f1|

Periodic wave

a wave that repeats after some finite interval of time

Partial

each since function that contributes to a complex wave

Harmonics

integer multiples of the fundamental frequency

Nonperiodic

no repetition, inharmonic partials

Free Decay

sound amplitude gets smaller as more cycles occur

Purpose of Outer Ear

• convert acoustic energy to mechanical energy

• protect the middle and inner ear

Parts of Outer Ear

pinnea, ear canal, eardrum

Pinna Purpose

helps with transition of sound from outside world to the ear canal

Ear canal purpose

resonance frequency around 2-6 kHz which amplifies sound

Eardrum purpose

vibrates transforming acoustical energy to mechanical energy

Middle Ear Purpose

transfer mechanical energy from outer ear to inner ear

Middle Ear Parts

auditory ossicles, oval window, eustachian tube

Auditory ossicles purpose

transfer vibration energy of the ear drum to the inner ear

Oval window purpose

membrane connecting the middle ear to the inner ear and transfers the force

Eustachian tube purpose

tube that helps the ear adjust to changes in atmospheric pressure

Inner ear purpose

translate mechanical pulses from the middle ear into neural pulses

Inner ear parts

cochlea, round window, semicircular canals

Cochlea purpose

shell-shaped organ filled with standing waves

the fluid forms standing waves from the signals received by oval window

translates the information into neural pulses for the brain

Semicircular canals purpose

help the brain sense head rotation and maintain balance

Round window purpose

helps provide the right conditions for standing waves in the cochlea

Regions of cochlea

upper duct, middle duct, lower duct

What cavity do the upper and lower duct join into?

helicotrema

What creates standing waves in the basilar membrane?

the pressure difference between the upper and lower ducts

Organ of Corti purpose

transfer the wave motion of the basilar membrane into neural pulses

Hair cell purpose

to bend as the basilar membrane oscillates which causes the connected nerve fibers to fire

Inner hair cell purpose

provide the most crucial sensory information via neural pulses to the brain

Outer hair cell purpose

amplify the basilar membrane motion

Where will low frequencies have the highest response?

near the helicotrema

Where will high frequencies have the highest response?

near the oval window

What determines pitch?

location and repetition rate of hair cell firings

What determines loudness?

number of hair cell firings per burst group

What determines tone color?

the existence of multiple regions of hair cell firings

critical band

frequency range where two waves interact that they compete for the same hair cells

Masking

one sound covers up another sound due to the wave motion of the basilar membrane

What frequency is better at masking?

low frequency mask high frequencies better

louder sounds

threshold of audibility

the SPL at which sound is just barely perceptible

• higher f higher threshold

Just Noticeable Difference

smallest difference in sound level or frequency that can be detected

How long must an echo wait so it can be heard?

50 ms after the first sound

localization

ability to detect the direction that the sound came from

Low frequency localization

time delay between ears

High frequency localization

intensity/SPL difference between ears

Conductive hearing loss

damaged outer/middle ear due to blocked ear canal, ear drum rupture, damaged ossicles

Sensorineural hearing loss

damaged inner ear due to excess pressure in cochlea, damaged hair cells

model for speech sound

source + resonator = speech sound

source

energy for speech

• diaphragm, lungs, trachea, larynx

What makes the vocal folds open?

positive pressure from lungs

What makes the vocal folds close?

negative pressure from airflow and vocal fold tension

Voiced sound characteristics

• from glottal airflow

• periodic, fundamental w/ harmonics

• spectrum is formant

Noise sound characteristics

• from construction in vocal tract

• non-periodic, wide frequency range

• broadband spectrum

Burst sound characteristics

• from sudden release of air

• short duration

• spectrum has high frequencies

resonator

filter of sound

• oral cavity, palates, nasal cavity, tongue, lips, teeth

formant frequency

frequency of vocal tract

fundamental frequency

frequency set by vocal folds

Vowel Phonemes

A, E, I, O, U, OO, UH, EE, AE

Vowel Energy

voice (A, E, I, O…)

Vowel Characteristics on Spectrogram

3+ formant frequency bands

Nasal Phonemes

M, N, NG

Nasal Energy

Voice (M, N, NG)

Nasal characteristics on spectrogram

low frequency dominant by first formant

Fricative phonemes

Unvoiced: WH, H, F, TH, S, SH, CH

Voiced: V, DH, Z, SH, JH

Fricative energy

Unvoiced: nosie

Voiced: noise/voice