SLHS 305: Test 2 (10/31/24)

How is sound made?

made when an object vibrates

Vibration

back and forth movement of particles

What is required for sound to occur?

a medium and a vibrating object

What are the different mediums

gas, liquid, solid

NOT vacuum: in space there are no particles, no sound

How fast does sound move through different states of matter from slowest to fastest?

1. gas

2. liquid

3. solid

Basic physical parameters of sound

- compression

-rarefaction

- cycle

- frequency

- period

- wavelength

- amplitude

compression

when particles are put together and creates a high pressure

rarefaction

when particles are spread apart and creates a low pressure

Cycle

one cycle: starts at equilibrium, max compression, then max rarefaction and back to equilibrium

frequency

we perceive it as pitch

the number of cycles per second

(Hertz/Hz)

Amplitude

we perceive it as loudness

height of the curve

(decibels/dB)

Wavelength

distance between waves (either two compressions or 2 rarefactions)

(meters/m)

As frequency increases what happens to wavelength?

wavelength decreases

Period

amount of time a cycle is repeated

(seconds/s)

What formula to use when given period and need to find frequency

Frequency = 1/period

What formula to use when given frequency and need to find period

Period = 1/frequency

Dampening

gradual loss of energy of sound over time

How does damping affect the wave motion?

the amplitude lessens over time

Phase

wave cycle that is measured in degrees

1 cycle = 360 degrees

constructive phase relationship

two sound waves that are in phase to create a bigger amplitude

deconstructive phase relationship

two sound waves that are out of phase and cancel out sound

three factors that influence speed of sound

temperature

elasticity

density

how does temperature influence speed of sound

higher temperature = energy in molecules is higher = sound travels faster

elasticity

ability to return to original shape

Which is more elastic metal or a rubber band?

metal because they are able to stay in their original shape better than a rubber band

how does elasticity influence speed of sound

higher elasticity = faster travel of sound

density

how tightly packed the molecules are

how does density influence speed of sound

higher density = faster travel sound

because denser materials are also more elastic

What happens to sound when it hits a barrier?

reflection

refraction

absorption

transmitted

diffraction

reflection

bounces off of an object

absorption

sound energy is taken in by the barrier, converts to heat and reduces sound

transmitted

goes through the object

sum of coefficient

absorption (α) + reflection (β) = 1

Factors that affect reflection/absorption of an object

frequency (high vs low)

physical properties (hard vs soft)

distance from sound source

How are high frequencies absorbed?

they are absorbed more because they have a short wavelength

How are low frequencies absorbed?

they are absorbed less because they have a long wavelength

refraction

bending of sound when passing different mediums OR density

What material do sound waves go towards?

slow material

diffraction

bending or spreading sound when theres an obstacle or small opening

sound intensity

power carried by sound waves in a certain direction

(watt/m^2)

sound pressure

air pressure caused by sound waves

(mPA)

Reference value for dB SPL

20mPa

Why is dB on a log scale?

dB is not a unit of measurement. It is a relationship between 2 values. It also crunches the numbers so that it is more digestible

Inverse square law

sound decreases by 6dB SPL for each doubling of distance from the source

What does 0 dB HL mean?

no hearing loss

What does positive dB HL mean?

hearing loss occured

What does negative dB HL mean?

better than average hearing

On the threshold of audibility graph, (above/below) the line are where sounds cannot be heard, while (above/below) the line are where sounds can be heard

below; above

complex wave

combination of 2 or more simple waves

periodic waves

simple waves within the complex wave are harmonically related

aperiodic waves

simple waves within the complex wave are not harmonically related. this is also called noise

examples of noise

white noise

a voice speaking

Fundamental frequency

lowest frequency and is perceived the most

harmonics

higher frequency components in a complex sound

How do you find a harmonic when given the frequency?

Harmonic number x F0 or F1

what is noise

aperiodic complex wave

SNR formula

SNR = signal sound - background sound

signal sound

sound that you want to hear

ideal SNR in a classroom setting

12 dB above background noise

Typical SNR in a classroom

Below 12 dB

reverberation time

how quickly sound fades away in a room

how to improve classroom acoustics

separating people, changing materials of the room, assistive technology, smaller rooms, microphones

band pass filter

passes a narrow range of frequencies

band reject filter

passes all EXCEPT a narrow range of requencies

low pass filter

lower frequencies are passes, while higher arent

high pass filter

higher frequencies are passed while lower ones arent