Learn: speech science - exam 2

incident wave

sound wave generated by a vibrating source, has traveled a certain distance & hits a boundary

what are the actions an incident wave can take when it hits a boundary?

can be transmitted, absorbed, reflected, refracted, or diffracted

transmitted

sound wave moves through the boundary (thick wall - not transmitted, thin wall - transmitted)

absorbed

damping of wave, with diminishing changes in air pressure due to the friction of the air

what materials are more absorbant?

soft, rough surfaces (ex. foam in recording studio)

what materials are less absorbant?

smooth, flat surfaces

reflection

portion of the wave is not absorbed or transmitted, it bounces back from the surface & travels in opposite direction of the incident wave

what does the amount of reflection depend on?

the surface type

what types of surfaces reflect sounds more easily?

smooth, hard surfaces

refraction

occurs when a sound wave changes direction because of a local difference in air temperature

which way will a sound bend (refract)?

towards cooler air

diffraction

refers to a change in direction as a wave passes through an opening or over an obstacle

the ______ the wavelength of a sound wave, the more it diffracts

longer

_____ frequency sounds have a longer wavelength, and they will travel ____ over a distance

lower, better

interference

the combination of incident & reflective waves occupying the same space

constructive interference

areas of compression and rarefaction of 2 waves combine at the same time & space, amplitude of resulting wave will be doubled

constructive interference leads to __________ of compressions and rarefactions

reinforcement

reinforcement

wave has a greater intensity

destructive interference

area of compression and rarefaction combine at the same moment in time, the amplitude of the wave is decreased

destructive interference leads to ______

cancellations

cancellations

wave has a weaker intensity

what happens if two sound waves of the same amplitude and frequency were combined to match the compression of one wave with the rarefaction of another?

complete damping, the pressure would go back to ambient because the areas of high & low pressure would combine

what would happen if two waves of different frequencies combine?

waves with different frequencies would combine, but the areas of compression and rarefaction are unpredictable

reverberation

sounds last slightly longer because of interference, happens when a reflected sound arrives at your ear slightly delayed compared with the arrival of the incident wave at the same time

too much reverb can interfere with the understanding of...

speech

why do you hear one, longer sound?

because the reflected waves arrive in time to keep your eardrum vibrating for longer than the incident wave

echo

a reflected sound wave, distance between the reflective surface and the ear is great, so the sound is perceived as separate

how can reverberation cause issues in a classroom?

classrooms are overly reverberant, uncarpeted floors, concrete walls, & windows (smooth surfaces)

how is intelligibility affected in classrooms?

the low frequency sounds (vowels) mask the high frequency sounds (consonants) & nearly all the information in speech is found within the consonants

the more reflective a room the _____ the incident sound & reflection take to damp & be absorbed

longer

frequency

cycle of vibrations in a second, objective & measured in Hz

pitch

perceptual correlate of frequency

low frequency of vibration =

low pitch

high frequency of vibration =

high pitch

what determines the frequency of a vibrating object?

length, mass, & tension

if you increase the length of an object, you ____ the frequency

decrease

if you increase the mass of an object, you ____ the frequency

decrease

if you increase the tension of an object, you _____ the stiffness & _____ the frequency

increase, increase

what can our vocal folds be compared to?

a rubber band

using a rubber band, increasing length ______ frequency

increases

why does increasing length increase frequency with a rubber band?

because the cross sectional area & mass is decreased

equation for the frequency of a vibrating strong

f = (1/2L) * √(T/m)

L = length

t = tension

m = cross-sectional mass

what ranges of frequencies can the human ear detect?

20-20,000 Hz

what are frequencies above this range called?

supersonic

what are frequencies below this range called?

subsonic

what range of frequencies do we hear the best in?

1000-4000 Hz, most speech sounds are in this range

amplitude

amount of displacement from rest of a vibrating object, for sound the amount of pressure change generated by the motion of the object

what is amplitude measured in (for speech)?

micropascals

root mean square

averages amplitude/pressure changes (peak-to-peak change), steadiness of wave overall, better measure of typical vs nontypical, RMS will always be lower than the peak-to-peak measure

intensity

power per unit area, the power of sound

what is intensity measured in?

watts/cm^2 (cgs)

loudness

how you perceive intensity which is based on the degree of pressure change (perceptual correlate of intensity)

how much a change in amplitude & intensity must occur before we perceive a sound has become louder?

a sound must be 10x as intense as the reference sound before it is perceived as 2x as loud as the reference sound

how are amplitude & intensity related?

intensity is proportional to the square of amplitude (I=A^2)

characteristics of a deibel

involves a ratio, uses a logarithm, is nonlinear, is expressed in terms of various reference levels, is a relative unit of meausre

decibel scale

a logarithmic ratio that either compares amplitude or intensity to a standard reference sound

why use the dB scale to describe sound intensity?

we can compress the great number of intensities we hear into fewer levels

log10 (100) =

2

log10 (1000) =

3

what is the standard reference sound for intensity?

10^-12 W/m2 (mks) or 10^-16 W/cm2 (cgs)

what is the standard reference sound for amplitude?

20 µPa (0.0002 dyne/cm^2 or 0.0002 microbar)

threshold of hearing

sound of interest has the same intensity/amplitude as the reference sound, sound of this amplitude/intensity is the softest humans can hear 50% of the time in good conditions

what does 0dB mean?

threshold of hearing, not no sound!

is it possible to have a sound at -5dB?why?

yes, sound is simply less intense/has less amplitude than the reference sound

what is the equation to find dB IL?

dB IL = 10 log10 I1/I0

what is I1 in this equation?

the target sound

what is I0 in this equation?

the standard reference sound of 10^-12 W/m^2

if you had a sound that was 100x as intense as the reference sound, it would be calculated as a ____ change

20 dB

how can you manipulate the intensity equation to account for amplitude?

because intensity is proportional to the square of amplitude, you can square the pressure values of the equation to change it to dB SPL

what is the equation for dB SPL

dB SPL = 10 log10 (P1^2/P2^2)

when measuring amplitude, all units are referenced to a ______ _______ ______

sound pressure level (SPL)

when measuring intensity, all units are referenced to an ______ _______

intensity level (IL)

what does a zero on the dB scale represent?

a one to one ratio of the targete sound and the reference sound

zero dB means that there is no sound (t or f)

false

what does a 1 dB step on the dB scale represent?

26% change in intensity

1 dB is the _______ change in sound that can be detected by someone with normal hearing

smallest

doubling of sound power

3 dB increase

halving of sound power

3 dB decrease

changing intensity by a factor of 10

10 dB change

doubling sound pressure

6 dB increase

halving sound pressure

6 dB decrease

changing sound pressure by a factor of 10

20 dB change

what is the advantage of the dB scale?

it can represent a large range of intensity of sounds we are capable of hearing

what frequencies of sounds are we more sensitive to?

midrange frequencies from 1000-4000 Hz

threshold of pain

any frequency with an intensity of around 130 dB will cause a sensation of pain in the ear

resonance

the tendency of a system or object to vibrate with the greatest amplitude in response to a frequency that matches its natural frequency

natural frequency

frequency at which an object vibrates freely without interference, this is based on its physical characteristics

which characteristics affect natural frequency?

mass, tension, length, stiffness, and density

forced vibration

vibrators from on object can set another object into vibration if the natural frequencies of the two objects are close to each other

the closer the applied (driving) frequency and resonant frequencies, the _____ the amplitude of the response of the resonator

greater

acoustic resonance

occurs when an air-filled container is forced to vibrate by an applied frequency or frequencies

Helmholtz resonator

a vibrator consisting of a volume of enclosed air with an open neck or port

smaller volumes vibrate with a _____ frequency

higher

larger volumes vibrate with a _____ frequency

lower

with an air filled tube (like the vocal tract) the natural frequency is determined by...

1) length of the tube 2) shape of the tube 3) where it is opened/closed

longer tubes resonate sounds that are _____ in frequency

lower

nodes

points along the wave that vibrate with a minimum amplitude (n - nothing)

antinodes

points along the wave that vibrate with maximum amplitude (all)

what is a tube open at both ends known as?

a half wave resonator

half wave resonator pressure relationship

pressure at the openings is Patmos, greatest pressure is somewhere in the middle