SLHS 302 Section 1

why study hearing science?

important for vocal communication, survival, and to understand/treat hearing loss

audibility

detecting sound

intelligibility

understanding sound

hearing loss

affects both audbility and intelligibility

17

percent of American adults that report some degree of hearing loss

signals and systems approach

the ear transforms sound waves into vibrations into neural signals

why we use a signal and systems analysis in speech and hearing?

to understand the physiological systems we are studying and to understand the technological signals and systems that we use in our work to study speech and hearing issues

sound

the vibration of an object that results in the oscillation of a medium through which energy propagates

media

air, water, floor and walls, string

sound source

a disturbance that produces a sound

elastic medium

the medium through which sound travels; any material with mass and elasticity

elasticity

the ability of a mass to return to its natural shape

air

easy to compress so not very elastic

sound pressure wave

how we visualize sound in the physical domain

waveform

how we visualize sound in the time domain

amplitude spectrum

how we visualize sound in the frequency domain

peaks

compressions or high pressure areas

troughs

rarefactions or low pressure areas

sound wave

the visualization of the physical propagation of sound

particle motion

air particles osscilate back and forth around their equilibrium position

sound waves

longitudinal waves

sine wave equation

d(t) = A sin(2πft+θ)

sine wave

indicates change in pressure over time

mechanical

variation in displacement over time

acoustical

variation in air pressure with time

electrical

variation in voltage with time

amplitude

how large is the displacement?

amplitude

how tall it is; related to loudness

instantaneous amplitude

amplitude measured at a given point along a wave

instantaneous amplitude

peak amplitude

maximum displacement from equilibrium; related to the size of the vibration

peak amplitude

peak-to-peak amplitude

maximum change in displacement

peak-to-peak amplitude

root-mean-squared (RMS) amplitude

a way to quantify the “power” of a signal; helpful representation of amplitude for zero-mean signals

RMS

the square root of the mean (average) of the squared instantaneous amplitudes

frequency

how many times per second does it repeat

frequency

how many squiggles; related to pitch

period

the time taken to complete one cycle

period of a sine wave

movement from equilibrium to maximum displacement in one direction, back to equilibrium, on to maximum displacement in the opposite direction, and then back to equilibrium

period (sec)

cycle

identifed as extending from any point in a wave to the next identical point in the wave

cycle

A

½ cycle

B

frequency

f = 1/T

1 Hz

1 cps

period (T)

T = 1/f

more periods

in a given time as frequency increases

phase

what is the displacement at a given time?

phase

which point along the “squiggle”

phase

differences between the ears are useful for sound localization

phase angle or instantaneous phase

the displacement in degrees at any given instant

phase relationship or difference

lead and lag

inertia (mass)

property that objects in motion tend to stay in motion

elasticity

property of an object, the tendency to return it to its resting state

friction (damping)

will decrease motion over time

amplitude of motion

gradually diminished as energy is lost due to friction

frequency of oscillation

controlled by mass and stiffness; not affected by damping

pressure

a measure of force per unit area

pressure

p = F/area

pressure

reduces if the same force is acting over a larger area

air pressure

a function of the force exerted on a given area by the molecules of air

air pressure increases when

number of molecules increases; volume decreases; density increases

density

amount of mass per unit volume; can change due to number of molecules or the volume

sound wave

alternations of condensation and rarefaction of a medium which propagates through space

wave propagation

a result of the successive oscillations of air molecules

frequency

a function of its sound source and in turn depends on the object’s elasticity and mass; unaffected by the sound transmission medium

wavelength

the amount of distance covered in a single period of a wave

speed of propagation

a function of the medium; measured in meters per second

speed of sound equation

water is more compressible

why water molecules are closer to one another

speed of sound in air

350 m/sec

why does sound move faster in water?

molecules are pushed to one side, encounter other molecules much faster, creating areas of condensation much faster

frequency

determined purely by the sound source

speed

independing of the loudness or frequency of sound

what happens to wavelength when c changes

wavelength becomes longer than in air

sound waves

propogate through a medium in all 3 dimensions

sound intensity

power per area

What happens to intensity as you get farther from a sound source?

the intensity of the sound that will reach your ears gets lower

inverse square law

intensity is inversely related to the square of the distance for spherical waves

inverse square law equation

I = P / (4pir²)

sound pressure

indicates how compressed or rarefied the air particles are

sound pressure

p = F/A

sound intensity

indicates how much sound power is transferred from the sound source to the surrounding area

sound intensity

I = P/A

loudness of sound is related to

its intensity and pressure

pressure

force per unit area

intensity

power per unit area

power

the rate at which energy is transferred by a wave

power

independent of area

sound pressure and intentisty

the amplitude of the sound wave

sound pressure and intensity

depend on the distance from the sound source

sound intensity

proportional to the square of sound pressure

sound intensity

Watts/m²

sound pressure

Newtons/m²

160 dB

instant perforation of eardrum

110 dB

prolonged exposure - hearing loss

0 dB

threshold of hearing

Bel

the logarithm of a ratio of two intensity values

Bel