ch. 2 (physics of sound)

sound

physical phenomenon that describes a mv’t or vibration of an elastic medium w/o permanent displacement of the particles

3 prereqs:

• source of energy

• vibrating obj. that generates an audible pressure wave

• medium of transmission (ie: air)

*measured in pressure

mass

quantity of matter present

force

a push or a pull on an object

elasticity

tendency of an object’s resistance to deformity & its return to the rest position

inertia

tendency to resist any change in motion

• Newton’s first law

  • outside force must be applied to overcome inertia

  • the greater an object’s mass, the greater the inertia

4 properties of simple harmonic motion

1. frequency

2. amplitude

3. period

4. phase

frequency

the number of complete vibratory cycles per unit time (cycles per sec)/speed of vibration

• unit of measurement: Hz

• one compression, one rarefraction

• psychological equivalent: pitch

amplitude

a derived unit of measurement describing an object’s distance from rest to maximal displacement

• psychological equivalent: volume

period

amount of time needed to complete one cycle of vibration

• shorter for an 800 Hz tone than 400 Hz tone

phase

relative timing of compressions and rearefactions of waves (how cycles relate to each other)

decibel

a ratio between measured sound pressure and relative sound pressure, using log. used to note the intensity of the range of human hearing

• unit of measurement: dB

• 1/10 of a Bel

• logarithimic (base 10)

• expressed as a ration

decibel scales

• sound pressure lvl (dB SPL)

• hearing lvl (dB HL)

• sensation lvl (dB SL)

process of hearing

1. pressure waves emulate from a souce

2. pressure waves propogate thru a medium (usually air)

3. waves reach the tempanic membrane (eardrum)

4. tempanic membrane transforms the energy to mechanical energy

5. mechanical energy is converted to hydraulic energy in the fluids of the cochlea

6. mv’t of cochlea releases nuerotransmitters to the brain

what sound requires

• a source of vibratory energy

• energy must be delivered to & cause a disturbance in a medium (air, liquid, etc)

• disturbance is propogated in the medium in the form of sound waves that carry energy away from the source (condensation/rarefaction)

waveform

shape of a wave-done so by plotting the disturbance over time

cycle

equal to one compression and one rarefraction

phase

any stage of a cycle

intensity

magnitude of a sound, changes in sound pressure lvls

• psychological equivalent: loudness

• unit of measurement: dynes/cm²

wavelength

distance (in meter or centimeters) covered by one cycle/speed of sound/frquencey

speed of sound

331 m/s at normal atmospheric pressure

what is the sound pressure needeed to produce a just audible sound in normal, healthy ears?

• 0.00002 Pa

• 20 micropascals

dBIL

expresses intensity lvl, a power measure

• formula: P²

• power can be converted to pressure (SPL)

dBsPL

expresses dBSPL, a power lvlv or sound pressure lvl

• formula: dBSPL = 20 log (P₁/P₂)

True or False: 0 dB means the absence of sound

FALSE

pure tones

has only one frequency of vibration

absolute sensitivity

audiotry system’s capability of detecting that a sound exsist

differential sensitivity

distinct features of sounds (frequency, intensity, and timing cues)

audiometric zero

the decibel lvl that is denoted as a solid black line on the audiogram & corresponds to 0 dh HL (represents average normal hearing acuity)

• 0 dB HL may not be the lowest lvl that a person w/ superiro hearing can detect

sensation lvl

a given number of dB above or below a certain threshold