3030 - ch. 1 Nature of sound

What are the components needed for the production of sound

1) energy source

2) body capable of vibration

3) transmitting medium e.g. air

How is sound produced

When a disturbance creates changes in pressure in a gas

Brownian motion

air molecules are in random, constant motion

The collision of air molecules produce

pressure

Pressure equation

P = F/A

Unit of force

dyne (d)

Unit of area

cm^2

Positive pressure

Pressure higher than atmospheric

Negative pressure

Pressure lower than atmospheric

Air always moves from areas of ______ to ______ pressure.

High, low

Volume velocity

rate of flow; speed of a volume of air traveling in a certain direction

Driving pressure

difference in pressure that causes air to move from high to low pressure

Molecules of air have a natural tendency to ______.

equalize

Air can flow with ______ degrees of ________ or _________.

various, smoothness, turbulence

Boyle's Law

inverse relationship exists between air volume and pressure if there is a constant temperature and density

As volume increases, air pressure _______ (at constant temperature)

decreases

As volume decreases, air pressure _______ (at constant tempreature)

increases

Ambient pressure

Air molecules move around and create a relatively steady pressure

For sound to be generated, ______ must be disturbed

ambient pressure

compression

area of positive/high pressure; when air molecules have an increased density

When there is compression, there is a ______ in pressure

increase

rarefaction

area of negative/decreased pressure, air molecules now have increased distance between them; decreased density of air

Elasticity

restoring force, an object's ability to spring back to its original form

Hooke's Law

restoring force of elasticity is proportional to amount of displacement undergone by object

Inertia

tendency of matter to remain at rest or continue in a fixed direction unless acted on upon another outside force

Over time, _____ acts on air molecules.

frictional resistance of air

Damping causes an object to vibrate with _____ amplitude

less

Wave

disturbance that moves through a medium

Wave motion is

longitudinal

Wave front

outermost area of sphere of sound wave

Cycle

one back and forth movement of the molecule

Frequency

number of cycles of vibration in one second

unit of frequency

Hertz (Hz)

Period

time that each cycle in a wave takes to occur

Period and frequency are ______

reciprocal

Period formula

T = 1/frequency

Frequency formula

Frequency = 1/T

Periodic wave

wave in which each cycle takes same amount of time to occur

Aperiodic wave

wave in which each cycle takes a different amount of time to occur

How fast a wave moves depends on the properties of the medium

1. Density

2. Elasticity

The speed of sound in air is _____ m/s

343

The speed of sound in air is _____ ft/s

1,126

Sound travels faster through _____ than through ______

solids, liquids

If there is a higher temperature, sound moves ______

faster

If there is a higher altitude, sounds moves _____

slower

Wavelength formula

Wavelength = speed of sound (c)/frequency (f)

The ______ the frequency, the shorter the period/wavelength

higher

The lower the frequency, the _______ the period/wavelength

longer

Incident wave

sound wave that hits a boundary

Transmission of incident wave

sound is propagated through the boundary

Absorption of incident wave

sound is damped

Reflection of incident wave

some portion of sound bounces back

Ratio of sound absorbed to sound reflected

Coefficient of absorption

Diffraction

the way sound changes when it encounters a barrier and passes around that barrier/through a hole in the barrier

Constructive interference

when two waves combine and intensify the amplitude of the sound

Destructive interference

when two sound waves are out of phase and decrease the amplitude of the sound

Reverberation

when a sound lasts slightly longer after the source stopped

Duration of delay depends on _____ between the reflective surface and your ear

distance

Pure tone

single frequency of a vibration pattern called simple harmonic motion

SHM

regular, smooth, back-and-forth movement

Complex wave

consists of two or more frequencies

Fundamental frequency

lowest frequency of a complex periodic sound

Harmonics

whole number multiples of the fundamental frequency

Types of aperiodic complex sound

1. Continuous

2. Transient

continuous aperiodic complex sound

prolonged sound e.g. radiator hissing or white noise

transient aperiodic complex sound

brief in duration, e.g. clapping hands together

Speech is composed of complex _____ and ______ waves.

periodic, aperiodic