Hearing Science Midterm

3 components needed for production of sound

1) an energy source
2) a body capable of vibration
3) a transmitting medium (the propagating medium most
relevant to humans is air)

How does a sound occur

A disturbance (movement) creates a change in pressure in a medium

• The pressure changes created by the disturbance are
  transmitted through the medium (e.g., air) and may end
  up at the listener’s ear to be perceived as sound

Sound

Vibrations propagated through air that are within the frequency range of our hearing

Pressure (P)

A force (F) that acts perpendicularly on a surface area (A) P = F/A

• Air pressure can move the eardrum inwards and outwards

Characteristics of air molecules

1) Natural tendency to equalize

2) Air can flow with various degrees of smoothness or turbulence

3) There is an inverse relationship between air volume and pressure, and a proportional relationship between air pressure and density

Flow

Movement of air through a particular area in a certain interval of time (l/s, l/min, ml/s, ml/min)
• The rate of flow is volume velocity (the speed of a volume of air
traveling in a certain direction)

Driving pressure

Difference in pressure that causes air to flow from higher to lower pressure (crucial in generating speech)

Ambient pressure

Air molecules move around, creating a relatively steady pressure; must be disturbed for a sound to be generated

Compression

When air molecules collide (increase in density)

Rarefaction

The displaced air molecules do not remain displaced, but swing back toward their original positions; they overshoot their marks and swing farther away to the other side of
their original positions, resulting in an increased distance between groups of molecules and decreased density

Wavelike motion of sound

increases & decreases in air pressure radiate outward from the source in all directions

Elasticity

A restoring force; the property of an object to be able to spring back to its original size, form, location, & shape

Inertia

The tendency of matter to remain at rest or to continue in a fixed direction unless affected by some outside force; causes the overshoot

Frictional resistance of air

Vibration of air molecules does not continue indefinitely. Because of the frictional resistance of air, each time molecules move back and forth around their rest
positions, they do so with less amplitude.

Amplitude

Maximum distance away from rest that an object has been displaced

Damping

occurs due to friction and causes an object to vibrate with less amplitude

Wave

Disturbance that moves through a medium

Longitudional waves

The individual air molecules move parallel to the direction the wave is traveling

Wave front

The outermost area of the sphere

Cycle

One back-and-forth movement of the molecule, typically measured in seconds

Frequency

The number of cycles of vibration in one second, measured in hertz (Hz)

Period

The time that each cycle in a wave takes to occur
• Period and frequency are reciprocal,
• Period = 1/frequency Frequency = 1/period