Lecture 3 (sound intensity and inverse square law)

Sound Intensity

The intensity of a sound wave defined as the mean value of the acoustic energy which crosses a unit area perpendicular to the direction of propagation in unit time.

Intensity of the sound wave

The amount of energy transported past a given area of the medium per unit of time

Sound Intensity Level aka AIL

Level of intensity of a sound relative to a reference value

inverse square relationship

Mathematical relationship between intensity and distance

Inverse square Law

States that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity

Sound Feild

The technical name given go the dispersion of sound energy within bounderies

Free feild

A region where the acoustics wave can propagate free from obstruction that would otherwise interfere with the sound path

Diffuse Field

Opposite of free field, diffusion is scattering or reflection of sound wave. Constructed of reflected waves.

Near Feild

The region of space close to the emitting source. typically a complex constructive and destructive interference pattern due to wave being generated from an aperture of a set geometric size

Sound Pressure

The result of the pressure variations in the air achieved by the sound waves

Hearing threshold

Lowest sound pressure which can be heard by humans

Pain Threshold

Highest sound pressure which can be endured by humans

Sound pressure

The force of sound on a surface perpendicular to the propagation sound.

Unit of sound pressure

Pa or N/m2

Sound Pressure Level

Pressure of sound related to a fixed reference.

Quantity that is actually measured when a microphone is placed in a sound field

Sound Power

The total airborne sound energy radiated by a sound source per unit of time environment and measured at a specific location.

Sound power level

• A measure of the energy output of a sound source.

• Is a measure of the acoustic

energy emitted from a source of

noise, expressed in decibels.

Sound absorption

Defined as the loss of sound energy when sound waves come into contact with absorbent material.

Sound reflection

Defined as sound bouncing back a medium.

Follows law of reflection: the angle of incidence equals to the angle of reflection.

Sound transmission

Degree to which sound is transferred

Refers to sound which penetrates the dividing room

Sound Phenomenon

The dispersion of a sound wave separating into its component frequencies as it passes through a material or medium.

Sound absorption coefficient

The ratio of absorbed sound intensity in an actual material to the incident sound intensity.

Sound-absorbent material

Materials with absorption coefficient greater than 0.50

Sound-reflective material

Materials with absorption coefficient with less than 0.20

Noise Reduction

To reduce the sound transfer between different spaces, vertical elements will be applied to cut down sound energy, either pending from the ceiling or free-standing

Noise Reduction Coefficient

A scalar representation of the amount of sound energy absorbed upon striking a particular surface.

NRC of 0

Indicates perfect reflection

NRC of 1

Indicates perfect absorption