16
7
Analyzing Data
7.1
Theory
7.1.1
Sound Intensity vs Sound Pressure
Sound Intensity is a vector quantity with a magnitude and a direction. It represents the rate of
sound energy flow through a unit area.
A sound intensity probe using a pair of pressure sensing microphones will pick-up only the vector
component which is in-line with the reference axis of the probe. Hence, a sound intensity probe
measures the normal component of sound energy flow through a surface.
Thus the normal energy flow will equal the full magnitude of the sound intensity vector when the
vector is in line with the reference axis. It will be positive when pointing in the reference direction
(from mic 1 to mic 2) and it will be negative when pointing in the opposite direction (from mic 2 to
mic 1). In addition, a null energy flow will be measured when the vector is perpendicular to the
reference axis.
Reference Axis
Vector
Energy Flow
Normal
Energy Flow
Measurement
Surface
Mic 1
Mic 2
Reference Axis
(Reference
Direction)
Positive
Energy Flow
Negative
Energy Flow
Null
Energy
Flow
