Intensity and Decibel Level
How loud we perceive a sound depends on both frequency and amplitude. Given a
fixed frequency, we can say that loudness is measured by intensity.
Intensity: I =Where P is the power produced by the source and A is the area over which the
power is spread. Consider a point source emitting a sound wave in all directions.
At a distance r, the A = 4πr^2 (the surface area of the sphere). Therefore, I ∝. If
a listener doubles the distance to the source, the sound will be heard one-fourth as
loud. An alternate way of measuring loudness is with the decibel level (sometimes
called relative intensity).
Listen Up!
There’s an easier way to
think about this formula.
Each time you multiply I
by 10, add 10 to β. Each
time you divide I by 10,
subtract 10 from β.