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TRG-TRC007-EN 9
period one
Fundamentals of Sound
notes
Sound Power and Sound Pressure
Sound power and sound pressure are two distinct and commonly confused
characteristics of sound. Both are generally described using the term decibel
(dB), and the term “sound level” is commonly substituted for each. To
understand how to measure and specify sound, however, one must first
understand the difference between these two properties.
Sound power is the acoustical energy emitted by the sound source, and is
expressed in terms of watts (W). It is not affected by the environment.
Sound pressure is a pressure disturbance in the atmosphere, expressed in
terms of pascals (Pa), that can be measured directly. Sound pressure magnitude
is influenced not only by the strength of the source, but also by the
surroundings and the distance from the source to the listener. Sound pressure
is what our ears hear and what sound meters measure.
While sound-producing pressure variations within the atmosphere can be
measured directly, sound power cannot. It must be calculated from sound
pressure, knowing both the character of the source and the modifying
influences of the environment.
Sound Power and Sound Pressure
I Sound power
K Acoustical energy emitted by the sound source
K Unaffected by the environment
I Sound pressure
K Pressure disturbance in the atmosphere
K Affected by strength of source, surroundings, and
distance between source and receiver
Figure 11