Trane TRG-TRC007-EN manual Sound Power and Sound Pressure, Fundamentals of Sound, period one

period one

Fundamentals of Sound

notes

Sound Power and Sound Pressure

ISound power

KAcoustical energy emitted by the sound source

KUnaffected by the environment

ISound pressure

K Pressure disturbance in the atmosphere

K Affected by strength of source, surroundings, and distance between source and receiver

Figure 11

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.

TRG-TRC007-EN 9