Sound POWER vs Sound PRESSURE - what's the difference?
Most the folks we work with are not acoustical consultants. But most of the projects are influenced by the sound that equipment creates. Understanding how HVAC equipment sound is measured and conveyed is important - and at the very core is the understanding of sound power vs sound pressure.
One of the easiest ways to grasp this concept is to think of your standard light bulb. Assume this bulb is in a lamp with a shade in the corner of the room. Now, no matter where you stand or what is between you and that bulb, the POWER of that bulb doesn't change - it is always 60 watts. However, if you stand over the lamp and look directly at the bulb, the light you see is very bright. And if you walk to the other side of the room, and the shade is in between you and the bulb, the light you see is significantly less bright.
The brightness you see, dependent on your environment and the distance between you and the bulb, is the PRESSURE of that bulb.
So - sound power is the independent rating of the equipment's sound, regardless of the environment. Sound PRESSURE is the sound rating of what you ultimately hear based on the environment and distance from the equipment.
AHRI has many sound testing procedures - it's important to understand these as they pertain to your specific equipment.