It’s very common to confuse sound pressure level, sound intensity level, and sound power level.
It’s important to know the difference so that you can understand technical specifications and communicate with others clearly.
In this article, you’ll learn the difference between sound power, intensity, and pressure levels. If explained properly, it’s easy to understand the difference.
Sound power level is the total acoustical energy created by a sound source.
Sound intensity level is the amount of acoustical energy flowing through an area of space.
Sound pressure level is the amount of force at a given point in space.
Sound Power Level vs Intensity Level vs Pressure Level
Power, intensity, and pressure levels are all ways of describing sound. Although they are different, they are related.
Sound power level is the total acoustical energy created by a sound source, sound intensity level is the amount of acoustical energy flowing through an area of space, and sound pressure level is the amount of force at a given point in space.
I was recently introduced to a visualization for understanding power, intensity, and pressure level by a friend who is an acoustics professor at a university. I found it very helpful for understanding the difference between the various levels used to describe sound.
Hopefully it will help you to better understand sound levels, too.
A Visual Aid for Understanding Sound Levels
Imagine a balloon coated in honey…
You can relate sound power level, pressure level, and intensity level to the characteristics of the balloon and the honey as the balloon inflates.
The inflating balloon is similar to a sound wave as it expands away from the sound source.
Sound Power Level
As the balloon is inflated, the total amount of honey remains constant. This relates to sound power level, because the quantity is the same no matter how big the balloon becomes.
A sound source produces a certain quantity of acoustical energy. This quantity of energy is called the sound power level and remains constant.
Power level is independent of the listening distance. Regardless of how far the sound travels from its source, the power created at the sound source remains the same.
Sound Intensity Level
If the balloon becomes larger while the total amount of honey coating the balloon remains the same, there will be less honey per square inch as the balloon continues to grow. The amount of honey per square inch relates to sound intensity.
Sound intensity describes the amount of energy flowing through an area of space.
As a sound wave radiates outward away from its source, it forms a sphere of acoustical energy. The sphere grows larger as the sound travels further from the source.
The intensity of the sound decreases as the sphere becomes larger, because there is only a finite amount of energy created by the sound source. That energy is spread thinner and thinner as the surface area of the sphere grows.
This is explained by the inverse square law, which states that the reduction of a sound’s intensity is proportional to the inverse square of its distance away from the sound source.
Read this Audio University article for more information about the inverse square law.
Sound Pressure Level
As the honey is spread thinner and thinner along the surface area of the balloon, the thickness of the honey coating is decreased. The thickness of the coating of honey at a given point along the surface area of the balloon relates to sound pressure level.
Sound pressure level describes the force at a point in space, such as a microphone diaphragm or an eardrum.
In audio production, sound pressure is much more relevant than intensity because our ears and microphones measure sound pressure changes.
Conclusion
Hopefully this model for visualizing the difference between sound power level, sound intensity level, and sound pressure level has been helpful.
In audio production, sound pressure level is the most relevant, because it relates to how we hear and how we measure sound with microphones.