Sound Pressure Level (SPL) vs Sound Power Level (SWL)

What is the difference?

Sound Pressure Level (SPL)	Sound Power Level (SWL)
What you hear	What the source produces
Measured at a specific location	A property of the sound source
Changes with distance	Does not change with distance
Affected by barriers, terrain and weather	Independent of surroundings
Measured using a sound level meter	Determined through laboratory or standardised testing
Used for compliance monitoring	Used for noise modelling and equipment specification

Think of it this way

Imagine a generator operating at a mine.

The generator has a Sound Power Level of 118 dB.

As you move further away, the noise you hear becomes quieter.

At 10 metres, the Sound Pressure Level may be 82 dB(A).

At 100 metres, it may reduce to 62 dB(A).

At 500 metres, it may be only 42 dB(A).

Even though the noise at the receiver changes significantly, the generator still has a Sound Power Level of 118 dB because the source itself has not changed.

Sound Pressure Level (SPL)

Sound Pressure Level is the noise measured at a specific location and point in time.

It is influenced by many factors including:

• Distance from the source
• Buildings and barriers
• Ground conditions
• Weather conditions
• Topography
• Other nearby noise sources

Because of these influences, the measured SPL can vary considerably even though the sound source remains unchanged.

Sound Power Level (SWL)

Sound Power Level is a measure of the total sound energy emitted by a source.

Unlike Sound Pressure Level, it is independent of distance and the surrounding environment.

This makes SWL an ideal value for describing the noise output of machinery because it allows different equipment to be compared under consistent conditions.

Why are both important?

Sound Power Level is used as the starting point for most environmental noise models.

Acoustic software uses the Sound Power Level of each source and then calculates the Sound Pressure Level at surrounding receivers after accounting for distance, terrain, buildings, vegetation and atmospheric effects.

Without Sound Power Levels, accurate noise predictions would not be possible.

When is Sound Pressure Level used?

Sound Pressure Level is commonly used for:

• Environmental noise monitoring
• Occupational noise assessments
• Community noise surveys
• Construction noise monitoring
• Event noise monitoring
• Compliance measurements

When is Sound Power Level used?

Sound Power Level is commonly used for:

• Environmental noise modelling
• Predicting future noise impacts
• Comparing machinery noise emissions
• Equipment specifications
• Mining and industrial noise assessments
• Selecting quieter plant and equipment

Which measurement do I need?

If you are measuring the noise that people actually experience, you are almost always dealing with Sound Pressure Level (SPL).

If you are predicting noise from new equipment or modelling future developments, you will generally need the Sound Power Level (SWL) of the source.

In practice, both measurements work together. Sound Power Level describes how much sound a source generates, while Sound Pressure Level predicts or measures how much of that sound reaches a particular location.