What do the different Sound Measurements mean?

TL:DR

Term	What It Means	How It Works	Where It’s Measured
Lw [dB] – Octave/Third Band	Sound power in different pitches (frequencies).	Shows how loud each sound pitch is.	Only looks at the machine itself.
Lw [dB]	Total sound power from the machine.	Adds up all the sound, no matter the pitch.	Only looks at the machine itself.
LwA [dBA]	Total sound, but how humans hear it.	Focuses on sounds humans notice more.	Only looks at the machine itself.
Lp [dB(A)] @ 3m	How loud the sound feels at 3 meters away.	Measures sound like a person standing nearby.	At a distance of 3 meters.

What is the difference between:

The listed terms describe different ways of measuring and representing sound. Here’s a breakdown of each, highlighting their differences:

a. Sound Power Level Lw [dB] – Inherent Octave/Third Band

Definition: This measures the sound power level of a source, expressed in decibels, but broken down into specific frequency bands (octave or third-octave bands).
Purpose: Provides a detailed frequency spectrum analysis of the sound power output.
Unit: Decibels (dB), without weighting.
Key Characteristic: Focuses on the frequency-specific distribution of sound power.

b. Sound Power Level Lw [dB]

Definition: Represents the total sound power level emitted by a source across all frequencies.
Purpose: Gives the overall sound energy output, summing contributions from all frequency bands.
Unit: Decibels (dB), unweighted.
Key Characteristic: This value is independent of the environment and measures the intrinsic power of the sound source.

c. Weighted Sound Power Level LwA [dBA]

Definition: This is the A-weighted sound power level, which applies a frequency weighting to mimic the sensitivity of the human ear (more sensitive to mid-frequencies, less to low and high frequencies).
Purpose: Provides a perception-based measure of sound power, emphasizing frequencies humans are more likely to notice.
Unit: dBA (decibels A-weighted).
Key Characteristic: Offers a more realistic assessment of perceived loudness from the sound power of the source.

d. Weighted Sound Pressure Level [dB(A)] Free Field @ 3m

Definition: The A-weighted sound pressure level measured in a free field (an environment without significant reflections, such as an open space) at a distance of 3 meters from the source.
Purpose: Measures the sound as perceived at a specific location and distance from the source, accounting for both the source’s power and the propagation effects.
Unit: dB(A) (decibels A-weighted).
Key Characteristic: Dependent on distance, environment, and atmospheric conditions. It reflects the perceived sound level at a particular point in space.

Summary of Differences:

Term	What it Measures	Frequency Weighting	Environment/Distance
Lw [dB] – Inherent Octave/Third Band	Frequency-specific sound power levels	None (unweighted)	Intrinsic to the source
Lw [dB]	Total sound power emitted by a source	None (unweighted)	Intrinsic to the source
LwA [dBA]	Total sound power with human perception	A-weighted	Intrinsic to the source
Lp [dB(A)] Free Field @ 3m	Perceived sound pressure at 3m distance	A-weighted	Depends on distance & field