Acoustics — in SI units, the “power” of a sound source is measured in which unit?

Introduction / Context:
Sound power is the total acoustic energy emitted by a source per unit time. It is a fundamental quantity in building acoustics, environmental noise control, and equipment specifications, distinct from sound pressure (a local field quantity) and from decibel-scaled levels used for comparison and regulation.

Given Data / Assumptions:

• We are asked for the SI unit of “power,” not “energy,” “force,” or “mass.”
• Acoustic power can be converted to sound power level (dB) using a reference power.

Concept / Approach:

In SI, power is measured in watts (W), equal to joules per second. In acoustics, sound power level Lw (in dB) is defined by 10 * log10(P/P0), where P0 = 1 picowatt for airborne sound. This should not be confused with sound pressure level (SPL) measured in decibels referenced to 20 micropascals, nor with force (newton) or mass (kilogram).

Step-by-Step Solution:

Verification / Alternative check (if short method exists):

Check dimensional consistency: energy (J) per time (s) → W. ISO acoustic standards confirm power in watts.

Why Other Options Are Wrong:

Joules are energy, not power; “neutons” appears to be “newtons,” a unit of force; “kgs” is mass; decibels are logarithmic levels, not base SI units of power.

Common Pitfalls (misconceptions, mistakes):

Confusing sound power (a source property) with sound pressure (a field measurement) or with subjective loudness metrics.

Final Answer:

watts