Question

What is the SI unit for sound?

Answer 1

The SI unit for sound is the **decibel (dB)**, which measures the intensity of sound. However, it is important to note that the decibel is a logarithmic unit that expresses the ratio of a particular sound level to a reference level.

In terms of sound pressure level, the reference level is typically set at 20 micropascals (µPa), which is considered the threshold of hearing for the average human ear. The formula to calculate sound pressure level in decibels is:

\[
L_p = 20 \log_{10} \left( \frac{p}{p_0} \right)
\]

where:
- \( L_p \) is the sound pressure level in decibels,
- \( p \) is the sound pressure in pascals,
- \( p_0 \) is the reference sound pressure (20 µPa).

For measuring sound power, the reference level is set at 1 picowatt (pW), and the formula used is slightly different.

In addition to decibels, the fundamental physical quantity related to sound is **sound pressure**, which is measured in pascals (Pa).

Answer 2

The SI unit for sound is the **decibel (dB)**. However, it's important to clarify that decibels are actually a unit of measurement for sound intensity or sound level, and they are not an SI unit in themselves. Instead, decibels are a logarithmic unit used to express ratios, such as the ratio of sound pressure relative to a reference value.

The fundamental SI unit for sound pressure, which is related to the intensity of sound, is the **pascal (Pa)**. Sound pressure level is often expressed in decibels using the formula:

\[ L_p = 20 \log_{10} \left( \frac{p}{p_0} \right) \]

where:
- \( L_p \) is the sound pressure level in decibels (dB),
- \( p \) is the root mean square sound pressure,
- \( p_0 \) is the reference sound pressure (typically 20 µPa in air).

For sound intensity (power per unit area), the SI unit is the **watt per square meter (W/m²)**. Sound intensity level in decibels can be calculated similarly to sound pressure level but based on intensity measurements.