What are the two intensities required to use decibels?

What are the two intensities required to use decibels?

• A. The reference or starting level
• B. Actual level at the time of measurement
• C. Both intensities are necessary to use decibels
• D. The reference or starting level and Actual level at the time of measurement

Answer: (D)

Decibels express a ratio between two levels, not an absolute quantity. To get a decibel value you must know both the level you’re measuring and the reference level you’re comparing it to—the two intensities involved. This is why the reference or starting level and the actual level at the time of measurement are both needed: the decibel value is derived from how much the measured level differs from the reference, using a logarithmic scale (for power, 10 log10(P/P0); for voltage or field quantities, 20 log10(V/V0)). For example, saying a sound is a certain number of decibels relative to the reference pressure requires knowing both the actual sound pressure and the reference pressure. Without the reference, the decibel value has no meaning, and without the measured level, there’s nothing to compare.

Decibels express a ratio between two levels, not an absolute quantity. To get a decibel value you must know both the level you’re measuring and the reference level you’re comparing it to—the two intensities involved. This is why the reference or starting level and the actual level at the time of measurement are both needed: the decibel value is derived from how much the measured level differs from the reference, using a logarithmic scale (for power, 10 log10(P/P0); for voltage or field quantities, 20 log10(V/V0)).

For example, saying a sound is a certain number of decibels relative to the reference pressure requires knowing both the actual sound pressure and the reference pressure. Without the reference, the decibel value has no meaning, and without the measured level, there’s nothing to compare.