How to Calculate Decibels Relative to Acoustic Power

Decibels and acoustic power are two closely related measures of sound. Acoustic power is the amount of energy a sound wave transmits per unit area in a specific direction. Decibels measure the intensity of sound according to a logarithm of the ratio of the sound power to a reference power. The unit is named after the inventor of the telephone, Alexander Graham Bell. The most important difference between the two units of measure is that acoustic power increases linearly, while decibels increase on a logarithmic scale.

Instructions

1. • 1

     Divide the acoustic power, measured in microPascals, by the reference power. The scientifically-accepted reference power for sound in air is 20 microPascals. For example, if the sound power is 40 microPascals, divide it by 20 microPascals to yield the value 2.

   • 2

     Take the base-10 logarithm of the answer in the previous step. Using the previous example, log base-10 of 2 is 0.3.

   • 3

     Multiply the previous result by 20 to find the decibel equivalent of the original acoustic power. In the above example, 0.3 times 20 is 6.02 decibels.