What is the formula for calculating noise level?

The relationship between dB power and dB pressure, along with the distance from the sound source, is expressed mathematically as dB power equals dB pressure plus 20 times the logarithm of the distance in feet, minus 2.5 dB. This formula encapsulates the complex interplay between sound intensity, measured in pressure levels, and its propagation over distance.

The inclusion of the -2.5 dB factor serves as a corrective measure, accounting for the moderate reflections of sound waves off surrounding walls. It's a simplification that helps adjust the calculation to more closely reflect real-world conditions where sound is not purely radial but also bounces off surfaces.

To illustrate the application of this formula, let's consider a scenario where we need to determine the dB noise power of a pump. Assuming we have a meter reading of 87 dB pressure taken at a distance of 9 feet from the pump, we can use the formula to find the corresponding dB noise power.

Plugging in the values into the equation, we get dB power equals 87 dB pressure plus 20 times the logarithm of 9 feet, which converted to decimal is approximately 0.954, minus 2.5 dB. This step involves performing basic arithmetic and logarithmic calculations.

Carrying out the multiplication and subtraction, we first calculate 20 times 0.954, which equals 19.08. We then add this result to the original dB pressure reading of 87 and subtract 2.5 dB from the total. Thus, the calculation becomes 87 + 19.08 - 2.5.