Use this calculation for a first-order acoustics estimate when the stated geometry, propagation model, averaging convention, reference quantity, and SI units match the measurement or design problem.

First Decibels

A finite measured or assumed value, expressed in dB.

Second Decibels

A finite measured or assumed value, expressed in dB.

The implemented rule is: Energetic mean, not arithmetic mean, of two equal-duration sound-level readings.^[1]

Mean Decibels

The calculated mean decibels, expressed in dB.

This is an idealized calculation rather than a complete acoustic simulation or measurement. Reflections, boundary conditions, directivity, damping, frequency dependence, near-field behavior, background noise, transducer response, temperature, humidity, and geometry can change a real result. Decibel values are logarithmic: arithmetic addition, averaging, or subtraction of the displayed levels would be physically wrong for the energetic model used here.

Confirm important results with calibrated measurements or a model that includes the actual geometry, materials, boundaries, source directivity, and frequency-dependent losses. Preserve the reference quantity and weighting whenever a result is expressed in decibels.

• Calibration Level Offset

  Signed level calibration offset to add to measured readings to match a reference calibrator.

• Db Addition Two Sources

  Energetic sum of two uncorrelated sound levels in decibels.

• Db Subtract Background

  Source-only sound level after energetic subtraction of measured background from total level.