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.

Reference Decibels

A finite measured or assumed value, expressed in dB.

Measured Decibels

A finite measured or assumed value, expressed in dB.

The implemented rule is: Signed level calibration offset to add to measured readings to match a reference calibrator.^[1]

Offset Decibels

The calculated offset 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.

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.

• Inverse Square Law Level Change

  Free-field point-source sound-level change in dB when observation distance changes from r1 to r2.

• Db Addition Two Sources

  Energetic sum of two uncorrelated sound levels in decibels.

• Db Mean Of Readings

  Energetic mean, not arithmetic mean, of two equal-duration sound-level readings.