Sound Intensity Measurement Errors in the Presence of Large Pressure to Intensity Ratios

Errors in sound intensity measurements are examined for situations in which a high reactive component is present. This occurs when the indicated sound intensity level is much smaller than the sound pressure level. In these situations, significant errors in the sound intensity measurement can occur for even very small phase mismatch between microphone channels. High reactive components may be encountered in the near field of an extended source such as a body panel, when the intensity vector does not coincide with the sensitive axis of the probe, or when measurements are made in the presence of high background noise, reverberant sound fields, air flow, or standing waves. Expressions for calculating sound intensity error due to phase mismatch with high reactive components present are developed and examples of calculated error for common instrumention are provided. Cases of sound intensity measurements with known amounts of phase mismatch are also examined.