EXPANDING THE SOUND POWER MEASUREMENT CRITERIA FOR SOUND INTENSITY P-U PROBES

The sound power of a machine or device provides a general description of its acoustic output. Sound intensity based methods determine this quantity by integrating the normal sound intensity over an area enclosing the noise source. Current ISO standards solely regulate the use of p-p intensity probes. A p-p probe consists of two paired pressure microphones that approximate sound intensity by combining the average pressure and pressure gradient. Sound pressure is strongly affected by the measurement conditions, especially in reverberant environments or the presence of background noise, which can significantly constrain the accuracy of intensity estimations. As a result, regulations define a set of parameters or “field indicators” to guarantee the validity of measurements and control the uncertainty limits of the estimated sound power level. Alternatively, it is possible to directly obtain sound intensity from the sound pressure and particle velocity acquired using p-u probes. However the measurement methodology that support this approach has not yet been established. This paper adapts the current measurement standards for the use of p-u intensity probes. A corresponding field indicator that determines the accuracy of the computed estimations is suggested and experimental data is presented, providing evidence for the viability of the measurement methodology introduced.