Empirical validation of an angle-error model for computing free-field sound power using a cylindrical enveloping surface

The angle error inherently biases the calculated sound power level when determined using free-field sound pressure level measurements over an enveloping surface. A regression equation was previously created to predict the angle error associated with omnidirectional sources using just a few easily obtainable input variables related to the geometry of the source and the enveloping measurement surface. This paper assesses the accuracy of that predictive regression equation through an empirical study. A dodecahedron loudspeaker was used as a noise source over a range of positions within the reference box. The modeled angle error correction was applied to the computed sound power levels using measurement data from multiple cylindrical enveloping surfaces in accordance with ISO 3744 and ISO 7779. The corrected sound power levels were compared to the measured sound power levels of the source per ISO 3741 direct and comparison methods.