The recent introduction of hand‐held intensity measurement equipment has created a growing need for verification of the measurement equipment in the field. The key feature for easy field use is the possibility of calibrating the two‐microphone intensity probe without dismounting the spacer. Working models were built, but none of them worked to more than approximately 3 kHz. Compliance with IEC 61043 requires the calibrator to work up to 7.1 kHz. A lot of modifications on these models were tried, but none of them worked. The development project was close to being stopped. A boundary‐element model of the sound intensity calibrator was built. It verified the measured result from the working models. Based on the boundary‐element model the best type and position of the sound source and the optimum dimensions of the calibrator cavity were found. Measurements on a final model verified the simulation results. The calibrations could now be made without dismounting the spacer.