Influence of reflecting plane having finite surface density on sound power level of reference sound sources calibrated in hemi free-field

The NMIJ, National Metrology Institute of Japan planned to start calibration service for reference sound sources (RSSs) by 2015 and we have been developing the RSS calibration system in accordance with ISO 6926. In our system, hemi-anechoic environment necessary for the calibration is realized by laying down wooden boards on a wire meshed floor of our anechoic room. In this study, we investigated the influence of such a reflecting plane having finite surface density on sound power level of the RSS theoretically and experimentally. We especially examined sound energy transmission through wooden boards and their vibration caused by the RSS operation. We also experimentally confirmed that our hemi-anechoic environment satisfies an inverse square law of sound intensity within a tolerance in ISO 3745. Furthermore, sound power level of the RSS determined by our system agreed with that by the SP, Technical Research Institute of Sweden within a range of SP’s expanded uncertainty. These results show that our hemi-anechoic environment is suitable to determine sound power level of RSSs in accordance with ISO 6926.