Potential inconsistencies in conformity declarations caused by different IEC 61672-3 acoustical test methods in current sound level meters

摘要

Issues regarding the results of acoustical tests according to IEC 61672 retrace to the Euromet Project 394 (1998), as well to the Euramet Project 1056 (2011). The second edition of this standard improved the determination of correction factors pointing to IEC 62585, demanding manufacturers to provide fitting data to each acoustical test method: multi-frequency sound calibrator, comparison coupler and electrostatic actuator. This paper shows results of tests performed on several sound level meters models, three samples of each, at an ISO 17025 accredited laboratory. The acoustical frequency responses in free field were obtained applying the correction factors provided by the manufacturers to the tests with multi-frequency calibrator and electrostatic actuator, and then compared to the actual free field response, obtained using Time Selective Technique. Doubts come up regarding the compatibility between results obtained through those methods, especially in frequencies above 4 kHz. That being so, laboratories using different acoustical test methods could come to opposite conformity statements regarding the same sound level meter, causing conflicts between laboratories and clients. This study also discusses the potential inadequacy of the current periodic acoustical test up to 8 kHz in assuring conformity of a sound level meter to the IEC 61672-1.