An estimate of the sound power measurement error due to sound source directivity for powered hand tools.
Zechmann-EL; Murphy-WJ; Hayden-CS
NOISE-CON 2008: Proceedings of the 2008 National Conference on Noise Control Engineering, Dearborn, Michigan, July 28-31, 2008. Burroughs C, Lim T, Kim J, Maling G, eds. Indianapolis, IN: Institute of Noise Control Engineering of the USA, 2008 Jul; :287-299
It is important for uncertainty budgeting and product labeling that ISO 3744 and 3745 include guidance on the error in estimating the sound power due to source directivity. ISO 3744 and 3745 give guidance on the reporting of directivity index because source directivity can be a significant source of sound power measurement error. As a safeguard against error, additional microphone positions are required if the difference between the maximum and minimum sound pressures at the key microphone positions is greater than the number of key microphone positions. For highly directive sources, a detailed directivity investigation is necessary. The ISO standards do not contain an upper bound for the variation in intensity from one microphone to the next. A theoretical method to consider the variation in directivity and calculate an upper bound for the error is developed. The Taylor series expansion of the sound intensity over the measurement surface has a remainder term which yields an error estimate. Data collected from the NIOSH powered hand tools database is analyzed with this method. Preliminary directivity analysis suggests that the average upper bound for the error is typically less than 5 dB for loaded tools and 1 to 3 dB for unloaded tools.
Noise-exposure; Engineering-controls; Control-technology; Power-tools; Hand-tools; Acoustics; Acoustical-measurements; Sound
Edward Zechmann, National Institute for Occupational Safety and Health, 4676 Columbia Parkway C-27, Cincinnati, OH 45226
Burroughs-C; Lim-T; Kim-J; Maling-G
NOISE-CON 2008: Proceedings of the 2008 National Conference on Noise Control Engineering, Dearborn, Michigan, July 28-31, 2008.