Sound power level (LW) is the fundamental acoustic descriptor used in machinery noise emission declarations and CE marking documentation under the Machinery Directive and Outdoor Equipment Directive. Unlike sound pressure level, which depends on the distance from the source and the acoustic environment, sound power level is a property of the source itself and allows fair comparison between different machines and valid prediction of installation noise levels.
Sound power level is determined by measuring sound pressure levels at a defined array of positions surrounding the source and integrating them to calculate the total acoustic power output. The measurement environment and array geometry are defined by the applicable standard. ISO 3744 (engineering grade) uses a measurement surface in a free field over a reflecting plane — a standard production or test floor is usually adequate. ISO 3745 (precision grade) requires an anechoic or reverberant room and provides lower measurement uncertainty.
The PLACID sound power measurement system comprises the PQ1601 16-channel DAQ, a hemisphere microphone array with 10 or 20 Class 1 microphone positions, matched calibrated microphone sets, interconnection cables, and PQ Analyst software with ISO 3744 sound power calculation. The complete system is supplied with a single calibration documentation package covering all microphone positions. Contact PLACID for a system quotation including configuration and calibration options. The calibration documentation includes an ISO/IEC 17025 accredited certificate for every microphone position in the array, satisfying the requirements of notified body test reports and CE marking documentation.