Determination of the sound power radiated into the receiving room of a transmission-loss facility at low frequencies by means of scanning laser Doppler vibrometry

摘要

The measurement of the transmission loss of building elements is typically performed according to ISO 140, by measuring the sound pressure level in the sending and receiving room, using standardized loudspeaker-microphone instrumentation. Recent proposals for new building acoustic standards taking into account frequencies down to 50 Hz, provoke new questions. At low frequencies (depending on the dimensions of the rooms), the modal density in the rooms is typically too low, impeding reliable measurements following standard techniques. In this paper the vibration level and distribution of the element is determined by means of advanced laser Doppler vibrometer measurements and the radiated sound power of the element is subsequently determined by means of numerical simulations that use the measured velocity distribution as input boundary condition. This approach to deduce the transmission loss is compared with the classical way of measuring the radiated sound.