Validity of intensity techniques for the measurement of sound radiation factor

The total radiation factor may be strongly dependent on the environment, other sources and the way of excitation. So, the measured radiation factor of a source cannot be applied directly to other circumstances. The validity of the measurements is best with the surface intensity technique and the valid frequency band is largest with the configuration having the microphone over the accelerometer. Whatever the method is, the maximum allowed critical frequencies are very low (about 1 kHz or less). So, the measurement of the radiation factor using these methods cannot be applied to machines and equipment in factories. The measurement can be suitable in some well-defined sector, e.g. in building acoustics, but in that sector the need of having an "in situ" measurement method is questionable. The errors in the measurement of radiation factor using intensity techniques have been examined in this paper only for large radiating plates and small sound sources. However, many sound sources in industry can be thought to be formed of large plates. More complicated structures may yield to stricter demands. If an "in situ" measurement of the radiation factor using intensity techniques is wanted, more work will be needed to chart the measurement uncertainties in different circumstances, in order to get the methods reliable. With the present knowledge, the methods are not suitable to be standardised for a general "in situ" method. The vibration measurement with a laser vibration meter or exploiting the acoustic holography may solve some problems.