These insulation performances can then be applied to the noise in the room housing the machine. In other words, the overall noise (air and structure-borne) generated by the machine minus the measured airborne isolation performance measured will determine the structural component of the sound caused by the equipment. This exercise identifies the main source of noise (air or structural) and helps select the right solution to reduce noise in specific areas, while quantifying the maximum impact this solution will have.
Identifying airborne noise generation mechanism
Certain noise sources have a clear transmission path, but it is sometimes difficult to determine their exact origin. The obvious solution is to measure the noise using a sound level meter and to identify, using a scanning procedure, the approximate origin of a noise (nearfield measurement). However, this technique has a maximum precision and is not always efficient in a reverberant environment. Additionally, some equipment can be difficult to access, which makes nearfield analysis impossible. However, there are solutions to remotely identify problematic parts on a piece of equipment.
Sound intensity probes measure not only noise amplitude, but direction (vector). Noise vectoring can occur when two or more microphones are linked on an sound level meter. Recent technological improvements have made it possible to increase the number of microphones used simultaneously, thus increasing the vectoring capacity of sound level meters technique on distant planes (acoustic holography). Furthermore, the combination of these holographic instruments along with sensors attached directly to the studied structure allows the use of consistency factors to reduce the false effects of reverberation and centre the instrumentation on a specific piece of equipment.