It is widely known the difficulty to reach Pass-By level reductions, mainly in such vehicles like trucks and buses.
One of the frequent questions is: which is the responsible source noise?
The answer to that question can be given using the combination of some Acoustic Holography tools, simultaneously to the Pass-By Noise measurement.
This paper presents an utilization technique of these tools that makes easy the identification of the noise sources.
The technique consists in getting a vehicle movie, during the Pass-By Noise measurement and, at the same time, doing the dynamic (non-stationary) holographic measurement of this noise signal, using the “NS-STSF IRREGULAR ARRAY” (Non Stationary - Spatial Transformation of Sound Fields) tool.
Overlaying the film to the Holographic image, we can see the acoustic propagation, emitted by the vehicle during the Passing By and we can determine the responsible region for Pass-By Noise peak.
With this information, we install the vehicle in the Semi-Anechoic Room and, using the same tool, however with a regular probe (NS-STSF REGULAR ARRAY), we make a complete map of the interest area, which results in the detailed identification of the noise responsible sources, as well as their characteristics like intensities and frequency spectral distribution.
Knowing the responsible noises sources and its characteristics, we can optimize the “acoustic package” around these sources or modify the project (exhaust, for instance), improving its acting, minimizing the material application and improving the engine cooling.