Come and see: How Sonocat finds the main sound source inside a moving vehicle!

To assess noise leakage in the vehicle cabin, we used the Sonocat multifunctional in-situ acoustic measurement device to conduct measurements inside a car driving on the NVH test track. Figure 1 shows the measurement device (Sonocat equipment and software). Initially, we performed discrete point measurements to obtain preliminary acoustic data inside the cabin and familiarize ourselves with the acoustic environment. Subsequently, we conducted a comprehensive scan of the target interior areas suspected of causing noise leakage. The total time taken was approximately 30 minutes. By post-processing the collected data, we were able to identify the details of the main noise emission surfaces inside the cabin.

Figure 1. Sonocat measurement system inside the car cabin

Measurements and Results

Figure 2 shows several marked areas where acoustic measurements were taken. These labels correspond to the scan identification numbers and descriptions of the respective scan areas, associated with the measurement data files presented in Figure 3.

Figure 2. Some scan areas inside the vehicle

Figure 3. Overview of the measurement files displayed in Sonocat software, indicating all measurement scans

The differences between the incident and reflected sound power through the scan areas (i.e., active sound power) and the absorption/emission coefficients (the ratio of active power to incident/emission power) were quantified. For visualization purposes, the emission coefficient is represented as a negative absorption coefficient, allowing both parameters to be displayed together, as shown in Figure 4. Thus, negative active power indicates sound emitted from the scan area, and a larger negative value of the emission coefficient indicates more effective sound emission. Therefore, the main noise entering the cabin comes from the areas with the highest negative values of the emission coefficient.

Figure 4. Absorption/Emission coefficients of the scan areas

Figure 5 shows the active sound power of all measurement areas. In this figure, solid bars represent positive sound power, while hatched bars represent negative sound power. It can be noted that in the 1/3 octave band from 500 Hz to 1 kHz, area 7 has the highest emission power. Other areas, such as 4, 10, 14, and 15, also show emitted sound power. Most surfaces seem to absorb sound, as the active power is negative (hatched bars).

Figure 5. Active power incident to the scan area (if the color is hatched) or active power emitted from the scan area (if solid color is used)

Conclusion

SonocatCan be used to locate noise leakage in the vehicle cabin, which has a very complex sound field. The results of this test show that area 7 is the main noise source within the evaluated frequency range, which is consistent with the observations of NVH engineers, who subsequently found misalignment at the soundproof carpet.