Automotive HVAC cockpit acoustic radiation analysis and source ranking
Sound power is one of the main characteristics defining the output of a sound source. The ability to rank it plays a critical role in acoustic design, particularly in the automotive industry. Manufacturers prioritize precise analysis and optimization of sound radiation and distribution to achieve superior acoustic performance. This, in turn, directly influences the perceived quality and comfort of vehicle interiors. Achieving this goal involves a detailed assessment of how sound propagates and is absorbed within the car cabin. Such assessment is essential for developing vehicles that not only meet stringent acoustic standards but also adhere to weight and cost specifications. Sound power ranking offers a granular and effective approach to quantifying noise sources. Its robustness and the possibility of reliable repeatable tests provide a solid tool for fundamental analysis even in challenging environments.
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FKFS research center
This case study was done in collaboration with FKFS research center, an independent research institute specializing in automotive engineering. It offers advanced testing facilities and expert development services to the global automotive industry, focusing on vehicle dynamics, efficiency, and electromobility, supporting innovations with state-of-the-art technology and industry collaborations.
GOAL & REQUIREMENTS
- HVAC noise analysis and source localization
- Panel-based sound power ranking
- In-situ sound power assessment
Main campaign stages and methodology
The process began with preliminary scans using the VOYAGER mobile NVH analyzer, which allowed the team to perform real-time data processing. This tool's ability to measure particle velocity allowed for quickly identifying critical acoustic focus areas within the vehicle's cabin.
A Scan&Paint 3D system was deployed inside the vehicle cabin following the initial assessment. This involved a detailed setup using a 3D sound intensity probe, attached to a sphere with IR reflectors and tracked by a stereo camera. The probe was equipped with a windscreen to ensure the integrity of acoustic data by minimizing flow-induced noise on the acoustic transducers. The entire cockpit was meticulously scanned over 15 minutes.
Data visualization
By integrating the measurement data and processing the scanned area, dynamic 3D visualizations of the radiated acoustic field were achieved, highlighting the main sound sources linked to different cabin components within the cockpit. Scan&Paint3D allows to perform a frequency sweep that clearly emphasizes various acoustic key components at specific points in the spectrum, as can be observed in the video.
Taking the next step in sound analysis
The final phase combines the directional information of 3D sound intensity measurements alongside a panel-based sound power framework. Its straightforward approach simplifies the process of selecting and grouping areas by panel, enabling the direct assessment of a multi-panel sound power from the data gathered by the sound intensity probe. This panel-based methodology not only enables the sound power assessment of multiple groups and sub-groups but also enhances the accuracy of quantifying and ranking acoustic sources, streamlining the overall evaluation process.
Findings & results
A sound power panel was defined for each air vent to compute the acoustic output of each HVAC outlet. The figure to the right illustrates the defined panels and the normal direction in which the sound power was extracted for the calculations. The software also generates a summary table for each panel, defining the total sound power level per panel area.
dominant sources
The most prominent source identified was the windscreen center vent. It is dominant for lower frequencies, from 55 Hz to 730 Hz as well as for the upper range above 2000 Hz. The footwell left contributes mostly between 730 Hz and 1kHz. If compared to the footwell right side, it shows a distinctive unsymmetrical behavior. Noise emission from the front center vent becomes dominant between 1000 Hz and 2000 Hz, radiating far more noise in this frequency region than other secondary sources.
Panel ranking
The vents were expanded into larger areas to observe the contribution of each panel as a whole. Each panel, contains the same naming convention as before, although having a larger area. Every panel is assigned to a group, in which it is possible to assess their contribution as a general panel section or its subdivisions. For low frequencies, the top side of the dashboard facing the windscreen is the most relevant section contributing to noise emission of the entire cockpit.
Conclusion
- The integration of the Voyager mobile DAQ with the Scan & Paint 3D solution has enabled the identification of noise and leakage sources, providing a visual representation of the entire sound field.
- Multi-panel sound power ranking has been demonstrated, proving to be a useful tool for assessing the noise emission of large and complex sources.
- The most significant radiation contribution happen in the three different areas of the dashboard and at different frequency ranges. All of them were identified and quantified.
- The sound power ranking performed demonstrated that there was uneven acoustic radiation from the air vents.
- Separating sound power per vent area and panel section contributes to a better understanding of both source separation and overall raking
Scan&Paint 3D
Voyager