Spatial Optimisation of Inner Dash Acoustic Performance using Reciprocal Holography

As acoustic requirements for NVH trim components become more demanding – driven by cost, weight, and increasingly, sustainability – there is growing pressure to optimise performance across multiple criteria. In complex components such as the inner dash, performance is often assessed in isolated. However, this fails to reflect real-world conditions, where contributions from ancillary systems, the instrument panel, and variable noise sources such as the power unit, gearbox, and tyres are significant. Traditional Transmission Loss (TL) measurements provide averaged results that can overlook spatial variation and lead to suboptimal design choices. To address this, an approach is presented that uses reciprocal holography to map the spatial TL performance of an inner dash. This method enables a more representative and targeted design process for achieving effective acoustic performance in fully built vehicle environments. Furthermore, the spatial Transmission Loss data can be combined with the radiated sound power of individual engine bay sources to create an insonified hologram. This allows the acoustic performance of the trim to be evaluated under realistic operating conditions, providing a more representative understanding of how the component behaves when excited by actual in-vehicle noise sources. Such an approach enables localised mass distribution, maintaining similar acoustic performance whilst reducing the overall weight of the component.