The challenge of a NVH development is to define a link between the target of the OEMs expressed in terms of acoustic performance, weight and cost and the design of the optimized acoustic package reaching this target. The “Vehicle Acoustic Synthesis Method” (VASM) has been developed in order to create this link. The VASM method, which is an energy based hybrid simulation technique, calculates the Sound Pressure Level at ear location from the combination of sound power measurements and acoustic frequency response functions (FRF) panel/ear, either measured or simulated with Ray-Tracing Methods.
This paper deals with the last developments of the 2nd generation of the “Vehicle Acoustic Synthesis Method” (VASM 2) using p-u pressure-particle velocity probes, for both sound intensity and transfer functions measurements, in order to speed-up the time to build a model of a fully trimmed vehicle in the middle and high frequency range, while increasing accuracy both in terms of source localization and source quantification and while addressing unsteady operating conditions like run-ups.
Intensity measurements inside a car in operative conditions give access to the net power flow of the in-coming (radiated) and out-coming (absorbed) acoustic power. This out-coming power can become predominant in the case of a panel trimmed with a high absorbing material and which does not radiate much. The VASM 2 method requires, especially for its optimization phase, robust injected power measurements (in-coming power), which may demand absorbing and/or insulating environments, even if p-u probes are not δ p-I sensitive. Both experimental and numerical investigations have been carried out in order to decide whether or not an absorbing and/or insulating environment is mandatory.