The acoustic specification of a new project, vehicle or engine, is facing the difficulty of cascading NVH targets to the component level quantitatively. However, these specifications are the basis of discussion between constructors and suppliers and each of them would appreciate to discuss on more reliable data input. It is so necessary to construct reliable database/references. It requires measurement tools able to determine on a previous project the contribution of each of the component to the complete noise emission. The sound power is one of the criteria used in the acoustic specification, but it can be completed with criteria aimed at controlling the acoustic signature, especially with the new electric technologies. The standard measurements usually based on sound intensity scanning or sound pressure emission to achieve sound power measurement do not permit to extract any sub-value without masking methodology which can be long for panel qualification or even unfeasible on engine. A new technology based on 3D acoustic array measurement permits to extract the individual sound power of each of the component or any other criteria from the spectral signature. It is parented to an experimental modelling. The complete sound field is recorded with several array positions and is then back-propagated on the 3D mesh of the source distribution taking account the object diffraction. It is carried out by a complex inversion of the system. The acoustic imaging usually used for fast acoustic diagnosis becomes a powerful tool to help in the definition of acoustic specification. This 3D technology can be used on engine bench to define the future target from the preceding experience, or coupled rooms to measure Transmission Loss or gas stand for Turbo Compressor… and any test bench useful for supplier to validate the acoustic target. This paper will briefly present the 3D array technology and its application on turbocharger component to quantify the duct transmission loss. The methodology will be applied on the same turbocharger line mounted on engine compartment and then on gas stand. The innovative 3D acoustic array measurement permits to quantify the sound power emitted outside the duct and a 3 microphones techniques permits to quantify the sound power inside the duct. By subtraction of interior and exterior sound power, the obtained transmission loss results in both experimental conditions will be compared. It will point out a nice example of component qualification on test bench with a good reproduction of true engine conditions.

Ms. Lucille PINEL LAMOTTE, MicrodB, FRANCE Mr. Alban Millot, CRITTM2A, FRANCE