## Operating Transfer Path Analysis (OTPA). Can this novel technology be applied successfully outside the automotive sector?

Juha Plunt, Müller-BBM Scandinavia AB

Marieholmsgatan 9

SE-415 02 Göteborg

E-mail: juha.plunt@muellerbbm.se

Transfer Path Analysis (TPA) is a technique used when there is a need for quantitative ranking of the contributions from different sources and transfer paths to a sound or vibration response that has to be modified (reduced or enhanced). It is a common method used during development of road vehicles.

The “classic” TPA relies on different methods for estimating the interface forces (or volume velocities if airborne sound sources) acting at different attachment points (radiating surfaces) of the sources and “true” frequency response functions between these forces (volume velocities) and the response of the transmitting system. These FRFs are measured using artificial excitation (hammer, shaker or loudspeaker), in addition to the operating sound and vibration measurements needed to derive operating excitations. Also, the force estimation methods rely on additional data; either extensive FRF measurements (inverse matrix method) or special measurements of resilient element dynamic stiffness (mount method).

A novel method, the Operating Transfer Path Analysis (OTPA), is now available. It can separate source and path contributions using only operational measurement data. The benefits are obvious in terms of significantly reduced measurement time and effort. No modifications to the measurement object are needed, like separating the source from the supporting structure when measuring transfer path FRFs. All data is measured simultaneously, and the method also allows accurate synthesis in the time domain of the individual path contributions as well as the calculated total response.

The large test effort has probably been the main obstacle for using “classic” TPA for more detailed problem diagnosis in structures such as buildings, off-shore platforms, ships or development of other products like construction equipment, heavy machinery, appliances etc. OTPA can be applied much more efficiently and without the need to turn off the operating equipment, which makes it clearly attractive for analysis of noise and vibration transmission in those applications.