Blocked forces for the characterisation of structure borne noise

During the development of complex assemblies such as aircraft the noise from installed components must be considered. For airborne sound sources this issue has been resolved to some extent by standard measurement procedures which allow equipment suppliers to transfer data to end users in an agreed form. The same cannot be said for structure borne sound sources however because no widely accepted standard test methods currently exist. The main complicating factor is that the procedures used for airborne sound source characterisation are not suited to the evaluation of structure borne noise because both source strength and coupling to the assembly must be considered and, as a result, no easily interpretable characterisation quantity can be found that applies beyond some special circumstances. The in-situ measurement of blocked forces is a promising approach for reaching some consensus in this area but it does differ in many ways from the accepted norms of the standard procedure because it favours the use of narrowband data and the inclusion of phase. In this paper we look at the advantages and disadvantages of the blocked force approach together with the associated uncertainties and how they might be presented or quantified in a standardised method