# Classical TPA

The classical TPA method is essentially intended to identify transfer path contributions in existing products. A classical TPA performs operational tests on the assembled product AB to obtain interface forces $$\mathbf{g}_{\mathrm{2}}^{\mathrm{B}}$$ between the active and passive side. These interface forces fully determine the responses at the passive side and are thus representative of the effects of the source vibrations at the receiver locations $$\mathbf{u}_\mathrm{{3}}$$. To calculate the receiver responses, the passive-side interface forces are applied to the interfaces of subsystem B.

Both steps pose some challenges in practice. The FRFs of the passive side are typically determined from impact or shaker tests or in a reciprocal fashion using, for instance, an acoustic source at the receiving location and accelerometers at the interface nodes. Either way, it requires dismounting of the active part(s) from the passive side. Concerning the determination of $$\mathbf{g}_{\mathrm{2}}^{\mathrm{B}}$$ operational interface forces, it could be impractical to mount force sensors between the active and passive part. Therefore, several indirect methods have been developed to circumvent direct force measurement.

Hence, the following three variants of classical TPA can be defined according to how $$\mathbf{g}_{\mathrm{2}}^{\mathrm{B}}$$ is obtained from operational tests: