Abnormal Behavior of Sound Velocity and Damping in the Vicinity of the Smectic-$A-\mathrm{S}\mathrm{m}\mathrm{e}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{c}-C$ Transition in Terephthal-$\mathrm{bis}-p-p^{\prime }$-Butylaniline (TBBA)

Sound velocity and damping measurements, taken at various angles $\theta$ between the normal to the smectic layers and the sound propagation direction, are reported for TBBA near its $\mathrm{Sm}A-\mathrm{S}\mathrm{m}C$ transition. Both velocity and damping present marked pretransitional anisotropic effects above $T_{\mathrm{Ac}}$. The anisotropy of the transition also manifests itself on the positions of the damping peaks of which that for $\theta =0^{\circ }$ moves towards low temperatures as the frequency increases, whereas no displacement is observed for 0=45° and 90°. The results are compared with the predictions of the current theories.