The electrooptic response of the planar samples of TB10A in book-shelf and chevron geometries has been measured in the frequency range 1 Hz - 100 kHz. In order to have a linear response 4% of ferroelectric liquid crystal DOBAIMPC has been admixed to the non-chiral TB10A to create ferroelectricity in the mixture. In the SCphase two low frequency relaxation processes have been found. The lower relaxation found in the region of several Hz corresponds to the deformation of the smectic layers, the higher one with the relaxation frequency of a few hundreds Hz corresponds to the azimuthal mode. These two relaxations give both positive resp. one positive and one negative contributions to the electrooptic response for the book-shelf resp. the chevron structures.