A measurement of the surface Andreev bound states of the superfluid He-B phase under different boundary
conditions is presented. Transverse-acoustic impedance spectroscopy was used to determine the bandwidth of
the bound states on a wall with various specularities. It was found that the band was broader for larger
specularity and filled up the superfluid gap above a critical specularity. Specularity was controlled by coating
the wall with thin layers of 4He and was evaluated separately using acoustic impedance measurement in the
normal-fluid phase.