It is a well-known result that the power of five-minute oscillations is progressively reduced by magnetic fields in the solar photosphere. Many authors have pointed out that this could be due to a complex interaction of many processes: opacity effects, MHD mode conversion, and intrinsically weaker acoustic emissivity in strong magnetic fields. While five-minute oscillations predominate in the photosphere, it has been shown that in the chromosphere three-minute oscillations are more common. Two main theories have been proposed to explain the presence of the latter oscillations based upon resonance filtering in the atmospheric cavity and non-linear interactions. In this work, we show, through the analysis of IBIS observations of a solar pore in the photospheric Fe I 617.3 nm line, that three-minute waves are already present at the height of formation of this line, their amplitude depends on the magnetic field strength, and they are strictly confined to the umbral region.