I have another basic inquiry. I applied a fixed base condition while performing modal analysis as I need to excite the base along the horizontal direction. The total scenario is vibration will be applied to support-plate on which the cell is placed. If I just want to know the natural frequency of the cell, then is it enough to apply fixed boundary conditions to get natural frequencies?

However, I saw that natural frequencies (first one) go down when I remove the fixed base condition or apply any other type of support other than fixed support. What is the significance of using a fixed boundary condition and not using a fixed boundary condition while performing the modal analysis?