It has been said that the ISO tapping machine does not yield data on representative flooring materials that accurately relate to the impact‐noise isolation provided for real, foot‐fall impacts. To understand this problem, we have measured the impact force under both the ISO hammer and a woman's shoe heel. The hammer force is found to be much more intense and generally to contain more high‐frequency components than the heel force. The differences between hammer and heel forces are found to arise from the different mechanical internal admittances and from the different approach velocities. Radiated sound levels for the measured force spectra applied to a concrete slab are calculated and found to agree closely with measured impact sound levels. We conclude that the ISO machine grossly misrepresents the impact isolation provided by some typical floor surfaces.