The response factor is a multiplier on the level of vibration at the threshold of human perception. Thus, a response factor of 1 would represent a level of vibration that is just at the threshold of human perception, and a response factor of 2 would represent twice the perceivable level. People are more sensitive to vibration at some frequencies than at others. The base curves for human perceivability are taken from BS 6472. Since the methods used in RAM Concept combine the results of the different modes of vibration, the baseline velocity value (v_RMS = 1) is taken from the curve using the frequency of the fundamental mode of vibration.