Why be modal: i.e. how to avoid the use of modes in the modification of vibrating systems

Modes and modal parameters are the magic and fundamental means through which every linear problem of vibration is usually developed. No doubt that this is the reason of the existency of a large number of codes performing curve fitting procedures apt to determine modal parameters from experimental transfer functions. The field of structural modification does not take exception to this rule. However modal identification often leads to significant errors: therefore, in order to avoid the derived pitfalls, a procedure which performs optimal structural modification without the use of modal parameters has been developed. Theoretical and experimental tests show the capability of the method.