The different dimensions posed in string theory will all operate on different frequencies.
So, you got your Atom which is made up of a Nucleus of Protons and Neutrons with electrons flying around it at random. The protons and neutrons (and electrons as well) are made up of quarks. The quarks are not really anyting but a collection of "strings" resonating at a given frequency that defines what the atom as a whole is. Each string, each atom, each proton, operates at a different frequency.
The real mind bending aspect of strings is that in this infinitely small area (so small we have no means of seeing them even with the most powerful microscopes) are collectively the missing dimensions of reality. Going any deeper than that needs someone more articulate than I to explain. While my mind can grasp what the theory says, I have no means of explaining it to someone that may or may not be interested in it (no way of explaining in layman's terms that is).
Speaking of harmonics, you hear about sound harmonic technology where opposite sound waves can cancel sound out completely? For instance, a jet equipped with sound harmonics would theoretically not make a sound at all during takeoff, flight and landing? Make living by the airport a lot nicer wouldnt it? All stuff for the very near future. Its a good time to be alive.