Figure 2. Illustration of linear versus nonlinear wave harmonics and modulation response in a bell. As illustrated in (a), we input two frequencies into the bell with a speaker. The inset at top, right shows the frequency spectrum of the bell illustrating that the two frequencies put in are the same we get out. In the cracked bell shown in (b), we observe nonlinear mixing (multiplication). The two frequencies multiply with themselves creating harmonics, and with each other creating sum and difference frequencies (sidebands). We call this method Nonlinear Wave Modulation Spectrscopy (NWMS), a subset of NEWS.