In this lecture we learned about how the wave is reflected and transmitted when they meet a certain flat surface of this continuity, and one graph essentially summarize everything you learned in this lecture series. Okay, this is the region when we have high frequency component, and this is transmission loss. Now transmission loss in this region follows mass law, mass law simply says if you increase one octave, in other words doubling the frequency, you will have 6 dB transmission loss increase. This region we call resonance region, therefore the transmission loss will increase if you have a resonance, If you have anti-resonance transmission loss will be increased. This recalls stiffness control with reason, therefore if we increase the stiffness, again, transmission loss will be increased. So understanding mass law is essential to understand where it's propagating into the different medium, or when waves meet the face of this continuity. In the next lecture series we will generalize what we observed in this case for two-dimensional case. In the next lectures we'll handle what if we meet the flexible surface of discontinuity, like a plate.