Welcome to introduction to acoustics part two. In part two, we will talk about a very difficult problem compared with what we learned in part one. We will talk about radiation, scattering and diffraction at the same time. It is rather very brave approach to understand those three physical behaviors at the same time. However, if you understand everything is it related with spacial discontinuity. In other words, how discontinuity exists in space. Okay and then we will talk about the concept of space. Compare with. So we will handle acoustically large space and acoustically small space. For example, acoustically small space example, we can think about the blowing small bottle. In this case, the wave length is much larger than the size of bottle. That case, we call acoustically small case. For acoustically large case, you can think about how sound is appropriating. And for example concert hall. In this case the concert hall, size of a concert hall is much much larger than the acoustic wave. We call that case acoustically large case. In part two, we will talk about as I mentioned earlier, scattering, diffraction radiation at the same time. And then, we will talk about acoustically large space as well as acoustically small space. I hope you can enjoy it.