Welcome to our course, Introduction to Acoustics. We will essentially talk about how the sound is generated, so generation of a sound and then generated sound will propagate. So propagation, that's what we have to understand. And then we will hear the sound, or we could say reception of a sound, hearing. So in this course what we are going to explain to you is, first, how the sound is generated like this. How the sound is generated. Or, [SOUND] how a sound is generated. And how this generated sound is propagating into medium and how degenerated sound propagated and how we receive or how we hear the sound, okay. In the first chapter we will talk about the relation between vibration and waves. Okay, vibration is something oscillating with a certain period of time, like this. So as you can see here, when I oscillate this more rapidly, then the frequency will increase. That's the very typical measure of time fluctuation in vibration. But if you have a string like this and if I oscillated this string over here with a certain frequency, say frequency f, then the wave will be generated and then propagating into this direction. Okay what if I have some boundary over here, in other words, this string is connected to a rigid wall. Then the propagated sound will be reflected. Therefore, different with a vibration. In this case, the waves will be propagating into a string. That is a typical one-dimensional wave propagation problem. Propagation. Okay, the reason why we attempt to use this rather simple one dimensional case is because one dimensional case is simple, therefore it is easier to understand. And we will keep using this one dimensional case to explain other physical phenomena related with sound generation, propagation and the reception. Okay, and then we will move to the second chapter that has to do with acoustic wave equation. Acoustic wave equation. The reason why we are going to study acoustic wave equation is because acoustic wave equation governs everything related with a sound generation, propagation, and the reception. But I mean as you can feel, if you hear about acoustic wave equation, it looks very complicated and difficult to understand. Therefore we will use again, similarly as we used it for explaining vibration and waves, we will use a simple one dimensional case. Say there is a dot, and I generate an acoustic wave over here like [SOUND]. Then wave is propagating compared with this case the waves inside of duct is longitudinal wave. This case is transverse wave. Because the medium, the string element will oscillate in this direction but wave propagate in this direction. But this case fully oscillate in this direction and wave propagate in this direction. Therefore we call this longitudinal wave, and we call this transverse wave. So this example very analogous with what we're going to study over here. So again, if I have rigid wall over here, wave is propagating in this direction and then reflected back. And what we observe in this case would be very similar with what we studied in one dimensional vibration and waves case. And then we will introduce the fundamental Physical measures that represent, again, generation, propagation, and reception of sound. What would be the fundamental and physical measures that represent the acoustic wave propagation of forced sound pressure that depends on space and time. Because we are handling the medium which is compressible, as we can anticipate using this rather simple case, the fluid particle will be, the fluid will be compressed and released by exciting the certain, if I exciting over here. So the fluid if the fluid part fluid is compressed and released there will be some density change. And if there is this density change and there is a pressure change, then fluid particles will also change. So essentially we will talk about the relation between acoustic pressure and the density and the velocity. The relation comes out with the acoustic wave equation. Of course, in this chapter, we will talk about how to solve a typical acoustic wave equation, and then we'll also talk about the fundamental measure that has to do with the acoustic pressure and density and velocity. Especially we will talk about how to measure and what would be the appropriate fundamental measure of acoustic pressure. Normally we would, I mean it would be a decibel scale. And how would we hear in frequency scale, well we introduce octa one third of etc. And then we will move to third chapter that handles the waves on flat surface of discontinuity. We already learned how the wave will be reflected when we have the rigid wall for the one dimensional test. But we expand the concept to two dimensional test, of course we will start with the one dimensional test over here too when we have a wall that has a certain mass. Then because of the presence of the wall, some wave will be reflected. And some wave will be transmitted. We would like to know how much wave will be transmitted or reflected compared with the instance. Of course it depends on the condition of the flat surface. Okay, this flat surface could be, could have some spring and dash part. Or the flat surface we have as if it is played, things like that. We will handle this problem in chapter three. Okay, chapter 1, 2, 3 will make part 1. Therefore, part 1 essentially handles a very basic concept that has to do with one dimensional acoustic wave propagation, generation, propagation, and reception. And we were at part 1, we will talk about fundamental acoustic wave equation and decibel scale that measures some pressure. And, octave scale that has to do with the frequency scale.
