In the Rigid Walled Room episode we seen how to model a rectangular room with rigid walls. We driven the room at the modal frequencies and compared the solution field with the theoretical modal shapes, finding that the results matched single modal shapes real well until, at a frequency high enough, the contribution of multiple modes (in addition to that related to the driving frequency) became important. In this episode we will look at making the model more realistic. To do so, we will investigate the low frequency response of a home studio.
In the previous episodes we often made use of the ParaView postprocessor to visualise our solution field from the ElmerFEM solver. ParaView can do all sorts of cool visualisations and animations, as well as providing the way of doing quantitative analysis. It is by far the best option to visualise and postprocess results from ElmerFEM. It also allows to export data in various formats, such as CSV, that allow us to do any additional kind of postprocessing of verification, by either using Julia, Python or any other language, or even spreadsheet software if you fancy that (for whatever reason…). ParaView functionalities are so many, and so advanced, that it is impossible to cover them all in a blog post. For that, you should instead refer to this page. In this page I will merely collect a few useful tips and tricks that I found useful when working on my studies. As I find more tips and tricks as this series goes on, I will update this page.
In the Acoustic Modes of a Rectangular Room episode we explored the analytical model of a rigid walled room with some Julia code. We focused on finding the resonance frequencies (or eigenfrequencies) of the room and calculating the related modal patterns (eigenfunctions). Now that we know how to setup Helmholtz problems with ElmerFEM we can approach the problem with the FEM method. In this episode we will solve for the modal patterns of a rectangular rigid walled room and compare their accuracy to that of the analytical solution we discussed in Acoustic Modes of a Rectangular Room. We will see that this is actually hard to do directly, as ElmerFEM does not have an Eigensolver, but we will obtain useful information anyway!
In the previous episodes we solved a few equations with ElmerFEM. We did some choices when we setup the solver parameters. What those parameters do, and how should we set them? This is perhaps the trickiest part in FEM (beside making the mesh right) and definitely the one I am the least expert about. Still, in this episode we will step back and look at those options more closely. This post is really not meant to be an exhaustive explanation. For that, refer to the ElmerFEM documentation.
Right, this episode was supposed to be published only a few weeks after the last one. Clearly, things drifted a little bit…
So, I was planning to publish one of these tutorial-style posts per month, but things slipped a bit. But I did not forget about this, and this post is the last episode of the Modelling Acoustics with Open Source Software series.
In this episode about Open Source Acoustic Modelling we will look at how to make a simple Julia model of one of the simplest systems in acoustics, a rectangular room with rigid walls, assuming adiabatic wave propagation. Even if this system is among the simplest in acoustics, it is actually already very complicated. As such, we will focus only on the modes, one part of the problem, without attempting impulse response simulation or other fancy things like that, for now.
Welcome to the first actual episode of the series about acoustic modelling with open source software. We will first try to understand what modelling acoustics means. In reality it doesn’t mean just one thing, as many phenomena of acoustic wave production and propagation can be modeled and simulated in various different ways, with higher or lower degree of accuracy. However, the core of the modelling problem resides in partial differential equations. This post will be a very, very, brief, intuitive and not rigorous introduction to the topic, mainly to give context to those that are not accustomed to the concept. If you are experienced about physics and acoustics, you can completely skip this episode.
As part of my profession as an acoustician, I often make use of Open Source software. It might surprising to few that the Open Source ecosystem is actually filled with very good packages for this task. As a result, I decided to try to publish a little series of tutorials about the topic, and this would be its first post.