Acoustics Apps: Interactive simulations for digital teaching and learning of acoustics
The Journal of the Acoustical Society of America 149, 1175 (2021); https://doi.org/10.1121/10.0003438
Authors: Lennart Moheit, Johannes D. Schmid, Jonas M. Schmid, Martin Eser, and Steffen Marburg
In this episode, we interview Dr. Lennart Moheit, formerly of the Chair of Vibroacoustics of Vehicles and Machines at the Technical University of Munich. Dr. Moheit co-created Acoustic Apps, an e-learning platform that offers an interactive and playful environment for teaching and learning the principles of acoustics and vibration.
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Katherine Setzer (KS)
Welcome to Across Acoustics, the official podcast of the Acoustical Society of America’s Publications office. On this podcast, we will highlight research from our four publications: The Journal of the Acoustical Society of America, also known as JASA. JASA Express letters, Proceedings of Meetings on Acoustics, also known as POMA, and Acoustics Today. I'm your host, Kat Setzer, editorial associate for the ASA.
Joining me today is Lennart Moheit, formerly of the Chair of Vibroacoustics of Vehicles and Machines at Technical University of Munich, and the lead author on the article, “Acoustics Apps: Interactive Simulations for Digital Teaching and Learning of Acoustics,” which appeared in the February issue of JASA. Thank you for taking the time to speak with us today, Lennart. How are you doing?
Lennart Moheit (LM)
Thank you very much for having me here. I'm very good. Thank you.
So first, tell us a bit about your background.
Yeah, I'm an acoustical engineer from Germany, currently working in the field of rail traffic noise. And maybe like many others, I came to acoustics through my passion for music. My major courses in high school were music and physics. And after high school, I decided studying engineering science at the Technical University of Berlin with a focus on engineering acoustics. And already during my studies, I started working as a student assistant in research and after graduation, I wanted to continue working in science. And so I did my PhD in computational acoustics at TU Munich. And then this time, I taught for many semesters, and I think the early idea of the Acoustics Apps came up. I somehow combined my experience from working with simulations and teaching.
That is so cool. So can you give us a bit of an overview of the Acoustics Apps website?
Sure. The Acoustics Apps is an online library of simulation tools for free use in teaching. And you can simply use these apps in a common web browser on your computer or smartphone at the website, vib.mw.tum.de. And in this library, there are many different apps dealing with sound and vibration. The subjects are quite diverse, so that the apps cover a wide variety of topics. For example, airborne sound, structure-borne sound, aeroacoustics, the physics of waves and musical instruments, and many other technical applications. And each of these apps deals with the calculation of a specific physical phenomenon, or a technical problem, and it deals with the illustration of the corresponding solution. They each provide a kind of framework of physical models and parameters which can be adjusted or manipulated by the user. And yeah, but most of the details and mathematical equations are hidden in the background so that expert knowledge is not necessarily required. The aim is that the user can simply hit the compute button and study the results. However, we also provide the detailed documentation for each app so that the expert user has the possibility to look at the underlying modeling assumptions and details. But let me give you an example for such an app and how simple it should be. There's the wineglass app, for example, where you can simply change the shape of a virtual wineglass using some sliders and buttons to approximate the glass you're currently holding in your own hand, and then you can view the vibrations of the wineglass and the liquid in it at certain frequencies and associate this animation to the real auditory event. So as a teacher, you can pick the app from this app library that best fits the current lesson and the knowledge level of your class. Or as a student, on the other hand, you can pick apps that might help you better understand a specific topic by introducing a new point of view.
That sounds like that must be so useful. So what is the technology used to create the apps?
The software we're using is COMSOL Multiphysics, which is a professional simulation software to model and solve complex physical and technical problems. It's using, for instance, the finite element method (FEM), the boundary element method (BEM), or ray tracing. And COMSOL also provides a feature to create such applications called application builder. The good thing here is that the computing power is used on a remote server, so the user does not need much more than a smartphone or a simple computer with internet access. This may help some people who do not have access to the computing resources. When our students develop new apps, they first model and solve a physical problem with COMSOL. And then they think about how this problem and the solutions can be presented as clearly and easily understandably as possible in such an app. Yeah, I would like to take this opportunity to thank all these students and supporters who have put and are putting a lot of work into this, in particular special thanks to you, Johannes Schmid, who's now in charge of the project.
That is very interesting. So what are some of the limitations to teaching acoustics and vibration in the classroom? And how does the website address that?
In general, you cannot see sound but only hear it. In teaching, we're often looking for ways to make phenomena and effects visible, either by illustrations in textbooks, or by conducting experiments. I think visualization clearly helps explaining and understanding the effects. But the problem is that many of the experiments in acoustics require expensive measurement equipment or laboratories. And this is of course not available in every university, institute, school, or at home. And during the pandemic, all over the world teaching and learning took place at home and experiments couldn't be conducted regularly. And simulations, on the other hand, can enrich teaching and learning; they can supplement or even replace real experiments. Measurement results can be verified or different visualizations can be used, you can, for instance, choose a different point of view, make a snapshot at a certain time frame, or slice through a solid body and look into it. And we can also think of virtual experiments that can hardly be conducted in reality, for example, the simulation of so-called sound-soft reflecting boundaries, which is just an idealized concept, for the reflection of a sound wave at the end of an open tube. But besides that, simulations offer a couple of opportunities. The reality can be modified with a few clicks, the speed of sound is increased, for example, amplitudes, and frequencies can be adjusted, or the test setup is modified within a few seconds and clicks. And at the same time, this interactive approach of these simulations is a great advantage over simple video representation. In general, expert knowledge, expensive software licenses, or powerful computers are required for such simulations. And this makes it a barrier under certain circumstances. And with the apps, we are addressing exactly these problems. In my opinion, the concept and the aim of these apps is primarily a matter of accessibility to knowledge and to virtual experiments.
That's so amazing. So what are some of the apps included in the website? How do you make them engaging for students?
We've developed several apps for practical applications such as the wine glass app, the loudspeaker app or the Helmholtz resonator app. And using these in the classroom seems quite easy as you can, for example, bring the sound of the real wineglass and the simulation results together in a quite comfortable way. We also developed the room acoustics app to visualize the acoustic modes, and the models we provide are very descriptive. We modeled, for example, the interior of a train car of the Munich subway, which all of our students know; they use it every day to get to the campus. And we modeled one of our lecture rooms. During the lesson, students can walk through the room and listen and identify nodes and antinodes of the sound waves, and using the app they can directly compare their observations with simulation results. The best thing is, the geometry can be adjusted, so you can also try to model your own lecture room. Some other apps deal with physical phenomena in a more theoretical way. But the interactive app concept provides a certain playful environment, so that it might be easier for some people to get in touch with these topics compared to just reading about them in theory in textbooks.
That does sound like that would be very helpful for students. It ties what they're learning in the classroom into their real lives. So let's get into some of the examples of how a teacher can use the Acoustic Apps in the classroom. Having a website be used for wave phenomena, the underlying physical principle of acoustics and vibration?
In our article, we described how the wave phenomena app was used in high school physics classes. It covers phenomena such as interference, diffraction, reflection, refraction, and radiation of waves, as well as the Doppler shift. In the given example, students learned about the characteristics of waves in general, not necessarily only in the context of sound. The teacher could show the animations directly on the whiteboard while explaining the effects. He could change parameters like the number of gratings for the virtual experiment on interference, or the angle and frequency of the incident waves that are diffracted at a wall, and he could move or resize the wall and study the difference. Furthermore, the teacher can even visualize various physical quantities together, such as sound pressure, and the particle velocity and displacement, and then explain the relationship between them.
That is very interesting. So in this article, you mentioned that there is also an app for teaching about bell vibrations. Can you talk about this?
Yeah. When I was working, teaching, during my PhD, I created a new seminar on sound radiation. And in this course, students design their own bells using numerical simulations. They optimize it with regard to certain frequencies. And so they study the connection between shape and sound. I think bells are wonderful for teaching acoustics and sound radiation. And a very important part of the seminar is that every semester, we all climb together into a bell tower in Munich, and we can touch a real, huge bell and really feel the vibrations with our own hands. And for that purpose, we developed the bell vibration app to bring the simulation results on a tablet computer directly into the belfry. And that's always a great pleasure.
That sounds like so much fun. What kind of apps does the website have for teaching about the acoustics of musical instruments?
Yeah, as a musician, I'm really fascinated by the physics of musical instruments and how sophisticated instrument makers have been making them for centuries. And simulations can now help to visualize and understand the underlying physics and sound generation. We have developed an app for this purpose that currently presents three instruments: a trombone, a timpani, and a violin. And in the article, we present the app using the trombone as an example. Here, you can manipulate the model, for example, by changing the length of the trombone, or the radius of the bell, and of course, the slide position as when playing the instrument. And the app can then be used to simulate and show how the sound pressure propagates within the tube and at which frequencies resonances can be found. And from my point of view, this gives you a good understanding of which tones you can play at different slide positions using only the tension of your lips. And it's very similar for the other two instruments in the app. Here, you can change the size and shape of the instrument and investigate what influence this has on the natural frequencies and modes.
That's very interesting. So are there any plans for expanding the platform in the future?
Yes, we are currently developing more apps that are suitable for teaching at our institute. But this all takes a bit of time. And we also have to maintain and improve the existing apps. So we have to be a bit patient, and it's more of a long-term project. We're always interested in ideas for new apps that might be needed in teaching acoustics somewhere else. So, dear listeners, if you have any ideas, feel free to contact us. We can also imagine collaborations with other universities. We now have a bit of experience and can support the development of the apps, and then make them available to everyone on the website, for example. In my opinion, that's the most important thing about this project: that in the end, everyone can benefit from it as a teaching and learning aid.
Yeah, it sounds like it is extremely helpful and will help a lot of people. Thank you for talking with us today about the acoustics apps. We will put like a show notes a link to your website and contact information for anybody who wants to be involved in the project. Thank you for coming and I think our listeners will be very happy with hearing what you have to say.
Thank you very much.
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