Typically, to block sound of a particular frequency, a structure of comparable wavelength dimensions is required. For low-frequency sounds with very long wavelengths, this can mean needing prohibitively large objects to reduce noise. In this episode, we talk to Trigun Maroo about his research regarding using 3d printing to create noise-attenuating structures that take up less space.
Associated paper: Trigun Maroo and Andrew Wright. “Sound transmission loss improvement using additively manufactured multimaterial.” Proc. Mtgs. Acoust. 46, 030001 (2022); https://doi.org/10.1121/2.0001609
Find out how to enter the Student Paper Competition for the latest meeting.
Read more from Proceedings of Meetings on Acoustics (POMA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
Typically, to block sound of a particular frequency, a structure of comparable wavelength dimensions is required. For low-frequency sounds with very long wavelengths, this can mean needing prohibitively large objects to reduce noise. In this episode, we talk to Trigun Maroo about his research regarding using 3d printing to create noise-attenuating structures that take up less space.
Associated paper: Trigun Maroo and Andrew Wright. “Sound transmission loss improvement using additively manufactured multimaterial.” Proc. Mtgs. Acoust. 46, 030001 (2022); https://doi.org/10.1121/2.0001609
Find out how to enter the Student Paper Competition for the latest meeting.
Read more from Proceedings of Meetings on Acoustics (POMA).
Learn more about Acoustical Society of America Publications.
Music Credit: Min 2019 by minwbu from Pixabay. https://pixabay.com/?utm_source=link-attribution&utm_medium=referral&utm_campaign=music&utm_content=1022
Kat Setzer (KS)
00:06
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.
Today we'll be talking to Trigun Maroo about his article, “Sound transmission loss improvement using additively manufactured multimaterial,” which appeared in the 46th volume of the Proceedings of Meetings on Acoustics and was one of five winners of the POMA Student Paper Competition for the 182nd meeting of the Acoustical Society of America, which took place this past May in Denver, Colorado. This episode is part of a five-episode series highlighting winners of the POMA Student Paper Competition. So, Trigun, congratulations, and thank you for chatting with me today. How are you?
Trigun Maroo (TM)
01:09
Thank you. I'm doing really well. Thank you for inviting me.
KS
01:13
Thanks for being here. First, tell us a bit about yourself. Where are you studying? And what do you research?
TM
01:18
I recently graduated with a PhD in engineering sciences and systems with focus in mechanical engineering and acoustics from the University of Arkansas at Little Rock in May 2022. I'm currently working as a Senior Research Engineer at Intertek in the Human Factors Lab with the Research, Innovation, Safety & Solutions Engineering team (acronymed as RiSE). At this role, I work as a consulting expert assessing the physical-mechanical hazards or risks associated with innovative products, that typically do not have standardized testing methods available.
KS
01:57
Okay, cool. And congratulations on finishing your PhD. That's exciting, and an accomplishment. So what is additive manufacturing and how is it used in acoustics?
TM
02:08
Additive manufacturing is the process of creating an object layer-by-layer. It could refer to any process, like molding, but it typically refers to 3d printing. 3d printing can manufacture custom-shaped structures inexpensively. One usage is in the fabrication of acoustic metamaterials. “Meta” is a Greek prefix that means “beyond.” Hence, a “metamaterial” is one that goes beyond the characteristics of a naturally occurring material.
KS
02:38
Okay, yeah, that terminology makes sense. So your main concern in this article was additive manufacturing to create structures for blocking sound transmission. Can you tell us a bit about what is known about creating noise attenuating structures?
TM
02:52
Typically, to block sound of a particular frequency, a structure of comparable wavelength dimensions is required. For example, the wavelength of audible lower-frequency sound could be several meters in length. To block such sound, barriers of the size of an outdoor sculpture would be needed. Contrarily, acoustic metamaterials attenuate sound several orders of magnitude smaller than the relevant sonic wavelength. Here, periodically repeating shape, for example, a cylinder with stark differences in the material properties between the mediums, causes destructive interference between the several scattered and reflected incident waves.
KS
03:34
Okay, yeah, that sounds significantly more convenient when you're talking about trying to reduce noise. So, what was the goal of your research?
TM
03:43
So far, majority of the 3d printing noise attenuating structures have been printed in a single material. In one research, the 3d-printing process was paused every few layers to manually insert the periodically repeating element, in that case steel cubes, in the outer 3d-printed matrix. However, this was not an entirely 3d-printed multimaterial structure. We wanted to test the concept whether fully 3d-printed multimaterials would result in a predictable sound transmission change or not. Thus, a thermoplastic polyurethane (TPU) cylinder was used as the periodically repeating element and polylactic acid or acrylonitrile butadiene styrene (ABS) material was used as the outer matrix.
KS
04:33
Okay, interesting. So what are the current challenges for creating noise attenuation structures via 3d printing and measuring their noise attenuation?
TM
04:42
In the literature, solutions to the 3d printing challenges with small surface area specimens (around 27 cm2) and single-material 3d printing are widely available. However, solutions to 3d printing large surface area specimens (around 270 cm2), especially with more than one material, or multimaterial 3d printing, are scarce. Therefore, combining large-surface-area 3d printing with printing in multimaterials in a single shot was significantly challenging.
Next, issues like nozzle clogging, warping, and bed adhesion were prominent.Nozzle clogging occurred due to the long nozzle idle times. To provide background to our audience, in our multimaterial printing, a dual-nozzle 3d printer was used. One nozzle was actively 3d printing in one material, while the other stayed idle until it was called upon to print in the second material. Because long idle times kept this nozzle hot for hours, the filament melted in the nozzle, and the nozzle got clogged. Hence, upon activation, this nozzle would not print, and the print would fail.
The second issue was warping. Warping over time, especially when printing in ABS, is a known problem in the 3d-printing community. Because we were pursuing multimaterial 3d printing, this issue was further magnified in our case due to the very long print times, for example, around 24 to 36 hours per structure.
Warping also affected bed adhesion, which means the ability of the 3d-printed structure to stay on the surface being printed. Because of the large surface area in our case, the thermoplastic cooling contraction forces were so high that even the build tape would get ripped off from the printing platform.
The other challenge was related to the measurement of sound transmission loss, or STL. There are two popular ASTM test methods for measuring the sound transmission loss, the ASTM E90, or the reverberation room method, which measures random incidence sound transmission loss, and second, the ASTM E2611, or the impedance tube method, which measures the normal incidence sound transmission loss. Both these methods provided limitations for sound transmission loss measurement in the high-frequency range. While we have covered these limitations in detail in a separate publication, for this audience, the high-level overview is this: The reverberation room method requires a large room, around 50 m3 in volume, that are financially expensive to maintain, and also very large specimen sizes, around 2.4 meters in one dimension, for testing ,that are impractical to fabricate via FFF 3d printing. The second method, impedance tube method, when measuring in the high-frequency range requires very small specimen sizes, which limits the averaging properties over the cross section.
KS
07:44
Okay, so it sounds like you had a lot to contend with. How did you solve these problems?
TM
07:50
In terms of 3d-printing fabrication challenges, the nozzle-clogging problem was solved by writing a new tool-change script in a .gcode script for the inexpensive Flashforge 3d printer. The custom tool-change script was required because even a commercial slicing software did not have this feature pre-built. Warping and bed adhesion challenges were addressed by making physical modifications to the 3d printer and finding the ideal 3d-printing settings. While general web solutions provided guidelines to some extent, the ideal settings were identified via trial and error by observing print failures over the 24-to-36-hour long print times. In terms of sound transmission loss measurement, instead of a standard reverberation chamber, we designed and built a custom small reverberation chamber of 0.49 m3volume—compare that to 50 m3 volume—to measure the sound transmission loss of small 3d-printed specimens, around 200 cm2, at high frequencies. Using this chamber then, we measured the random incidence sound transmission loss of multimaterial 3d-printed specimens and compared it with the sound transmission losses of the single material counterparts. We gathered more than 4,700 data points experimentally to provide our observations.
KS
09:15
Oh, wow. So what was the overall effect on sound transmission loss in the 3d-printed multimaterials?
TM
09:20
Overall, all multimaterial specimens provided improved noise attenuation compared to their single material counterparts at a targeted frequency. Specifically, 50 percent infill PLA plus TPU sample offered a sound transmission loss improvement of around 5.5 dB at 6,300Hz relative to a 50% infill PLA sample of same thickness. The sound transmission mass law states that to increase the sound transmission loss of a structure by just 6 dB, its thickness should be doubled. Therefore, by this law, there is a potential to achieve approximately an 85% reduction in thickness with the employment of a multimaterial design.
KS
10:04
Oh, wow. That would be amazingly helpful. So what's the significance of your findings?
TM
10:09
The multimaterial specimens show the potential to improve sound attenuation at a desired frequency, without the expense of addition in thickness. Such structures could be used potentially in any noise mitigation application. Because the structure can be entirely 3d-printed, this result can be achieved cost efficiently. Moreover, because our fabrication solutions were applied to a low-cost 3d printer, these solutions could benefit a large community of researchers, including hobbyists.
KS
10:40
Was there anything about your research that you found exciting or interesting or unexpected?
TM
10:45
The biggest excitement was the concept that the multimaterial structures do show improvement than the single-material structures. Before diving into this research, we just did not know anything about this, whether they would show any improvement or not. But the fact that when we conducted the research, solved all of these challenges, and we did find results that were positive in this sense, it was very contending and satisfying to know that the concept shows some potential in terms of improvement of sound transmission loss.
KS
11:20
Yeah, I agree. That must be very exciting, like you said, very satisfying. It's like oh, this thing I've been studying actually works, or this idea that I had.
TM
Yeah.
KS
So where do you see your research heading next?
TM
11:32
the random incidence sound transmission loss characterization of multimaterial specimens with different infill percentages is one path. Much is yet to be discovered in this direction, which is why this path. In our multimaterial structure, while we used as cylinder as the periodically repeating element, any other shape, for example, triangle, square, or the creative imagination of the designer, could be used instead as well. This, then, could give rise to interesting sound transmission loss phenomena, interesting to be observer.
KS
12:07
Very cool. So thanks again for taking the time to speak with me today about your research.
TM
12:11
Thank you very much.
KS
12:12
Yeah, I know I've learned a lot about additive manufacturing and metamaterials from this conversation. It's really cool how 3d printing may be useful for noise reduction, incredibly useful. I wish you luck in your future research. And of course, once again, congratulations on winning the award for POMA and also for finishing your PhD.
TM
Thank you very much
KS
For any students or mentors listening from around the time this episode is airing we're actually holding another Student Paper Competition for the most recent meeting in Nashville. So, students, if you presented at the national meeting, now's the time to submit your POMA. We're accepting papers from all of the technical areas represented by the ASA. Not only will you get the respect of your peers, you’ll win $300, and perhaps the greatest reward of all, the opportunity to appear on this podcast. And even if you don't win, this is a great opportunity to boost your CV or resume with an editor-reviewed proceedings paper. The deadline is January 8, 2023. We'll include a link to the submission information on the show notes for this episode.
Thank you for tuning into Across Acoustics. If you would like to hear more interviews from our authors about their research, please click subscribe or find us on your preferred podcast platform.