Do you think this Comsol simulation result of Bass Trap make sense?

[MengW]

The small room size is 4.5x3.1x2.7 meter.

Bass trap, Radius=0.6m, Height=2.7m

Flow resistivity=10000 Pa·s/m²

The radius is 0.6 meters, which should not be too small for home use.

But this simulation result only works above 110Hz?

Do you think this is reasonable?

Thanks.

 

[abdo123]

Well you're only covering one corner.

 

[ppataki]

The small room size is 4.5x3.1x2.7 meter.

Bass trap, Radius=0.6m, Height=2.7m

Flow resistivity=10000 Pa·s/m²

The radius is 0.6 meters, which should not be too small for home use.

But this simulation result only works above 110Hz?

Do you think this is reasonable?

Thanks.
View attachment 275698

View attachment 275696

View attachment 275697

@MengW
A bit off-topic but I would really appreciate if you could please share how this simulation was done in Comsol
I would love to perform the same for my traps in my room too
Thank you very much

 

[MengW]

@MengW
A bit off-topic but I would really appreciate if you could please share how this simulation was done in Comsol
I would love to perform the same for my traps in my room too
Thank you very much

Hope to have more friends to do more interesting applications with Comsol.
There are some videos to teach you to use it step by step. You could search the key words comsol acoustic to find out.
The challenge is to find out the acoustic performance of some materials.

 

[NTK]

Your results look like pretty much the same as the room mode plot at 110 Hz. Below is the screen shot of the output I did using @ylio's room mode simulator. Your plot looked very similar to this except it plotted the absolute magnitude in dB instead of Pa.

Room eigenmodes calculator

Hi all! I want to share this application to calculate and evaluate the natural frequencies of rooms modeled in 3D. At the moment, the application does not consider materials, only rigid surfaces, but it is a very useful tool to evaluate the eigenmodes in irregular rooms. It is recommended to...

www.audiosciencereview.com

I've never used COMSOL's acoustics module, so I may not be able to provide much help. I strongly suspect you have used the wrong COMSOL "study". Room modes are computed using "eigenfrequency" study, and in-room response, I believe you need to use the "frequency domain" study. I also did not see any sound source. You'll need at least one sound source to simulate the room response (you don't need sound source for compute room modes). Also, what quantities were you plotting in the lower graph?

 

[MengW]

Your results look like pretty much the same as the room mode plot at 110 Hz. Below is the screen shot of the output I did using @ylio's room mode simulator. Your plot looked very similar to this except it plotted the absolute magnitude in dB instead of Pa.

Room eigenmodes calculator

Hi all! I want to share this application to calculate and evaluate the natural frequencies of rooms modeled in 3D. At the moment, the application does not consider materials, only rigid surfaces, but it is a very useful tool to evaluate the eigenmodes in irregular rooms. It is recommended to...

www.audiosciencereview.com

I've never used COMSOL's acoustics module, so I may not be able to provide much help. I strongly suspect you have used the wrong COMSOL "study". Room modes are computed using "eigenfrequency" study, and in-room response, I believe you need to use the "frequency domain" study. I also did not see any sound source. You'll need at least one sound source to simulate the room response (you don't need sound source for compute room modes). Also, what quantities were you plotting in the lower graph?

View attachment 275833

View attachment 275836

Thanks for your reply.

I setup two 1.2m height points. One is speaker source with Prms=0.00332W. The other is listening position to receive the frequency responce.

 

[MengW]

Your results look like pretty much the same as the room mode plot at 110 Hz. Below is the screen shot of the output I did using @ylio's room mode simulator. Your plot looked very similar to this except it plotted the absolute magnitude in dB instead of Pa.

Room eigenmodes calculator

Hi all! I want to share this application to calculate and evaluate the natural frequencies of rooms modeled in 3D. At the moment, the application does not consider materials, only rigid surfaces, but it is a very useful tool to evaluate the eigenmodes in irregular rooms. It is recommended to...

www.audiosciencereview.com

I've never used COMSOL's acoustics module, so I may not be able to provide much help. I strongly suspect you have used the wrong COMSOL "study". Room modes are computed using "eigenfrequency" study, and in-room response, I believe you need to use the "frequency domain" study. I also did not see any sound source. You'll need at least one sound source to simulate the room response (you don't need sound source for compute room modes). Also, what quantities were you plotting in the lower graph?

View attachment 275833

View attachment 275836

From the result, it just start to work at 110Hz, and it's very useful at 280Hz.

 

[NTK]

Thanks for your reply.

I setup two 1.2m height points. One is speaker source with Prms=0.00332W. The other is listening position to receive the frequency responce.

View attachment 275851

Your results didn't show any sign of the source. You should be able to see high SPL next to the source. It is usually not a good idea to model a point source in discretized space such as in FEA. The source needs to spread out across a number of elements for the simulation to simulate it accurately.

 

[MengW]

Your results didn't show any sign of the source. You should be able to see high SPL next to the source. It is usually not a good idea to model a point source in discretized space such as in FEA. The source needs to spread out across a number of elements for the simulation to simulate it accurately.

At some frequency, the source is easy to find out.

 

[MengW]

Well you're only covering one corner.

There is the result of 4 corners.

 

[Keith_W]

Your last graph looks confusing. It seems as if one bass trap is worse than no basstraps. Did you mislabel the legends?

 

[alex-z]

For a trap which is 60cm thick you should use a material with lower flow resistivity. That will improve low frequency absorption, as the sound waves are able to pass further into the bass trap and be absorbed more gradually.

However, even with optimized density, corner traps will not have a big impact on your axial room modes. The pressure difference exists across two complete parallel surfaces. You need to cover more surface area, or use a multi-sub setup.

 

[MengW]

Your last graph looks confusing. It seems as if one bass trap is worse than no basstraps. Did you mislabel the legends?

You are right！
I did check and fix it.
Thanks a lot.

 

[MengW]

For a trap which is 60cm thick you should use a material with lower flow resistivity. That will improve low frequency absorption, as the sound waves are able to pass further into the bass trap and be absorbed more gradually.

However, even with optimized density, corner traps will not have a big impact on your axial room modes. The pressure difference exists across two complete parallel surfaces. You need to cover more surface area, or use a multi-sub setup.

Great!
From your reply, I remembered the relevant comments on this page.

Rock wool, glass wool, hemp - which material is best suited for absorbers? — Jochen Schulz

Are you determined to improve the acoustics in your recording studio or home theater? Then a broadband absorber is the first choice! The only question is which material do you use best? I will use examples for different absorber depths to show you which flow resistance achieves the best absorption a

www.jochenschulz.me

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I did test with flow resistivity 5000 and 3500 Pa·s/m².

 

[NTK]

At some frequency, the source is easy to find out.
View attachment 275861

Ask yourself the question, are these results reasonable. If you are in this room, standing next to the sound source (or place a measurement mic next to the sound source if you think the presence of a human body may affect the sound field too much), will you detect sound from the source only at certain frequencies? Does your model resemble reality to the best of your understanding of reality?

 

[MengW]

Ask yourself the question, are these results reasonable. If you are in this room, standing next to the sound source (or place a measurement mic next to the sound source if you think the presence of a human body may affect the sound field too much), will you detect sound from the source only at certain frequencies? Does your model resemble reality to the best of your understanding of reality?

There is the listening distance from sound source to the listenning position, right?

 

[NTK]

Do you see any higher SPL near the source in the 3D density plot in the your first post?

 

[MengW]

Do you see any higher SPL near the source in the 3D density plot in the your first post?

This blue image is SPL of surface.
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If want to check the 3D spatial distribution, should find out from the image of Isosurface.

 

[NTK]

OK, I guess you already have your own answer to the question posed by the thread title, and it is "yes". I'm out

 

[MengW]

OK, I guess you already have your own answer to the question posed by the thread title, and it is "yes". I'm out

Still thank you for your reply!
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However, I still haven't found an answer.
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I have no actual experience with similar bass traps, have not found out A/B comparison.
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In my opinion, R=0.6 meter x 4 pcs，should at least handle with the 80Hz, but from this simulation results, it is only effective above 110Hz.
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There is a little disappoint.
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Is it normal？make sense？