Analytical Analysis - Room Gain

[René - Acculution.com]

How is room gain affected if the rear wall for example is essentially all glass?

Room gain (as it is understood in this post, although I don't think there is agreement about the usage of the term) hinges very much of hard walls, so you would see the effect as described here. In practice, your room will probably not be airtight, and the other walls may be heavily damped. Erik from Perlisten did some measurements in his room as shown here https://audioxpress.com/article/simulation-techniques-room-gain

 

[sveinse]

I have a room which is not a cuboid, but has a 25 degree roof that creates a 7th plane to the left of the sitting position. The cross section is conceptually like this (not to proportion, the "bevel" of the roof is significantly bigger)

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I have for a long while wanted to simulate the room gain and/or nodes to understand better where the pressure zones gather for this shape. Because the shape is not symmetric, the normal standing wave models no longer applies (at least for two of the axis)

What is the best approach to simulate this? I am an engineer and programmer, so I've started looking into openCFS and want to use PDEs. But it's somewhat a learning curve to get everything modelled and setting the right boundary conditions. Are there any free tools that are able to input a 3D shape to do the basic simulations?

 

[janbth]

I have a room which is not a cuboid, but has a 25 degree roof that creates a 7th plane to the left of the sitting position. The cross section is conceptually like this (not to proportion, the "bevel" of the roof is significantly bigger)

/---+
/ |
| |
+-----+

I have for a long while wanted to simulate the room gain and/or nodes to understand better where the pressure zones gather for this shape. Because the shape is not symmetric, the normal standing wave models no longer applies (at least for two of the axis)

What is the best approach to simulate this? I am an engineer and programmer, so I've started looking into openCFS and want to use PDEs. But it's somewhat a learning curve to get everything modelled and setting the right boundary conditions. Are there any free tools that are able to input a 3D shape to do the basic simulations?

Check out Amroc pro: https://amcoustics.com/. This uses openCFS for computations. There is a small fee for getting the full computation for non-rectangular rooms, but doing only the five lowest lying modes is free.

 

[sveinse]

Check out Amroc pro: https://amcoustics.com/. This uses openCFS for computations. There is a small fee for getting the full computation for non-rectangular rooms, but doing only the five lowest lying modes is free.

Currently Amroc pro is only able to simulate non-rectangular floor shapes (or cross sections) and no 3D shapes like angled ceilings unfortunately.

 

[janbth]

Currently Amroc pro is only able to simulate non-rectangular floor shapes (or cross sections) and no 3D shapes like angled ceilings unfortunately.

Ah, yes, I see that now. My bad…

 

[NTK]

I have a room which is not a cuboid, but has a 25 degree roof that creates a 7th plane to the left of the sitting position. The cross section is conceptually like this (not to proportion, the "bevel" of the roof is significantly bigger)

/---+
/ |
| |
+-----+

I have for a long while wanted to simulate the room gain and/or nodes to understand better where the pressure zones gather for this shape. Because the shape is not symmetric, the normal standing wave models no longer applies (at least for two of the axis)

What is the best approach to simulate this? I am an engineer and programmer, so I've started looking into openCFS and want to use PDEs. But it's somewhat a learning curve to get everything modelled and setting the right boundary conditions. Are there any free tools that are able to input a 3D shape to do the basic simulations?

You can find the link to an irregular shape room mode simulator in this post.

Y

'Room eigenmodes calculator'

Nov 1, 2022

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 make the models in sketchup (they can be done for free with sketchup online), export in .stl format and import them in the simulator.

It allows calculating the Schroeder frequency (manually entering the Tmid) and there is an excel spreadsheet to evaluate the modal distribution according to Bonello's...

• ylio
• acoustics calculator eigenmodes room simulator
• Replies: 11
• Forum: Room Acoustics and General Speaker Discussions

• 

 

[sveinse]

You can find the link to an irregular shape room mode simulator in this post.

This is just perfect. Finally got confirmation of some suspicions that I've had to where those nodes are. Thank you.

 

[Flaesh]

Hornresp:

 

[sfogg]

When I built my theater I designed it to try and take advantage of room gain. All walls are double drywall (on their own studs decoupled from the outside walls), poured concrete floor and the ceiling is double drywall on its own joists not connected to the floor above. No windows, and I built the door out of multiple sheets of 3/4" plywood with acoustic seals beween the inner and outer layers that expand to seal the door when it closes. The door is held shut with a hydraulic arm. The room isn't perfectly sealed but it is cerrtainly sealed better than most rooms.

My L/R subs each have (2) JBL Sub1500s in 6 cubic foot sealed boxes. It has been a long time (15 or 18 years) but as I recall they should have been around a Q0.5 with a F3 point of 32ish hz. My room is small and gain should start to kick in at right around the same point. This is my FR (unsmoothed) at the listening position with both subs going.

The bottom end rolloff is due to the high pass filter in the Crown K2 that drives my subs.

 

[Raj21p]

Room gain is the natural low-frequency boost from a room’s lowest mode. Proper sub placement, especially sealed subs in corners, maximizes it for deeper, smoother bass.

 

[Dj7675]

How drastic of an effect does removing one wall have on room gain? For example in a 23’x16x room, if one of the long walls is mostly gone? Does the missing wall remove all room gain or will some remain?

 

[René - Acculution.com]

How drastic of an effect does removing one wall have on room gain? For example in a 23’x16x room, if one of the long walls is mostly gone? Does the missing wall remove all room gain or will some remain?

It might not be as bad as one would think. Now, 'removing a wall' is not a clear-cut boundary condition, so I did the most extreme of having zero pressure on a side wall, and then so-called PML to emulate radiation. In reality, there will be 'something' on the other side, so this is just quick stuff. For a case from https://audioxpress.com/article/simulation-techniques-double-bass-arrays, I show here the ideal responses:

The entire wall on either end is moving, hence the perfection. Next, zero pressure on a side wall:

Could be better, but still... We are also not looking at anything more than an idealized situation with no damping and such. The pressure can be seen here for 90-ish Hz. No perfect absorption, but we would not expect that.

Finally, the PML bc. Better responses, so one should be careful to actually model for the physical setup in question, as the simulation software has no idea what that is:

So, it could work, but if it were me, I would make a more accurate model of the physical situation, and then I would run an optimization routine to figure out better filters for a desired DBA-like response.