AFMG Network Forum

shanfly · Member

Hi all.

I'm working on a truncated model that I've been handed. Therefore the model has certain surfaces which actually are not there, and in reality the building continues beyond these boundaries. Now, IR measurements were taken, and the source was relatively far from these unreal boundaries, and so were the majority of the microphone positions. So my concern is how I can deal with these unreal surfaces to make the EASE model as close as possible as the real one. Has anyone worked with truncated models before? I was thinking of applying a relatively high absorption and much diffusion, as the expected returning reflections will have bounced several times before returning to the reading positions.

All suggestions are welcome Smile

AFMG Pedro Lima · Forum Moderator

Hello,

Not sure I understand what you mean by "truncated model".

Would it be possible to send a copy of your model with a couple details to my e-mail? Then I might be able to assist you. Wink

Best Regards,
Pedro

Charlie · Member

A truncated model, where only a portion of the room is modeled and the rest of it is not, can never be expected to give results that could be considered representative of the room in its entirety. But to answer your question, I think it depends somewhat on the details of the room that are truncated (left out of the model). The farther away reflecting surfaces are located the lower in level the reflections may be due to increased propagation. This also may affect the spectral shape of the reflections that come back to the modeled part of the room. That is to say an increased loss of HF in the reflections. So the shape of the absorption coefficient curve assigned to the truncating plane (surface) in the room should try to account for this.

Yes, I think high scattering should be used for truncating plane.

One thing that may be quite difficult to account for is the increased propagation time of the reflections occurring in the truncated area which might re-enter the modeled area of the room. These reflection will re-enter the modeled area of the room at a later time than they would when modeled as reflections from the truncating plane. Be aware of this & know when it might not be a good idea to truncate a model.

Hope this help.

shanfly · Member

Thanks Charlie. Yes, I was a bit concerned about that. Whereas absorption and diffusion of the sound returning from the excluded section could be assigned to the truncating surfaces, there is no much that can be done regarding the actual delay of the sound, I guess. It is actually the first time I am working on a model like this, and to be honest, I'm not quite happy with the model they've built, so I was curious to know if someone had tackled a similar situation before.

Thanks again and regards.

Ron Sauro · Member

Hi....
We have done truncated models before and generally find the results not to be very useful....
The truncation will work if and only if the room beyond has surfaces beyond the largest size dimension of the modeled room. In other words....if you are truncating a hallway.... you need to know that the other end has to be farther away than the length of the hall in existence in the model.
If you can meet this requirement then you can make the surface of the model that opens into the truncated part have an absorption of 1.0 and prevent any reflection from coming back out of the surface.....Scattering is not needed here as it acts just like absorption in the model