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Mapping with shadow
PostPosted: Wed Jul 12, 2017 2:19 pm Reply with quote
charles
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Joined: 23 Jun 2017
Posts: 5




Hi Guys,

Some time since I've used EASE and I'm about to do an outdoor model of a large site, so I thought I'd first try something very simple. I have a 50m x 50m face which I am using as the ground (concrete) and a 20W horn loudspeaker. All the mapping looks OK. Then I've added a cylinder, (just happen to be concrete surfaces) 10m diameter, 15m high 5m in front of the loudspeaker. When I now do mapping I get a black shadow behind the cylinder but I get coverage "inside" the cylinder. Why is this?
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PostPosted: Wed Jul 12, 2017 2:39 pm Reply with quote
Agustín Arias
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Joined: 10 Apr 2013
Posts: 26
Location: Caseros, Buenos Aires, Argentina




Hi charles!

The black shadow is ok, as EASE interprets a full sound attenuation, but it has nothing to do with the reality, of course.
The mapping inside the cylinder is due to a drawing mistake. Make sure that the yellow sides of the faces of the cylinder point to outside and the white sides point to the inside of the cylinder

_________________
Eng. Agustín Arias
Environmental Protection Agency, Buenos Aires, Argentina
Ottobre & Ottobre, Acoustical Consultants, Buenos Aires, Argentina
e-mail: agustin.arias@outlook.com
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PostPosted: Wed Jul 12, 2017 7:42 pm Reply with quote
charles
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Joined: 23 Jun 2017
Posts: 5




Thanks Agustin, you are correct and I've inverted the faces. I inserted the cylinder from the "Create Shape 3D" so it's a little disappointing that the faces aren't the correct way round! When I make the space a cube, with one side made of concrete, and I "map with shadow" it is black, if I un-check shadow it is exactly the same as if the cylinder wasn't there, so what am I doing wrong?
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PostPosted: Wed Jul 12, 2017 8:37 pm Reply with quote
Agustín Arias
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Joined: 10 Apr 2013
Posts: 26
Location: Caseros, Buenos Aires, Argentina




Hi Charles!
I do not fully understand that "cube drawing" error Neutral . Can you send me the packed project (EASE main window - File>Pack project) so I can check it? My e-mail is below.

_________________
Eng. Agustín Arias
Environmental Protection Agency, Buenos Aires, Argentina
Ottobre & Ottobre, Acoustical Consultants, Buenos Aires, Argentina
e-mail: agustin.arias@outlook.com
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PostPosted: Thu Jul 13, 2017 3:44 pm Reply with quote
Agustín Arias
Member
 
Joined: 10 Apr 2013
Posts: 26
Location: Caseros, Buenos Aires, Argentina




Hi Charles! I have seen your model and I understood what you meant by "make the space a cube"

So, you said: "When I make the space a cube, with one side made of concrete, and I "map with shadow" it is black, if I un-check shadow it is exactly the same as if the cylinder wasn't there, so what am I doing wrong?"

Nothing at all!! That's the way "Shadow cast" option works!!

If you read the EASE Tutorial it says:

"When Shadowing is On, EASE take into account the shadowing effect of any objects in the room, such as columns and balconies. When it's Off, it doesn't."

"Since simulations run without shadowing are misleading if there are obstructions in the room, many users automatically turn Shadowing On all the time"

So don't worry, that's how it works!

*********************************

In the other hand, here are some hints to consider and will help to understand the so called "Statistical Acoustics" (the one that is based on equations):

1)EASE does not consider the transmission of sound through surfaces, as in your case.
Your cylinder has (in the real life) a typical sound reduction or Sound Transmission Class (STC) or Sound Reduction Index (Rw) which cuantify the sound level reduction. But EASE does not calculate this. EASE will set SPL = 0 behind the "barrier" (the cylinder in your case, but it can be also a plane inner wall or anything that interferes between source and receiver). So, the results in that "shadowed" area are not the real ones.

2)Total SPL calculation are based in this equation:


Lr=Lw+10 log[4/R - Q/(4*pi*r^2 )]+0,1

where:
Lr: SPL at the receiver (each ponit in the audience area grid)
Lw: Sound Power Level of the source (loudspeaker)
Q: directivity of the speaker
R: room constant


The term Q/(4*pi*r^2 ) is related to the direct sound field (it only consider the source characteristics and receiver distance. In EASE, it is the Direct SPL parameter)
The term 4/R is related to the reverberant sound field [ R = Si*alphai/ (1- alpham) ] (it only consider the room absorption and surface. It has an indirect relation with the reverberation time because it is based on the absorption coefficients and S (surface)).

So, when you calculate Total SPL in EASE, the results will depend of the room characteristics.
In your case, you draw a cube with full absorption (alpha = 1) to simulate an outdoor place. But, if you change the dimensions of your cube, the room constant R will increase (alpha is still 1, but the surface S is increased) so, the Lr (SPL at the receiver) will be decreased (remember the 4/R term in the equation. Increasing R means decreasing Lr). But in the real life, there is no R at all!!! Because there is no room (S = 0)

Note: That alpha = 1 is only for the walls and ceiling of the cube (the floor is still concrete). Because if all the faces where 100% absorbent, the room constant R will be infinit (R = S/0) and 4/R will be 0 and then the Lr will be only the direct sound. You can check it if you set all your faces with alpha = 1 and calculate both Direct SPL and Total SPL. Both of them will give you the same result.

So, it is not correct to use the parameter Total SPL in EASE to calculate SPL in outdoor spaces.

You can't use any parameter that depends of any Room characteristic.

You have to use the Direct SPL calculation, but it will set 0 dB behind the cylinder. There is no way to calculate "real values" in that area with EASE.

3) When you model an outdoor space in EASE, you have to check the "Room Open" option (Edit > Room Data) and verifying that the Room Volume is 0. Then, it is not necessary to draw an absorbent cube. If you calculate the Total SPL, the results will be the same as Direct SPL (with the shadow behind the cylinder).

Best regards!

_________________
Eng. Agustín Arias
Environmental Protection Agency, Buenos Aires, Argentina
Ottobre & Ottobre, Acoustical Consultants, Buenos Aires, Argentina
e-mail: agustin.arias@outlook.com
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Mapping with shadow
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