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Not accurate or optimal geometry definition for use in ODEON.
Not accurate measured reference data to which simulations are compared.
9.1.1 Approximations made by ODEON
It should be kept in mind that algorithms used by software such as ODEON are only a raw
representation of the real world. In particular, the effect of wave phenomena are only to a
very limited extend included in the calculations. There is very little to do with this fact for you
the user, except to remember that small rooms and rooms with small surfaces are not
simulated at high precision.
9.1.2 Optimum calculation parameters
A number of calculation parameters can be specified in ODEON. These settings may reflect
reverberation time, a particular shape of the room or a trade of between calculation speed and
accuracy.
Number of Late rays
ODEON by default specifies a suggested Number of late rays to be used in point response
calculations. This number is derived taking into account the aspect ratio of the room as well as
the size and number of surfaces in the geometry. In short this means that ODEON will suggest
more rays for very long room with many surfaces, than for a basically cubic room with few
surfaces. This suggested number of rays will be sufficient for many rooms, however in some
cases more rays may be needed in order to obtain good results, in particular in rooms with:
1) Strong decoupling effects
2) Very uneven distribution of the absorption in the room
Ad 1)
If a dry room is coupled to a reverberant room, then more rays may be needed in order to
estimate the coupling effect well. An example could be a foyer or a corridor coupled to a
classroom. If the room where the receiver is located is only coupled to the room where the
source is located through a small opening, then more rays are also needed.
Ad 2)
In some rooms the reverberant field in the x, y and z dimensions may be very different. An
example of this could be a room where all absorption is located on the ceiling while all other
surfaces are hard. Another example could be an open air theatre. In particular if surfaces are
all orthogonal while having different materials in the x, y and z dimensions of the room and if
low scattering properties on the surfaces are used, then more rays should be used.
More rays needed?
There are no way of telling if more rays are needed for a certain calculation, but to get an idea
whether a room has strong decoupling effects, you may try to run the Global Estimate calculation.
If:
Global Estimate stabilizes slowly
The Global decay curve make sudden jumps, like steps on a stair
The Global decay show ‘hanging curve’ effect
this could be an indication that more rays are needed. Let the Global Estimate run until the decay
curve seems stable, then use say 1/10 – 1 times the number of rays used in the Global
estimate to specify the number of rays to be used in the calculation of the point responses
(specified in the room setup).
Transition order
The Transition order applies only to point sources. Current recommendation is TO=2 for most rooms.
For rooms that are heavily packed with various fittings or rooms where no or few image
sources are visible from the receivers, a lower Transition order of 0 or 1 may be used.
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