Download - Odeon

1000 Hz is approximately 0.34 metres). It should be possible to model a concert hall with no
more than a surface count of say 100 to 2000 surfaces.
3.1.3 Curved surfaces
All surfaces in ODEON must be (almost) planar; so curved surfaces have to be approximated
by dividing them into plane sections. The question of how finely to subdivide depends on the
type of curved surface and how important the surface is.
Convex curves naturally disperse sound energy, so if the surface is in an exposed position
(e.g. the end of a balcony near the stage), one should avoid for example simply replacing a
quarter circle with a single plane at 45°, which might then act like a reflector.
Concave curves naturally focus sound energy, and since focussing is a fault we wish to model,
we must try to arrange that it be preserved. However, this does not mean that a large number
of subdivisions are the solution. Using many surfaces in the model will:
Make the model visually complex, and increase the probability of errors in the model,
typically small leaks may become a problem.
Not combine with the image source theory used for the early reflections (point
sources).
Increase the calculation time
In order to calculate focusing from concave surfaces, the wall type of surfaces forming a
concave shape should be set to fractional in the Materials List otherwise the concave surface will
scatter sound too much, taking into account the small areas of the individual surfaces forming
the concave shape - rather than the total area of the concave shape. The Reflection based
scattering method would produce too much scattering in this case.
Subdivisions about every 10° to 30° will probably be adequate to reproduce focussing trends
of concave surfaces, without excessive number of surfaces, thus walls in a cylindrical room
may be modelled from 12 to 36 surfaces. A cylindrical column which disperses energy may
probably be modelled from, say 6 to 8 surfaces.
3.1.4 What to model?
How to model an audience area?
Modelling each step between the rows in an
audience area is not recommended, the audience
area can be simplified a lot without compromising
the quality of the results – in fact using one of
the suggested methods below is likely to produce
better results.
Audience A) Modelling the floor surfaces
a) Define the floor area below the audience.
b) Assign appropriate 'absorption material' e.g.
ODEON material 11001.
c) Assign a high scattering coefficient of 0.7 to this area.
d) Place the receivers some 1.2 metres above the
floor.
Audience B) Modelling the audience as boxes
Model the audience area as 'audience boxes' with a
height of approximately 0.8 metres above the
audience floor.
b) Assign appropriate 'absorption material' e.g.
ODEON material 11001.
c) Assign a high scattering coefficient of 0.7 to the
surfaces of the ‘audience box’.
d) Position the receivers some 0.4 metres above
the modelled 'audience box’.
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