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10 Directivity patterns for point sources
10.1 Generic point sources
Generic point sources such as the OMNI or SEMI directional sources are typically used for
calculating the frequency response and parameters characterizing the room-acoustics.
Typically for the generic source is that it is defined mathematically.
10.2 Natural point sources
With natural sources we refer to sources such as human voice, an acoustical instrument or
similar. Natural sources are typically used for auralisations and/or calculation of acoustical
parameters that depends on a specific sound power of a natural source. E.g. speech
intelligibility of a person or sound pressure level by a smaller machine.
A recorded signal for auralisation is
associated with the directivity pattern of the
actual source present during the recording.
In an auralisation the directivity pattern for
natural sources in ODEON is used together
with the recorded frequency spectrum of
e.g. a voice and if not handled correctly this
will result in auralisation where the overall
frequency response is included not once but
twice; first time through the directivity
pattern which includes the overall frequency
response, second time through the
recorded source signal, which inherently
include that response.
For calculation of acoustical parameters it is
desirable that the true frequency content is
included in the directivity pattern, in order
for example to correctly estimate SPL or
STI. However for auralisation the directivity
pattern should be equalised with the
inverse spectrum of that recorded at the
font axis of the natural source signal (i.e.
the wave file with human voice recorded
with a microphone at the front axis).
Directivity with spectrum
of natural source
Calculating reflections
Adding
inverse
spectrum
Calculating BRIR
Calculating
acoustical
parameters
Signal from
anechoic recording
with spectrum of
source
ODEON version 8.5 and later can manage to create correct estimates of parameters from
natural sources and at the same time create correct auralisation, where the overall spectrum
is only included once. But it is necessary to use a source marked natural:
ODEON is installed with some directivity patterns which have the word NATURAL attached to
their names e.g. BB93_Normal_Natural.So8. When natural directivity patterns are selected from within
Point Source Editor, a green natural label is displayed next to the equalization entry fields.
If having existing directivity patterns of natural sources which are not marked natural, this can
be done using the Tool|Directivity patterns|Mark So8 file as natural directivity. When creating new directivity
patterns this information is part of the input data.
Always use the _Natural versions of the directivity files when defining new natural point
sources. The old versions of the files are kept in \old_so8\ a subdirectory to the \Dirfiles\ directory.
If you wish to use the old directivities in old /existing projects, then open the Source receiver
list and click the Repair broken directivity links button (shortcut Ctrl+L).
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