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Nodes
Sub
Sub
Each Octave band has the centre frequency f c , defined according to ISO (31.5, 63, 125, 250,
500, 1000, 4000, 8000 and 16000 Hz). For each of the octaves there are Ns (number of Subbands)
nodes of the Sub type, the center frequency of the sub bands are defined from the
following algorithms:
The frequency f 1 of the lowest sub-band in an octave is defined as follows:
1
f c 2N s
1
2
f
2
And the following frequencies f n sub-bands are defined as:
Where n=2 to n
f n
f n
12
1
N s
The 6 sub bands (Ns=6) centered around 1000 Hz have the following centre frequencies:
Sub band number – n
Frequency (Hertz)
1 749.153538438340749
2 840.896415253714543
3 943.874312681693497
4 1059.46309435929526
5 1189.20711500272106
6 1334.83985417003436
Frequency of n th sub band in 1000 Hz octave for N s = 6
Results of calculations should be for full octave bands for the octave bands 63, 125, …8000 Hz
ISO suggests that center sub octave frequencies should be derived from 1000 Hz. For an
uneven number of bands e.g. 1/3 rd octave bands this gives us one band below, one band at,
and one band above the center frequency of the Octave center frequency – so the 3 suboctaves
are in balance relative to the octave band – however for an even number of sub-band
frequencies thing becomes unbalanced if using ISO frequencies; there will be 2 sub-bands
below and 3 sub-bands above the full octave band centre frequency (or opposite 3 below, 2
above)
Attributes
Re
Img
The energy of the transducer is emitted in N s Sub nodes. The center frequencies of the Sub
bands are centered around the full octave band centre frequency, in order best to simulate the
energy in each octave band. If N s is odd, e.g. 5 then these frequencies will coincide with ISO
centre frequencies. Be aware though that the centre frequencies used will differ if an even
number .e.g. 6 is used.
Getting the voltage and energy right
Values are in tension [V]. The values should be reduced by a factor which compensates for the
NumberOfSubBands, N s used, if N s sub-bands are used then the Re and Img attributes of each node
should be multiplied by a factor √
.
If there were 6 sub-nodes in each band and Re= "1.15534266201273234" and Img= "0.0" for each of
them then the equivalent voltage for one sub-band representing the total power in that band
would be 1.15534266201273234xSqrt(6)=2.83 V. 2.83 V is the standard voltage for which sensitivity at 1
metre is given for loudspeakers, so with this setting it will reproduce the sensitivity values at a
distance of 1 metre, se the Dipol_Domain_Frequency.xml sample. 2.83 V may seem like an arbitrary
value, but it is generally agreed upon as ‘standard voltage´– this is the voltage at which an 8Ω
App-16