Fons Adriaensen wrote:
On Sat, Dec 05, 2015 at 06:06:08PM +0000, Stefan Schreiber wrote:
Fons Adriaensen wrote:
* The hedgehog is at least twenty times as big.
Hardly...
Depends on which picture you look at, but OK, let's say ten times
(see Fig.12).
No, Fig. 12 very obviously is something different.
Since both microphones
layers are identical they are working as an A/B configuration also in
the vertical axis.
The supercardioid hedgehog is pictured on p. 19 and labelled as such. I
wrote this, the dimensions are the ones I have cited.
The OZO's will
be omni over most of the frequency range and turn into
something like subcardioid only at very frequencies
(above 4 kHz or so).
And how can/could you know this?
Basic theory really.
No matter what type of mic you place behind such a tiny hole,
it will pick up the pressure at that tiny hole. So apart from
diffraction effects the result will be omni.
But the pressure will come from -90º to +90º, at least mainly? If so,
the capsule "view" is 180º, not 360º. (Case as shield)
It's not too difficult to compute the diffraction caused by
a solid sphere. You can see the resulting polar patterns for
16 cm diameter sphere here:
<http://kokkinizita.linuxaudio.org/export/sphere16.pdf>
Serious question: Is this not (more or less) a cardioid response?!
Even if the OZO isn't exactly spherical, the results will
be similar.
It's also interesting to look at the result of taking the
difference signal of two diametrically opposed capsules:
<http://kokkinizita.linuxaudio.org/export/sphere16-diff.pdf>
This produces a usable fig-8 up to 1 kHz or so (with lower
frequencies requiring additional gain). Above that, chaos
takes over. Using more mics (e.g. the four frontal ones
minus the four at the back) will not improve things.
But if it IS a hedgehog based mike, this is no issue.
Which doesn't mean my theory is proven, but also no argument against
here... O:-)
Probably it would be helpful to ask Nokia, in any case.
Best,
Stefan
Note that such a fig-8 pattern is a component of any first
degree directional pattern and also of most higher degree
ones. If can't be obtained then the same is true of any
pattern of which it is a component.
Caio,
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