> Nt1a have only one membrane so it does not have fig-8 option as David
> mentioned.
Someone said it has two diaphragms, but one is enough to get a cardioid
pattern. The misconception was that the two diaphragms work separately.
There is only one output connection at up to 1000MegOhms impedance, hence
the need for good screening.
An Omni capacitor (condenser) mic has a solid backplate and this picks up
rear sounds which diffuse around the capsule but remain in phase with the
front. This causes some attenuation in higher frequencies which can be seen=
in the polar diagram, but it essentially omnidirectional.
A fig-8 version has a perforated backplane, and rear sounds produce the
opposite phase to the front sounds as it is now working as a velocity
microphone, not a pressure mic. Sounds from the sides cancel out hence the=
figure of eight polar pattern.
Combining both principles, a cardioid has a partially perforated backplane=
with small holes which cancel out the rear sound as it combines the effect=
of the two types above. This still only needs one diaphragm and one
backplane.
The tricky part is getting a nice flat response and an acceptable cardioid=
polar response at all frequencies which is what you pay your money for.
Having a second, rear, diaphragm is used by some manufacturers to get a
better polar response. The two diaphragms are connected, normally both to
ground.
David Brinicombe
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