> Is this due to a the rear element being a figure 8?
> I must admit the shotgun mic is the only one Ive never taken apart &
> I own the NTG3.
Mike,
A gunmic has a single hypercardioid capsule near the rear of the
slots/holes, but the rear lobe is small and the rear rejection is
around 12dB or greater for most frequencies. The total pickup from the
rear hemisphere solid angle is usefully low.
The enhanced forward directional sensitivity is produced by the
director tube, also called an interference tube, which acts like a UHF
television antenna with multiple elements (Yagi array). Sounds coming
from am angle take a double path, direct to the capsule and indirectly
with a delay through the director tube. With careful design these two
signals cancel out for side sounds and enhance for on-axis sounds.
Baffles inside the director tube shorten its effective length for
higher frequencies.
A longer director tube gives a narrower forward cone and more
directivity for lower frequencies. In practice, a long gunmic (aka
rifle mic) is too directional for off-axis use as in a stereo pair,
but I am experimenting with two MKH-816's and may try three of these
for a more consistent stereo image with a high "fetch".
> My faulker rig (2xfig8's) has such a good off axis rejection I can
> simply tilt it down to the floor to make the motor way din vanish. -
> Great for sfx capture.
Fig-8 mics are the only ones with a controlled directional response
for all frequencies and they produce good stereo. Their problem is
that the response of a rig is front/rear symmetrical. As you say, you
can aim off this rear response, but you can also use a baffle like
your own body, a car, a building or whatever is handy.
David
David Brinicombe
North Devon, UK
Cogito cogito ergo cogito sum - Ambrose Bierce
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