I am still out of town but checked my e-mail and saw this.
The pattern of the slits in the side of a shotgun I do not believe
makes much difference. The length does and the diameter is more
importantly just matched to the size of the pickup element at the
base.
In case phase relationships need to be revisited.
Sound is not like light and differs in that if a forward moving wave
strikes a wave 180 degrees out of phase the result is, no more sound.
Difference in volume and frequencies all have effects.
Complex natural sound spaces have all kinds of little holes punched
into the sound as it travels over a distance. This is why when you
are in a room full of people you can not understand someone 10 feet
away even though there is plenty of volume. But in that same room if
the people are all women with only one low pitched man you will be
able to understand the man's conversation if you listen well.
Now for shotguns which is a pickup element with a tube full of slits
in the side of a long tube in front of it. When pointed direct at a
sound the wave will pass down the tube and be heard. The only effect
of the slits for a direct sound is to eliminate a hollow sound that
would result by a tube without slits. There the sound would be
amplified at the freq of the tubes own resonance or pitch as well as
having a "fog" effect as the sound bounces off the side of the tube
giving multiple arrival times.
For sounds comming from the side the sound is arriving at multiple
times based on the many slits. The longer the tube the better chance
that these multiple paths will be cancelled out before it reaches the
pickup element at its base. The multiple slits makes the sound from
the side interfere with itself more often and be cancelled out. That
is why the long tube on a shotgun mic is called an interference tube.
As a general rule, the longer the tube the more directive the shotgun.
Also as a general rule the side sounds that are not completely
eliminated by the tube don't sound as good anymore. That said MS is
still very popular and it often uses a shotgun as part of a stereo
microphone for picking up a wide area of sound and those will tell
you they sound great.
Let me know if my experience and observations are out of line with
theory. My background is only based on use as well as misuse.
Rich
--- In wrote:
> That's an interesting question. I would try to explain it as
follows:
>
> The key to the directionality of a shotgun microphone is that the
sound
> waves arriving from the side reach the capsule at the end of the
tube via
> various path's (through the holes or slits along the tube). Due to
the
> different path lengths, the various sound components will be
delayed against
> each other. Sound waves entering the tube via slits close to the
capsule
> arrive earlier than those entering the tube via more distant slits.
These
> time delays cause phase cancelations that attenuate the sound.
>
> On-axis sound reaches the capsule via one single path only (along
the axis
> of the shotgun) and therefore the attenuating phase cancelations do
not
> occur.
>
> Usually, all phase cancellations are frequency-dependent.
Therefore, the
> manufacturers try to arrange the holes along the tube in a very
special
> pattern in order to minimize the off-axis coloration.
>
> Regards,
> Raimund
>
>
> > All,
> > I don't understand how a shotgun microphone attenuates the sound
> > >from the side. Is it possible to put that function into
layman's
> > terms for me? I know that the longer the shotgun tube the more
> > efficient it is. My thoughts are that sound waves near the axis
are
> > allowed to pass down the tube with less interference than waves
from
> > the side. Perhaps the tube causes the wave to be reflected more
> > often when it enters from the side? If the side wave is being
> > redirected within the tube why doesn't that effect the waves on
axis?
> > 1GDW
>
> --
> NEU : GMX Internet.FreeDSL
> Ab sofort DSL-Tarif ohne Grundgeb=FChr: http://www.gmx.net/info
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