Thanks everyone for the input, it still boggles my mind that all
these waves can co-exist in an area as small as the microphone
tube. I had done some searching on the web before my post and found
that another wave at 180 degrees would cancel a sound.
1GDW
--- In "Rich Peet" <>
wrote:
> 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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