Walt, thanks for an absolutely clear and concise comparison. I really
can't contribute to this forum yet but hope to repay the generosity as
I gain experience. I do have some experience with active noise
cancellation (ANR) in aviation headsets and am wondering such circuits
are used in canceling noise in nature recording applications.
Donald
--- In Walter Knapp <> wrote:
>
> Posted by: "Donald Berk"
> >
> > Thanks, Danny. Is there a discussion somewhere on shotgun vs.
> > parabolic mics?
>
> That's practically a religious war sometimes.
>
> Shotgun mics are a mic inside a interference tube to narrow it's field
> of pickup. The idea being to attenuate unwanted sounds from directions
> other than your subject. A shotgun mic does not provide any extra gain
> to pick things up at distance. So, to get distance you amplify their
> output considerably. Unfortunately you amplify the mic's self noise,
> input circuit noise and so on right along with your wanted sound
signal.
> This means that to use a shotgun it must be a very high end design for
> nature recording.
>
> Parabolic mics are a mic or mics set at the focus of a parabolic
> reflector. The reflector provides gain before the sound get's to the
> mic. ie it amplifies the actual sound wave before it's converted to an
> electronic signal. This is "free" amplification that does not increase
> the system's electronic noise. It also means that it's not as
necessary
> to use the highest end mics in a parabolic for the same signal quality
> as a shotgun.
>
> The Telenga Stereo, for instance, uses 4 relatively inexpensive
capsules
> on each channel, positioned as boundary mics with the central barrier.
> Thus gaining not only the parabolic's contribution but a bit of boost
> from being boundary mics as well.
>
> The gain of a Parabolic covers all frequencies, but increases with
> increasing frequency. This somewhat compensates for the loss of sound
> with distance that occurs from high frequencies downward. (why distant
> thunder is a low frequency sound). There has been considerable
> confusion about parabolics in this regard, sound does not behave like
> radio waves and many try to apply electromagnetic radiation theory to
> parabolics working with sound. Do not be surprised to find a lot of
> conflicting literature on parabolics.
>
> One design feature of the parabolic reflector is that the reflection
off
> it sets up an interference wave out in front of the dish. A microphone
> near that will experience a band of attenuation in fairly low
> frequencies. So for good response you want the parabolic's focus to be
> at or inside the front plane of the dish. The farther in the better up
> to about 1/4 the dish depth, but practicality of design generally
limits
> most to just a little inside the dish.
>
> The parabolic dish is also a directional system like the shotgun mics,
> but a much narrower pickup. Shotguns rarely get tighter than about 60
> degrees, parabolics sometimes are as tight as a few degrees.
>
> You might also want to read the white papers at:
> http://www.telinga.com/
>
> Walt
>
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