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Re: Seeking Low-cost Commercially Available Parabolic system

Subject: Re: Seeking Low-cost Commercially Available Parabolic system
From: Walter Knapp <>
Date: Sat, 12 Mar 2005 18:10:09 -0500
From: Klas Strandberg <>

>>>With the parabolic it is in focus or out. There is no smooth
>>>transition.
> 
> 
> 
> Yes, there is. The size of the focus varies with frequency.
> 
> Klas.
> 
> 
> 
> 
>>>With a shotgun the center is more like the ear to find the sweet spot.
>>>
>>>You can read that a shotgun has no gain but the truth is a bit more
>>>gray.  If you have a sensitive directional mic that is has a pattern
>>>more close to the ear in direction ability, then it is easy to find
>>>the sweet spot in the blind.  It still can do a selective receive
>>>that a dish can do.

First off this grew out of the assumption that being blind means a 
person cannot hear the direction of the sound. Nothing could be farther 
from the truth. Friends I have that are blind can point exactly where 
some sound is and describe it far better than a person with sight, they 
don't need to see the bird. I see no problem in their using a parabolic, 
in fact I've handed my parabolic to a blind person, and he had no 
problem using mine. No instruction necessary he already had what he 
wanted to point at nailed. And he could scan up new things too.

It's not just that the size of the focus varies with frequency, I 
certainly agree with Klas on this. The focus is also variable depending 
on target distance. The bottom line is that a parabolic is hardly a 
straight line only as to it's pickup. While the angle of acceptance of a 
parabolic is narrower than a shotgun, it's still very wide and does have 
a transition zone that's easy to use as a guide for centering the 
direction of the mic. It's easy to zero in by ear with good headphones. 
I submit it's even easier if you use a stereo parabolic, like the 
telinga stereo. In frog survey recordings I'll usually survey a site 
entirely with my headphones on, zeroing in on each little calling group 
by ear. Bird folks need to try this more, with frogs your chances of 
seeing the calling frogs are very low, so you always do it by ear. Try 
recording with your eyes closed, listen to the sound.

The problem with shotgun mics in addition to having no extra gain that 
won't increase the self noise as well, is that they tend toward the high 
priced end, hard to cheaply hand make a quality shotgun mic, though I 
have a few ideas. You will get more bang for the buck with a parabolic, 
particularly at the less expensive end. Even once you get the shotgun 
pointed at the bird, it's still hampered by less gain and a wider pickup 
zone. Shotguns tend to have polar patterns that have a fairly even 
pickup for the center 60 degrees or so, much harder to get exact aim by 
ear. If anything they have greater need of visual sighting.

Try both a parabolic and a shotgun blindfolded, I think the parabolic 
will win as far as aiming.

As far as the ear's angle of acceptance, it's more like the SASS than 
either of these. It's our brain that then filters out all that came in 
to make it appear like we were only listening in one limited direction 
to a single caller.

Walt




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