The nature of parabolics??
First of all I want to say that I have no interest of interfering into the
present discussion. Let it go on as it is!
So therefore, instead, I would like to simplify a bit.
First of all, a parabol needs to be small and practical enough so that
people use it. I know at least hundreds of excellent parabols in Sweden
only, which have spent most of their life's under the bed or on the garage wall.
Then it needs to have low self-noise, low output impedance, a steep traffic
filter and low battery consumption. Low handling and wind noise.
Once you have that, there isn't much more to do, if you also want to keep
the price at a realistic level. Still, remember!! that most cheap mikes
today are as good as the best mike's 20 years ago - and they were good!
I have done lots of experiments with both the Telinga and other dishes. A
loudspeaker 30 meters away, - outside - a controlled sine sweep, and a
printer at the output of the mike. Realistic conditions!
My findings are that if I make 10 similar measurements, the result will be
different up to +/- 6 db from case to case. This is because of the wind
(blowing frequencies away) and general acoustics, randomly changing. All
such changes are taking place all the time when we are "out there".
If I make 10 different measurements, like holding the dish 1 meter up in
the air, or moving the tripod 3 meters aside of the previous position, the
measurements are VERY different from one another.
All such changes are taking place all the time when we are "out there". Very
few recordists, (they DO exist though!) - look for the best position to
record, like a photographer sitting down, standing up, moving three steps
left etc.
I am fully convinced that ALL SUCH ERRORS DESCRIBED, CAUSED BY DISTANCE,
WIND AND GENERAL ACOUSTICS - ARE MUCH GREATER THAN THE ERRORS CAUSED BY THE
PARABOL DESIGN (unless is is a poor design, that is.)
So what do we have? Parabols + mike are rather "coarse" designs, which are
not very precise, not very controlled, but still work when nothing else works.
The development of the Telinga has taken several "natural" steps, as birders
have used it, and they have given me valuable feedback. 90% of such feedback
has been about practical concerns, all from a new design of a shoulder strap
to which mosquito spray you can use on the dish.
"Sound quality" has been judged by my own ears and, if possible, inside and
outside measurements. Inside measurements are very good when designing the
mike capsule itself. It took many sleepless weeks to force some sense out of
4 electrets working in parallel, towards a separating plate, for example.
For this I used a sound dampened "box" with a loudspeaker on top, making a
sine sweep, 300 to 20.000 Hz. Fairly flat. Then I could work with the
capsules, move them around, try different positions and dampening materials
and so on, and all the time look at a display showing the frequency
response. After some time I got a feeling for what was right and wrong,
getting more and more acquainted with the mike. I could get rid of peaks and
gaps and get a reasonably good polar diagram. I have no idea how the stereo
DATmic connects to Sten's math, however. What happens when such a mic is
placed inside a parabol's focus?
Still, I claim, the errors, which may follow, are lesser that "the errors"
caused by reality.
The Twin Science is very conventional, especially when using the omni
looking out of the dish. I'm sure that Sten's math explains very well the
Telinga with the omni working. When the directional mike is used, facing
inwards into the dish, one can expect that some of the sounds reflected by
the dish also hits the back of the membrane and cancels some of the gain.
Perhaps you also get other effects. As I mentioned above, it is almost
impossible to make accurate measurements under realistic conditions, outside.
I have thought of, though, to try to make a curve over "average errors
caused by distance" - as the Telinga picks it up, and then build a filter to
be used at replay. A common filter, like 6db/octave doesn't work. It should,
theoretically, but it doesn't sound good.
Please go on with the present discussion!! Here is a combination of skills
in math added to overwhelming practical experience! As a matter of facts, I
think this is the first time in history that such a discussion has taken
place. We are making history, gentlemen!
Thank you, all.
Telinga Microphones, Botarbo,
S-748 96 Tobo, Sweden.
Phone & fax int + 295 310 01
email:
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