Over the weekend I built a couple of versions of a Curt Olson-inspired
183 boundary array. Both of them hinged to allow trying various mic
angles, one at the front in a "V" and one as an "H" with the mics
mounted at the crossbrace to keep mic distance constant. I'm not sure
the few inches of change will cause a huge difference, but wanted to
hear for myself. Here are some photos:
http://www.pbase.com/kdurling/183_arrays
As you can see I also tried applying a flexible brass leading edge
filler on the H array to fill the gap between the necessarily
separated boundary plates. My first impression was that this did
slightly improve stereo definition - I imagine because it prevented LH
signals from striking the back of the RH plate? Not sure how much
these 183s pick up from the back field when mounted like this. I may
or may not retain this feature on the "final" version. Thoughts?
The mics themselves are wrapped in electrical tape (thanks Curt) and
mounted in a strip of wood to allow them to be easily changed from
array to array.
The V array will also swing forward to allow a psuedo XY arrangement.
But as per Curt's experiments, initial tests will be to see if
there's any distinct advantage to a ORTF 110 degree, vs other angles,
such as 90 or less.
With the H array, I'm thinking of trying the two plates parallel with
the a 3rd mic, a cardioid, mounted in the center for a psuedo M-S
array. I'm not to the point yet of precisely controlling phase
relationships - I'll probably do that only if and when the need
becomes clear. I will do mono compatiblity tests on anything I do,
and I imagine that's where it will show up.
I also want to hear what happens with the H array if a large vertical
plate is put in the center between them. I''m hoping for an
ever-so-slight gathering or concentrating effect, like a parabola, but
have no idea what the side-effects will be, or whether it will even
have the intended focusing effect. I imagine it will increase biaural
separation, mayve to an undesirable extent.
Anyway, there are lots more things I want to try, and am open to
suggestions!
I have a pair of those wire mesh Post-It holders that Curt used, and
about a yard of fake fur. :-) I will try that and probably some
other materials - fleece, cotton, etc - once i devise a "modular"
approach to attaching wind protection.
The only tests I've done so far have been placing the arrays outside
my apartment, which is on a busy corner, so nothing very subtle. But
it did give me sense of the stereo separation, there were some
passers---by, and I walked back and forth in front of the array at
various distances counting out loud and recorded that, which was
interesting. There was a very pronounced acceleration of crossing the
0 point at close range, which I suppose is inevitable but I'd like to
reduce it (ideas?), but I thought very good spatial definition when I
did the same thing across the street - perhaps 50-60 feet from the
mics. I was pleased for intial tests. I did try some various angles
with the H array, and the V array swing forward into a psuedo X-Y.
Nothing dramatic, but like I say it was far from a precise testing
environment. I also tried just throwing the fake fur over the whole
array to see how much it altered the sound. The answer was noticeably
but slightly. Probably less when I have small patches cut that will
be held away from the mic face by the screens.
With the mics outside I noticed a lot of fairly constant low freq
rumble that seemed independent of the fluctuating traffic noise,
almost a hum. At first I feared something in the system, but when I
tested the arrays indoors later it was gone.
I have a friend who's a recording engineer and we;re going to do some
more detailed spectrum analysis with the arrays in his studio later
this week - if anything interesting turns up I'll report.
Any observations, needless to say, are welcome. I'm hoping to try
this out down by the bay for more tests, including wind screens,
sometime this week, and get it out in the field with the Snow Geese
sometime in the next couple of weeks.
OK, sorry to be so long-winded. Thanks for reading.
Ken
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