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Re: Split Parabola Boundary Array

Subject: Re: Split Parabola Boundary Array
From: "John Hartog" hartogj
Date: Wed Jan 16, 2008 9:16 pm ((PST))
Hi Rob, 
I will try to address some of your comments as I prepare dinner.
[now opening a bag of potato chips, and pouring some beer]

> I've always admired the way dishes can isolate details-- getting more 
> stereo "liveliness" would be a great plus.
> Just to be sure, your dish is divided in half vertically, correct?

Yes vertically.
[chomping chips and beer while chopping a large beet into slices]

> It sounds like the highway(?) is on the left in the recording. Is 
> that that correct orientation, field-wise?  I noticed the right 
> channel of the sound file is showing more resonance between 250-500 
> Hz than the left and I was trying to explain this flip.  
> The gain is also lower on the right channel so the difference in 
> resonance is probably more pronounced than this.

Thank you for analyzing the recording. 
The wetland is completely surrounded by highway noise, and train
noise, though most of the roar emanates from the rear and left of the
microphones. It would be hard to say where the resonance you see is
coming from.  There are shipping ports with typically loud industrial
activity to the right.  I was aiming the mics toward a silent mounded
landfill in the distance. I should probably provide the unfiltered
[thinly slicing a large red onion, tearing oyster mushrooms and
slicing shitakes]

> Regarding stereo localization in a dish. If the back of the dish is 
> more responsible for the most, on-axis "centered" sounds (like the 
> water splashing in the take-offs), then one could surmise that that 
> the sides of the dish are more involved with (moderate) off-axis 
> pick-up.
> When I look at the geometry, it seems like the (moderate) 
> off-axis sounds coming from left of center would be 
> reflected/amplified a bit more by the right side of the dish and 
> vice-versa. The effect gets greater as you move towards the sides. If 
> your rig defeats this flip-phenomenon, that result could be 
> unexpected.

Solving the flip-flop problem was my fundamental reason for
experimenting with a large barrier that extends beyond the dish.  The
LP barrier seemed to work well for eliminating flip flop.  This one,
for some adjustability for mic position in both directions, behind and
forward of true focus, meant leaving more space behind the barrier.  I
seem to notice some flip flop bleeding through as the gap increases.  
[starting the rice and toasting cashews and sunflower seeds]

> As for reducing some of the resonance in the two dish halves, did you 
> try some higher density foam or other deadening material on both 
> sides of the divider? It could be that facing the capsules towards 
> the dish works better in dealing with the resonance from the two dish 
> enclosures. As Curt says, one would expect the centered sound to be 
> clearer with the capsules directed towards the back of the dish (the 
> focus point).  As the dish only has one focal point, all stereo 
> imagery is an "enhancement," so I'd also try placing the capsules 
> directly on the divider (or foam).

Both ideas are worth further exploration. Inward facing capsules does
make sense.
I like the idea of a sound absorbing divider to help with resonance,
but the challenge would be to not absorb the focus. Maybe a small
reflective plate on larger absorptive divider.
[heated olive oil, throw stuff into the pan]

> For greater stereo "side" imagery with a dish, your project makes me 
> think that one could also use 4 mic capsules (2 in series for each 
> channel) and place one capsule of each pair outside of the dish 
> (left-right crossed) and pointing hard left and hard right. This 
> would surely create phase issues but the arrangement might add width 
> and liveliness with less ill-effect on the tonality and localization 
> of the off-axis sounds. Thanks for sharing this project. Rob D.

That sounds like fun. But since supplied PIP is not likely to be 
sufficient two power more than two capsules, I might not be trying
that for a while.  If I had a Zoom H2 to cannibalize, I just might try
it with that.
[I hear someone else in the kitchen messing with my cookin, I better
get back]

Thanks, Rob, for taking time to appreciate my recording work.

-John Hartog

[adding some chicken so nobody thinks I'm a veg head - not that
anything is wrong with veggies]

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