I wrote:
> As I mentioned the other day, I dragged a pair of Crown GLM-100s out
> of long-term storage and am getting reacquainted with them. These are
> really impressive mics. To my ear, they seem to perform best in free
> space (with respect to boundaries) and with no barrier of any kind
> between them. Would anyone here disagree with those findings or have
> any additional comments regarding boundaries/barriers and omni mics of
> this type (similar, I'm guessing, to the Sure 183s)?
>
> As to spacing, I reported my first impression that there was a nice
> "sweet spot" at approximately 26 inches. But now I feel that that
> spacing presents an unnaturally wide image (I like it, but it seems
> unnatural to me). With the particular pair I have, 8.5 inches seems to
> be yielding the best compromise between width, "naturalness" and mono
> compatibility. Anyone here willing to share their own experiences with
> spaced omni pairs? In particular, I'm wondering if the size of the
> sound source makes a big difference (for example, indoor point source
> vs. "all outdoors"). My goal here is a relatively simple
> stereo/binaural array with these mics that will deliver nice results
> in most field recording conditions.
Lang replied:
> If you want binaural, then try a Jecklin disc kind of setup, rather
> than spaced omnis. Keep your mikes about 6.5-7 inches apart,
> simulating the ear spacing of the human head. This will yield a fairly
> decent binaural recording.
>
> http://www.josephson.com/tn5.html
Thank you, sir, for the link. I made some terrific binaural recordings
a few years ago with a similar setup, albeit considerably more crude
looking than the Jeklin disk. I'm tinkering with some ideas along those
lines once again. If I get decent results, I'll post a photo.
Rob added:
> I was curious about the GLM specs when you mentioned them before.
> GLM-100/100E
> Open Circuit Sensitivity:
> GLM-100: 3.2 mV/Pa*(-50 dB re 1 volt/Pa*).
> GLM-100E: 8 mV/Pa* (-42 dB re 1 volt/Pa*)
> Equivalent Noise Level: 28 dB SPL typical
> (0 dB = .0002 dyne/cm2), A-weighted.
> S/N Ratio: 66 dB at 94 dB SPL.
>
> Shure MX183
> Open Circuit Sensitivity (at 1 kHz,MX183: -27.5 dB (42.2 mV)
> Equivalent Output Noise (A-weighted) MX183: 20.5 dB
> Signal to Noise Ratio (referenced at 94 dB SPL)
> MX183: 73.5 dB
>
> The 100E has more output than the 100. Spec-wise, the 183 exhibits
> less self noise and higher gain (sensitivity).
I appreciate you pulling together the comparison. After the discussions
here lately about the 183s, I can tell you that a pair of them is
definitely on my shopping list for 2005, with some kind of high-end
Sennheisers still on the on the long-range wish list. Meanwhile, to
bastardize a recent statement from a controversial public figure, you
go into the field with the mics you have, not the mics you wish you
had.
Rob continued:
> Your observations about sweet spots seem right on. I'd add that
> spacing/stereo imaging depends on immediate and long term playback
> systems you're recording for. No spread meets all needs. Does one
> spread meet more needs? There's a section in Bernie's book, Wild
> Soundscapes" (pg 149-50) drawing from Lang's research that is
> excellent regarding binaural playback issues.
>
> The most reproducible stereo imaging scenario might be recording
> strictly for headphone playback. A hinge in the middle of two ~12"
> extension arms allows one to adjust the spread from 1-26" and find
> sweet spot(s) for every situation.
Yup. That's exactly how I identified the multiple sweet spots with the
GLM-100s.
> I have a 8" X 8" piece of foam core to use as quickie Jecklin-like
> divider for the < 8" range. This is the only way I've ever felt the
> listener can hear a very similar field to that I hear in the field if
> they use headphones.
>
> Then there's polar pattern. Omni-directional mics have greater
> high-end response to sources that are directly in front of the
> capsules (though much less pronounced than with cardioids).
I've used cardioids extensively over the years, mostly in the studio
but also in the field in XY and ORTF arrays. But I've never worked much
with omnis, thus my current line of questions.
> For recording "wrap around space," mounting the capsules so that they
> point away from each other tends to work better than the typical A/B
> "front" facing. The later is used when a portion of the field is of
> greater interest. Birders, for example, might like A/B front facing
> better.
I experimented with both arrangements last week, and found that I
preferred the capsules facing forward. I'm thinking that it better
approximates ears, which have an omni pick-up pattern, but a
forward-facing collector.
> For "typical" stereo living room playback, room
> architecture/furnishings often dictate speaker locations. Some people
> experiment with placement options, but they're probably using tight
> field music when they adjust to taste. When we start guessing what
> omni mic spreads will work best for living rooms, it might be
> realistic to account for speakers that are too close (within 3') and
> way-too-far-apart, like in the corners of a large room.
And that's the crux of the problem -- accommodating many possible
playback environments. As with all things audio, it's like nailing
jello to the wall.
> Perhaps the only way to know you're using a fixed spread you like is
> to make a test recording of a large, outdoor setting using several
> spreads without a divider. Then make additional recordings of front
> facing events like a bird call, a person speaking at 4' and even a
> small, close object. Record all of these with different mic spreads
> and the closer objects with and without a divider. Play them back
> through too-close and too-far speaker spreads.
>
> You might notice that with field recordings (which are typically much
> drier than produced music) exaggerated timing differences can give
> the listener more clues to assemble "space" with when playback is
> through speakers.
>
> Note that if you find yourself enjoying a larger mic spread, the
> greatest timing differences are created when sources are directly in
> front of one or both sides. When there is a single object or objects
> on both sides, by twisting the axis, these sources move towards the
> center and the timing difference(s) can be adjusted, even reduced to
> that of ear spread. Rob D.
Good suggestions here, Rob. There's no end to the experimentation one
can do. That's a big part of the enjoyment. For example, yesterday I
stopped in to a nearby salvage store. There I found a bin full of
high-density foam "bumpers" -- cylinder-shaped, about 4.75" in diameter
and about 4.5" long, with a .75" hole through their length. In another
bin were wooden dowels that happened to fit the hole almost exactly. So
this morning, with $.50 worth of material, I cobbled together a simple
"head-like" array that upon first impressions sounds absolutely
stunning. If that impression holds up through some additional testing,
I may have to go back and buy up a large quantity of the stuff. (And I
haven't even begun to tinker with parabolas! I'm watching Rich's latest
reports with great interest.)
Thank you Lang and Rob for your insights,
Curt Olson
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