Topic: Don't have a wide mic bar? Give PAS with figure 8's a try

[Gutbucket]

Was messing around with setups on Michael Williams' multi channel microphone array design website and clicked over on the good old 2-channel arrays (the original Stereo Zoom stuff) and pulled up the Stereo Zoom table for figure 8s (linked below).   I remember thinking about near-spaced figure-8s but only really trying Blumlein.  Then I remembered all the LD mics (many switchable to fig 8 ) I see on standard narrow-width mic bars (can't space those mics much anyway, they are big and heavy), often setup inside the SBD cage for protection, but not in optimal configurations (like switched to omni pattern, but only 10" apart or whatever).  Looking at the figure-8 table for a while, I realized that figure 8's would be an excellent solution for tapers using standard mic bars which aren't wide enough to space the mics sufficiently as recommended by the improved PAS with optimal spacing table which is intended for cardioids or supercards (threads on Improved PAS are here, and here).

Here's the basic principle in a nutshell-
For a given PAS angle between mics, the more directional the pickup pattern is, the less spacing is required between them for a decent stereo image.

Omnis require the most spacing, figure-8s require the least. The progression of first-order microphone directional patterns, which are simply points along the directional sensitivity continuum, goes like this: omni-subcardioid-widecardioid-cardioid-supercardioid-hypercardioid-figure-8.  So when you aren't capable of spacing the mics much, and want to use a minimal angle between them to Point At Stacks, patterns closer to the fig-8 end of the directional spectrum are a wise choice.  Why not leverage that as far as possible and get a great stereo-image? Especially outdoors where there is no room verb or back wall reflection?  Using 8's allows for the least amount of spacing required between the mics of all mic patterns.

Note that switched to fig-8 pattern, the mics will exhibit more low bass rolloff, but that bit of built-in low-cut may be a good thing for taming overactive subwoofer boom.

So break out those ADK TL's, ADK 414's, or the big Neumanns and and give this a try at an outdoor fest if you are setup at the board or stuck behind it and can't get very FOB.  You'll get reach, you'll get improved stereo imaging, you'll get something sort of Blumlein-like in it's "airiness" but with a narrower SRA window focusing on the stage, which will produce a wider, less monophonic stereo image on playback.

http://www.mmad.info/MAD/2%20Ch/SRA%20Bi.pdf

^ Example: mics spaced 7" (~18cm) apart, which is totally doable with common mic bars, and angled ~50 degrees apart, which is probably a typical PAS angle from back there, provides a Stereo Recording Angle of a bit more than +/- 45 degrees or 90 degrees total.  Figure-8 nulls maximally reduce audience noise pickup from below and greatly off to the sides.   SBD is in back where the rear lobes point, and those lobes provide a welcome diffuse ambience.  Win!

Edit- Since fig-8 is the most wind/handling-noise susceptible of any pickup pattern, you'll want good windscreen protection outdoors even in calm conditions, and it's probably best to switch to an alternate setup that uses less directional pattern in windy conditions.

[F.O.Bean]

I wish I had [2] mk8's, because I would DEF try that outdoors Or run Blumlein FOB/DFC

[Gutbucket]

Should work nicely, although I doubt very many tapers have two mk8 on hand.  However, a good number of tapers use LDCs with switchable patterns that include fig-8 and cannot easily space them further apart than a standard near-spaced micbar.  I imagine this will be most applicable for them.

And yes, one way of thinking of this is a modification of Blumlein (figure 8s arranged in coincident X/Y with a 90 degree angle between them) by using a bit less angle and a bit more spacing between the mics.  That should help it to work better from a position further back than straight Blumlein.

It won't sound exactly like Blumlien, probably sounding something like a near-spaced config. And it won't have the same omnidirectional 360 degree pickup sensitivity as Blumlein due to the narrower included angle between mics.  Instead it will have more of a forward facing fat8 shape without the deep side nulls, sort of a fat oval, or a forward pointing "jelly bean" if you like  with less sensitivity to the sides.

Because the directional sensitivity of the forward lobe of a figure 8 is tighter than any other pattern as a source moves from on-axis to 90 degrees off-axis, that allows for the use of less angle and spacing of the stereo pair than using any other pickup pattern, while still getting sufficient difference information between the two channels. 

[F.O.Bean]

So you would point the 0* left lobe facing forward at an angle like a front address capsule like my mk4x, but using the side-address side of then caps, with the rear lobe facing behind the mic setup pointing towards the SBD area, like pointing hypers/supercards PAS?? I'm trying to picture this in my head lol

Sorry if that's really confusing GB

[Gutbucket]

Exactly.  Figure-8's are "side-address" type mics.  They have one positive polarity side and one negative polarity side just like a supercard or hypercard does, the primary difference is that the front/back lobes of an 8 are the identical in size and shape, symmetrical front/back, where as with a supercard or hypercard they are different sizes, larger in front than in back.  With the Schoeps mk8 I think the positive polarity side is the one marked with the '0' (the side you'd point towards the left if using it as the Side mic in a Mid/Side setup).

Think of this as PAS using two mk8 in place of two side-address mk41v, with the positive polarity lobes of both figure-8's facing forwards.

[2manyrocks]

Hmm, wide mic bar vs. two mk8sand two CMC6 bodies.   And the bill comes to ....ouch.   

[ArchivalAudio]

I ran a "Faulkner Array" with my Milab DC-196's at 20cm in figure 8 pointed straight ahead,  at DSO outdoors at the Cuthbert Amphitheater and was impressed how it sounded especially in comparison to Phish at  the Les Schawb in July that I ran Blumlein.
I'd do it again in the right outdoor venue.
see:
http://www.sengpielaudio.com/TonyFaulknerPhasedArray01Engl.pdf

[Bruce Watson]

I ran a "Faulkner Array" with my Milab DC-196's at 20cm in figure 8 pointed straight ahead...

Yep, that Tony Faukner guy is pretty cleaver. AB-8s works really well in spaces with reverb problems like stone shoebox churches that are just a bit too small, so the reflections from the walls/ceiling are just a little too quick, and/or too loud. Calms them right down. I'm not surprised it works in the opposite -- outside where there are basically no reflections. Point them down a bit so the rear node is pointing up toward the sky, and you essentially loose the rear node entirely. Unless a plane flies by. 

[noahbickart]

I wish I had [2] mk8's, because I would DEF try that outdoors Or run Blumlein FOB/DFC

You get close to blumlein with an mk8 and one of your mk41 as M/S which your tascam can decode on the fly.

[Gutbucket]

Yep.

As long as you're okay with a slightly wider recording angle / narrower playback stage and with sharp coincident imaging as opposed to near-spaced phase goodness.

[down2earthlandscaper]

I ran a "Faulkner Array" with my Milab DC-196's at 20cm in figure 8 pointed straight ahead,  at DSO outdoors at the Cuthbert Amphitheater and was impressed how it sounded especially in comparison to Phish at  the Les Schawb in July that I ran Blumlein.
I'd do it again in the right outdoor venue.
see:
http://www.sengpielaudio.com/TonyFaulknerPhasedArray01Engl.pdf

I'd still love to hear how your recording turned out, Ian
Is it posted anywhere? Dropbox link, perhaps?

[ArchivalAudio]

I ran a "Faulkner Array" with my Milab DC-196's at 20cm in figure 8 pointed straight ahead,  at DSO outdoors at the Cuthbert Amphitheater and was impressed how it sounded especially in comparison to Phish at  the Les Schawb in July that I ran Blumlein.
I'd do it again in the right outdoor venue.
see:
http://www.sengpielaudio.com/TonyFaulknerPhasedArray01Engl.pdf

I'd still love to hear how your recording turned out, Ian
Is it posted anywhere? Dropbox link, perhaps?

No It's still not posted... I will try soon to up it to LMA .... I'm slacking too many other things to share  where I was the only taper.

[F.O.Bean]

Exactly.  Figure-8's are "side-address" type mics.  They have one positive polarity side and one negative polarity side just like a supercard or hypercard does, the primary difference is that the front/back lobes of an 8 are the identical in size and shape, symmetrical front/back, where as with a supercard or hypercard they are different sizes, larger in front than in back.  With the Schoeps mk8 I think the positive polarity side is the one marked with the '0' (the side you'd point towards the left if using it as the Side mic in a Mid/Side setup).

Think of this as PAS using two mk8 in place of two side-address mk41v, with the positive polarity lobes of both figure-8's facing forwards.

Gotcha, thanks GB! So the 0* lobe[Red Dot] of an mk8 would face FORWARDS towards the stage just like an MK4v/MK41V? Check, now I got it Now I just need [2] mk8's

Hmm, wide mic bar vs. two mk8sand two CMC6 bodies.   And the bill comes to ....ouch.   

Actually, I just need the [2] mk8's, that's all

I wish I had [2] mk8's, because I would DEF try that outdoors Or run Blumlein FOB/DFC

You get close to blumlein with an mk8 and one of your mk41 as M/S which your tascam can decode on the fly.

True that Noah Id probably decode that in post in WaveLab 6 though, but DEF badass that the 70d can do the on-the-fly MS decoding on both stereo channels[1/2 and 3/4]

I ran a "Faulkner Array" with my Milab DC-196's at 20cm in figure 8 pointed straight ahead,  at DSO outdoors at the Cuthbert Amphitheater and was impressed how it sounded especially in comparison to Phish at  the Les Schawb in July that I ran Blumlein.
I'd do it again in the right outdoor venue.
see:
http://www.sengpielaudio.com/TonyFaulknerPhasedArray01Engl.pdf

I'd still love to hear how your recording turned out, Ian
Is it posted anywhere? Dropbox link, perhaps?

No It's still not posted... I will try soon to up it to LMA .... I'm slacking too many other things to share  where I was the only taper.

Id LOVE to hear this too

[jazzgtrl4]

hi
thanks

i might try this with my 414s this weekend at Huck Finn Jubilee, outdoor bluegrass fest. ill let you know what happens if i do.

[Gutbucket]

Cool.  Please post your thoughts about it here.  The greater bottom end roll-off inherent with figure 8's shouldn't be any drawback at all for that music genera, but sensitivity to wind-noise could be an issue if it's breezy, so dust off your fatty windscreens and/or miniature fur muumuus so you're sufficiently prepared.