Topic: Mid side w/ 3 channels and 3 cards?

[zip]

Can you do a m/s recording with 3 cards? Do you get the same effect if you had a figure 8 cap? 1 card pointed at the source, and the other 2 at 180 degrees of each other?

[Javier Cinakowski]

I don't think it would be ideal, but should work.  You would have to reverse the phase of one of the side cards...

[zip]

I don't think it would be ideal, but should work.  You would have to reverse the phase of one of the side cards...

Why wouldn't it be ideal? Isn't a figure 8 cap basicly 2 cards back to back?

[Javier Cinakowski]

I don't think it would be ideal, but should work.  You would have to reverse the phase of one of the side cards...

Why wouldn't it be ideal? Isn't a figure 8 cap basicly 2 cards back to back?

As I understand it, two cards back-to-back do not provide exactly the same pattern as a figure8.  Also, the logistics of getting the capsules close enough together to avoid phase issues and retain coincidence is a challenge. 

[Gutbucket]

There are some cheap M/S DIY mic kits and camera mounted mics and that use that method since true fig-8 caps are $$$.  No idea how well they work.  It may be enlightening to experiment with, though.  I'd think you'd want to get the two side facing caps (well, all three caps ideally) as close together as possible to actually get a pattern approximating a fig-8 pattern with a real null facing forward and back, but the kit version I came across a few years back was built into a project box with the side facing caps on either side of the box.  Sorry I can't remember the name or the link.

Fred is right, you'd flip the polarity on the left facing mic to simulate an actual fig-8 mic pointing right.  To better optimize it you could then point both side mics in the same direction, mounted as close together as possible, and adjust the gain balance between the two to get the most cancellation.  Adjust the balance between them until the sound is as quiet as possible, though it won't cancel completely (the more it does the closer you can come to a true figure .  Then rearrange them facing 180° apart.

Keep in mind that you can use other patterns for the Mid or forward facing mic, it doesn't have to be a cardioid.  Have fun.

[Patrick]

I don't think it would be ideal, but should work.  You would have to reverse the phase of one of the side cards...

Why wouldn't it be ideal? Isn't a figure 8 cap basicly 2 cards back to back?

No, not exactly.  Most cardioid patterns have a slight rear lobe that creates a "heart" shape around the capsule.  The Figure 8 pattern is a little more uniform.  And as stated above, there is not a way to position both cardioid caps next to each other in order to get a true bi-directional, positive and negative sides of the "side" mic.

Not saying that M/S can't be done with three cards, it's just not going to be true M/S.

Card:


Fig 8 (bi directional):

[Gutbucket]

You certainly won't get anything close to an idealized fig-8 like the drawings, but that doesn't mean you can get something that might work somewhat. You won't know 'till you try it.  There aren't many cardioids are perfectly cardioid shaped throughout the spectrum either.

In theory this works perfectly.  Here's the deal-
Mathematically (and sometimes in the real world) a cardioid pattern is the result of combining equal amounts of an omni and a figure eight. Two cardioids in the same location in space is then the combination of 2 omnis and 2 figure eights all mixed together evenly.  When you flip the polarity of one cardioid, the omni portion cancels out leaving only the 2 figure eights.  If you point the two mics in the same direction, the figure eight patterns cancel out too (That's why you can try and optimize your real world experiment by going thought the step I mentioned in my previous post).  But if you point them in opposite directions then the positive lobe of one figure eight now lines up with the now positive lobe of the other (the reversed polarity negative side) and you are left with 2 fig-8's summed together (or one fig-8 that is 6db more sensitive).

In reality you can't get the two microphones in the exact same location so the cancellation and summing and resulting pattern won't be perfect. 

^^^
That doesn't stop people from micing using coincident stereo X/Y techniques though, which is just as physically impossible to set up perfectly. 

[beanstalk]

It sounds interesting to try at least. Might work good.

[BayTaynt3d]

I say go for a super wide XY cards (maybe 120+ degrees), then throw one hyper shooting straight up the middle. All coincident.

Then just add the centered hyper to the mix as needed. I'd like to hear how that'd sound, heh...

[DSatz]

Many condenser figure-8s are indeed synthesized from two back-to-back cardioids in opposite polarity--nearly all switchable-pattern dual-diaphragm microphones work that way (Neumann, AKG, etc.). Contrary to what someone posted, in principle the pattern is the same; in practice it's usually pretty nearly the same, except for a narrowing at high frequencies; dual-diaphragm microphones are most often large-diaphragm microphones, and those tend to get beamy toward the high end no matter what pattern you set them to.

Apart from that, however, the figure-8 setting usually has the most consistent pattern across the frequency range of any pattern that a multi-pattern mike will have. You can see that if you look at the polar diagram for a U 87, a C 414, a KM 56, etc.

And some stereo microphones do use separate cardioid elements for M/S. For example, the excellent Neumann RSM 190 and 191 stereo shotgun microphones actually have three capsules inside--one of which is used by the shotgun "M" microphone and a pair of back-to-back, side-facing cardioids whose signals are combined with a polarity inversion (i.e. subtracted) to form a figure-8 for the "S" signals. Neumann's KM 86 microphone actually had two complete KM 84-type (i.e. KK 84) capsule heads inside its own, larger capsule head, and that's how it got its figure-8 pattern. The extra spacing between the two capsules enhanced the low-frequency response of that pattern (though its high-frequency response off axis was rather peaky).

In practice you'd need to set the gains of the two cardioids very precisely (to within tenths of a dB) so as to match their sensitivities--and then having placed their membranes so that they're in the same vertical plane, you have to place a third (M) microphone as close as possible to the same point in space without, however, disturbing the acoustic symmetry of the pair of cardioids (which would distort the figure-8 pattern of the result), and without creating worse acoustic shadows or reflections than necessary.

All in all I think that for the most reliable results, a good small-diaphragm, single-diaphragm figure-8 with essentially flat frequency response is strongly preferable. But most of all, it's preferable to make a recording (if it's worth making) than not to make a recording. So don't wait for perfection, since I just heard that that's going to be delayed for yet another three weeks, no matter when you read this message.

--best regards

[Javier Cinakowski]

I say go for a super wide XY cards (maybe 120+ degrees), then throw one hyper shooting straight up the middle. All coincident.

Then just add the centered hyper to the mix as needed. I'd like to hear how that'd sound, heh...

Hmm, 3-channel mixer, cards paned L/R, hyper in the center.  Good times!





Man, DSatz knows his shit...  T+

[Gutbucket]

Well, he's got way more experience in this oyster diving gig than most any of us.  I clear my snorkel every time he chimes in with a few pearls.  Deserves every +T.

Here's a link to a guy DIY'ing it on the cheap with Panasonic capsules.  Check out the 4 cap Blumlein stack at the bottom of the page.