Why you should never use multi pattern mics

[k brown]

Most sources are large enough that that is not true for the entire soundboard, all the strings, etc. Probably brass instruments or voice, where the sound nearly all comes from a relatively small opening fit the criteria, but certainly a large ensemble in front of a stereo pair would not.
Just something to keep in mind when thinking about what spacing you can tolerate and what situations it may or may not cause a problem.

This sort of thing is only ever an issue in theory, and virtually never audible in practice.

Take for example using two LDCs in MId Side, where the usual placement is one above the other; a considerable vertical dispacement between capsules, but sounds just fine when matrixed together.

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Not to mention the fact that someone as serious as David Josephson wouldn't bother with such an idea if it had any serious phase issues in actual use (the C700A and C700S).
https://soundliaison.com/products/carmen-gomes-inc-dont-you-cry


Or Schoeps, with the M 201 (which is what inspired the Josephson).

Sound doesn't happen on paper, but in our ears.

 

[FetMe?FetU!]

Polar pattern question. You often see different polar patterns on SDC pencil microphones with multiple heads. I have been told that all of the capsules are OMNI, and the change in polar pattern is determined by the slits on the side of the capsules as well as the capsule's height. (See Attached Photo). Microphones like the AKC C1000S come with slip-on capsule attachments that change the microphone's polar pattern from cardioid to super or hyper-cardioid. (See Attached). I see Dynamic microphone capsules with similarly designed external components. Do these also determine the microphone's polar pattern? (See Attached). Even if the last does not apply to Dynamic capsules, couldn't a similar technique be used on a medium or large condenser microphone capsule to change its polar pattern? Silly, Newb question, I'm sure, but tell me what you think?

 

[kingkorg]

I have been told that all of the capsules are OMNI, and the change in polar pattern is determined by the slits on the side of the capsules as well as the capsule's height.

It's a gross oversimplification. And it's more the other way around. You can turn many of directional mics into omnis by blocking the vents. That doesn't mean you'll get even omni response throughout the spectrum.

Just recently i got in an argument (yet again) here on the forum regarding true omni mic superior performance in windy conditions. We kinda landed on the agreement that in order for omni to have that superior performance, the diaphragm has to be tuned considerably higher than a typical directional mic. So in a theory at least, just by blocking the vents you don't get all the goodness that comes with a properly designed omni.

This also adds to one of the reasons of the original intent of this thread not to be crazy about multipattern mics.

Microphones like the AKC C1000S come with slip-on capsule attachments that change the microphone's polar pattern from cardioid to super or hyper-cardioid. (See Attached). I see Dynamic microphone capsules with similarly designed external components. Do these also determine the microphone's polar pattern? (See Attached). Even if the last does not apply to Dynamic capsules, couldn't a similar technique be used on a medium or large condenser microphone capsule to change its polar pattern? Silly, Newb question, I'm sure, but tell me what you think?

Not a silly newb question at all actually. I'd say this is possible and quite a few mics use this or similar techniques. However it is difficult to give straightforward instructions on how to DIY this. These addons or modifications are usually carefully designed, calculated, measured with a particular goal in mind. If done badly they create resonances, anomalies on both frequency response and pattern response.

What makes things even more complex is that specified directionality of a mic is usually limited to a specific frequency range. Most of directional mics, if not all of them, go towards omni anyways the lower you go in frequency. Things also become more complicated above say 10k...

This is the reason why manufacturers publish polar plot. Which could be tricky to interpret. And sometimes they omit troublesome frequencies. One mic i love is Shure ksm32. It's polar plot shows phenomenal rear rejection at the frequencies they published. Once i measured it myself, i found the mic had lousy rejection at about 8K IIRC. They haven't plotted that frequency.

 

[FetMe?FetU!]

But as a thought exercise - let’s say I have a SDC pencil microphone with only an Omni pattern head. If I copied the design from another SDC hypercardioid casing and made a 3D print inserting an Omni SDC size capsule with similar specs, or maybe not, into it do you think that the tolerances are so tight between the capsule type and vent design that it would work or that it would fail? More importantly has anyone ever tried this? I can’t be the first person to consider this? Is complex mathematical calculations so critical that a little trial and error is not worth the effort? What if I 3D printed the AKG C1000S adapters and put them on a different front address SDC microphone? The 3D files are on the internet for free download. What if I scaled up that same adapter to fit a LDC capsule? Or am I just living in the blissful fog of the ignorant?

 

[Murdock]

Here is an interesting patent paper from Rudolf Görike, one of the founders of AKG.
I don’t know how accurate the frequency response plot is but the rear rejection looks exceptionally good.
I’m not sure but think this is about the AKG CK28 capsule.

https://patentimages.storage.googleapis.com/6c/a7/c3/f2c33124643abf/US3031538.pdf

 

[k brown]

But as a thought exercise - let’s say I have a SDC pencil microphone with only an Omni pattern head. If I copied the design from another SDC hypercardioid casing and made a 3D print inserting an Omni SDC size capsule with similar specs, or maybe not, into it do you think that the tolerances are so tight between the capsule type and vent design that it would work or that it would fail? More importantly has anyone ever tried this? I can’t be the first person to consider this? Is complex mathematical calculations so critical that a little trial and error is not worth the effort? What if I 3D printed the AKG C1000S adapters and put them on a different front address SDC microphone? The 3D files are on the internet for free download. What if I scaled up that same adapter to fit a LDC capsule? Or am I just living in the blissful fog of the ignorant?

It's more than the external slots you see on the outside of a capsule; the internal parts also require venting that an omni capule doesn't have.

 

[kingkorg]

And delay network is missing as well. You can turn directional mics into omni relatively easily, but not the other way around. Omni lacks additional parts, it's not just about the slots, which K Brown already pointed to.

 

[FetMe?FetU!]

Ok. Omni conversion is out using an adaptor, but what if I start with Cardioid, like the C1000S? Is this only possible because this is an Electret capsule? Yes, I know I can just try it, and I may, but I think this conversation is a necessary time and resource saver if you all think the idea is just insane. And it's a fun conversation for me and hopefully you.

(From Recodinghacks)

"The pickup pattern can be switched from the mic’s native cardioid pattern to hypercardioid simply by attaching the included PPC 1000 Polar Pattern Converter to the top of the microphone capsule.

The mic’s native frequency-response curve can be modified via the PB1000 Presence Boost Adapter, which effectively adds 3 to 5 dB of high-end enhancement between 5 and 9 kHz, improving speech clarity and adding definition to instrument sounds. This part can be purchased from retailers for about $3.

Both the PPC1000 and PB1000 are little plastic widgets that can be installed (one or the other, but not both simultaneously) on the mic capsule. The installation requires no tools and takes only a few minutes. The mic capsule is easily exposed by unscrewing the top half of the microphone body; this also reveals the battery compartment."

 

[GeorgeToledo]

Uwe Sattler from Neumann maintained that using a ball on a km84 or 184 gives poor results. There is still the rear venting of the actual capsule regardless of covering the body vents and I guess that not being able to eliminate it leads to some strange anomalies.

 

[k brown]

Uwe Sattler from Neumann maintained that using a ball on a km84 or 184 gives poor results. There is still the rear venting of the actual capsule regardless of covering the body vents and I guess that not being able to eliminate it leads to some strange anomalies.

Simply covering the external vents/slots of a cardioid capsule will never result in a usable omni; internal mods can sometimes work.

What can work with most SDC cardioids is covering a portion of the slots to create an 'open' or 'sub' cardioid. As long as the diaphragm can still 'breath', it can function properly but the pattern will be widened. Highly esteemed British Classical engineer, Tony Faulkner often tapes over the bottom-most slits of his Rode NT6s when using them in his dual pair rig*, as he prefers subcardioids for that (Schoeps MK21), and Rode doesn't offer a subcard capsule.

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* A 26" spaced pair of omnis on the same bar as an 18-19" spaced pair of subcardioids; all angled 90 degrees. One pair usually leads in the mix by ~6dB (which pair, depending on the situation/acoustics).

 

[RCAguy]

I use the internally switchable Schoeps MK5 that produces fine omni or cardioid polars. However the omni\cardioid\fig8 MK6 was discontinued for its imprecise polars.

 

[GeorgeToledo]

Simply covering the external vents/slots of a cardioid capsule will never result in a usable omni; internal mods can sometimes work.

What can work with most SDC cardioids is covering a portion of the slots to create an 'open' or 'sub' cardioid. As long as the diaphragm can still 'breath', it can function properly but the pattern will be widened. Highly esteemed British Classical engineer, Tony Faulkner often tapes over the bottom-most slits of his Rode NT6s when using them in his dual pair rig*, as he prefers subcardioids for that (Schoeps MK21), and Rode doesn't offer a subcard capsule.

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* A 26" spaced pair of omnis on the same bar as an 18-19" spaced pair of subcardioids; all angled 90 degrees. One pair usually leads in the mix by ~6dB (which pair, depending on the situation/acoustics).

That’s interesting to go with a wide pattern and then combine it with the omni. I’m not quite sure how the distance in spacing fully interplays, but adding the omnis to the subcardioid would cancel out some of the width of the subcardioid. Maybe that’s what he is going for, the ability to control that some.

 

[k brown]

That’s interesting to go with a wide pattern and then combine it with the omni. I’m not quite sure how the distance in spacing fully interplays, but adding the omnis to the subcardioid would cancel out some of the width of the subcardioid. Maybe that’s what he is going for, the ability to control that some.

If you plug the numbers into the Sengpiel visualizer you'll see that the subcard spacing producing about the same image width as the omni spacing.
https://sengpielaudio.com/Visualization-AB60-E.htm
That's why those spacings were settled on; one can have either pair dominate the mix and the stereo image remains essentially the same. The smaller spacing of the directional pair compensates for the fact that they're directional. If one uses a pair that's more directional (card/supercard/hypercard/figure-8) then the spacing is accordingly reduced to keep the stereo width as close to that of the omni pair as possible. (If you experiment with different patterns in the Sengpiel visualizer, set the mic angle to 90 degrees. One could of course try different angles with accordingly different spacings, as long the resulting image width matches that of the omnis fairly closely)

The middle directional pair can be any pattern; Faulkner prefers subcardioid over cardioid not because of the pattern, but because he finds the sound of most SDC cardioids to be "too 'brittle'". I used it many times with hypercardioids with wonderful results.

Your last comment is backwards. Adding omni to subcardioid would widen the the overall pattern, not "cancel out some of the width...". The only 'cancelling out' that would occur when mixing omnis with other patterns would be with supercard, hypercard, and figure-8 because these all have anti-phase rear lobes that would be reduced in amplitude by mixing with an omni - but even in those cases their patterns would be widened, not narrowed.

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Anyone who records acoustic music in reverberent acoustics at 'Classical' distances owes it to themselves to try this dual-pair array. The mix of the two pairs has qualities unobtainable by any single pair alone. It's behavior is quite different from a Straus-Paket, where an omni is strapped to a cardiod and mixed at the same level in order to achieve a subcardioid pattern (that was done before subcardioid SDCs were available).

The Faulkner array is not about 'pattern alteration', but about combing the positive attributes of an omni pair with those of a directional pair. It's really rather magical to slowly mix in the directional pair to the omni; the sound gains three dimentionality and 'focus' without losing any of the richness and bloom of the omni pair. The array also has the property of 'forward gain'; it can pull in instruments from the back of an orchestra such that Faulkner has said he often ends up not using any wind spots in the mix.

None of this will occur unless the spacings are such that the image widths of the two pairs line up well; it's not just a matter of 'mixing some spaced omnis with any old near-coincident cardioid pair' - that's a whole different kettle of fish.

 

[GeorgeToledo]

Thanks for setting me straight, I’m in bed with the flu and didn’t think that out clearly.