ribbon mics in cardioid

is it just a matter of restricting the air to one side of the ribbon?

To get a cardioid from a ribbon you will need a carefully tuned time delay network and infinite volume behind the ribbon. The last is created by whether acoustical labyrinth (which can be pretty complicated), or damping system, or combination of both (that's what they use most of the time).

The "somewhat cardioid" (with a pad on the rear of the motor in attempt to damp the back wave) is used in Reslo.
Also, I saw some back wave absorbant panels from sE, but not sure how well they work.

Best, M 

thanks marik. I was always curious as to how they made that happen and never had a need to investigate it further until I was asked about them the other day.

The naked ribbon is bi-directional.

If one side is exposed and the other side leads to an infinite pipe, it is omni-directional.

If you mix omni and bi-di, just-right (including frequency responses), you have cardioid.

Olson did it this way. His pipe was not infinite, being folded and stuffed inside a lage base.

There's other ways.

PRR said:

If you mix omni and bi-di, just-right (including frequency responses), you have cardioid.

Olson did it this way.

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At least he had good intentions and tried to materialized those ideas in commercial products. With all due respect to the genius of Harry Olson, while his earlier products (like 77C) because of combination/mixing two different patterns (fig8 and omni) had much better pattern control, unfortunately, his later mics (with mechanical shutters) in terms of the "tightness" and pattern integrity were quite mixed. Indeed, his search for "reducing production costs" inevitably reflected on a quality of the product (of course, it has nothing to do with commercial success).
In those RCA's the only "solid" pattern was an omni, while fig8 was quite asymmetrical and cardioid all over the place. Because of very loose production tolerances it is almost impossible to find two even remotely matched pairs in the cardioid. IF one would like to have those matched there should be taken painstakingly time consuming mechanical adjustments.

The more "specialized" cardioid ribbons had much better and consistent patterns. The notable mics to mention here would be BeyerDynamic M320 and M360. Both had labyrinths, but the transformers had quite a bit of low end roll off, so while pretty rare those did not get deserved respect. Later M160 is a double ribbon and in fact, is a very nice hyper cardioid. The problem with all of those is for the ribbon they used Duralum, which tends deteriorate and be serviced every 10-20 years, depending on the climate conditions.

Another line is RCA KU3--terrific mic--very expensive and scarce--the source of inspiration for many VO talents, widely used in Disney classics production, and BK5--an OK cardioid mic with some "weirdness" going on in the mids and in the especially lower mids, many people are complaining about.

One of my favorites is Oktava ML19--combines acoustic labyrinth, quite a big back chamber, and acoustical resonator. Can be had for  quite cheap ( I found both of mine for $190 and $200 respectively on ebaby) and sonically beat socks off the BK5s with a good margin, for at least third of the price. The problem with those is ever deteriorating foam used for time delay. In many cases need to be serviced.  Still, one of my absolute favorite cardioid ribbons.

Another classic would be Shure 330-333. In the bass department and overall probably not as nice as Oktavas, but still a terrific classic, with very carefully and nicely designed horn to preserve a full range response and provide a wonderful performance for many applications.

There are some others, much more scarce models, however, all of them share the same approach to the concept.

Best, M

What situation are you using a pseudo-cardioid ribbon mic in? I'm curious (not skeptical).

SamRyan said:

What situation are you using a pseudo-cardioid ribbon mic in? I'm curious (not skeptical).

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Beatles used them (Reslos) for vocals  8)

Best, M

> RCA's ... very loose production tolerances it is almost impossible to find two even remotely matched pairs

In fairness: when Olson was dominant, the main interest in directional mikes was film and especially (at RCA) TV. Very often one mike on a swivel-mount manually tracked to the person speaking (a bad place for a ribbon). So all mono, no pairs.

Shure 330 is a lovely mike.

PRR said:

Shure 330 is a lovely mike.

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Its horn is a Piece of Art--by far the most sophisticated and well designed I've seen in any ribbon mic. There is only a small undamped back-chamber and the microphone response mostly relies on the horn.

Best, M 

PRR said:

If you mix omni and bi-di, just-right (including frequency responses), you have cardioid.  Olson did it this way.

Click to expand...

By coincidence, I have a 77C on the bench, which nicely demonstrates the concept. The upper half of the ribbon is a 'normal' figure of 8. The rear of the lower part is a funnel that connects to the acoustic chamber in the body of the mic, which is full of hair!

hi,
Why are there, actually, no big ribbons as a cardioid? Hangs together with the labyrinth? Must it be dimensioned then so largely that the microphone becomes too big and heavy?

greetings dix

https://www.facebook.com/LMWattsTechnology

Les Watts is ex-Shure and worked with some of their greats (including Bob Schulein who did SM81, IMHO one of the 2 best cardioids ever).

His POLYRIBBON updates Olson's 77 with modern materials and the benefit of 21st century design tools.

Some really special parts, eg the transformer, and loadsa individual TLC for each mike.

dix said:

Why are there, actually, no big ribbons as a cardioid? Hangs together with the labyrinth? Must it be dimensioned then so largely that the microphone becomes too big and heavy?

Click to expand...

Most of the cardioid ribbons on the market are older designs from Beyer, RCA, Oktava, and Shure. Traditionally those companies were making small ribbon microphones (with exception of very old RCA's). The AF11 cardioid ribbon has a large geometry ribbon, but is quite light and compact--it is 1" diameter and some 7" long, so no, it doesn't have to be big.

Best, M

Hi, and thanks for kind words Ricardo.

Yes we spent the last couple years trying to make an improved multi pattern ribbon mic. I basically poured over every single equation that Harry Olson ever wrote! Ben Bauer and Wente and Thuras too.

The RCAs were either a pressure ribbon summed with a pressure gradient ribbon, or a transmission line terminated single ribbon shunted with an inertance to outside forming a constant group delay low pass filter.

What we wanted to improve on was:
the 10 kHz bandwidth
The giant midrange peak (observed in the pressure portion of the signal)
the variability from one mic to the next
less than ideal polar patterns

I'll spare all the lurid details...but we got into some interesting things. Like acoustical transmission lines.
Olson Stuffed them with sound absorbing fiber to prevent reflection due to the finite length. The telegrapher's equations
showed us that the seemingly resistive stuffing made the transmission line go reactive! That gave some bad effects.
It was quite similar to the problems encountered in early trans ocean telegraph cables.

The giant peak I mentioned was from an impedance discontinuity in the transmission line. We found that fairly quickly and made it go away. I don't understand why Olson didn't easily find it as well. Perhaps because they used phasor analysis
rather than network theory. The peak popped right up in our math model.

The double ribbon ones had poor polar patterns because the basic preface of omni +figure 8 = cardioid is violated. Why?
Because the omni really isn't omni above about 2kHz due to diffraction. It's an interference microphone. RCA partly dealt with that by rolling the pressure gradient ribbon off before the back lobe started to grow at increasing frequency.

The single ribbon had better polar patterns (basically a single D configuration) but suffered in the figure 8 setting due to the hardware hanging on the back of the ribbon.

The best mic they did was the single ribbon single pattern BK-5B. It wouldn't be wrong to call it variable D...or very nearly so.

So we did the obvious thing...two ribbons. One free and open on both sides for figure 8, and one with a transmission line termination and inertance leak controlled with a valve. When you turn the pattern switch both electric contacts are connected and the mechanical valve actuates.

Our biggest problem...the omni setting. The ribbon has to be resistance controlled, and that load greatly reduces the volume velocity and output of an already low output microphone. It's like driving with the brakes on. RCA dealt with that by making VERY narrow ribbons to get the output up, but that created other problems. We dealt with it another way.

Then there's the Shure 330 type...being from there I could comment on that. Beautiful mic. Some big flaws.But that's another story!!

Les
L M Watts Technology

Thanks for the summary Les, that's a great read!