The proof is right there in the photo: the AKG CK6 contains a CK2 omni capsule and a CK1 cardiod capsule. The switch selects either capsule, or the two mixed out of phase.I'm not sure that's right. An omni and bidirectional can give you cardioid, depending upon how the signals are mixed. An omni and a cardioid should just give you omni, sub-cardioid, cardioid depending upon how the signals are mixed. You can get bidirectional from two cardioids back-to-back.
I'm not sure either, but considering Card= 1/2(Omni+Fig8), one could writeI'm not sure that's right.
Yep - my tests with a pair of Behringer B-5s show this to be true; deepest 90 degree null is with card up 6dB.I'm not sure either, but considering Card= 1/2(Omni+Fig8), one could write
2Card-Omni=Fig8
Processing is not only reversing polarity, it should also apply gain of 2 on the cardioid.
Mixing a coincident cardioid mic and an omni results in a fig8 polar pattern. Mix the omni out of polarity with equal sensitivity. A "downside" is anomalies at shorter wavelengths compared to the space between two small diaphragm condensers (SDC), beginning above 9kHz for 19mm (3/4in) center to center (An LDC mic breaks down on its own above 9kHz). Mixing coincident mics equally reduces noise, as the correlated signal gain is 6dB while the uncorrelated noise gains 3dB, for an improved SNR of 3dB.
The math (ideal) is (Acr + Bcr*cosC) - Aom + B*cosC) where the coefficients (A, B) are each mic's (pressure, velocity) and C is the source angle off axis. The coefficient-only shorthand for a cardioid (cr) minus an omni (om) is (1, 1) - (1, 0) = (0, 1), which is a fig8. Note that native fig8 mics are single diaphragms having, if SDC e.g. a Schoeps MK8 or CCM8, fewer HF anomalies, but not the improvement in SNR.
Mixing a coincident cardioid mic and an omni results in a fig8 polar pattern. Mix the omni out of polarity with equal sensitivity. A "downside" is anomalies at shorter wavelengths compared to the space between two small diaphragm condensers (SDC), beginning above 9kHz for 19mm (3/4in) center to center (An LDC mic breaks down on its own above 9kHz). Mixing coincident mics equally reduces noise, as the correlated signal gain is 6dB while the uncorrelated noise gains 3dB, for an improved SNR of 3dB.Any two coincident microphones with different polar patterns can be mixed to algebraically add to any other pattern. The math can be fun making a cardioid from a fig8 and an omni, a fig8 from two cardioids, or a hypercardioid from a fig8 and an omni. Here’s how using SDC mics…
The polar pattern for a "1st order cosine" microphone output level is L = A + BcosѲ where A is the non-directional (pressure) coefficient, B is the directional (velocity) coefficient, A+B adding to 1.0, and Ѳ is the incident angle (in 3D). So a cardioid, expressed as L = 0.5 + 0.5cosѲ, can be made by mixing a coincident -6dB attenuated fig8 (A=0, B=0.5) and an equally attenuated omni (A=0.5, B=0). On axis, an ideal cardioid's output (rotated about its axis in 3D) is 1.0; at 90deg off axis it is 0.5 (-6dB); in back it is 0.0 (-∞dB).
In this way, you can make a fig8 using two cardioids aimed opposite as L1-L2 = 0.5 + 0.5cosѲ -0.5 + 0.5cosѲ, where the opposite mic's cos coefficient is minus a minus, or a plus, adding to 0.0 + 1.0cosѲ, the expression for a fig8. (A popular application is M-S using three cardioids, the S mixed from two cardioids aimed left & right mixed equally out of phase for a fig8.) Or make a variable hypercardioid (A=0.25 to 0.33, B=0.75 to 0.67) by mixing e.g. about -3dB a fig8 (A=0, B=0.71) and a -9dB attenuated omni (A=0.29, B=0).
Other combinations prorate A & B to arrive at the coefficients of any desired pattern: a wide cardioid (A=0.75 to 0.67, B=0.25 to 0.33) can be approximated by mixing a -9dB attenuated fig8 (A=0, B=0.29) and a -3dB attenuated omni (A=0.71, B=0). Understanding this reveals some "audio malpractice:" A typical host-guest interview with two cardioids close together is the same as a single omni. And many recordists do not envision when aiming a directional mic or combination above that its polar pattern is actually 3D, spun about its axis.
Mixing a coincident cardioid mic and an omni results in a fig8 polar pattern. Mix the omni out of polarity. A "downside" is anomalies at shorter wavelengths compared to the spacing between fwo small diaphragm condensers (SDC), beginning above 9kHz for 19mm (3/4in). LDC mics also break down above 9kHz. Mixing coincident mics reduces noise, as the correlated signal gain is 6dB while the uncorrelated noise gains 3dB, for an improved SNR of 3dB.As was done with the AKG CK6, combining an omni and a cardioid out of phase, one gets a figure-8 pattern.
Anyone ever DIY'd sich a thing?
Curious if it has sonic advantages over the back-to-back cardioids approach.
I tested with two Behringer B-5 bound together; 90 degree null wasn't perfect at highest frequencies, but about the same as I've heard on Sony's top-line MS mics. Dropping the hi EQ on the card mic at the mixer improves the null considerably.Simplest thing that comes to mind is to test the concept using two end adress mics bound together. I would go for two that have identical frequency response, i don't think you would get desired effect if responses are different.
Not quite the appropriate math - please see my posts, which in your terms would be more like "Card= Omni+Fig8" and then Fig8 = Card – Omni. To get the rear lobe, delete your "1/2."I'm not sure either, but considering Card= 1/2(Omni+Fig8), one could write
2Card-Omni=Fig8
Processing is not only reversing polarity, it should also apply gain of 2 on the cardioid.
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