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Author Topic: Near Field Cardioid Mics  (Read 952 times)

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Offline obsidian

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Near Field Cardioid Mics
« on: January 11, 2017, 12:13:42 AM »
Has anyone used near-field mics for live concert (read:  >:D) ... I have always wanted to try a set just to see what the results would be.  I currently use Hyper-Cardioids and Cardioids ... any words of wisdom?


Offline Gutbucket

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Re: Near Field Cardioid Mics
« Reply #1 on: January 11, 2017, 10:47:44 AM »
It's not clear what you are asking.  I'll clarify some terms and describe the generally accepted meanings which apply-

The terms near-field and far-field describe different acoustic regions based on distance from the source and room size.  The free-field (or near-field) is where the sound arriving directly from the source is dominant, the diffuse-field (or far-field) is where the sound arriving from all directions in combination is louder than the direct sound from the source.  Although the concepts are more or less interchangeable, the terms near/far-field is typically used when talking about reproduction, monitoring, and PA reinforcement.  The terms free/diffuse-field are typically used when talking about the original soundfield and the placement of microphones.

The demarcation between those close and far regions, where the direct and diffuse sound components are equally loud, is called the critical distance, or reverberation radius and is considered a generally optimal place for a stereo pair of microphones intended to make a well-balanced recording of a source "as it sounds in the room".  A closer position will sound more dry and direct (appropriate for "close-mic'ing", as done for PA reinforcement or isolated multi-track recording), and a farther position more reverberant.  Most AUD positions are back in the diffuse-field region with respect to radiation from the instruments themselves on stage. A recording position which is on-stage or at the stage-lip is likely to be close to the critical distance.  A directional PA changes that by projecting it's near-field region into the room along it's primary axis, so with respect to the PA the critical distance is usually a few rows back.  Still, most AUDs are made from back in the far-field region of the PA, whereas stack-tape is made up close in the near-field region of the PA.

When microphones are described as "free-field response" or "free-field equalized" verses "diffuse-field response or equalized" that describes the frequency response of the mic as being intended for recording from up close or from further away.  Omnis are more frequently described in this way.  A free-field omni is flatter when measured on-axis at a standard measurement distance of typically one meter.  A diffuse field omni measured at the same one meter distance will have an increased sensitivity bump in it's response curve at high frequencies, which compensates for both the attenuation of high-frequencies in the direct sound due to increased distance and the frequency response of diffuse sound (that which has bounced around the room and arrives from essentially all directions with equal energy) which has less high frequency energy due to the high frequencies being more easily absorbed by the room surfaces and all the other stuff in the room.

Take the Schoeps omni capsules as an excellent example.  Schoeps offers four different omnis which vary in response from free-field through diffuse-field.  Look at the differences in the response curves of these omni capsules when both are 1 meter from the source (the images and description in italics below are from Schoeps' website) :

First the MK2 at the near/free-field end of the spectrum, which Schoeps describes as-

"omnidirectional pattern
very flat frequency response
corrected for a free sound field
for use close to the sound source (frontal sound)
often preferred for relatively close miking of instruments, vocalists, etc.

This capsule type has a flat frequency response for frontal sound incidence. This yields a very natural sound when recordings are made within the reverberation radius, where the direct sound (frontal incidence) predominates over the reverberant sound (random angles of incidence)."




..and compare that with the MK2XS, at the far/diffuse-field end of the spectrum, which Schoeps describes as-

"omnidirectional pattern
diffuse-field capsule
for miking distances at which the predominant sound is no longer direct
useful for relatively distant placement in reverberant environments.

The MK 2XS (formerly 3) is designed for placement in a diffuse sound field, i.e. at distances in reverberant environments where the greater portion of arriving sound has already been reflected from various room surfaces. In such placement the integrated frequency response of this capsule is essentially flat; the on-axis high-frequency response elevation shown in the graph below is not heard as such."





With respect to a cardioid mic, in addition to the high-frequency response differences, the inherent low-frequency cardioid roll-off and related proximity effect also come into play.  A cardioid appropriate for nearfield use may have less low-frequency sensitivity, which gets compensated for by proximity effect and close placement to the source, resulting in a flatter response at it's intended recording distance.  The response of a cardioid appropriate for use at far-field distances generally will have "more bass" so it doesn't sound thin when used well beyond it's proximity effect range, perhaps in combination with a high frequency lift.  Cardioids are not typically referred to as "free-field" or "diffuse-field" response like omnis are, probably because their behavior varies in a more complex way, based not just on critical distance but also proximity effect.
« Last Edit: January 11, 2017, 12:22:59 PM by Gutbucket »
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Offline Gutbucket

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Re: Near Field Cardioid Mics
« Reply #2 on: January 11, 2017, 11:00:41 AM »
Now having said all that, there is nothing preventing you from using any mic from any location.  The frequency response differences can be compensated for afterwards using equalization.  The differences between those four Schoeps omnis are simply differences of frequency response.  The polar responses of all four are identical, so a recording made with one can be equalized to sound just like a recording made with another.   As mentioned above, the response behavior of cardioids are more complex, yet equalization is in all cases the most powerful tool we have in compensating for differing recording distances after the recording has been made.

What you describe as "near-field mics" may sound "dull and lacking treble" when used from a typical AUD distance. Careful EQ can correct for that, although it's easier to use a microphone with an appropriate response to begin with.

Hope that helps.
« Last Edit: January 11, 2017, 12:24:02 PM by Gutbucket »
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Offline ~Jon Stoppable

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Re: Near Field Cardioid Mics
« Reply #3 on: January 11, 2017, 12:11:36 PM »
The comparable Schoeps capsule would be the MK4P:

http://schoeps.de/en/products/mk4p/graphics

Offline obsidian

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Re: Near Field Cardioid Mics
« Reply #4 on: January 11, 2017, 12:21:08 PM »
Gutbucket, that was ABSOLUTELY amazing.  Thank you.  I like to experiment, so I think I will give these a try in the very near future.  I appreciate your ability to take the very little amount of information I provide and still be able to give me all the answers that I need.  Absolutely amazing.

Offline obsidian

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Re: Near Field Cardioid Mics
« Reply #5 on: January 11, 2017, 12:24:32 PM »
The comparable Schoeps capsule would be the MK4P:

http://schoeps.de/en/products/mk4p/graphics

Thank you, Jon.  Your mics are such high-quality at an incredible price it makes these Dr. Frankenstein-style experiments of mine affordable, and most of all, FUN!

Offline Gutbucket

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Re: Near Field Cardioid Mics
« Reply #6 on: January 11, 2017, 12:36:48 PM »
Glad to help. I enjoy getting these things clear enough in my head to put it in words.  At the same time, I recognize many probably regard these posts as tl;dr, but it's one of the reasons I enjoy TS.

The comparable Schoeps [cardioid] capsule would be the MK4P:

http://schoeps.de/en/products/mk4p/graphics

Thanks Jon, I wasn't aware of that one. 

obsidian- You probably know this, but the MK4 is the "standard" Schoeps cardioid capsule against with the MK4P should be compared.
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Offline noahbickart

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Re: Near Field Cardioid Mics
« Reply #7 on: January 11, 2017, 03:04:40 PM »
cool colors for the mk4p! I wonder why the other capsules only have B&W images.
Recording:
Capsules: Schoeps mk41v, mk4v, mk22, mk3 & mk8
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Offline Gutbucket

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Re: Near Field Cardioid Mics
« Reply #8 on: January 11, 2017, 05:17:09 PM »
Looks like the newer Schoeps stuff gets color coded graphs.  Check out those for their SuperCMIT and even more recent MiniCMIT shotguns.  I expect at some point the others will eventually be redone in similar fashion.

obsidian- the MK4P Jon posted a link to (and it's sibling the MK4XP which has the same low frequency response slope but a higher corner frequency, which means the downward curve if its low frequency response has the same steepness angle but starts dropping off at a higher frequency) are examples of microphones intended for use quite close to a source.  The more exaggerated low frequency roll off, which the bottom graph indicates is quite significant in comparison to the MK4, counters the bass emphasis of the proximity effect at the intended mic'ing distance, producing a response closer to flat when used for its intended application. Even though it's low end response rolls off significantly in comparison the the MK4, it is similar to a large number of other commonly used cardioids.

I'll insert the low frequency response curves comparison graph from that Schoeps page below. The top curve represents the MK4, the middle curve the MK4P, and the bottom curve the MK4XP-



The miniature super/hypercardioids which I'm currently using at a distance (marketed as hanging choir mics intended for use relatively close to the choir) have a low frequency response similar to that of these Schoeps "near-field cardioids", as will most small directional mics intended for use either "on-talent" as lavaliers or mounted directly onto acoustic instruments.  I always use them in combination with a pair of omnis, partly because the omnis take care of the low frequency stuff and negate the problem.. although in some of my setups that response and the divided frequency workload between these mics and the omnis serves as a purposefully designed "feature", rather than simply constituting a response "bug" that begs for correction.  But when I first started using them, I intentionally recorded a few things with them in a standard stereo microphone configuration even though I didn't plan to use them that way, partly to get a good idea of how they sounded compared to other microphones used in the same configuration, and partly to see if I could successfully EQ the resulting recordings to my liking regardless of the rather dramatic low frequency rolloff of the mics at the distances I planned to use them.  That I was able to make a satisfyingly transparent EQ correction of that pair on it's own, without inclusion of the omnis, was one way of testing the quality of the microphones (the low bass was there, just reduced in a linear fashion and pretty easily restored without problems), as well as further real-world confirmation that such EQ correction can be done in a general sense, at least using directional microphones of similar quality.
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Offline obsidian

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Re: Near Field Cardioid Mics
« Reply #9 on: January 11, 2017, 09:56:03 PM »
Gutbucket, Thank you (again).  I'm learning as I go, so I always enjoy reading and saving your posts as PDF files.  I'm making a journal for later references if I need it.

Offline Gutbucket

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Re: Near Field Cardioid Mics
« Reply #10 on: January 12, 2017, 10:04:10 AM »
One more thing before I let this go, which I mentioned previously yet bears repeating-

Keep in mind that the measurements which produced the low frequency response curves shown in that Schoeps MK4/MK4S/MK4XS comparison graph were taken with the microphones 1 meter from the source, at least I'm pretty sure that's the measurement distance standard which Schoeps uses.  The point I want to emphasise is that in actual use, the response of these microphones will only match those curves when they are 1 meter (100cm) from whatever is being recorded.  Used from further away, the MK4 will have a response which is going to be much closer to that of the other two curves on that graph.  And conversely, when MK4S is used closer than 1 meter (less than 20cm away is the design intent) it will produce a response which will be closer to that shown for the MK4 at 100cm.  Same goes for the MK4XS, but at <10cm, or half the intended use distance of the MK4S.
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