NoKey
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What determines the pickup pattern of a microphone?
Dear forum people,
Some mics are omni-directional, and others cardioid, or super-cardioid in their pickup patterns.
However, since basically the pickup cartridge is some sort of a round or cylindrical element, I have wondered what is it that establishes that some microphones have peculiar patterns.
I thought maybe it was the enclousure or some thing of that sort, but I have seen data that some microphones have switches so they can actually change patterns (unless I've misread).
So asking due to curiosity, and maybe I can hack some old inexpensive mics.
Thanks.
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ohhey
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Re:What determines the pickup pattern of a microphone?
2010/06/07 15:16:28
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NoKey
Dear forum people,
Some mics are omni-directional, and others cardioid, or super-cardioid in their pickup patterns.
However, since basically the pickup cartridge is some sort of a round or cylindrical element, I have wondered what is it that establishes that some microphones have peculiar patterns.
I thought maybe it was the enclousure or some thing of that sort, but I have seen data that some microphones have switches so they can actually change patterns (unless I've misread).
So asking due to curiosity, and maybe I can hack some old inexpensive mics.
Thanks.
Good question. In a dynamic mic it's just the head design that make it directional. That's what those vents are on the side of some and others it's behind the ball so you can't really see everything. It's not anything electronic. That's why you get feedback when you hold your hand too close to the head or cover the vents, you just turned the mic into an omni ! I could never get singers to keep from doing that, maybe they think it looks cool or something. Anyway with a condensor mic it is an active electronic system. You use two capsules so the one in the back does the signal to cancel everything out from back there. There may also be some enclosure design elements but that's the basic idea. Some small condensors use the vents on the side method and some even have a collar you can push up over the vents to change the pattern to omni. Both type use cancellation to reduce the amount of pickup from the back of the mic. The dynamic type is really a fine art and years of research goes into getting that little piece of plastic or metal just the correct shape and size. The vents on a shotgun mic are even more critical.
post edited by ohhey - 2010/06/07 15:18:26
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/07 15:43:51
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Thanks Ohhey for a clear and great explanation.
I put things in perspective...Yes, it's been on some condenser mics that I see they can change their patterns.
I did have the feeling that much of that is a lot of art, tweaking, and testing with some sophisticated acoustic equipment, time and effort.
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ohhey
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Re:What determines the pickup pattern of a microphone?
2010/06/07 15:58:34
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NoKey
Thanks Ohhey for a clear and great explanation.
I put things in perspective...Yes, it's been on some condenser mics that I see they can change their patterns.
I did have the feeling that much of that is a lot of art, tweaking, and testing with some sophisticated acoustic equipment, time and effort.
Yep one tiny change and the specs go out the window. Some of the older moving coil and ribbon mics had very complex shell designs, the element and electronics were the easy part of the engineering. Once it was perfected they became a classic and didn't change for decades. Some Shure mics use the same element but have very different specs. So if you take a mic apart all bets are off as to what kind of sound you get, even the tone will change. On condensor mics the first thing you notice is a lot of humm because that screen is also the emf shield for the head amp. You are talking gigaohm impedance on some of those things so you can imagine how easy it would be to pick up a radio station or random noise. You even have to clean the flux off the solder connections from the capsule to the head amp or you can get noise, everything has to be perfectly clean in there. Dust and moisture are enough to short it out and cause a problem.
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feedback50
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Re:What determines the pickup pattern of a microphone?
2010/06/07 15:59:34
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I read an article on this a few years back. As I remember, an omni mic cartridge is basically sealed except for the diaphragm. There is actually a very small vent hole in the case to prevent it from blowing the diaphragm if the barometric pressure changes radically.
A dipole mic (like most ribbons) suspend the diaphragm (or ribbon) so that it is open on both sides. Some use dual diaphragms mounted back to back instead (typical of multi-pattern mics).
A cardioid works a bit like a single headed drum (i.e conga), but of course with a much shorter cylinder. The idea is that sound coming from the back of the mic agitates the diaphragm equally but out of phase with the vibrations going around the cylinder reaching the front of the diaphragm (causing partial phase cancellation). Sound from the front of the mic vibrates the membrane but looses energy (and gains a slight delay) as it works its way to the back of the cylinder and up the cylinder again to the back of the diaphragm. The sound reaching the back of the mic is what make's it directional (counter-intuitive as it may seem). This design also tends to exaggerate low frequencies as the sound source gets closer which contribute to the proximity effect of directional mics.
I've found through practical experience that these explanations are beyond the comprehension of some rap "artists" that are complaining about feedback from the floor monitors on a live gig. Especially when they hold a directional mic by the back of the capsule housing (in an attempt to look cool), which effectively turns a cardioid mic into an omni.
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/07 21:05:41
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Thanks Ohhey and Feedback50, for the additional explanations.
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The Maillard Reaction
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Re:What determines the pickup pattern of a microphone?
2010/06/08 07:37:01
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NoKey
Thanks Ohhey for a clear and great explanation.
I put things in perspective...Yes, it's been on some condenser mics that I see they can change their patterns.
I did have the feeling that much of that is a lot of art, tweaking, and testing with some sophisticated acoustic equipment, time and effort.
It's not a lost art... the latest issue of AES has an article about designing mic capsules. The researchers are comparing field observations to modeled predictions and tweaking their models so that they can better understand how the parameters effect the end result. best regards, mike
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ohhey
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Re:What determines the pickup pattern of a microphone?
2010/06/08 10:27:34
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mike_mccue
NoKey
Thanks Ohhey for a clear and great explanation.
I put things in perspective...Yes, it's been on some condenser mics that I see they can change their patterns.
I did have the feeling that much of that is a lot of art, tweaking, and testing with some sophisticated acoustic equipment, time and effort.
It's not a lost art... the latest issue of AES has an article about designing mic capsules. The researchers are comparing field observations to modeled predictions and tweaking their models so that they can better understand how the parameters effect the end result.
best regards,
mike
I wonder what kind of gear they were working with in the 1940s and 50s when many of the great microphones were designed ? Might have just been ears..  You would think with all the technology they have today it would be easy.
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/08 12:05:00
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Thanks Ohhey.
It makes much sense that with the advent and advances of end-user computers and modeling software, and hi-tech software, much of what was art is blending or flourishing into science.
But no doubt some tech abuse or mis-use can kill or diminish some art forms and diminish results.
I gather, though, from previous thoughts and from the info you gave us that designing/making mics is somewhat like the making of stradivarious violins or good guitars: materials, art, techniques, and the right efforts.
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wst3
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Re:What determines the pickup pattern of a microphone?
2010/06/08 14:13:23
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Some minor clarifications...
microphone pickups come in two flavors:
1) Velocity (or pressure gradient) sensitive - responds to a difference in pressure between the front and the back of the diaphragm. These are inherently directional, in fact bi-directional.
2) Pressure Sensitive - responds to changes in pressure. Only one side of the diaphragm is exposed, which makes them omni-directional by themselves. (Yes, I know that is not entirely intuitive.)
which can then be divided once again based on the motor:
1) Dynamic (includes ribbon designs) - involves magnets and conductors
2) Condensor - involves conductors and dielectrics.
and then there are the pickup patterns, which are actually infinite, but we usually think of:
1) Cardiod or directional - the pattern is often the result of the choice of element and the housing. By allowing energy to reach the rear of the diaphragm after a specific delay we can create a directional pickup patter for an omni-directional pickup.
2) Omni or non-directional - what it says, within the physical limits of the diaphram.
3) Figure 8 or bi-directional - ribbons are usually bi-directional.
(ok, I am cheating, and leaving out piezo, carbon, and optical pickups.)
Of course no microphone is perfectly directional or non-directional. Physical geometry plays a big part in the equation. I don't remember the rule of thumb off the top of my head, but the diameter of the diaphragm needs to be smaller than the highest frequency of interest in order for it to remain omni-directional.
-- Bill Audio Enterprise KB3KJF
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ohhey
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Re:What determines the pickup pattern of a microphone?
2010/06/08 15:03:11
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wst3
.....
(ok, I am cheating, and leaving out piezo, carbon, and optical pickups.)
....
You can't leave out the carbon microphone !! That was the patent applied for microphone after all. That deivce made long distance telephone calls possible, without it Alexander Bell's so called "invention" was just an intercom at best. All thanks to Emile Berliner (patent holder of the microphone) who also invented the Gramophone that had duplicatable media for the first time in history. That made the entire audio industry possible. Emile Berliner was the Les Paul of his day... wicken mad skills dude.
post edited by ohhey - 2010/06/08 15:04:44
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wst3
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Re:What determines the pickup pattern of a microphone?
2010/06/08 15:13:01
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Believe it or not I have a couple of old carbon microphone elements in the locker... can't remember the last time I used them, but every once in a while they do come in handy!
And since we are getting all trivial here, I just recently learned that Walter Schottky, he of diode fame and fortune, is also credited with the invention of the ribbon microphone. I always figured it was someone at RCA, but a friend recently gave me a copy of Olson's infamous 'blue book' - "Elements of Acoustical Engineering", and that little reference was in there. Must be true if Harry says it is<G>!
-- Bill Audio Enterprise KB3KJF
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/08 21:02:34
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Thank you Wst3 for the clarifications you added.. I found them interesting and meaningful. I'm still trying to digest that exposing only one side of a diaphragm makes them omni-directional, and I suppose that's what you mean being counter-intuitive. But no worry, I take your word for it being so, plus I did open up an old inexpensive omni mic up a few days ago, and its bottom is sealed. And after reading your post, I've been wondering about drilling a little hole in the bottom and see what happens. But I do stop, from not knowing how far the diaphragm is from that bottom....There's two wires coming out from the bottom..And I also think maybe debris from the drilling would get in there and start causing things..Like, I remember carbon mics would make a little rattling noise whe shaken.
post edited by NoKey - 2010/06/08 21:03:37
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feedback50
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Re:What determines the pickup pattern of a microphone?
2010/06/09 16:43:28
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NoKey
Thank you Wst3 for the clarifications you added.. I found them interesting and meaningful.
I'm still trying to digest that exposing only one side of a diaphragm makes them omni-directional, and I suppose that's what you mean being counter-intuitive.
But no worry, I take your word for it being so, plus I did open up an old inexpensive omni mic up a few days ago, and its bottom is sealed.
And after reading your post, I've been wondering about drilling a little hole in the bottom and see what happens. But I do stop, from not knowing how far the diaphragm is from that bottom....There's two wires coming out from the bottom..And I also think maybe debris from the drilling would get in there and start causing things..Like, I remember carbon mics would make a little rattling noise whe shaken.
As far as Omni's being exposed on only one side, it might help to think of an Omni Mic' as a really fast barometer. It responds to rapid, minute air pressure variations in the general vicinity (aka sound). I generally don't need to point my barometer at the sky to measure the barometric pressure, but I'm hoping someday to own a cardioid barometer. 
post edited by feedback50 - 2010/06/10 13:27:07
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/09 18:31:40
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Hi Feedback, and Wst3, good explanation. From previous post, I had indeed figured it was like a pressure regulator or something like that. Tje barometer analogy is much better. I have succesfully hacked the old low cost dynamic omnidirectional mic unto a neck-strap, so that when I play the keyboards and move the head, hands and body to push buttons, or look down sometimes to see the keys, or pedals, I can still record the voice with some consistency. It is working really well. Better than what I had bought, and have had for some time. The sound quality is much better, and the distance, and placement is much more to my preference than on the side of the cheek. I had that other head-worn small mic that I was not satisfied with, I record all at once and playing keyboards makes it hard for me to keep a fixed distance to the mic, so this hacking was not just for fun. The heeadset I was using use electret mic that seem to be overresponsive to sudden voice raising, and are much more difficult for me to use. Also, it uses a battery, and plugs with an adapter into a 1/4" jack. The hacked one plugs into the XLR, which is I believe better for mic signal too. I am not sure if this is a general thing, but it does seem to me that dynamic microphones are somewhat more smooth in response to voice volume changes. But on vocals, and much more, I am basically a beginner, so my thoughts are just that. The thought of drilling a hole on the bottom was on the idea that since I also use that neck starp to play an acoustic guitar and sing (learning), It does pick up the guitar rather well but a little weak, So I was thinking if the mic had a small hole in the bottom, maybe it would improve picking up sound from the guitar. But that is not much of a real need, anyway, and It probably is not a good idea. Thanks for the good info and comments.
post edited by NoKey - 2010/06/09 19:52:46
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The Maillard Reaction
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Re:What determines the pickup pattern of a microphone?
2010/06/09 22:04:38
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"As far as Omni's being exposed on only one side, it might help to think of an Omni Mic' as a really fast barometer."
fantastic explanation... I've never heard the barometer metaphor before. Thanks!!!
Nokey,
I own a book named "Microphones" by John Borland.... I read it every few years.
I am guessing you would really enjoy having your own copy to use as a primer and a reference.
best,
mike
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/10 10:42:01
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Hi Mike_mccue,
Thanks for the suggestion..I'll look into that.
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wst3
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Re:What determines the pickup pattern of a microphone?
2010/06/10 13:28:07
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not to kill your budget, but if you are going to invest in a text, look for Lou Burrough's book "Microphones: Design and Application"
Borland, Eargle, and a couple I can't think of off the top of my head are all good, even great, but Burroughs literally wrote the book!
Or, if you are feeling really flush, get Harry Olson's Acoustical Engineering.
-- Bill Audio Enterprise KB3KJF
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The Maillard Reaction
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Re:What determines the pickup pattern of a microphone?
2010/06/10 13:34:35
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oh boy.... I need to go shopping now. :-)
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ohhey
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Re:What determines the pickup pattern of a microphone?
2010/06/10 14:03:32
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wst3
not to kill your budget, but if you are going to invest in a text, look for Lou Burrough's book "Microphones: Design and Application"
Borland, Eargle, and a couple I can't think of off the top of my head are all good, even great, but Burroughs literally wrote the book!
Or, if you are feeling really flush, get Harry Olson's Acoustical Engineering.
Another good read. Emile Berliner - Maker of the Microphone http://www.amazon.com/Emi...ications/dp/0405060629
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NoKey
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Re:What determines the pickup pattern of a microphone?
2010/06/10 14:04:42
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Thanks wst3 for sharing info on resources.
Will be kept in mind, though everyone's replies here have been plenty helpful.
It think good people beat books more than often.
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