Understanding Audio - DIY 'true capacitor' condensor microphone

This video and this microphone are for teaching and demonstration purposes only.
Pre-manufactured condensor capsules are too small, too fragile and too difficult to disassemble to show how they really operate, so I decided to make my own ridiculously large transducer assembly from household / hardware store parts. This transducer can operate without a back-can for figure-eight (bidirectional) pickup, with a ported back-can for cardioid (unidirectional) pickup, or with a sealed back-can for omnidirectional (non-directional) pickup.
As soon as I get the signal-to-noise problems under control (see the closing comments in the video), I'll add another video with demonstrations of various pickup (polar) patterns resulting from variations of the rear exposure of the diaphragm (adding, removing, or modifying the "can" over the rear of the transducer assembly).
Thanks
-Andy Sickle
Columbia College Chicago Faculty

[@NicuIrimia]

Please continue this. Thanks

[@BrianJamesKeller]

Great video man, excited to see more

[@perrybakalos7340]

Nice DIY project for learning... what you mentioned about getting the diaphragm closer to the backplate for higher output is true. But the output of this "design" will be very low (except at higher frequencies), significantly contributing to the poor S/N ratio. This is because of front to back acoustic pressure cancellation around the diaphragm. The concept is identical to a loudspeaker not mounted in a baffle (large sealed box) . You would need to acoustically isolate (seal) the front from the back of the diaphragm at the frequencies of interest to get the diaphragm to move due to incident acoustic pressure, and hence get output signal from the mic...

[@AndySickle]

That's not quite correct. Bidirectional ('figure-8') microphones have no baffle, directional (cardioid, hypercardioid, etc.) microphones have a partial or vented baffle, and omnidirectional microphones have a sealed baffle. In a later iteration of this project, with proper grounding and shielding, we achieved a S/N of 51db (lab measured). A design engineer from Sure suggested that the low output was largely due to the materials being poorly suited for the capacitive (electrostatic) field required between the diaphragm and the backplate. When we rigged a 260 VDC charging bias for the microphone (think of this as 'jacked-up phantom power') we raised the S/N to almost 63dB and had output levels comparable to a modern large diaphragm condensor.

[@perrybakalos7340]

@@AndySickle Thanks, good point about the figure of 8 polar response...you are correct in that for this case with both sides exposed, it's a pressure gradient mic. I forgot about this, and was thinking of all the other types. I like the simplicity of construction and resourcefulness of available materials (i.e paint cans and xmas wrapping). A large diaphragm surface area like this should have relatively high sensitivity compared to commercial designs...wonder why it is apparently not. There is a lot to it of course, but I don't quite know why the Sure engineer told you that the materials do not lend themselves to the electrostatic field. I'm guessing maybe there is significant charge leakage from the diaphragm material for some reason, but i will guess that a bigger factor is the capacitance is much lower than desired due to the separation distance.

[@perrybakalos7340]

It would be good to see how you tested this also...test setup. How close source was to mic, etc. That said I realize that people have time and priority constraints!

[@rickrick1545]

sweet can't wait..

[@pierpaolop9534]

Can you please explain how it works and how to make it. Can this contact mic capsule be used even though it is not piezoelectric type? Can you listen to conversations from a partition wall? Thank you very much.

[@MrSamAli]

i think 48v wasn't enough for that. And also the thing you used for diaphragm isn't gonna vibrate on every soundwave so these are the reason for your output SNR

[@josephkeichline838]

Any update about this project? I would love to know how it sounded!

[@praveenkumar-wi3ej]

Very good demo of how externally polarised condenser microphone works.

[@Itsadrianyay]

nice video, interested to see (well, hear) the results! no idea christmas wrapping could be used as a diaphragm. thanks for posting!

[@berwynschoolofmusic9760]

Hi Andy, I"m one of your former students. I was hoping to reach out to you to discuss star grounding. I have inherited a recording studio that's really nice but the power is filthy. I can't seem to find any other way to reach you so this is a long shot. Here's my FB - John E Bomher, Jr. If you see this comment and you have some time to catch up and give me a bit of direction. Thanks

[@AndySickle]

Hey John! I'm glad to hear from you. I don't know how I missed this comment when you posted it. I'm not on FB but you can email me at apsickleAThotmailDOTcom

[@moisescobretti]

Fantastic

[@krakadoros8605]

Congratulations for this DIY manufacture of a large diameter (really large !) diaphragm. Please, i do not understand two things : 1) The non conductive side of the diaphragm, has placed opposite (face to face) to the metal backplate. Then, how an Electric field will be created ? I thought that, in a Capacitor there are two plates, placed opposite and very closed, but both are good conductors for electricity. 2) What for, are the holes in the backplate ? Are they obligatory ? The material of the backplate, can be INOX (without loosing in quality of the result) ? Thanks

[@AndySickle]

1) The electric field in any capacitor is created by the charge difference between two conducting layers separated by a non-conducting layer (dielectric). In a capacitor microphone (condensor), the two conducting layers are the diaphragm (usually a layer of gold impregnated on to mylar or a similar plastic) and a fixed backplate (usually brass or similar metal, sometimes with an added gold plating to prevent oxidation / corrosion over time). The insulating layer is an air gap between the diaphragm and the backplate. Sometimes the diaphragm itself is also acting as a dielectric by having its conductive treating only on the side that faces away from the backplate (the sound-field side). This adds a functional protection for the conductive treatment by preventing a short circuit of the polarizing charge. 2) The holes in the backplate serve two primary functions- First, the holes allow air to equalize pressure between the dielectric gap and the external sound-field. This means that the diaphragm will always have a fixed resting distance to the backplate. Second, the holes act as an acoustic 'widow', allowing the same sound that is acting on the front side of the diaphragm to act on the rear side of the diaphragm, but through a 'baffle'. This baffle changes the time (phase delay by lengthened signal path), the amplitude (by different geometry and area of exposure), and the frequency response (by diffraction and resonance tuning) of the sound as it reaches the rear of the diaphragm. Careful control of these holes and the attached enclosure (if any is used) are what create the directionality (polar pattern) of the microphone. The diaphragm's movement is induced by the difference in pressures acting on its front and back sides. I.E. If sound has equal sound-field exposure on both sides of the diaphragm then it will exhibit a bi-polar or "figure eight" directional response. If the sound has no exposure to the back side of the diaphragm then it will be omnidirectional. All other polar patterns (variations of unidirectional response) are the result of unequal soundfield exposure of the front and back side of the diaphragm. 3)The backplate can be any conductive material. I could only guess at the trade-offs of using INOX (stainless steel). ¯\_(ツ)_/¯

[@topstarsmusic]

Hi Andy! Thank you for the video. Where are the audio demonstrations?

[@pointofview654]

This is a very interesting question! Especially after 10 years

[@topstarsmusic]

@@pointofview654 hahahaha you are right i didnt realize XD

[@NicuIrimia]

Please continue this. Thanks

[@dedskin1]

he didnt , i am too interested, but seams like hes just spaming YT . probably didnt go down as planned so he didnt make part 2 where we actually get to hear his 20 buck mic capacitor... i think i will by my self mic capacitor in my build cuz for shore some Chinese farmer has done it properly and sells it for like 10 bucks, ima go out and try to find another video , hopefully it will be finished

[@TeleVisionSystem]

The shielding is the responsible of the bad S/N ratio. But I would like to watch the video in which there is the demo, because mechanically it seems well done

[@shayhan6227]

Were you ever able to get this capsule to work properly? I'm very eager to see it in action.

[@AndySickle]

I did get it to work much better. It was only intended to serve as a teaching tool on the operating principles of condensor microphones; and in that regard, it worked very well. The biggest improvement in S/N was shielding. It never got better than about 36 dB S/N, but that was more than good enough for proof of concept. I never continued the video(s) because I retired work as a college teacher.

[@shayhan6227]

I see. Although it is a bit sad to hear that this video will not be continued, I learned a great deal from this. I’m glad that there are professors like you as I feel most professors today, at least in the university I go to, rarely give demonstrations of the inner workings of fundamental technologies. It’s comforting to know this knowledge isn’t some magic that only large corporations know and won’t share or something that will fade into obscurity through generations. I really appreciate it, thank you.

[@generalawareness101]

I am interested in that Christmas wrapping. Do you remember where you got it from as I find it remarkable it was conductive only on one side.

[@AndySickle]

I got it here- goo.gl/maps/3HjMHrxh2212MDhZ6

[@generalawareness101]

@@AndySickle Seriously? WOW. I will see what I find at the Dollar Tree since they took over FD a lot of the stuff is in both. Is it paper on one side or how is it non-conductive but is on the other?

[@AndySickle]

@@generalawareness101 I'm pretty sure it was some kind of polyethylene or polypropylene sheet with a metallic coating on one side.

[@generalawareness101]

@@AndySickle Interesting indeed. I often wonder about those Mylar balloons they have Helium in.

[@AndySickle]

@@generalawareness101 Mylar is a very common base material for condenser microphones- usually 24k gold vapor coated.