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Old 26th January 2013, 03:09 PM   #51
xrk971 is online now xrk971  United States
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Originally Posted by tschrama View Post
Nice to see this thread being active again.

I once tried to to do excactly that: building a shotgummic from PVC tube. I am not sure if you need a cardioid-mic inside the tube? Or figure-8? Or a true omni?..maybe two wm61s back-to-back-sideways for a true omni-directional.

I am still interested in the design of mic..Thanks for the patens.. !

Grtz, Thijs
I think a single omni capsule at the end is all that is needed. If you think of the markup they charge for these things it's incredible as it is nothing more than a slotted tube added on.
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Old 10th March 2014, 03:00 AM   #52
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I'm interesting too in making a shotgun mic, I have just started building mics and would like to lean towards there.
Did you finally made something similar to the sennheiser? Building it from a PVC pipe shouldn't be too difficult.
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Old 15th March 2014, 08:07 PM   #53
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Originally Posted by xrk971 View Post
I think a single omni capsule at the end is all that is needed. If you think of the markup they charge for these things it's incredible as it is nothing more than a slotted tube added on.
An omni won't care about the slotted chamber behind it because the omni is sealed. I would guess you want a figure 8 mic. A cardoid might also work, but a cardioid is sort of "semi-sealed", so I would expect the figure 8 to interact more with the rear chamber.
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Old 15th March 2014, 09:55 PM   #54
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Reading patents is difficult. They must go to a lot of trouble to make everything as incomprehensible as possible, while still being technically correct and legal.

It sounds like AKG found a more refined way to do what needed to be done. One thing I believe is necessary is to have two mic elements, back to back, wired out of phase with each other, to simulate a diaphram with nothing in it's way on either side, so the "interference tube" can work, attenuating anything that is not straight in front of the diaphram that is directly exposed to the outside world.

It appears that the openings in the interference tube can be almost any size and any spacing, and still be effective. I'm guessing that with strategic spacing and sizing, the tube would have improved effectiveness.

Apparently no shotgun mics are full wideband 20HZ - 20kHZ. Apparently the length of the tube determines how low in frequency it's shotgun effectiveness can go in frequency. Apparently these mics will need to have electronic bandwidth limiting to do the job well, so the very low and very high frequencies that don't largely cancel out, don't add in a bunch of undesirable room noise in those frequency ranges.

A high-tech version might use separate mic capsules at some of the holes of the interference tube, and/or even possibly use electronic delay to further optimize the correct interference effect. This may reduce noise and improve effective bandwidth.

What to do with it when it's done? Camcorder.
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Old 16th March 2014, 03:29 PM   #55
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What to do with it when it's done? Camcorder.
After looking into this out of curiosity, I would suggest you try using just a ~1/2" diameter ~2 foot long tube with slots cut into it in front of a cheap omni and/or cardioid microphone cartridge. If it fails, you won't be out much money or time.
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Old 16th March 2014, 08:51 PM   #56
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I'm pretty sure those Panasonic mic capsules are omni-directional, which means they have closed backs, which means that for this shotgun mic to work right you'd have to put in two mic capsules back to back, wired out of phase with each other, to simulate an open back mic capsule. Otherwise I don't think it will work.
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Old 8th May 2014, 03:20 PM   #57
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I just did an experiment with a 6mm dia. omni . Drilled a hole behind the diaphragm (.8mm) and its sensitivity dropped by about 40% but it became cardioid.
The construction of these capsules include a inner plastic 'seal' inside of the alum. can. Also the J-FET is a bit like an SOT 23 device and it blocks the PCB fairly well. I chose to drill just above the JFET and on the opposite side to the gate connection. I figured this out by slicing one open with a dremel cut off disc.

The Panasonic WM61s are supposed to be back electrets so a 'side' hole prob. won't work for those.

Last edited by Mosaicmerc; 8th May 2014 at 03:24 PM.
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