Would the Bunderstag use Audio Technica mics?
EDIT: This is it, and it's German.
http://microtechgefell.de/index.php...ling-microphones/439-kem970#magictabs_UhCqm_2
EDIT: This is it, and it's German.
http://microtechgefell.de/index.php...ling-microphones/439-kem970#magictabs_UhCqm_2
Yes, that looks like a linear array. To a first approximation, waves are waves whether sound or radio. Yes I know it breaks down at the second approximation due to transverse vs longitudinal etc. Antennas, mike arrays, and analogue filters all end up using the same patterns so bright ideas from one can be translated to another.
Not sure if anyone has been looking at this thread lately but I was just wondering how to make one of those tubular shotgun mics too. I recently bought a bunch of Panasonic WM61A capsules for measurement purposes. They are real nice, very flat and sensitive - all for $2 ea. So I have spares lying around and thought I should try to make one of these shotguns. If you want to see how Sennheiser does it, it all comes down to a patent by Otto Hoffman, 1969. US Pat number 3444955. The theory and how to build one is all in there. Basically the slots (or holes in this case) farthest away from capsule are large and get smaller as it gets closer to capsule in the back. In this way, a wide range of frequencies are directional.
Sennheiser Patent:
https://docs.google.com/a/google.com/viewer?url=www.google.com/patents/US3444955.pdf
If you compare the 1969 Sennheiser patent with the more recent one from Audio Technica in 1988. It is still basically the same thing. These designs are nice in that they use just one mic capsule and they are passive aero-acoustic 1/4-wave devices - essentially a flute in reverse.
Rather than make it out of aluminum, there is no reason why this should not work if made out of PVC piping which is cheap and very easy to drill holes in or cut slots, what have you.
AKG Patent:
Patent US4757546 - Narrow directional microphone - Google Patents
I might have a go at this. Very similar to making PVC flutes (one of my other DIY hobbies).
If you look at the Sennheiser MKH416P48 carefully (see attached picture), you will see that it looks like they are using a single width slot along the sides. Single width is probably not ideal bu manufacturing costs are much cheaper than variable width slots. From photo and specs, the mic body dia is 0.74 in and the pitch of the slots is 9 slots per 0.74 inch with a total of 77 slots. Use a hacksaw or miter box saw and cut about 12 slots per inch.
Sennheiser Patent:
https://docs.google.com/a/google.com/viewer?url=www.google.com/patents/US3444955.pdf
If you compare the 1969 Sennheiser patent with the more recent one from Audio Technica in 1988. It is still basically the same thing. These designs are nice in that they use just one mic capsule and they are passive aero-acoustic 1/4-wave devices - essentially a flute in reverse.
Rather than make it out of aluminum, there is no reason why this should not work if made out of PVC piping which is cheap and very easy to drill holes in or cut slots, what have you.
AKG Patent:
Patent US4757546 - Narrow directional microphone - Google Patents
I might have a go at this. Very similar to making PVC flutes (one of my other DIY hobbies).
If you look at the Sennheiser MKH416P48 carefully (see attached picture), you will see that it looks like they are using a single width slot along the sides. Single width is probably not ideal bu manufacturing costs are much cheaper than variable width slots. From photo and specs, the mic body dia is 0.74 in and the pitch of the slots is 9 slots per 0.74 inch with a total of 77 slots. Use a hacksaw or miter box saw and cut about 12 slots per inch.
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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 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.
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.
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.
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.
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.
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.
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.
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.
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