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Old 27th November 2011, 09:43 PM   #41
Pano is offline Pano  United States
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1/4 wave for 1KHz audio would be about 8.6cm
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Old 27th November 2011, 09:46 PM   #42
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Actually joking aside, It probably could be done. Think of a collinear antenna, not so different in theory to a column loudspeaker.
Reverse the process and make a column mic array, Hmmm thinks ...
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Old 27th November 2011, 09:51 PM   #43
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Quote:
Originally Posted by Pano View Post
1/4 wave for 1KHz audio would be about 8.6cm
Agreed, speed of sound in air is much slower than speed of RF (light).
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Old 27th November 2011, 09:53 PM   #44
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Chancellor Merkel was addressing the Bundestag this week in front of what looked like line array mics. With the windscreen, it was hard to tell, but certainly not your typical mic. Anyone know?
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Old 27th November 2011, 09:59 PM   #45
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I was having a chat with the Audio Technica rep the last time he was around, and got on to the subject of the 747, (the worst conference mic in history), and he mentioned that they were doing stuff with line array mics. Wonder if that's what you saw?
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Old 27th November 2011, 10:06 PM   #46
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Would the Bunderstag use Audio Technica mics?
EDIT: This is it, and it's German.
http://microtechgefell.de/index.php/...ictabs_UhCqm_2
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Old 27th November 2011, 10:33 PM   #47
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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.
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Old 18th January 2013, 05:17 AM   #48
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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.../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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Last edited by xrk971; 18th January 2013 at 05:47 AM.
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Old 20th January 2013, 08:52 AM   #49
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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
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Old 20th January 2013, 03:34 PM   #50
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The RCA MI-10006A "Vari-Directional Microphone" had 19 tubes from 2" to 60" long, with a single omni condenser mic capsule.

Often shotgun mics use the term rifle mic

It be fun building one, but once you hae it, what do you do with it? E
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Last edited by mickeymoose; 20th January 2013 at 03:41 PM.
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