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Old January 19th, 2010, 12:06 AM   #1
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Making the AT4073a less OMNI?

I have an Audio Technica AT4073a boom mic that I normally use for DEAD room interviews for documentary work and I love it. And when I say dead I mean it cause this mic picks up everything in the room.

Problem: I have a big reunion to shoot that's in a large, loud conference hall where I will be walking around with the camera and my sound guy will be following me around holding the mic on a little boom handle pointing it at the action. My experience with this mic is that it would completely fail in this environment cause its such a sensitive mic but I cant afford to get a new one right now.

My question is, can I tape up or cover the sides of this mic so that only the tip of it is exposed? Would this be a way of making it more uni or multi directional?

Here is a pic of the mic and you can see the openings on the sides that I would cover somehow:
http://i591.photobucket.com/albums/s...illow/mic3.jpg

Here is just the tip that would be exposed:
http://i591.photobucket.com/albums/s...illow/mic2.jpg


Also, in this picture, is that a bass notch and what exactly does it do? Ive never messed with it.
http://i591.photobucket.com/albums/s...illow/mic1.jpg

Thanks,
O.D.
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Old January 19th, 2010, 05:15 AM   #2
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whoah! no

The slits in the tube are the exact opposite of how you are seeing them.

The mic itself is in the back of a shotgun mic, past all the slits. The slits are what is called an "interference tube" and that is precisely what makes a shotgun microphone directional. The sound you want comes in the front of the tube, and sounds from the side enter through the slits, off axis from the main sound and this causes interference which cancels out the sounds coming from the side from the signal which reaches the mic diaphragm. Its a very simple way to take advantage of complex acoustic physics.

So, if you were to cover up the slits you'd take away the interference and then you'd have an even LESS directional mic.

I also have a 4073a, and while it isnt nearly as focused as say a 416, it still functions quite well as a shotgun when positioned properly. If the mic is a couple feet or less away from a speaker and pointed at his mouth at such an angle that the tail is aimed at a hopefully dead ceiling, then whatever the mic is not pointed at will be significantly quieter than what the mic is pointing at. In a reunion setting the goal isnt to make all the other sounds go away (not really possible), its to lower the unwanted sounds enough that the desired talking dominates.

If you hold the 4073 4 feet away from a subject in a crowded room, you'll get barely any isolation. If you hold it 1 foot away aimed down and at the mouth of a speaker, the speaker will be loud enough that when you turn your mic input down to the correct level of the speaker, the room noises will be reduced that same amount. viola.

I've used the 4073 in noisy bus stations. If the camera gets close, and the mic gets closer, it can work. Its not "isolated dialog" nor is it ideal, but its what you hear on the news every night.

To answer your question more directly: If you've done everything else correctly and the 4073 is still not directional enough for your needs? The only option is to buy/rent a more directional mic. There really isnt a mod for it.

The bass rolloff switch cuts out the lowest frequencies before they go to camera. Shotgun mics (except for the sanken cs3e) are not directional in low frequencies, so if you are near a bunch of idling diesel engines or a tractor pull or wind stronger than your wind protection, you flick it to cut all the low noises so they dont overwhelm the signal. The down side is it also yanks all the bass out of what you are pointing the mic at as well.

Hope that helped or something!
-a
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Old January 19th, 2010, 05:53 AM   #3
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An At 875 may be a better mic for your application as it is less sensitive and will be better suited for a close run and gun situation inside.

Taping over phase cancellation slots is not a good idea as it will change the way the mic works and may give you more problems than selecting a different mic for the shoot.
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Old January 19th, 2010, 06:09 AM   #4
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Quote:
Originally Posted by Oliver Darden View Post
...
Problem: I have a big reunion to shoot that's in a large, loud conference hall where I will be walking around with the camera and my sound guy will be following me around holding the mic on a little boom handle pointing it at the action. My experience with this mic is that it would completely fail in this environment cause its such a sensitive mic but I cant afford to get a new one right now.

My question is, can I tape up or cover the sides of this mic so that only the tip of it is exposed? Would this be a way of making it more uni or multi directional?

...

Also, in this picture, is that a bass notch and what exactly does it do? Ive never messed with it.

Thanks,
O.D.
Andrew pretty well summed up why you should not cover the interference ports. Don't forget that shotgun mics do not maginify the sounds coming from where they're pointed, they're not like a telephoto lens. Nor are they more sensitive than other mics. All they do is supress the sounds arriving from the sides and rear. But that supression is a matter of degree and they still pickup up sounds from all directions, just not as much from off-axis as from the front. This means you still need to have the mic close to the subject in order to properly isolate him from the other sounds and the noisier the environment the closer you'll have to be - generally for a short 'gun like your AT the mic should be around 2 feet away from the subject's mouth. Remember too that there are sound sources BEHIND the subject. If you hold the mic at head-height and point it at him like a pistol, those other sources are also going to right in the line of the mic's maximum sensitivity and if the mic is at the camera, they'll be about the same volume as the subject's voice as well. To avoid that, your assistant needs to get the mic above the subject so it makes about a 45 degree angle toward the ground when pointed directly at his mouth (So he can't be following you, he has to be in front of you just outside of the camera's field of view.)

That switch is a bass roll-off, also called a high-pass filter. It's a shelving filter with its knee at 150Hz on that mic. It's purpose is to reduce the rumble and thumps of handling noises and to work with the wind shield to further reduce wind rumble. There's usually very little information that low with most voices so you'd normally want it on except when the mic is on a mic stand and you're recording a bass fiddle or James Earl Jones doing a voice-over <g>.
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Old January 19th, 2010, 09:13 PM   #5
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Thanks for all the great info guys, VERY VERY useful.

What about using one of my friends condenser mics? Would this work better?

AKG Perception 200
http://www.musikmarkt-plauen.de/cata...eption_200.jpg
http://www.akg.com/site/products/pow...nguage,EN.html

or

Audio Technica At2020 (not usb)
http://obiaudio.com/1/Images/Reviews/AT2020.jpg
http://www.sweetwater.com/store/detail/AT2020/
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Old January 19th, 2010, 11:52 PM   #6
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also in this conversation would be if your using AUTO volume control or not.
if you have a seperate sound person they wouldnt "need" auto volume control, so therin the levels arent raised for stuff that you dont even want to hear.
ANY mic used with AVC will snag whatever it can, out of whatever is there. As soon as any sound is not stronger than another at the mics pickup point. It wont mater much how you alter the pickup area , if the camera/recorder keeps pumping up the levels. There are also some really Fast AVCs and they will "compresss" so quickly that even if a person is talking right into the mic, the volume will still go to "ambient" in between words themselves :-(.

if your trying to "roll-off" (bad word for it) all other sounds, then you really would prefer a stage cardoid ball type of mic, Being totally opposite of what your trying to do, because they are often OMNI acting, those stage cardoid ball type mics are designed to reduce feedback , so they dont pick up stuff that is at a distance from the mic.
I actually hate :-) trying to pick up sounds with a cardoid type ball mic, Unless the thing your trying to record is close to it.
there is more to just the Class or designation of a mic, different mics can have completly different ways that it seems to work, beyond the element or containment, so i couldnt even tell you Which type of cardoid ball, i am just indicating that some stuff will roll stuff off so fast, a mere change from 12"-18" will change everything.

I suspect that because you have an adequite shotgun, then are going to add a human to control the sound, that setting up the equiptment right (AVC and limiters off) and having a human to control it, and constantally monitor it. will fix most of the problems your trying to "fix", without changing anything else. Else Get a hand mic and hand it to the person your trying to hear, use the audio guy to assist in the handing.

if you cover the mic sides, you will get a nice tin can sound :-) but then that was already covered.
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Last edited by Marty Welk; January 20th, 2010 at 12:26 AM.
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Old January 20th, 2010, 03:55 AM   #7
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Quote:
Originally Posted by Oliver Darden View Post
Thanks for all the great info guys, VERY VERY useful.

What about using one of my friends condenser mics? Would this work better?

AKG Perception 200
http://www.musikmarkt-plauen.de/cata...eption_200.jpg
Perception 200 (Discontinued)

or

Audio Technica At2020 (not usb)
http://obiaudio.com/1/Images/Reviews/AT2020.jpg
Audio-Technica AT2020 | Sweetwater.com
Nope, just the opposite. Not only are they large and bulky, way too cumbersome for hand-held or boom-mounted field use, they are cardioid pattern mics which are much LESS directional than your shotgun. If you want a viable alternative, try something like a cardioid pattern, dynamic, reporter's "stick mic" like this one ...

Sennheiser USA - Dynamic Vocal Microphone, MD 46, Reporter - Professional Audio

or this ...

Electro-Voice RE50/B RE Series Broadcast Interview Microphone

assuming you can have an on-camera interviewer to hold the mic. Dynamics like this cannot really be used on a boom because they need to be within about 5 inches of the speaker's mouth.
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Old January 20th, 2010, 08:06 AM   #8
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Quote:
Originally Posted by Oliver Darden View Post
I have an Audio Technica AT4073a boom mic
That is a very directional "shotgun microphone". It is the opposite of an "OMNI" directional microphone. It may have seemed "omnidirectional" to you because you were trying to use it in a small room with acoustic reflections. This is NOT a recommended application for shotgun microphones. A "hypercardioid" microphone is more typically used indoors for the very reason you have demonstrated.

Quote:
that I normally use for DEAD room interviews for documentary work and I love it. And when I say dead I mean it cause this mic picks up everything in the room.
Shotgun microphones are not generally very effective indoors and you can see why. It is not "picking up everything in the room". It is picking up the REFLECTIONS of everything in the room. To be effective, a shotgun microphone needs to "hear" all the sound around it to be able to distinguish on-axis (desired) sound vs. off-axis sound. When sound reflects off nearby surfaces, it enters the microphone from multiple directions and defeats the designed directional mechanism of a "shotgun" microphone.

Quote:
Problem: I have a big reunion to shoot that's in a large, loud conference hall where I will be walking around with the camera and my sound guy will be following me around holding the mic on a little boom handle pointing it at the action. My experience with this mic is that it would completely fail in this environment cause its such a sensitive mic but I cant afford to get a new one right now.
If you have had experience using this mic in "a large loud conference hall", then you didn't mention it here. Your experience using it in small, reflective rooms is not an indication of how it will work in a large room. Of course we are only guessing what you mean by "large"?

Quote:
My question is, can I tape up or cover the sides of this mic so that only the tip of it is exposed? Would this be a way of making it more uni or multi directional?
No you cannot do that. The microphone is only directional by its ability to hear all along the side openings. Many "shotgun" microphones actually have no opening at all at the tip. Many have a "fake" grille there because people expect it to be able to "hear" from the end (like the opening on the end of a firearm where the bullet comes out.) But microphones don't work anything like firearms.

Quote:
Also, in this picture, is that a bass notch and what exactly does it do? Ive never messed with it.
That is a switch, not a "notch". It turns on and off a bass roll-off filter. It is useful especially outdoors to reduce low-frequency noise (as from wind, traffic rumble, etc.)

My guess would be that your AT4073a will work better for the large room noisy reunion than it has been in your previous (mis-)applications in smaller rooms.
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Old January 20th, 2010, 12:28 PM   #9
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From everything you guys have said it seems my best option would be to just use the AT4073a as is and have the sound guy get as close as possible to the subjects. I will also turn the bass roll-off filter on to help eliminate any boomy noises and loud walking around as the room will be pretty busy. I'll run the cameras audio settings in manual (I normal always do this) so the sound guy can adjust it as needed.

Thanks everyone for their feedback on this.
O.D.
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Old January 20th, 2010, 01:28 PM   #10
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The AT4053b Hypercardioid pencil mic would be a much better choice for indoor work. I`ve been using the AT4053a ( older model ) for the past couple of years with great success when recording in small reflective rooms.

Audio-Technica | AT4053b Hypercardioid Condenser | AT4053B | B&H
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Old January 20th, 2010, 02:49 PM   #11
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Guy, I don't have the time or the budget to pick up a new mic but I will consider it for the next shoot. Thank you.
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Old January 21st, 2010, 03:00 AM   #12
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In my experience, a loud, crowded room is normally fairly dead due to all the bodies in it. Unless it is a basketball arena or something. In a dead space a shotgun doesn't suffer from reflections and it will have a longer "reach" than a hyper. It won't make the annoying voices go away, but it should make them low enough you can hear the annoying person you are interviewing.

4053 is great for dialog... but a loud banquet room filled with drunk people isnt exactly "dialog". In that scenario i think the 4073 is a very good choice and if you boom it close and angle it and mix to it as people have described, i think you'll find a new love and respect for the 4073. It really is a heck of a mic.

One tip... take a minute early in the night for the sound guy to do a direction test. You should find that when you position mic at certain angles relative to the band/dj (in theory 90 degrees off axis) you'll get better isolation. Once you figure out the best direction relative to the band to be, he should be able to reproduce that relative angle no matter where in the room you are.
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Old January 21st, 2010, 01:54 PM   #13
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Generally at 1kHz the greatest null point will be about 120-degrees, which is good because when used at the typical overhead booming angle, this will put one null zone towards the ceiling that may be a source of hotter reflections. The other 120-degree zones then point out across the room, again a good thing.

However there are three frequency-dependent issues to keep in mind. First as the frequency of sound gets lower, directional mics become more omnidirectional. Second as the frequency gets higher, mics (especially omni's) become more directional. Third with shotgun mics, their off-axis response can be so irregular (look at all the spikes on their directional plot in the 90-degree to 180-degree area) that you can clearly hear the off-axis coloration and how it changes as the mic is moved. That's why it's difficult to use some shotguns in these indoor circumstances that we're discussing.

Now an off-shoot about your question on the AT2020. If your friend purchased their AT2020 as part of the kit with the AT2021 cardioid pencil mic, then you could use the AT2021 on a boom. While it is a cardioid and would need to be kept as close as possible to the source, it would be much easier to keep close to the source due to its very short length and very light weight. It does require full 48v phantom power, but its sensitivity would be moderate as opposed to the very high output AT4073a. It should also have less off-axis coloration if the room turns out to be very reflective. The AT2021 might be a case where you get more bleed-in from off-axis sources but since it has minimal coloration it becomes less noticeable in relation to your subject. If you have one available from your friend and can provide full 48v power, it would be worth it to take along. It is the same diameter as the AT4073a (21mm) and would fit in the same shockmount as long as the supports aren't too far apart since the AT2021 is only 4 inches long (less than 4 inches counting the cardioid holes around the head but you can also use the XLR connector inside one of the shockmount supports if you need more length).

Otherwise it is too bad you don't have access to a hypercardioid like those suggested.

Last edited by Jay Massengill; January 21st, 2010 at 05:45 PM.
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