"pointing" an omni

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lysander
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"pointing" an omni

Post by lysander » Mon Sep 23, 2013 8:02 pm

Just a quick question for the experts here. I have been using a small condenser omni mic as a drum overhead. I have the mic pointed down at the kit, but never really thought about why I positioned it that way. Does where it's pointed make any difference at all if it's an omni mic?

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Post by drumsound » Mon Sep 23, 2013 8:04 pm

Move it around and listen. Just like any other mic, it makes a difference.

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Nick Sevilla
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Post by Nick Sevilla » Tue Sep 24, 2013 6:26 am

Hi,

Every microphone has a slightly different polar pattern, which depends
on the quality of the capsule, contamination on the capsule, age and quality
of the internal components, and even the body itself.

All microphones exhibit different responses when you near the opposite end of the mic body, due to the body itself. Thisis called its "shadow" and the good news is that it is consistent.

Some microphones even have cavities near the back of the body, to adjust the frequency response of the mic pickup at different angles. See the AKG D202 'bottle rocket'.

As to the specific polar pattern of OMNI, in your case, if you are curious, you can actually do a rough measurement, byplacing the mic on a stand with the mic body facing exactly parallel to the ground, and a speaker source in front of it at the same height. Then, pump pink noise into the speaker, and record the mic as you slowly rotate it in place. The resulting difference in level will give you a very rough estimate of the real world sensitivity of the microphone.

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Nick Sevilla
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Post by Nick Sevilla » Tue Sep 24, 2013 6:28 am

One more tip. Try to keep the mic capsule in the same spot in space.

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dfuruta
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Post by dfuruta » Tue Sep 24, 2013 9:03 am

As frequencies get higher, omni mics get more directional. This is true for all omnis, but how much this happens depends on the size of the capsule - a smaller capsule can have closer to a true omni response due to diffraction effects. There's more of an explanation here.

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Post by lysander » Tue Sep 24, 2013 12:25 pm

Thanks for the responses! I'm a one-room recorder so mic placement is pretty much a trial-and-error thing, but I'll mess around with it and see what different orientations sound like.

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Post by mwerden » Tue Sep 24, 2013 2:18 pm

There's also a difference between pressure omni and dual diaphragm omni. Pressure is more textbook omni response, dual diaphragms are often darker on the rear side.
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IanWalker
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Post by IanWalker » Fri Sep 27, 2013 12:18 pm

dfuruta wrote:As frequencies get higher, omni mics get more directional. This is true for all omnis, but how much this happens depends on the size of the capsule - a smaller capsule can have closer to a true omni response due to diffraction effects. There's more of an explanation here.
^^ This.

Since it's more directional at higher frequencies, I tend to think of it simply being brighter on-axis. So exactly where I point it varies depending on the source.

And obvious, but worth stating, is that if it's closer to something, that thing is going to appear more forward than something further away. It doesn't exhibit proximity effect like a cardioid, but proximity clearly matters.
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Post by dfuruta » Fri Sep 27, 2013 6:37 pm

IanWalker wrote:And obvious, but worth stating, is that if it's closer to something, that thing is going to appear more forward than something further away. It doesn't exhibit proximity effect like a cardioid, but proximity clearly matters.
Definitely, due to the ratio of direct to room sound.

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SafeandSoundMastering
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Post by SafeandSoundMastering » Wed Oct 02, 2013 1:52 am

Nothing specific to add regarding an omni....but worth knowing that most microphone polar responses change with frequency and start becoming omni-directional in the low end of the spectrum. (even cardioids)

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