Need info regarding use of omni mics

[omtayslick]

I am searching for info on the potential pitfalls and advantages of using multiple omni mics (up to 3) on sources such as a drum kit, etc.

Are omnis subject to the same considerations regarding Phase issues (3 to 1 rule etc.) as other types of mics?

Can omnis be used in XY configuration?

What are the differences between nearfield and diffusefield omnis?

Do omni condensers and dynamics behave in the same manner?

And please feel free to add any other words of wisdom regarding the use of omni mics.

Thanks.

 

[moresound]

The use of two omni microphones as over heads can be common practice. Again as always you'll have to find the sweet spot. For you'll get a lot of the room in your recording.

What are the differences between nearfield and diffusefield omnis?
Do omni condensers and dynamics behave in the same manner?

I've found THIS to be helpful with some of your questions Tom.

 

[mixsit]

I'll be guessing here just for the fun of it.

...Are omnis subject to the same considerations regarding Phase issues (3 to 1 rule etc.) as other types of mics?

The ratio might be a bit higher as you don't have the cardi's side attenuation.
Remember all it says really is some amount of distance to attenuate enough so cross pollination it isn't heard as a problem.

Can omnis be used in XY configuration?

I'd suspect since it's an equal time arrival position you'd have maybe just a bit of the directional intensity part of the XY in the very high end?

What are the differences between nearfield and diffusefield omnis?

A high freq rise (relative.) Which is which? Rise on the diffused field?

Do omni condensers and dynamics behave in the same manner?

Probably? Pass.

And please feel free to add any other words of wisdom regarding the use of omni mics.

I use a QTC-1 pair on the kit, but my room is small so they go to the sides, low and to the rear a bit.
Cozy nice and room-dry like down in the gobos.

 

[omtayslick]

The use of two omni microphones as over heads can be common practice. Again as always you'll have to find the sweet spot. For you'll get a lot of the room in your recording.

What are the differences between nearfield and diffusefield omnis?
Do omni condensers and dynamics behave in the same manner?

I've found THIS to be helpful with some of your questions Tom.

Thanks for the replies guys. Very cool glossary Henry! The rest of you reading this thread may want to click on his link and save it!

I have been using a Sennheiser MD211U omni dynamic for a lot of things lately. It just sounds great on everything I've tried it on. I have two more of these on the way now, and I'm wondering if I can get all three on a drum kit without experiencing unintended consequences. Perhaps two overheads and one room mic? Room is treated and I have gobos, so omnis do fine in my environment.

 

[moresound]

Tom the three omni microphone question kinda threw me. I wasn't sure if you meant as in a decca tree configuration.

Using omni microphones as overheads do sound great believe me but not so much with certain types of music like heavy metal and the likes.

The one thing that is bad/good about omni overheads is the drummer has to be extremely good at dynamics while preforming his skills as an artist with his instrument. Then and only then will you to really appreciate the out come of omni overheads.
The recordings will sound very natural sounding and the skills of a proficient high-hat player combined with some show off playing with brushes on the snare are to die for with in a mix.

Just experiment with your placement for if you get them to far apart you will find a *hole* in the middle, and you don't want them to close to the drum set either.




TOM ..... I'm very surprised that you don't have any Naiant microphones!
HERE is the web site link and HERE is a shout out from Recording Hacks. At those prices you should have no less than two each in your microphone locker!!!

I've been finding different models for sale used on the net and been scooping them up left and right!
These will be collectors items for sure ..... well I'll have to ask MSHilarious how many he has put out there in the market.
I sure wish he would turn his PM function back on. He just comes and going through here so quickly now a days.

 

[mshilarious]

I am searching for info on the potential pitfalls and advantages of using multiple omni mics (up to 3) on sources such as a drum kit, etc.

Are omnis subject to the same considerations regarding Phase issues (3 to 1 rule etc.) as other types of mics?

Are we talking as overheads or as close mics? With stereo overheads the 3:1 rule doesn't apply as you aren't mixing the sources, you are recording left and right, and the phase differences are your stereo image with omnis. If you try to set a stereo pair that "obeys" the 3:1 rule you'll get a stupid wide stereo image (read: giant hole in middle). You'd need the overheads 10 feet apart or something silly.

For close mics and avoiding bleed, yes in theory you need to get a bit closer, but practically you probably already have your close mics at a higher ratio.

Can omnis be used in XY configuration?

Sure, but your stereo image will be limited to >10kHz or so, depending on diaphragm size. You would only do that if you wanted a very narrow stereo image. Omnis are traditionally spaced.

What are the differences between nearfield and diffusefield omnis?

Technically it's "free-field" and diffuse-field. Diffuse-field has signal arrivals from random (all) directions, free-field is a theoretical reflection-free environment (outside or an anechoic chamber). As the room gets large and you get relatively closer to source vs. size of room, then you approximate a free field. That is why you might think of it as "near-field"; because you'd probably want to select a free-field omni for close-micing.

The difference is diffuse-field omnis are designed to be flat off-axis, but they will have a rising high frequency response on-axis (again dependent upon diaphragm size, but let's use the same >10kHz figure). Free-field omnis are flat on-axis, but will have a decreasing high frequency response off-axis (in theory you don't care because there are no off-axis signals).

The amount of difference between on- and off-axis high frequency response is mainly dependent on diaphragm size; in theory a point-sized capsule will exhibit no difference. As capsule size grows, the difference gets larger. Some omnis are designed with accessories that can accent the on-axis response (and decrease the off-axis response), like the DPA APE (acoustic pressure equalizer) balls. This effect is frequency-dependent according to the size of the device; at the large extreme you get a boundary mic.

Normally you would select diffuse-field for applications like recording an ensemble and free-field for close micing, but truthfully if you have a HF shelving EQ (like on practically every mixer) you can convert from one to the other.

Do omni condensers and dynamics behave in the same manner?

As far as everything above, yes, but consider that due to operating principle omni dynamics have far less high frequency response than condensers, so it makes all points related to high frequency response moot. Pretty much all dynamics are designed for nearfield use because they don't have a choice; signal-to-noise will be unacceptable on most far-field sources.

And please feel free to add any other words of wisdom regarding the use of omni mics.

Use them, early and often.

 

[moresound]

Wait! There he goes again!

 

[mshilarious]

Just don't start singing Whitesnake or you'll get the beating the vocalist in that other thread deserves

 

[moresound]

Boom! Zoom! And he is Gone.

I'll have to find that thread.

 

[hueseph]

You can't use omnis in XY. Well you can but it's purposeless. Since omnidirectional microphones are non directional, the whole point of coincident pair is subverted. You can't get a stereo image if you use omnidirectional microphones as a coincident pair. The most useful way to use omnis is on a decca tree or a spaced pair. However on a drum kit, a spaced pair is the only practical solution. Decca tree will only be a source of frustration and very likely a load of phase issues.

You are going to get room sound. That is part of the purpose for using omnis.

 

[John Willett]

Can omnis be used in XY configuration?

If you want - but they will act like a single mic. at low frequencies and give you a little stereo spread at high frequencies. But this depends on what microphones you choose - a normal SDC omni acts like this (see polar-pattern below).

What are the differences between nearfield and diffuse field omnis?

A nearfield omni will have a flat frequency response, a diffuse field omni will have a treble boost to compensate for the loss of high frequencies in the diffuse field.

See below (top is nearfield omni, bottom is diffuse field omni):-

Do omni condensers and dynamics behave in the same manner?

As regards the polar pattern - yes.

And please feel free to add any other words of wisdom regarding the use of omni mics.

An omni is a pure pressure microphone and reacts only to changes in pressure (unlike a directional mic. that reacts to differences in pressure).

An omni mic. does not have any proximity effect and you get no bass tip-up as you get closer to the source as you do with a directional mic.

 

[moresound]

omni microphones are omnious.

 

[omtayslick]

Thank you everyone for taking the time to post your well thought out responses. All of my questions were answered fully.

The Sennheiser Md211u mic that I mentioned is an exceptional dynamic omni. Frequency response from 30 to 20K. Amazing clarity, and sweet sounding. Since I have been using it I don't even need to touch the EQ. These mics are discontinued, made in the 70's I think, and not very common. But if you ever get a chance to try one, do so. I doubt you'll be disappointed.

 

[John Willett]

Thank you everyone for taking the time to post your well thought out responses. All of my questions were answered fully.

The Sennheiser Md211u mic that I mentioned is an exceptional dynamic omni. Frequency response from 30 to 20K. Amazing clarity, and sweet sounding. Since I have been using it I don't even need to touch the EQ. These mics are discontinued, made in the 70's I think, and not very common. But if you ever get a chance to try one, do so. I doubt you'll be disappointed.

The MD 211U is certainly an exceptional mic.

But take care, don't drop it, the diaphragm is very close to the front end and dropping it can easily damage it.

You can download the PDF of the Owners Manual HERE.

 

[elbandito]

Since it seems that the OPs original questions have been answered, I'd like to pose a related one of my own: Do dual-diagrahm omnis have the same "neutral" off axis response as single diaphragm ones? If not, how much do they differ (in general, of course) and what benefits might there be to a dual diaphragm omni, of there are any at all?

 

[John Willett]

Since it seems that the OPs original questions have been answered, I'd like to pose a related one of my own: Do dual-diagrahm omnis have the same "neutral" off axis response as single diaphragm ones? If not, how much do they differ (in general, of course) and what benefits might there be to a dual diaphragm omni, of there are any at all?

It depends on what you mean by a "dual-diaphragm omni"?

If you mean making an omni by back-to-back cardioids as in a switchable-pattern mic. The answer is no as the single diaphragm one is much better in both frequency response and polar-pattern.

Sennheiser MKH 20:-



Sennheiser MKH 800 in omni:-



Please note that the MKH 20 frequency response is only drawn to 20kHz - the MKH 800 response is drawn to 50kHz - so for a meaningful comparison you should only use the 800 response below 20kHz.

Please also bare in mind that the MKH 800 is more than double the price of the MKH 20 - you can see clearly that the frequency response is not so smooth and the off-axis response is very different. And the MKH 800 is technically about the best dual-diaphragm mic. on the market when it comes to frequency response and polar-pattern, others would be a lot worse in this respect.



However, of you are talking about a dual-diaphragm mic. like the new DPA, where they use two small omni capsules wired together to give a higher output and lower noise - then it would be similar to a single diaphragm omni. Unfortunately DPA do not publish the polar-pattern so I can't link to it.