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Author Topic: Directional vs Omnidirectional Mics  (Read 1970 times)

zimzum

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Directional vs Omnidirectional Mics
« on: August 29, 2004, 07:09:47 pm »

Hi,
I have been hanging around on this board on and off over the last 2 years and i learn so much every time im here, thanks to all of you.
Ive been doing sound for a while and i only use directional mics for live sound. I was recently told about the advantages of using omnis over cardiods for SR which kinda surprised me. I was referred to the DPA microphones site where they have an article on the same subject (Ive attached a copy of the document)..Well it makes sense but i haven't yet had the privilege of using DPA mics so im not sure of its effectiveness in live applications.
So i was wondering, if any of you could comment on your experience using omnis for live applications ?
Cheers

zabi
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Tom Young

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Re: Directional vs Omnidirectional Mics
« Reply #1 on: August 29, 2004, 10:44:14 pm »

In certain live sound situations where there is the presence of critical ingredients such as very good acoustics, well designed and optimized ldspkr system, controlled stage volumes and disciplined players.....omnis may work successfully and they certainly bring their own characteristics to the party.

Back in the real world, where some or all of the above ingredients is lacking or absent, directional microphones provide benefits that cannot be ignored.  First, foremost and most obvious is simply that they reject off axis sound.  This means that leakage from other nearby sound sources (instruments, monitors) are greatly reduced in level compared to the on-axis sound. This also often means there is less feedback (not always). The other very important characteristic is proximity effect which has been used to very great effect by many players and singers and specifically male singers..... for decades and decades.

Omni's are smoother/flatter and provide better phase characteristics than cardioids.  If one was after "truer" reinforcement then perhaps omni's would prove to be superior over cardioids.  A good example of where they can work well is in reinforcement of a symphony orchestra. Here you will still find cardioids, in some positions, to be superior. But in other avenues of live sound where we are faced with less than optimum acoustics (presence of non-constructive reflections), the need for nearby loud stage monitors and the need to closely group the players so that they are musically connected, omni's will almost always not work as well as cardioids.

In commercial recording studios, where it is very likely to have far more controlled conditions, cardioids are used far more often than omni's. Along with the desireable directional characteristics they possess, the coloration that cardioids provide is also very desireable.
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Tom Young
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bgavin (Bruce Gavin)

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Re: Directional vs Omnidirectional Mics
« Reply #2 on: August 30, 2004, 09:27:08 am »

The one huge advantage of the omni is the lack of proxmity effect that over emphasises the bass.  They excel at close micing sources without fattening the bottom or making things muddy.

A true pressure omni is one where the rear side of the capsule is completely isolated from the front.  These are "end address" types, and not the "side-address" type, as are most large diameter condensers with capsule-adjusted multiple patterns.  

When compared to an end-address type, there is a slight loss of bass response in the side-address type due to the rear side of the capsule hearing low frequency waves at nearly the same instant as the front side, and the resulting phase cancellation.  This aside, side-address omnis perform well and have all the other desired characteristics.

Citing examples, the Audio-Technica AT4049 or DPA 4006 are examples of an end-address, pressure omni type.  The Audio-Technica AT4050 is a side address type, with multiple patterns including omni.  

As pointed out above, omnis work well in excellent conditions.  They will give you fits in most live venues due to feedback problems.  Omnis hear "everything".

DPA produces an excellent tutorial on omni vs cardioid with a focus on PA system use:

   http://www.ofgb.org/reference/music/dpa%20microphones/articl e%20-%20directional%20vs%20omni%20microphones.pdf
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Too Tall (Curtis H. List)

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Re: Directional vs Omnidirectional Mics
« Reply #3 on: August 30, 2004, 10:46:07 am »

zimzum wrote on Sun, 29 August 2004 19:09

Hi,

Ive been doing sound for a while and i only use directional mics for live sound. I was recently told about the advantages of using omnis over cardiods for SR which kinda surprised me


So i was wondering, if any of you could comment on your experience using omnis for live applications ?
Cheers

zabi



I get to use Pat Brown's favorite line. Smile
"Well it depends".


I have seen and used hundreds of omni mics while working live theater. The Lav mics for voice reinforcement of classic Broadway plays were almost exclusively omni.


This is something where you would think "gain before feedback" would rule, but omnis dominate. The main reason being visual constraints. Everything is driven by the fact that the mic must be as near invisible as possible. So the mic must be in the hair, taped against the side of the face or further down on the chest.


A cardiod mic is only as good as where you can aim it. If you can not aim it directly at the source (the mouth in this case) its pattern control works AGAINST you. A headset mic would work great as a cardiod because you can aim the center of the pattern at the mouth, but is unacceptable because it can be seen. So you use an omni, put it in her wig and do what you can with what it picks up of the mouth which is off axis where a cardiod would totally reject it.


Beyond that I have used the cheap line Shure wireless (early 90s vintage) that came with a little postage stamp omni and a cardiod lav. The frequency response on the cardiod was so uneven and peaky I could get better gain before feedback with the omni no matter where the mic was.


The other time I remember using an omni was doing sound for " Quartetto Gelato "
http://www.quartettogelato.ca/
in the small theater at MSU. They had one very nice omni mic I used ground plane in the center of where they were sitting. It worked great meshing with their natural acoustic stage sound. Any cardiod I have ever used would not have sounded as natural, though I may have been able to make them louder, but that was not the goal. (Keep in mind I have never worked in a studio and do not get to work with the kind of microphones they have access to so there may be a cardiod that would have worked as well).
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Too Tall
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