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Omni mic orientation...in an imperfect world

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Omni mic orientation...in an imperfect world

Postby SableTones » Tue May 01, 2012 1:48 pm

Hello. I have one more question for a recording gig next saturday (SOS & all have already given great advice)

Large choral event in a Cathedral. I have one track left from my 8, and one unused condensor (Rode NT55/omni)

What seems like hundreds of lower school children, for 2 songs only, converge upon and surround the conductor and filling the space in front of the raked choir seats. They will be literally on top of my Mid/Side rig (M/S positioned optimally for other singers), and they are fully the width of the Nave both sides. Some of them are slightly behind 180 deg line of the conductor. (ORTF high above conductor)

I want to put/try a Rode NT55/OMNI on a regular mic stand at less than optimum height (4/5'?)and only 2' BEHIND conductor! (there is a movement performance also and this is as far back i am allowed)

Novice question: how should i best orientate/point the mic? I am guessing just upward of horizontal (straight at conductors back who is on a small podium)

any advice?

cheers
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Re: Omni mic orientation...in an imperfect world

Postby Sam Inglis » Wed May 02, 2012 2:03 pm

I'm not sure how this affects what you do with the Rode, but the one time I recorded a children's choir, I found that the sibilance was absolutely deadly. All the condenser mics I tried just made them sound like fireworks going off in a snake pit, and the only thing that worked at all was a ribbon mic.
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Re: Omni mic orientation...in an imperfect world

Postby Hugh Robjohns » Wed May 02, 2012 2:18 pm

That's not an uncommon problem, Sam. You can sometimes tame the HF response of an omni by arranging for the main sound to arrive off-axis -- it depends whether the mic is equalised for direct (the norm) or diffuse sound fields. If the former, then pointing the mic straight up will tame the HF quite nicely -- almost ribbon mic-like!

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Re: Omni mic orientation...in an imperfect world

Postby shufflebeat » Wed May 02, 2012 3:34 pm

Hugh Robjohns wrote:That's not an uncommon problem, Sam. You can sometimes tame the HF response of an omni by arranging for the main sound to arrive off-axis -- it depends whether the mic is equalised for direct (the norm) or diffuse sound fields. If the former, then pointing the mic straight up will tame the HF quite nicely -- almost ribbon mic-like!

Hugh

Hugh, a while back you discussed the technique of using an omni against a flat surface in the style of a pressure zone mic. Would this be a worthwhile experiment for the reasons discussed above?
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Re: Omni mic orientation...in an imperfect world

Postby Hugh Robjohns » Wed May 02, 2012 4:24 pm

You certainly can place an omni on a flat surface and benefit from the boundary layer effect. Don't think that would be hugely helpful in this instance, though... although it is an interesting thought to try putting the mic on the floor!

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Re: Omni mic orientation...in an imperfect world

Postby Jeraldo » Wed May 02, 2012 8:40 pm

Pointing is everything with omni's, and often 90 degrees is about flat. So you can "gradiate" between between lift and flat and dark.
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Re: Omni mic orientation...in an imperfect world

Postby John Willett » Thu May 03, 2012 8:25 am

Jeraldo wrote:Pointing is everything with omni's, and often 90 degrees is about flat. So you can "gradiate" between between lift and flat and dark.

NB: this is only true of diffuse-field omnis with a treble lift.

It actually works very well - I recorded several piano CDs like this.

Image

But - a nearfield omni, with a flat frequency response, will show a treble droop when you turn it off-axis.
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Re: Omni mic orientation...in an imperfect world

Postby John Willett » Thu May 03, 2012 8:30 am

shufflebeat wrote:

Hugh, a while back you discussed the technique of using an omni against a flat surface in the style of a pressure zone mic. Would this be a worthwhile experiment for the reasons discussed above?

If you do this, you will need a TURTLE


Image

It protects the mic. from being walked over and includes Rycote "Lyre" suspensions to minimise vibration noise from the floor.
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Re: Omni mic orientation...in an imperfect world

Postby Jeraldo » Thu May 03, 2012 12:21 pm

To cover every base, which I didn't think was necessary here, I should have said that all omni's exhibit HF roll off to about 6k when moving off axis. Some omni's are compensated for a more distant placement by an HF lift, which determines the roll off and when then determines pointing to achieve a desired effect. The lift is not the same, and generally varies from about 2 dB to 8 dB, and is usually peaking but is sometimes more of a shelf.

Of course, if you don't fancy a particular omni's HF profile, one need only to reach for the EQ.

Does that cover all the bases?
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Re: Omni mic orientation...in an imperfect world

Postby Jeraldo » Thu May 03, 2012 12:39 pm

John Willett wrote:
shufflebeat wrote:

Hugh, a while back you discussed the technique of using an omni against a flat surface in the style of a pressure zone mic. Would this be a worthwhile experiment for the reasons discussed above?


If you do this, you will need a TURTLE


Image

It protects the mic. from being walked over and includes Rycote "Lyre" suspensions to minimise vibration noise from the floor.


No, the OP does not need a turtle.


I can only imagine this contraption on a wall or ceiling!


To paraphrase a comment existing elsewhere today by a moderator:

"He (the OP) could take a look at a lot of [mounting options].... but I hope their manufacturers and distributors don't all pile into this thread to start promoting them!"

It is interesting that John-who sells this product, BTW-has always discouraged anyone from surface mounting a mic in the way his product does rather than use a "real" boundary mic. Now he seems fine with the idea-no doubt because he sells a product to do so.

At least you could identify your relationship to the product, don't you think?




For the OP, you can put an omni against any surface, flat or not, with different boundary effects. This includes walls, ceilings, pillars (big ones are great), piano lids, etc. Gaffer tape is just as good as anything. With a real omni, you will get very, very little-if any at all-shock born transmission. You will get acoustically transmitted sound, of course. There is no reason not to place on omni directly on the surface-in fact, there are advantages to doing so.

If you want some mechanical protection, there are various metal grids from hardware stores available that offer much less acoustic shadowing than the product John offers for sale, and just as rugged-not to mention hugely less expensive.

For directional mic's, which are prone to shock transmission, you can either roll them off or use a simpler and far less costly solution for shock control, along with either no mechanical protective device, or a device which offers-again-less acoustic shadowing.

BTW, you can also mount an omni with the capsule in a non perpendicular manner-either parallel, or at an angle which will produce a variety of HF effects.


For the OP and others: see if you can access a Crown publication from several years ago. It is an 10 pager with diagrams, illustrating everything that happens to mic's when they are placed on various boundaries of all sorts of shapes, and the effects intersecting boundaries produce. It's a great and informative read.
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Re: Omni mic orientation...in an imperfect world

Postby The Elf » Thu May 03, 2012 1:12 pm

Jeraldo wrote:For the OP and others: see if you can access a Crown publication from several years ago. It is an 10 pager with diagrams, illustrating everything that happens to mic's when they are placed on various boundaries of all sorts of shapes, and the effects intersecting boundaries produce. It's a great and informative read.
I imagine you mean THIS?

Very useful document. I used to have a similar (better in some ways) document by Shure that I picked up when I bought my SM91s, but I can't seem to find that one anywhere.
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Re: Omni mic orientation...in an imperfect world

Postby Hugh Robjohns » Thu May 03, 2012 7:12 pm

John Willett wrote:If you do this, you will need a TURTLE

maybe, but he'll never find a bank willing to offer a mortgage to get one!

Stop the drive-by promotion posts please mr W.

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Re: Omni mic orientation...in an imperfect world

Postby Urthlupe » Thu May 03, 2012 8:16 pm

The Elf wrote:
Jeraldo wrote:For the OP and others: see if you can access a Crown publication from several years ago. It is an 10 pager with diagrams, illustrating everything that happens to mic's when they are placed on various boundaries of all sorts of shapes, and the effects intersecting boundaries produce. It's a great and informative read.
I imagine you mean THIS?

Very useful document. I used to have a similar (better in some ways) document by Shure that I picked up when I bought my SM91s, but I can't seem to find that one anywhere.

Interesting, thank you Elf and Jeraldo.

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Re: Omni mic orientation...in an imperfect world

Postby John Willett » Thu May 03, 2012 9:22 pm

Jeraldo wrote:
John Willett wrote:
shufflebeat wrote:

Hugh, a while back you discussed the technique of using an omni against a flat surface in the style of a pressure zone mic. Would this be a worthwhile experiment for the reasons discussed above?

If you do this, you will need a TURTLE


Image

It protects the mic. from being walked over and includes Rycote "Lyre" suspensions to minimise vibration noise from the floor.

No, the OP does not need a turtle.


I can only imagine this contraption on a wall or ceiling!


To paraphrase a comment existing elsewhere today by a moderator:

"He (the OP) could take a look at a lot of [mounting options].... but I hope their manufacturers and distributors don't all pile into this thread to start promoting them!"

It is interesting that John-who sells this product, BTW-has always discouraged anyone from surface mounting a mic in the way his product does rather than use a "real" boundary mic. Now he seems fine with the idea-no doubt because he sells a product to do so.

At least you could identify your relationship to the product, don't you think?



The Turtle is not "my" product - I saw it at Musikmesse and thought it such a great idea I persuaded the manufacturer to let me distribute it in the UK.

And I put a winkie in the post and the link was to my website - so it was pretty clear.

I have never said to anyone not to mount a mic. in this way and to use a "real" boundary mic.

But there is now only one really good boundary mic. on the market - and that is the Schoeps (now that Neumann have discontinued the GFM132).

Yes, of course you can gaffer tape a mic. to a wall or floor, or whatever to make it a boundary mic.

The Turtle is ideal for the floor as it protects the mic. and provides excellent vibration protection - and the designer talked very closely with Schoeps during the design stage, so it does work very well.

But my suggestion was a bit tongue-in-cheek as I clearly indicated by putting a winkie in the post.
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Re: Omni mic orientation...in an imperfect world

Postby shufflebeat » Thu May 03, 2012 11:21 pm

The Elf wrote:
Jeraldo wrote:For the OP and others: see if you can access a Crown publication from several years ago. It is an 10 pager with diagrams, illustrating everything that happens to mic's when they are placed on various boundaries of all sorts of shapes, and the effects intersecting boundaries produce. It's a great and informative read.
I imagine you mean THIS?

Very useful document. I used to have a similar (better in some ways) document by Shure that I picked up when I bought my SM91s, but I can't seem to find that one anywhere.

That is a seriously helpful document. I've read descriptions of the 'PZMs on a hinged panel' arrangement but couldn't quite picture the finished article. I'm sure the concept is pretty obsolete now but I'm tempted to give it a go if just for curiosity's sake.

Cheers for that.
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