Topic: Omni configurations

[Phil Zone]

Hi

In reading about different mic configurations such as din and orft they all says cardioid mics, so can you use them with omnis? And when using omnis what's the best setup? And when outside, when Im using omnis, what is the best configuration?

Thank you

[Chuck]

Good idea for a thread!

I'm getting good results using Audix Micro omni's split 12" - 24".
The closer I am to the source, the smaller the split I use.

[Phil Zone]

Good idea for a thread!

I'm getting good results using Audix Micro omni's split 12" - 24".
The closer I am to the source, the smaller the split I use.

Are you using an ab setup?

[Chuck]

I do point them at the stacks, because they are still directional in the higher frequencies. I should try it A/B sometime just to see how that changes things.

[thunderbolt]

I see at the Sengpielaudio site that AB120 gives an SRA of only 50 degrees.  Still trying to get the geometry/distance relationships straight in my head.  I'm going to try .6 m outdoors at a small amphitheater (60' from stage), which gives an SRA of 118 degrees.

[John Willett]

Hi

In reading about different mic configurations such as din and orft they all says cardioid mics, so can you use them with omnis? And when using omnis what's the best setup? And when outside, when Im using omnis, what is the best configuration?

DIN and ORTF are for cardioid microphones only.

If you use omnis like this it will work but cannot be called DIN or ORTF.

There are many many ways to set up omnis and you choose the best configuration depending on the individual situatiuon.

For recording a solo piano I would normally use 20cm spaced omnis pointing slightly out at about head high and about 2m from the piano (and then move to suit the exact situation).

For a choir, I often use omnis on a Jecklin or Schneider disk.  Though some people often use a wider spaced set-up for this.

I also sometimes use an MS or ORTF pair with a pair of omnis on the same long bar spaced about 60cm apart for room ambience.

I hope this helps.

[Gutbucket]

Here's a link to the Williams diagram showing Stereo Recording Angle as linked to microphone spacing for omnidirectional microphones-
http://www.mmad.info/MAD/2%20Ch/SRA%20Omni.pdf

The above is hosted on Michael William's website.

Comments:
Recording amplified PAs with two widely spaced stacks producing identical mono bass information from a distance is standard procedure around here but is an outright oddity in the acoustic recording world.  That means the normal guidelines don't necessarily apply.  Wider spacings that would be unwise for acoustic recording can work very well.  When recording amplified stuff in outdoor amphitheaters and big outdoor festival setups I'd start with a 3' (1m) spacing for a 2-channel stereo pair of omnis.  Actually in those situations I run a three main mic setup with either an omni or a cardioid in the center, which safely allows me to space the omnis twice that distance (6' / 2m) from each other and the recordings are better for it.  It's possible to space two microphones that much or even considerably more and make great section recordings, but doing so becomes more of a gamble unless you can accurately monitor the setup.  Part of the attraction of using a third mic in the center is that it eliminates most of that over-wide risk.  A SBD patch can work much the same way as the center mic, allowing for safe use of and often benefiting from wider spacings.

Besides modifying the SRA, changing omni spacing changes the apparent quality of the bass and the nature of the surrounding 'room' sound.  When listening back, those changes are likely to be more obvious than changes in SRA .    Wider spacing lowers the frequency at which the mics are decorellated and changes the timbre of the bass.  If you can listen on very isolating headphones while adjusting the microphone the spacing, you can 'tune' the spacing to find the most appropriate spacing and a few inches one way or the other can make a big difference in the quality of the bass, while not changing the SRA that significantly.  You probably won't want to make the effort to do that every time you run spaced omnis, but it can be very instructive to play around with a few times to get a good grasp on how it works in a practical sense.  That lower decorellation frequency is what produces the big, wide, enveloping sound of wide spaced omnis.  It’s also partly why they combine very well with a SBD out or with a center mic without producing 'phase' problems that can occur when mixing together pairs of microphones that were placed in close proximity to each other.

Besides going wider than what the William's diagram suggests, you can go narrower if you put a baffle between the mics, effectively blocking sound from "crossing-over" to the other microphone from the opposite side, at higher frequencies (the baffle has no effect at low frequencies).  That's where the Jecklin and Schneider discs come in to play.  I don't know why those things aren't called Blumlien disks, since as far as I know; Alan Blumlein was the first to use a baffle between head-spaced omnis back in the early 1930's before he had access to figure-8 microphones and produced the microphone technique which bears his name to this day.

[noahbickart]

Don't discount using an omni as the M microphone in an M/S array.

[Chuck]

I'd say experiment if you have the opportunity to. It's very handy knowing how omnis sound with different spacings. Especially for outdoor festivals, as wind doesn't affect omnis as much as it does more directional mics.

[F.O.Bean]

I like the Healy method for omnis

[tgakidis]

AB, 3 foot split for Outdoor OTS recordings.  I have evven done that onstage a few times.

[cashandkerouac]

I like the Healy method for omnis

Healy Method: "[T]he near coincident 180 degree Omnidirectional microphone method. Here a pair of Omnidirectional microphones are placed approximately ear distance apart and oriented at 90 to the sound source, facing outward."  (http://www.oade.com/Tapers_Section/streicher-healy.html)

unless you're really close to the stage i think that A-B 3 ft. apart is the way to go.

[F.O.Bean]

I like the Healy method for omnis

Healy Method: "[T]he near coincident 180 degree Omnidirectional microphone method. Here a pair of Omnidirectional microphones are placed approximately ear distance apart and oriented at 90 to the sound source, facing outward."  (http://www.oade.com/Tapers_Section/streicher-healy.html)

unless you're really close to the stage i think that A-B 3 ft. apart is the way to go.

Yea I agree. I have only used the healy method when I'm FOB/DFC

[Gil]

I like the Healy method for omnis

Funny; that was probably my least favorite configuration with omnis. Outside of a 2'-3' split, I'm pretty sure the best results I managed were running them with NOS spacing and angle.

[Gutbucket]

unless you're really close to the stage i think that A-B 3 ft. apart is the way to go.

Even close to the stage I'd prefer to space them a couple feet usually, maybe more.  Part of what makes omni recordings attractive sounding to me is the open sound and envelopment which only comes from using enough spacing.

I think part of why Healy Method is as popular as it is around here has a lot to do with using standard narrow-spaced mounting bars to set it up which everyone already has, plus its easier to setup on a single stand stand than spacing the mics 3'.  Putting a baffle between similarly narrow-spaced omnis is a PITA and and can make for a sight-line blocking problem but gets you a few more octaves of seperation through the mids, even though the bass will still be mono.  If I had to mount them that close together I'd want to use a baffle and would compensate for any apparent reduced sensitivity in the highs with EQ.

Healy method will produce a rather mono recording in the bass region through the lower mids, with significant difference information really only coming into play in the mids up into the treble range.   That actually makes it appropritate for headphone listening (it's similar to switching in a 'cross-feed' circuit on a headphone amp) more so than for loudspeaker playback, and as I understand it that was Healy's intention- as an on-stage mic setup providing ambient stage sound into the Dead's then new IEM setup.  It's pretty much a binaural setup without a dummy head.

Some prefer recorings that are somewhat mono heavy and there's nothing wrong with that if you do.  Cardioid X/Y recordings are that way, as are near spaced cardioid setups which don't have much angle between mics such as PAS using standard near-spaced mounting bars.