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Reporter Mics (omni, noise, etc.)

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Reporter Mics (omni, noise, etc.)

Postby Gizmo1977 » Tue Jun 08, 2021 12:49 am

I was trying to find some information about reporter microphones and saw that the most famous ones seem to be omni dynamics.
Funny I also found an article where I understood (mind English is not my mother language) Hugh Robjohns says that omni dynamics are preferred "because of their reduced susceptibility to handling and wind noise (compared to directional dynamic mics), and the fact that dynamic mics are inherently cheaper to make than electrostatic types".
- Why does an omni microphone get less handling noise? Less pieces inside or what?
- In an ENG, reporter scenario and the kind isn't the use of an omni more prone to get noise from everywhere in busy environments than a cardioid or supercardioid? I imagine a demonstration, parade. etc. and would consider any other dynamic one. In really noisy sets like car races I've seen the famous Coles 4104 which is a bidirectional ribbon (and I would think a cardioid pattern would be better),

I guess reporter mics' shape (particularly long) has to do with handling, avoiding medium shots where the hands and elbow would be "cut", ease to aim guest's mouth (versus a regular SM58). Am I wrong?

Thanks for all your comments and suggestions :)
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Re: Reporter Mics (omni, noise, etc.)

Postby Mike Stranks » Tue Jun 08, 2021 7:21 am

I started using omni mics for radio interviewing back in the 1970s.... :)

The advantage for me over a directional mic such as a cardioid is that you don't have to constantly wave it around and thrust it at someone to be sure of a good pickup.

(Recording interviews in noisy environments is another matter. If at all possible, don't do it and find somewhere quieter - I have some anecdotes about where 'somewhere quieter' might be - or use some form of two-mic, closely-worked, arrangement.)

The other advantage is the removal of proximity effect. so if the mic is moved around you don't get the 'up close' artefacts that a cardioid would give you.

Physical/seating/standing arrangements for interviews, such that the interviewee remains relaxed and not over-conscious of the technology are a topic in their own right.

I haven't found that the fact that the mic is an omni in itself reduces handling noise or the effects of wind-noise. All mics handheld for speech need to be handled carefully. I was taught various techniques for keeping this to a minimum. The cable is often a source of noise and rattle.

I recall one set of interviews on a very windy airfield where I was required to interview charity-parachutists immediately after they landed. Not having specialist NR 'blimps' available I had to resort to a dense foam windshield over-covered with a 'dead kitten'. The frequency response suffered a bit - fixed in post - but the wind-noise was all but eliminated.
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Re: Reporter Mics (omni, noise, etc.)

Postby Tim Gillett » Tue Jun 08, 2021 8:13 am

Gizmo1977 wrote:...Funny I also found an article where I understood (mind English is not my mother language) Hugh Robjohns says that omni dynamics are preferred "because of their reduced susceptibility to handling and wind noise (compared to directional dynamic mics)...

Yes that's right, all things being equal the omni dynamic has less wind and handling noise than the directional dynamic. The omni mic's diaphragm is only exposed to the air on its front side but closed at the back, so is less vulnerable to wind blasts. Maybe proximity effect (bass boost close up) also exaggerates wind noise in the directional mic because the wind registers as very close to the mic.
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Re: Reporter Mics (omni, noise, etc.)

Postby Hugh Robjohns » Tue Jun 08, 2021 8:59 am

Gizmo1977 wrote:- Why does an omni microphone get less handling noise? Less pieces inside or what?

It's because of its 'operating principle'.

There are two fundamental types of microphone: pressure operated (which always have omni polar responses) and pressure gradient* (which always have fig-8 responses).

*Sometimes also known as 'velocity microphones'

Cardioid -- and (sub-) hypo-cardioid, hyper-cardioid and super-cardioid-- all rely on different ratios of the two operating principles. (Cardioid is 50/50).

An Omni pressure operated mic capsule is built (in simple terms) as a diaphragm stretched across an empty box -- a bit like a drum. So the diaphragm movement can only be due to the difference between the static air pressure inside the box versus the changing air pressure (due to passing sound waves) outside the box.

This happens to provide a pretty flat and extended frequency response (right down to 10Hz or so in many cases).

In contrast, the pressure gradient capsule is just a diaphragm stretched between two mounts, but open to the air on both sides. In this way the diaphragm movement is due to the pressure difference on each side of the diaphragm -- and that's what makes it sensitive to sounds from some directions but not others others. Sounds arriving along the plane of the diaphragm don't create a pressure difference across it, so it doesn't move, which is which it's deaf to sounds from the sides and directly above/below.

The diaphragm also moves in different directions if a compression waves arrives at the front or rear, so the front and rear 'pickup lobes' have opposite polarities.

However, at low frequencies the wavelength is very long, and that results in a phase difference between the sound wave at the front and at the back (which it passes a short time later) being very small. That means the actual pressure difference across the diaphragm is very small and so it doesn't move much.

In contrast, at higher frequencies the wavelength is much shorter so the pressure difference is much larger and the diaphragm moves much more.

The upshot of all this physics is that a PG capsule has a frequency response which is inherently much stronger at high frequencies than low -- it slopes upwards at 6dB/octave.

Obviously, that's not much use as a microphone, so the designers arrange the diaphragm suspension to be very floppy at low frequencies and much stiffer at high frequencies in a way that largely rebalances the natural frequency response, since the diaphragm finds it easier to move at LF where the pressure difference is small, but harder to move at HF when the pressure difference is large.

there is a practical limit to how floppy the diaphragm suspension can be, which is why the low frequency response of directional mics tends to be less extended and have a steeper roll-off than omni mics. Few cardioids have a bass response below 40Hz, for example, and many roll-off even higher.

But... the downside of this engineering is that, since the diaphragm can't tell the difference between the wanted LF sound waves and any other low-frequency vibration (like mechanical handling vibrations, or wind) it tends to reveal the latter very well, and so is said to be much more sensitive to handling and wind noise than a pressure operated (omni) mic.

And that (in simplistic terms) is why a fig-8 mic is much more prone to handling and wind noise than an omni.

And since cardioid (and all the other directional patterns) involve some portion of pressure gradient operation, they also suffer the same handling noise issues to varying degrees. Fig-8 is worst, then super- and hyper-cardioid, then cardioid. The sub- or hypo-cardioid suffers the least while omni barely suffers at all.

Having said that, even omni capsules will reveal handling noise and wind in extremis, which is why the capsules are usually mounted on internal shock-mounts and reporters are taught appropriate handling techniques...

So, if you're going to have a reporter holding a mic and waving it around, an omni is a very good choice.

Another factor is that pressure operated capsules don't suffer proximity effect (something that's related to the PG capsule design again) so the tonal quality wont vary too much if the reported holds the mic 18 inches away from the interviewee, but stuffs it right under his own nose!

- In an ENG, reporter scenario and the kind isn't the use of an omni more prone to get noise from everywhere in busy environments than a cardioid or supercardioid?

Potentially... although there are three ways of controlling unwanted ambient sound. One is to use a more directional mic to try and reject ambient sounds while favouring the wanted sound -- which is why hyper-cardioids and other more directional mics are often used. A second is to get the mic closer to the source so that the ratio of wanted to unwanted changes in your favour. This is why lavalier mics are often used, and in very noisy environments, headset mics.

Moving a directional mic closer invokes the proximity effect and the sound gets bass-heavy, but you can move an omni much closer and retain the natural sound tonality.

Short shot-gun mics are often used for ENG purposes -- typically inside blimps or covered in 'dead cats' -- as they reject quite a lot of high-frequency ambient sound. The short shot-gun mic employs an 'interference tube' in front of a hyper-cardioid capsule. The tube improves the rejection of high frequency sounds from the sides while favouring sounds from directly in front. However, there are some significant downsides to their use as well, and if they are not aimed accurately the sound quality suffers enormously!

In really noisy sets like car races I've seen the famous Coles 4104 which is a bidirectional ribbon (and I would think a cardioid pattern would be better),

You'd be wrong in your thinking! ;)

The Coles 'lip-mic' exploits the third way of excluding ambient sound. Since it is bi-directional (fig-8) is picks up ambient sound from both the front and back, but in opposite polarities, and since ambient sound level is, by definition, consistent in all directions it tends to cancel itself out.

However, the presenter's voice reaches the front of the diaphragm massively louder than it reaches the rear (because of its proximity) , so it doesn't cancel out very well... and therefore the ratio or wanted to unwanted sound is very much improved.

Also, because the voice is so close the proximity effect is very strong, boosting the bass of the voice. Consequently, the designers don't need to adjust the diaphragm suspension to restore the bass response in the same way that they do in conventional PG mics. As a result, the bass response falls off steeply for distant -- meaning ambient -- sounds and, since most sound ambient energy is at low frequencies this gives a further useful reduction in the ambient sound level being captured.

I guess reporter mics' shape (particularly long) has to do with handling, avoiding medium shots where the hands and elbow would be "cut", ease to aim guest's mouth (versus a regular SM58). Am I wrong?

It's to give more physical 'reach', and to to make handling easier.
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Re: Reporter Mics (omni, noise, etc.)

Postby Gizmo1977 » Wed Jun 09, 2021 11:17 pm

Mike, Hugh, I’m just overwhelmed!!!
They’re such pedagogic and detailed answers I can’t thank enough!!
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