Types of Microphone

[Stuart Graham]

Hi

I've been busily reading up on audio, to help me decide on microphone purchases, and have found some terminology a bit confusing. I guess there are lots of other people with the same problems too. I've prepared a list of basic questions I would like answers to:

1. What is the definition of a shotgun microphone? Does it simply refer to the microphone being mounted in a long tube or does it relate to its pickup pattern or both?
2. Is a polar microphone the same as a shotgun microphone?
3. Do all shotgun microphones have pickup patterns like this..?
http://upload.wikimedia.org/wikipedi...irectional.png
3. What is a short gun microphone?
4. What is a short shotgun microphone? Is it the same as a short-gun microphone?
5. How can a microphone be referred to as both shotgun and super cardioid? If this:
http://upload.wikimedia.org/wikipedi...irectional.png
- is a shotgun pickup pattern how can the microphone also be described as having a pickup pattern like this:
File:Polar pattern supercardioid.png - Wikipedia, the free encyclopedia
For instance the R0DE NTG-3:
RØDE Microphones - NTG-3
- is described as having a supercardioid directional pattern but is called a shotgun microphone.
6. What does line + gradient mean? Lots of Audiotechnika microphones describe their pickup pattern in this way, is it a way of saying hypercardioid or shotgun?
7. What does Lobe or Lobed mean when referring to pickup patterns? For instance lobe/cardioid, supercardioid/lobe, hypercardioid/lobe.
8. Should a microphone purchaser ignore the manufacturer's pickup pattern description and only look at a microphone's polar diagrams?
9. Why can't all the companies stick to one way of describing audio pickup patterns?
10. Will these moronic questions ever cease? They have, for the time being at least.

Thanks!

[Steve House]

Good questions, due in part to the somewhat confusing terminology various people use and the way some terms are interchanged in casual conversation.

The polar pattern of a microphone is the shape of a graph of its pickup pattern: Omnidirectional, Cardioid, Hyper-Cardioid, Super-Cardioid, and Lobar.

"Shotgun" refers to a certain physical type of mic, named after its appearance, and it describes the manner in which it achieves its directionality. They consist of a tube with ports down the side with the mic capsule at the bottom. Sounds entering the tube from on-axis interacts inside the tube with the sounds coming in through the side ports, the two interfering with each other in such a way as to partially cancel sounds coming from off-axis and reinforce those arriving on-axis. The tube is called an "interference tube" from the physical principle on which it operates and the mic is referred to as a "line gradient" microphone. Short shotguns ("short 'guns") have shorter tubes and are somewhat less directional than are long shotguns.

There are other ways a mic can be made directional besides an interference tube and the most directional are called hypercardioid or supercardioid depending on how tight their pattern is. Thus the Schoeps CMC641 small diaphram mic is called a "supercardioid" by the manufacturer because its pattern is tighter than the typical small-diaphram hypercardioid might have, yet it is not a shotgun because it doesn't use the interference tube principle. But just to make it confusing, you'll read some authors who call any highly directional mic a shotgun. So all shotguns are supercardioids but not all supercardioids are shotguns.

A hypercardioid or a super-cardioid mic is most sensitive along its axis of the mic and its sensitivity falls off falls off as you go around the circle. The super' falls off quicker than the hyper' as you move off of dead-ahead. By the time you get to 90 degrees either side of straight ahead both their sensitivities are quite reduced. Going further back the sensitivity gets even less, but both of them regain some sensitivity again as you get to dead aft. They're still not as sensitive there as to the front however. Just plain cardioid doesn't fall off very much forward of the 90 degree mark but drops fairly quickly after that point, and doesn't have the rear-pointing increase - it's more like a hemisphere.

One of the characteristics of the interference tube principle that makes a shotgun a shotgun is it has a "lobar" pattern. The is a variation of the super-cardioid, think of it as a sub-category if you like. When you look at what happens to the pattern as you move in the area from +/- 90 degrees from on-axis on around to straight back, a mic with a "lobar" characteristic will have a couple of narrow spikes on increased sensitivity at around 120 and 150 degrees. Non-interference tube hyper' and super' mics like the Schoeps CMC641 mentioned before don't have those spikes in the pattern.

Another characterisitic of the interference tube design is its directionality is very frequency dependent, super-cardioid when you look at frequencies in the mid-range but becoming almost omnidirectional at low frequencies. This is why its not a good choice for normal interiors, since in a normal room there's a lot of reflected sound coming at the mic from the sides and rear and its lower frequencies portions will still be picked up clearly, interacting with the direct sound arriving on-axis and colouring it. The result is that "recorded in the bottom of a well" kind of ringing distortion you often hear in event video.

So if you see a mic described as "supercardioid, line+gradient" interpret that as meaning a highly directional mic with a lobar pattern that is built on the interference tube principle.

[Jordan Block]

Steve, you appear to have swapped your super- and hyper-cardioid explanations. Super is a wider pattern up front with greater rear rejection. Hyper is tighter up front with a little more rear pickup.

[Stuart Graham]

Thanks Steve, that's a great set of answers and extremely helpful.

I'm still a bit confused about the difference between supercardioid and hypercardioid. I thought super' was less directional than hyper'?

These diagrams sort of show what I mean...

http://www.sweetwater.com/shop/studi...s/cardioid.gif
http://www.sweetwater.com/shop/studi...ercardioid.gif
http://www.sweetwater.com/shop/studi...ercardioid.gif

Though from the diagrams it looks like the hyper' and super' are almost the same except for the bigger rear pickup area on the hyper'.

What types of mic are good for recording interiors?

I guess a non-shotgun supercardioid mic (for instance the Sennheiser ME65 mic head) would be a good all-rounder for mounting on a boom to capture ambience and speech indoors?

[Paul R Johnson]

The Sennheiser ME65 is designed to be a hand held microphone, designed for singing into, primarily. As a result, it could be used on a boom, but the frequency response is optimised for close in use when proximity effect gives a bass boost - using them at a distance means they are a little thin sounding. In hand held microphones, supercardioid is used to denote a microphone that has the ability to allow a little more gain before feedback when used on stage with a PA with monitors. The wedge type monitors usually found on the stage floor, looking up at the performer need plenty of volume, and the polar pattern needs to try to ensure that the mic is least sensitive in the direction the loudest sound is coming from.

Probably also worth noting that mic descriptions are also biased to Countries and therefore manufacturers - so here in the UK, I've noticed people tend to talk about hyper cardioids when people in the states call them super cardioids, despite what the manufacturers calls them. There's also technical vocabulary that does describe what principle a microphone uses - so 'pressure operated' and 'pressure gradient' are terms that get bandied about. Also, it's quite common here to hear shotguns refered to as rifles - same mic, same use - different names. Remember Shure always used to call their microphones uni-directional, not cardioid - with the old 545, 515 and 565 called unidynes.

[Mike Demmers]

Originally Posted by Stuart Graham

Hi
8. Should a microphone purchaser ignore the manufacturer's pickup pattern description and only look at a microphone's polar diagrams?
9. Why can't all the companies stick to one way of describing audio pickup patterns?

Looking at the polar patterns of the better microphones is really the best way to get a feel for this, especially on the major manufacturers sites (where there is at least a good chance you will be getting accurate data ;-) ). Neumann's site, for example:

Georg Neumann GmbH - Products/Current Microphones/KMR 82 i/Technical Data

has a nifty little pop up that lets you click on polar response charts at 6 or 8 different frequencies for their shotguns. This shows very clearly how the polar response changes over the audio range. Comparing short and long shotguns in this way will give you a feel for the difference.

It's also instructive to look at the different patterns on a completely different kind of mic, for example the large diaphram TLM-170:

http://www.neumann.com/?lang=en&id=c...id=tlm170_data

which achieves a hypercardiod pattern in a completely different way (no interference tube). The omni and figure 8 pattern polar charts are enlightening as well. (These are a bit heavy to boom with though ;-) )

Part of the problem with the inconsistent descriptions is that there is quite a lot of difference in the polar responses between even different mics of the same basic type, since some parameters can be enhanced at the expense of others in the design of these mics.

All directional mics involve compromises of one sort or another.

In the end it will come down to a personal and situational choice.

-Mike

[Steve House]

Originally Posted by Jordan Block

Steve, you appear to have swapped your super- and hyper-cardioid explanations. Super is a wider pattern up front with greater rear rejection. Hyper is tighter up front with a little more rear pickup.

You are correct, I had a senior moment there.

[Stuart Graham]

Thanks for enlightening me everyone! You've been a great help

I'm really pleased I was just promoted to major player :) Methinks Obstreperous Rex is some way off!

[Ty Ford]

Originally Posted by Steve House

You are correct, I had a senior moment there.

But Schoeps does call the cmc641 a supercardioid.

SCHOEPS supercardioids

Regards,

Ty Ford

[Anthony Ching]

Although there're mathmetic definition on super and hyper, in pratical market, these are the same thing: higher rejection at about 135 degree and less rejection on 180 degree compared with cardioid.
Suggest check the polar pattern (real measured charts, not a simplified icon). Especially different frequencies. Most of the microphones exhibits different polar pattern across frequency spectrum, such as a cardioid at 100Hz, and super cardioid at 1KHz.
The more uniform polar pattern across frequencies, the better.
A pratical way, try the microphone yourself. Try it with different angle, and tell how the tone change. The more apparent tonal difference, the worst the microphone.