Dumb question

K

krs

New member
Well maybe. A student asked me today, and I didn't know the answer.

'Is it possible to have a hypercardiod pattern without the rear lobe?'

I understand in principle how the back vents work on a cardioid, but not well enough to truly understand how hyper- and super- mics are made.

Thanks for any info.
 
Actually I have read it, and this the only post (that I found) that pertains the issue (by the inimitable Harvey):

Omnis work on pressure, figure 8's work on velocity; cardioids are an equal mixture of the two.

An omni is simply a mic with only oneside exposed to the sound, so that it responds to pressure, not direction. A figure 8 responds to velocity and the sound comes in equally from the front and back.

The back sound gets in thru a large opening behind the mic. As you shut off the back opening, the mic becomes more and more like an omni.

Look at the three heads on an Oktava MC012. The omni has no slotted openings, the cardioid has a couple, and the hypercardioid has more. Look at the pattern layout of any multipattern mic; it's always omni at one end and figure 8 at the other end. All the other inbetween patterns are just varying mixtures of these two patterns, with cardioid being equal proportions of both patterns and always in the center of pattern choices.

Here's the breakdown:

Omni = 100% Omni Pattern, 0% Figure 8 Pattern
Wide Cardioid = 75% Omni Pattern, 25% Figure 8 Pattern
Cardioid = 50% Omni Pattern, 50% Figure 8 Pattern
HyperCardioid = 25% Omni Pattern, 75% Figure 8 Pattern
Figure 8 = 0% Omni Pattern, 100% Figure 8 Pattern

Or you could say:

Omni = 100% Pure Pressure Pattern, 0% Velocity Pattern
Wide Cardioid = 75% Pure Pressure Pattern, 25% Velocity Pattern
Cardioid = 50% Pure Pressure Pattern, 50% Velocity Pattern
HyperCardioid = 25% Pure Pressure Pattern, Velocity Pattern
Figure 8 = 0% Pure Pressure Pattern, 100% Pure Velocity Pattern
Click to expand...

I guess I have hard time visualising the difference between 'velocity' and 'pressure' and how opening up the back of the diaphragm changes that (?) (I understand how phase cancellation creates the directional pattern)

Maybe some one has a simple image or explanation to make it clearer for me.

Thanks a million, much appreciated Kirk
 
102 views and only 1 'read the mic thread' reply?

(Maybe it's not a dumb question? :D )
 
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of course it's not a dumb question.

not to be rude or take a personal shot in any way, but I really hated when you ask your teacher a question they can't answer and they automatically think its a "dumb question". you lose points for being smarter than they are. I guess things don't change. Now I have a job and its the same story...
 
thare's no such thing as dumb questions, only dumb answers :D

thare is no way that i've ever heard of to get rid of the "tale"
it is, after all, a by-product of the phaze cancelation that is the reason for the more narrow pickup in the front.

aka, it's part of the package.

maby it's better to say that the pickup pattern is simply what fails to be phaze canceled.

whatever, thare are some smart people out thare and i suspect if it could be done (the physics don't seem possible to me) thay would have found out how by now.

(i hope that wasn't a dumb answer)
 
krs said:
102 views and only 1 'read the mic thread' reply?

(Maybe it's not a dumb question? :D )
Click to expand...
Not a dumb question at all, but I think "dumb question" is a dumb subject line. :)

A subject line like "Mic polar pattern question" might draw more people who actually know something about polar patterns and microphone design. "Dumb question" will tend to get a lot of views just because it's vague.

I'm sorry to say that I fall into the group that knows little about the physics of microphones. As far as I know, the only directional microphones that don't have rear lobes use a parabolic reflector to achieve the directional characteristic.

Here's a link to a page that touches on the mathematical/physical explanation of polar patterns: http://www.notaviva.com/physics/mic02.html

Don
 
FALKEN said:
of course it's not a dumb question.

not to be rude or take a personal shot in any way, but I really hated when you ask your teacher a question they can't answer and they automatically think its a "dumb question". you lose points for being smarter than they are. I guess things don't change. Now I have a job and its the same story...
Click to expand...
Of course it's not a dumb question, but it's gonna take a lotta drawings to explain how it works, even in very simple terms. It might take me a little while, but it's a good idea to know how the different polar patterns are created. Lemme think about this for a while.
 
Harvey Gerst said:
Of course it's not a dumb question, but it's gonna take a lotta drawings to explain how it works, even in very simple terms. It might take me a little while, but it's a good idea to know how the different polar patterns are created. Lemme think about this for a while.
Click to expand...

dang. if harvey has to think about it, I apologize. maybe it was a smart-ass question.
 
FALKEN said:
not to be rude or take a personal shot in any way, but I really hated when you ask your teacher a question they can't answer and they automatically think its a "dumb question".
Click to expand...

Which is why I told the kid I didn't know the answer, and I would consult my extremely knowledgable (and good-looking friends) to the find the answer, as expeditiously as possible :D
 
Ok, here we go. There are three basic types of microphones:

1. Pressure
2. Velocity
3. Combinations of #1 and #2 (called "pressure gradient")

For now, we're only interested in #1 and #2, so here's a drawing showing both types. The gold thing on the left is a singer facing the mics. The black circles indicate a Velocity mic's polar pattern, and the red circle would be a pressure mic's polar response pattern:
 

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Hooray!!!! Harvey's BACK and sharing knowledge again!! Everybody shut-up and pay attention!

(Oh, that means me too...) :D
 
Awesome Harvey!

So to reiterate my confusion, basically I want to know what changes in order to make a diaphragm either pressure based or velocity based? Is it only a question of the vents?

Thanks a million, Kirk
 
I'm getting there, Kirk - it's not as simple as that. I'm actually gonna show you how the different pressure gradient patterns are created, just using a mixture of these two basic patterns. Once you understand the principles, the answers that you're looking for become kinda obvious.
 
Harvey Gerst said:
I'm getting there, Kirk - it's not as simple as that. I'm actually gonna show you how the different pressure gradient patterns are created, just using a mixture of these two basic patterns. Once you understand the principles, the answers that you're looking for become kinda obvious.
Click to expand...


harvey is da man.
 
OK, first, let's look at how a pressure (omni) mic responds to a signal. Since it pretty much only responds to pressure changes, it's not very directional and it'll pick up sound equally from anywhere in the room, no matter which way it's pointed. Here's a picture showing an omni polar pattern and how a positive signal can come from anywhere and be heard. Even though it's shown from the top, looking down, the polar pattern is really more like a balloon, surrounding the mic in all directions:
 

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OK, here's a velocity mic's polar pattern. Big difference.

Speaking into the front of the mic produces a plus (red) signal; speaking into the back of the mic produces a minus (blue) signal; speaking into the side of the mic (or into the top of the mic) produces no signal at all (white).

These are all very important points to remember.

Everybody with me, so far? (Don't assume anything more than I've just explained.)
 

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Awesome Harvey.

Hope I'm not jumping the gun on this question, but with pressure and velocity mics, are we dealing with different types of diaphragms or different electronics? How is this difference achieved?

Keep it coming :D

ps FALKEN for the record I do not teach audio engineering....(which is a good thing :D )
 
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Now THIS is what I'm talking about. There are no dumb questions ... at least not when they get really good answers anyway!!! :)

Nik
 
In a pressure microphone, the sound waves hit the vibrating surface on one side only. In a velocity microphone, sound waves hit the surface from both sides (coming and going, so to speak). That's why, in the velocity microphone, sounds coming from the sides are rejected -- the forces on the opposite sides of the vibrating surface are equal, so they cancel out.
 
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