mic polarity

[smoothmoniker]

So, I was pulled up short by a question from a kid in the studio today, and I didn't have a good answer for him. Maybe the Slutz can edjumacate me.

What causes mic polarity patterns (cardiod, omni, etc.)? I know how the different patterns function, but what's actually going on inside the capsule that yield the results? Particularly when a mic has a switchable pattern, without a capsule change.

One of those things I never stopped to think through, but seems like i ought to know.

Thanks all
-sm

[Marshall Simmons]

most of these mics have a dual digaphragm that adds different patterns together to get one patter. For instance, an omni plus a figure 8 pattern will equal a cardiod patter.

I'm sure someone can give a better answer then i, but this is the idea


Marshy marsh

[SaxonSound]

Here's a really good read on the subject from Harvey Gerst in his Pro Sound Web forum http://recpit.prosoundweb.com/viewtopic.php?t=3517

[Roland]

I'll stab at a quick explanation here!

Imagine two diaphrams back to back. Both are effectively cardiod response.

Add the two capsules in equal amounts you produce an omni response.

Add the rear capsule in negative phase you produce a figure of eight response.

Now you really want to get creative....... add a little of the rear capsule and you will get wht we call these days wide cardiod, reverse the phase of the rear capsule and this is then hypercardiod.

All this is how mics like the AKG 414, U87, and other alike dual diaphram mics switch their polar patterns.

In the case of mics with a single diaphram polar patterns are achieved using an accoustic housing on the back of the mic. Think of it like a loudspeaker baffle. By controlling the amount of rear leakage of sound into the capsule you can control the response that way. In the case of pencil type microphones this system works well. Good examples are things like the Schoeps, DPA's Sennheisers etc. I am not personally a fan of large single element condensors like the Audio Technica 4033 where the element is in an upright configuration as I find the off axis response too coloured for my taste. Hope this is of some help.

Good luck!

Roland

[smoothmoniker]

thanks guys. very helpful. The prosoundweb post is a really well written brief on the matter.

-sm