baffling question about cardioid mics pickup pattern

[groover]

It is my understanding that the way a cardioid mic pickup pattern in controlled is through some kind of interaction/cancellation between sound hitting the mic from the front and sound hitting it from the rear. (thus a cardioid works more like an omni when the rear of the mic is closed off, like when cupping it in one's hand for example)

This made me wonder about baffles and isolation. Let's say we are mic'ing sound source A with a cardioid mic placed south of the source, facing north. South of the mic is another sound source B which we want to keep out of the cardioid as much as possible.

If we put a baffle up just south of the mic to block source B would this not cause less sound pressure to hit the mic from the southerly direction, thereby interfering with the internal cancellation, and causing the mic to reproduce more of the sound of B which is hitting it from other indirect directions than if there were no baffle? Or am I missing something?

Alternate form of question - what is the most effective placement of baffles to keep source B out of the mic?

[Scodiddly]

The baffling has to be right around the back of the capsule - it's like an omni with a leak in the shell surrounding the backside of the diaphragm.

[groover]

huh? or should I say to do which?

[Scodiddly]

If you just hang a diaphragm in open air, it's going to be a figure-8. If you enclose the backside, it'll be an omni. Cardioid is produced by mixing figure-8 with omni, basically by letting some sound leak through the enclosure. So cardioid mics have the back enclosed by a material (cloth or foam like stuff) that allows some sound to get through. Or maybe just tiny holes... but the important thing is that it's part of the enclosure around the back of the diaphragm. Bear in mind that all this is happening in a very localized area. It happens in a space where a wavelength of about the same size would be 10KHz or higher.

Your hypothetical baffles out in open space aren't part of that enclosure.

[groover]

Yes, the baffles are farther away, but don't they effectively change the direction of the sound source, thus changing the way it will be cancelled by the capsule?

Or maybe the baffles are cutting/blocking the direct sound and what I am dealing with is reflected sound, which is thus coming from a different direction than due south in my hypothetical.

[Scodiddly]

I think you're taking the very special (and weird) case of how a cardioid works and trying to apply it to all baffles in general.

A baffle very close to the back of a mic might compromise the pickup pattern somewhat, but otherwise it'll act as a baffle and block some sound from that direction.

[ott0bot]

this question is truly baffling!