Cardioid to Omni

[Grandflash13]

I know this wouldn't be an ideal thing to do, but I was kind of curious. Would it be possible to take a cardioid mic, let's say a lav mic, and "tape" off the "vents" at the back of the mic and make it an omni.

My mic knowledge is limited but it seems to me that if you did something like that you would be blocking the chambers in which sound coming from the back of the mic is used to cancel itself out.

Just curious

 

[Harvey Gerst]

Yes, it will become "more" omni, but the larger back chamber will cause bumps in the response, compared to a true omni. When singers cup a mic live and get feedback, it's because they're partially closing the back vents, changing the pattern to omni, causing feedback.

 

[Grandflash13]

Ok, that's what I thought but I figured I'd get a more educated response to see.

The reason I am asking is, I work at a TV station and I need to replace a bad mic and 1 of the spares I found is a cardioid kind but it doesn't work well in my current situation. It makes the anchor sound very hallow, for obvious reasons. I was just wondering if there was a way to make this mic more useful for my application.

Thanks Harvey.

 

[clmx]

The diaphragm suspension ist different in Pressure Transducers compared to Pressure Gradient Transducers. Closing these "holes" or "vents" (don't know the correct english term) of a cardioid mic will result in a very odd and unpredictable frequency response. I can't explain it very good in english, but maybe you find the information you are looking for on this site:
http://www.tonmeister.ca/main/textbook/node463.html

 

[Harvey Gerst]

The diaphragm suspension ist different in Pressure Transducers compared to Pressure Gradient Transducers. Closing these "holes" or "vents" (don't know the correct english term) of a cardioid mic will result in a very odd and unpredictable frequency response. I can't explain it very good in english, but maybe you find the information you are looking for on this site:
http://www.tonmeister.ca/main/textbook/node463.html

The "diaphragm suspension" is the same, whether you're talking about Pressure mics or Pressure Gradient mics. The difference between Omnis and all other types is that some of the sound is allowed into the back of the diaphragm in Pressure Gradient mics. The backplate is sealed on Pure Pressure mics (Omnis).

Closing off the rear ports of a Pressure Gradiant mic make it "more" omnidirectional, but the chambers inside will still create some unwanted bumps in the response, because of the holes in the backplate feeding into a resonant chamber behind the capsule.

 

[clmx]

The "diaphragm suspension" is the same, ...

Maybe I used the wrong words, but I know that the "diaphragm calibration" (in german: "Membranabstimmung") is different in Pressure mics and Pressure Gradient mics. Unfortunately I can't find the correct translations for german terms like "hoch/mitten abgestimmt" and "reibungsgehemmt" - it could be something like "high/medium balanced" and "friction-inhibited"? The "resonant frequency" of a "medium balanced" diaphragm in Pressure Gradient Transducers is between 500 and 1000 Hz and damped by friction, pure Pressure Transducers have a "high balanced" diaphragm. (That's all related to condenser microphones and different for dynamic mics).
A german explanation is here: http://de.wikipedia.org/wiki/Mikrofonabstimmung

 

[Harvey Gerst]

Perhaps you meant diaphragm "tensioning"; how tightly the diaphragm is pulled. But that can also vary with diaphragm size, thickness, specific design goals, as well as the manufacturer's overall philosophy.

 

[TragikRemix]

i must, excellent english man. your german and speak better english than some of the people i know.

 

[TragikRemix]

why would i get a negative rep for complimeting someone on their english skills?... thats a first.