Turning cardioid to omni?

[ekwon]

I was considering getting a some omni capsules for my nt5s. That purchase will probably be next month...

While I was looking at the capsules, an idea occurred to me. Since a cardioid pattern results from the superimposition of an omni and a fig-8, the cardioids have two membranes. The front membrane is sealed on one side (thus it is omni), and the back membrane is open on both sides (thus it is a fig-8). So could I just tape up the vents on my nt5s and turn them into omni patterns?

If the front of the mic only exposes the front diaphragm, and the two vent rings allow exposure for the rear diaphragm, then my theory seems good to me. Since I can't totally isolate the rear diaphragm, it would probably only muffle it and I'd end up with a sub cardioid at high frequency and a mostly cardioid at low freguencies. The mic would loose some sensitivity too. I don't know how the diaphragms are mounted of if they are flush with the capsule interior, but any thoughts from y'all?

Unless anyone has a good argument as to why I shouln't try this out, I'll be doing it. (I've got two pairs so I've got a good comparison.) Any suggestions on my choice of tape?

 

[darrin_h2000]

I wouldnt use tape though...try pipe insulation...you dont want sticky mics.

 

[mshilarious]

I was considering getting a some omni capsules for my nt5s. That purchase will probably be next month...

While I was looking at the capsules, an idea occurred to me. Since a cardioid pattern results from the superimposition of an omni and a fig-8

Kinda.

the cardioids have two membranes. The front membrane is sealed on one side (thus it is omni), and the back membrane is open on both sides (thus it is a fig-8).

No. Most (not all) cardioids have only a single diaphragm. You can derive a cardioid pattern mathematically (electrically) from a pressure-gradient (fig-8) and pressure capsule, but that's not the most common way. With a single diaphragm you create an acoustic delay chamber on the backside such that you impart a delay on rear incident sound so it strikes the front and back of the diaphragm at the same time. That's what the NT5 does.

So could I just tape up the vents on my nt5s and turn them into omni patterns?

Yes, but probably not one that you would want. A cardioid diaphragm is tuned differently than an omni diaphragm, so it will have a resonant frequency somewhere you probably don't want a giant peak, often smack in the middle of the midrange.

Also, since you aren't plugging up the backplate but rather cutting off easy access to the acoustic chamber, the resulting resonances can actually get rather complicated. Read: several steep peaks somewhere in the upper mids.

Those are just my wild guesses as to what will happen (not having experimented with this particular capsule), but I bet I'm pretty close. It isn't likely to be a response that you will enjoy, but go ahead and try, it doesn't cost anything. Just don't think that is what the omni capsule will sound like; the real omni will sound much much better.

 

[ekwon]

Been there done that now

MsHilarious... you are mostly right.

I taped up the vents and I did get an omni pattern. The sound wasn't that bad. I was expecting horrific peaks in the mid, but really they were pretty tame and even more tamable with some eq. I would do it again, but I would way rather spend the 180 dollars on a pair of capsules. The index cards I taped tightly to the mics were just not aesthetically okay.

 

[mshilarious]

MsHilarious... you are mostly right.

I taped up the vents and I did get an omni pattern. The sound wasn't that bad. I was expecting horrific peaks in the mid, but really they were pretty tame and even more tamable with some eq. I would do it again, but I would way rather spend the 180 dollars on a pair of capsules. The index cards I taped tightly to the mics were just not aesthetically okay.

It varies a lot by the capsule. My favorite capsule to "omni-ize" just gets a broad, flat peak centered at 500Hz. But it still doesn't have the high-frequency or especially low-frequency response of a pressure omni. I'm pretty much devoted to pressure omnis because they sound so much better to me than any cardioid capsule. And I like fig-8s too. Anything in between, not so much

 

[Bob Ross]

I wouldnt use tape though...try pipe insulation...you dont want sticky mics.

Or use 3M #8402 polyester tape; leaves no residue. None. Best Kept Secret in recording studio paraphenalia.

But yeah, MSHilarious is right, taping up the ports, while usually succeeding in converting your cardioid mics to non-directional mics, has always ime also succeeded in turning a decent sounding cardioid into a lousy sounding omni.