Turn a figure-8 ribbon into a hyper?

[Brackish]

I'm guessing I already know the answer but
am not positive. Is there any way to
take a figure-8 ribbon and make it behave
like a hypercardioid? Maybe cover up
one side of the mic with acoustic
deadening material?
Now, don't be too harsh on me with this
because, remember, "there are no stupid
questions".

 

[Warhead]

Find the end of the universe where sound doesn't travel, point one side towards the universe.

You can cover it up, give it a shot. You're going to want to put the most non-reflective surface available behind the mic, one that is non-reflective at all frequencies if possible (typically it isn't).

You can't hurt by trying!

War

 

[Brackish]

You're going to want to put the most non-reflective surface available behind the mic, one that is non-reflective at all frequencies if possible (typically it isn't).

War

Something like Auralex?

 

[Warhead]

Not necessarily, Auralex is going to do decent in the upper end of things but not on the low end unless you go pretty BIG. If you go the foam route make sure it's real thick and let us know how it works out for you!

War

 

[Brackish]

If you go the foam route make sure it's real thick and let us know how it works out for you!

War

Any alternatives to foam?

 

[mshilarious]

Any alternatives to foam?

I've had a Shure 315 (fig 8) and a Shure 330 (cardioid), both use the same ribbon motor assembly, so it would have to be the case that causes the pattern. The 330 had a rubber flange on the front side of the motor assembly, sort of like a miniature horn driver for a PA speaker. The back side of the ribbon was enclosed in a chamber in the mic case, vented at the sides, but otherwise sealed off by the mic case. There was no absorbing material used.

 

[sjjohnston]

Take a coincident omni mic, and mix the two outputs to a single channel, with the level of the omni about 2/3rds as high as the figure 8.

 

[Brackish]

I've had a Shure 315 (fig 8) and a Shure 330 (cardioid), both use the same ribbon motor assembly, so it would have to be the case that causes the pattern. The 330 had a rubber flange on the front side of the motor assembly, sort of like a miniature horn driver for a PA speaker. The back side of the ribbon was enclosed in a chamber in the mic case, vented at the sides, but otherwise sealed off by the mic case. There was no absorbing material used.

So you're saying that it appears that the only difference
between a figure-8 and a cardioid is that the cardioid
has the back side of the case closed off?

 

[mshilarious]

So you're saying that it appears that the only difference
between a figure-8 and a cardioid is that the cardioid
has the back side of the case closed off?

No, there was also that rubber thing on the front of the ribbon assembly.

 

[dgatwood]

So you're saying that it appears that the only difference
between a figure-8 and a cardioid is that the cardioid
has the back side of the case closed off?

No, there still has to be a partial opening in the back for you to get a cardioid pattern. If you just block the back, you'll have an omni with reduced high frequency response from the back.

The way you get a cardioid pattern, if memory serves, is that you try to get just the right amount of sound coming from the back into the front of the capsule so that sound coming from the rear is at about the same level on the back of the diaphragm (through the rear ports) as the amount of sound that bends around the mic and comes in from the front. By doing this, you physically cancel out a majority of the rear noise at the capsule.

Of course, the trivial implementations of that result in significant differences in polar pattern depending on frequency, I believe, and there are various tricks in mic design to minimize this. I'm not familiar enough with the details to say much more than that, though.

Some interesting links on the subject:
http://www.prosoundweb.com/install/spotlight/cardioid/cardioidmics.shtml
http://www.soundonsound.com/sos/sep00/articles/direction.htm
http://www.musiciansfriend.com/document?doc_id=99533&g=home&src=3SOSWXXA
http://media.zzounds.com/media/0300_0714_05_briefguidetomics-6d507907f3b552b3477e0fb1bc70f4ce.pdf
http://www.wipo.int/cgi-pct/guest/getbykey5?KEY=00/03559.000120&ELEMENT_SET=DECL

 

[mshilarious]

No, there still has to be a partial opening in the back for you to get a cardioid pattern. If you just block the back, you'll have an omni with reduced high frequency response from the back.

That's right. In the 330, the back is blocked from direct sound, but the chamber to the rear of the ribbon is open at the side. Of course ribbons are quite null at the sides normally, but somehow the rubber horn on the front must delay sound incident at the front and side enough to produce the cardioid pattern.