Figure of Eight Question

[longsoughtfor]

Anyone here experiment with summing back to back condensers to mimic a Figure 8 mike? Any tips on phase or placement?

Cheers
Kevin.

 

[DigitMus]

In theory putting the capsules as close together as possible and reversing polarity on one will yeild a figure 8 emulation. In practice the distance between the diaphragms will cause phase anomalies. Specifically, there will be big phase problems at and around the frequency whose half-wavelength is equal to the distance between the 2 diaphragms [e.g. if the capsules are about 1" apart, frequncies around 6500hz will be most problematic] - the closer the capsules are, the higher the frequencies affected. You would need to get the distance between the diaphragms below 1 cm. to raise the problem frequncy above the range of human hearing. What will this mean to the sound? Well, that will depend on the source, and what you're trying to do with the "fig.8" - it won't hurt anything to try it and see. If you're trying to do a M/S pair, I suspect you will end up with very unnatural stereo imageing and/or loss of high frequency detail.

Scott

 

[arcanemethods]

Anyone here experiment with summing back to back condensers to mimic a Figure 8 mike? Any tips on phase or placement?

Cheers
Kevin.

Join the micbuilders Yahoo group for a lively ongoing discussion of doing that with OEM capsules.

It works very well. One of them should be inverted and then the two summed.

For a number of reasons it is my preferred way of achieving a figure 8. The way to align them is not back to back, that will give high frequency anomolies. Speaking in terms of capsules, they should be placed one atop the other with the diaphragms in the same plane. This will minimize the anomlies from sources on the plane that bisects them where they join.

Even a dual diaphragm design will suffer from there being a delay between the diaphragms on their axis but the main reason I prefer to do it with two cards atop each other is symmetry of the response. Few real figure 8 mics I've seen have the same sensitivity or the same frequency response on the two sides which is really a must for mid/side usage. Using two well matched cards this way will usually give a much more symmetric response.


Bob

 

[Marik]

<Even a dual diaphragm design will suffer from there being a delay between the diaphragms on their axis but the main reason I prefer to do it with two cards atop each other is symmetry of the response. Few real figure 8 mics I've seen have the same sensitivity or the same frequency response on the two sides which is really a must for mid/side usage. Using two well matched cards this way will usually give a much more symmetric response.>

Unless you gonna use the true fig8--ribbon.

 

[arcanemethods]

Unless you gonna use the true fig8--ribbon.

True. But I don't like this in a MS arrangement because the response of the ribbon is likely to be so different from the mid.

That's the other advantage I forgot with using the two side capsule approach for mid side. If you use the same capsule type for the mid and can expect reasonable matching, the mid and side will then also be well matched.

This is hard to accomplish in any other way.

Of course, add one more capsule in the proper geometry and add a little more sophisticated mixing and you've got Ambisonics, my current passion.


Bob

 

[longsoughtfor]

Thanks guys - just what I was looking for. An AKG 414 is on "the list" but for now I'll try Bob's suggestion of keeping them in the same vertical plane.

I read an interview with Geoff Emerick where he said they used to use a Fig 8 mic about 6 feet in front of a bass cabinet. Thought I'd give it a go.

Cheers
Kevin.