3D polar pattern for fig-8 ribbon mics

How different is the polar pattern over frequency of ribbon mics
(say R-121...  or... actually the ACM-3 ) w.r.t. sounds coming from the front or rear,
off-axis from above/below or from the sides ?
(both well away from the inherent fig-8 null)

( Attached pic of the ideal 3D-polar fig-8 plot )

Could be re-formulated as:
would the sound change much when the mic would not be positioned vertically but now horizontally ?
(so the actual ribbon still oriented in the same plane,
but now it's rotated 90 degrees in its own plane).

This results in the '8' of the picture being rotated, but still occupying the same space.
Could imagine this would result in a changed off-axis pickup over frequency... what do you think ?


Background of my question is if it'd be OK w.r.t. the stereo-image to re-position the lower-mic of a Blumlein setup like this.


Thanks,

 Peter

Round condenser bidis have round lobes.

A ribbon is tall and narrow. A Line Array on top of the bidi directionality. For usual dimensions, the horizontal is "ideal" to the top of the audio range, but the vertical narrows above maybe 5KHz-10KHz.

Thanks for the response.
Was fearing that doing this 'repositioned Blumlein' with ribbons would have consequences
while indeed doing such with condensers would not. At least good to know, thanks for the quantification.


The complete story is that this is about a 3-mic array: Blumlein (2* fig-8 side address mics) with a top-entry omni in between
('Native-B format').
A few web-pages suggest so solve the directionality... directivity ? of the omni by putting it in the bottom
position (so facing the ceiling, swapping it with the lower fig-8. Doing so would give that horizontal position,
so it's a matter of an exchange of potential problems here.

Using dual diaphr. condensers here i.s.o. the ribbons might give other problems.

I figure I either just try them all to see what works best - or buy some soundfield-mic or one of the poormans alternatives right away some might suggest...

Thanks

I usually figure that the bigger the diaphragm (or ribbon), the more directional the mic gets at higher frequencies.  Nice thing about the figure-8 is that you really can't get any less directional than those 100% side nulls - live I use figure-8 mics now and then to get isolation between instruments.

If a vertical directionality is a problem you might want to get (or make) a short ribbon. With a smart design the vertical pattern can be equal or better than LD condenser.

What matrix do you use for the Native B?

Best, M

Thanks all for the responses, much appreciated!

Marik said:

If a vertical directionality is a problem you might want to get (or make) a short ribbon. With a smart design the vertical pattern can be equal or better than LD condenser.

Click to expand...

I ran into that Native-B setup (probably more exact: poormans soundfield ignoring Z-axis), so X, Y & W,
and then had a look at my modest mic-collection as to which ones would be suited best.
The article ( http://www.radio.uqam.ca/ambisonic/native_b.html ) mentions SDC (the author uses small AKG fig-8 capsules) & the potential problems of using
the fig-8 of dual diaphr. LDCs.

So when the Royer SF-1 was mentioned as a suited candidate I simply compared it to the dimensions of my cheap ACM-3's & got the impression these were not too unlike, at least w.r.t. dimensions (...).

Next in the article was the issue of the directivity of the third mic, the omni, so then then question came up
what the consequences would be of repositioning the lowest fig-8 ribbon.
Not unlikely it might be better to keep the two fig-8 positioned 'as usual' (so a '45 degrees rotated Blumlein') & stick to the imperfections of the omni, but couldn't say yet.

No idea if the ACM-3 qualifies as a short ribbon; I thought it does.

What matrix do you use for the Native B?

Click to expand...

Nothing yet, I'm still in the mic-selection phase. Have downloaded a few free plugins for it already,
but not tested these yet.

Best regards,

 Peter

clintrubber said:

So when the Royer SF-1 was mentioned as a suited candidate I simply compared it to the dimensions of my cheap ACM-3's & got the impression these were not too unlike, at least w.r.t. dimensions (...).
No idea if the ACM-3 qualifies as a short ribbon; I thought it does.

Click to expand...

IIRC, the SF1 has 1" long ribbon and the ACM3 1.5". Try it first, might work just fine, esp. with low ceilings, etc. I'd think Beyer M130 would be a good candidate there.

Nothing yet, I'm still in the mic-selection phase. Have downloaded a few free plugins for it already,
but not tested these yet.

Click to expand...

I meant, how the signals are mixed together? Is it Blumlein panned to the R and L, and then omni is in a middle?

Best, M

Marik said:

clintrubber said:

So when the Royer SF-1 was mentioned as a suited candidate I simply compared it to the dimensions of my cheap ACM-3's & got the impression these were not too unlike, at least w.r.t. dimensions (...).
No idea if the ACM-3 qualifies as a short ribbon; I thought it does.

Click to expand...

IIRC, the SF1 has 1" long ribbon and the ACM3 1.5". Try it first, might work just fine, esp. with low ceilings, etc. I'd think Beyer M130 would be a good candidate there.

Click to expand...

Should indeed just try it. No M130 here so far, just those cheaper ribbons...

I meant, how the signals are mixed together? Is it Blumlein panned to the R and L, and then omni is in a middle?

Click to expand...

A Blumlein but then the whole thing rotated 45 degrees. It better not be called Blumlein then,
but M/S with the M being a fig-8 as well. Added to that the omni (in between) for the 'W'.
The 'X' & 'Y' are to be fed into one of those plugins (or some day a hardware box...), converting 'X', 'Y' & 'W' to 'L', 'R'. The link above also has some pics.

Adding a third fig-8 mic for 'Z' would make it a complete Native-B setup then I guess, but let's skip 'Z' for now.

It might all be less suited for the kind of stuff I record, but I can't help it that I like to toy around with setups.

Regards,

 Peter