Tried MS for the 1st time - WOW

[d_fu]

Originally Posted by pkautzsch

MKH 80 is dual-diaphragm, isn't it.

Yup... Dunno about the 30, though. Don't really know any other double-diaphragm SDC apart from the MKH80/0...

[0VU]

Originally Posted by pkautzsch

....
But, you're right in saying that two cardioid mics can never be in the EXACTLY same position. So for high frequencies the resulting pattern may slightly differ from the ideal.
Theoretically the best fig-8 is one diaphragm which the sound can access from both sides equally. Schoeps MK8 is an example of this.

Good point on the first part but just to pick up on the second.....

The Schoeps MK8 and MK6 are single diaphragm capsules but they're not symmetrical in their frequency response/polar patterns. The only completely symmetrical single diaphragm fig-8 condensor capsules that I know of are the Neumann AK20 and the Sennheiser MKH30. It used to be only the MKH30, which uses a unique capsule design involving a single diaphragm moving between two "backplanes" to achieve symmetry but this was joined by the Neumann AK20 (as pointed out to me elsewhere by David Spearitt), which uses a more conventional single diaphragm/single backplane design and some acoustic modifications around the capsule to give it a symmetrical response. Of the two, the MKH capsule is the more technically pure in it's performance as the acoustic diffraction elements in the AK20 cause a small irregularity in the polar patterns at higher frequencies (though, of these two, I much prefer the AK20).

Afaik, the only completely pure bi-directional pressure gradient mics are those with single diaphragms moving in symmetrical fields, producing a perfect symmetrical output (so ribbon mics (at least, those which haven't been designed to have different responses front and back), and the MKH30 (though that has other issues). Any dual diaphragm/dual capsule mic, or mic using acoustic modifications within the capsule to achieve a bi-directional pickup will have some (possibly very small) errors somewhere in it's frequency and/or polar response. Whether they're audible or problematic is another matter.

On the other hand, if mics sound good I don't let the technicalities stand in the way of using them. I've been very happy with my MK6s and MK8s for many years - I even find the asymmetrical response can be useful sometimes - even in MS (I know it screws the theory - but it sounds fine so I don't really care ).

Related question - can any one tell me what it takes to make the backside of a ribbon have different frequency response? Was it originally an accident or intentional? And how difficult is it to make a symmetrical sounding figure 8?

I do a lot of MS recording with a pair of AT4050s and am very happy with the results. I have a new pair of inexpensive ribons and use them in ORTF to keep the two sides similar, with very good results!

<L>

[roonsbane]

Certain ribbon mics. The Royer 121 and 122 for instance, has an offset ribbon on purpose. It makes the front side a tad bid darker than the back side and this side will distort before the front side as well. It does add a bit more flexibility to the mic.

Cameron

[Yannick]

0VU, what is the AK20 ?

Always looking for a good fig8, but I don't know this one.

[0VU]

Originally Posted by Yannick

0VU, what is the AK20 ?
...

It's the fig-8 capsule for the KM100 Series. Also referred to, when attached to the preamp body to make a complete mic, as a KM120.

[pkautzsch]

Neumann KM 56/76/86 are dual-diaphragm switchable pattern SDCs, as is the S part of the RSM stereo shotgun series.

[JP66]

Originally Posted by David Spearritt

As is the underrated single diaphram KM120. Also, all ribbons are like this as well.

I've heard some great mid-side recordings with the km120. I have a friend that does field recording almost exlusively with a km120/km140 mid-side setup and decodes on the fly with a lunatech V3 pre.

I really dig both mid-side and blumlein. I do mostly field/location recording and in my experience I have found that blumlein is not the best technique to use in less than ideal sounding rooms. however mid-side is pretty good for those situations if you decode the signal back in the studio. It gives you more opportunity to dial in how much room sound you want (at the expense of stereo image).