Topic: AKG CK63 ULS - How important is a matching pair?

[TheMetalist]

I ordered two AKG CK 63 ULS capsules (hypercardioid) and got them a few days ago. For some reason (which I can't remember) I never asked for a matching pair. I compared the graphs of the frequency responses enclosed in the boxes and to me they don't look very close.

Anyone here with better knowledge than me... Are these close enough or should I ask for a replacement? I guess an identical match is almost impossible but how close is okay? How will a slight frequency difference affect my recordings?

A picture of both graphs:

[jbell]

I don't think that AKG matches capsules, but I could be wrong!

[DSatz]

If you're recording in stereo with a coincident or closely-spaced pair, a close match is quite important. The closer your microphones are placed to one another, the more the accuracy of the overall stereo pickup depends on their having well-matched characteristics--and that includes more than just the on-axis response that these graphs show in a highly smoothed fashion.

The thing is, unfortunately, one of your capsules (the one in the lower graph) has distinctly less bass than the other one--and that same capsule also has a tipped-up midrange (which is crucial), and somewhat more elevated high-frequency response.

I wouldn't be happy with this pair for coincident or closely-spaced stereo recording. For ordinary studio use as single mikes, though, they'd be fine, I'm sure. Each microphone has a response curve that would be useful for certain preferances and situations--just not the situation where you need them to both have the same response to the extent possible, which is more of an issue for recording with just two "overall" or "main" mikes than it is for most other applications.

--best regards

[TheMetalist]

Thank you both for your reply.

I contacted the seller and he will send my graphs forward to the supplier and ask for a better match. Hopefully he will find something (at least slightly) better than this.

[goodcooker]

There is a way to account for the difference with a parametric EQ curve, which is a pain but achievable, since you have the graphs. I would work with your vendor to get a better matched pair if at all possible. I don't think AKG offers matching service from the factory but a dealer may be able to sort through their inventory and get two graphs that are closer ( ideally ~1 dB +/- across the graph ).

[audBall]

Nope, no AKG matching from the factory that I'm aware of (edit - on the ck6x capsules). The AKG ck6x capsule boxes they come in are sealed with large sticker labels and need to be cut open. I'm not sure how a vendor would be able to verify the frequency response beforehand, unless they're willing to open them up.

edit - for clarity

[DSatz]

I don't know of any vendor, except maybe for an acoustical consulting and engineering firm, who could do that. Even the U.S. distributors of Neumann and Schoeps can't do that--if acoustical measurements are needed, they send the microphones to the mother ship in Europe. I think the question is whether AKG in Vienna is prepared to handle special orders for matched capsules "gegen Aufpreis" (= for an extra fee). They individually measure each capsule during production, so that's the logical place for the selection to occur.

I was offered selected, matched pairs of AKG microphones by their head of U.S. operations years ago (a Mr. Geoff Langdon), but that was before the company was acquired by Harman International. The capsules in their stereo microphones are (or had better be!) selected, matched pairs, so they presumably have a protocol in place for doing it even now, whether they advertise it or not. I'd suggest a call to their U.S. headquarters.

[audBall]

You are correct, DSatz. I was referring to the ck6x capsules and edited my post for clarity. I did own a c414b-xls pair at one time that were factory matched. There may be a possibility of obtaining them from the manufacturer 'matched' prior to distribution.

[TheMetalist]

The dealer sent me an e-mail that the 1 dB difference is minimal and should not cause any problem.


So my friends, is it an issue or not? I'm getting confused here. What should I tell them? Maybe the best thing is to just let it go... 

[rocksuitcase]

The dealer sent me an e-mail that the 1 dB difference is minimal and should not cause any problem.


So my friends, is it an issue or not? I'm getting confused here. What should I tell them? Maybe the best thing is to just let it go... 

I think dsatz has the best point here, but I see a bit more then 1dB difference below 300Hz, closer to 2-3dB at points. The differences with the high end is a bit noticeable, but not as different as the low end.
That's my opinion re the freq response. my opinion re AKG capsule matching is that aside from the 414 series I do not think they do it by default. OTH, if these are new out of the box and you've never used them I'd ask to swap out at least one of them (the one in the bottom graph).
Again, what someone wrote is if you are a studio guy and using them to close mic instruments etc these would be perfectly acceptable. Doing mid to far field recordings it would be great if they were "matched" a bit closer.
in summary, did the dealer say he wouldn't refund or replace? if not, ask them. You've got to be within a reasonable return timeframe (IMO).

[goodcooker]

The dealer sent me an e-mail that the 1 dB difference is minimal and should not cause any problem.


So my friends, is it an issue or not? I'm getting confused here. What should I tell them? Maybe the best thing is to just let it go... 

If it were me the only thing that would really worry me looking at the graphs is that the lower frequencies (below ~130hz on the graph) are off by ~3 dB. That is an easy fix in post production.