Level difference between 2 AKG CK91 capsules

Question

I have recently borrowed two AKG SE300B preamps from a friend each with a AKG CK91 capsule.

The two CK91 capsules seem to have a difference in level of about 6db, which seems quite a lot to me. I have realized this when I put them on a stereo bar in an A/B-stereo setup (being parallel to each other and facing forward) and pointed them at different sound sources including a speaker.

To investigate further I have wired up one of the SE300B preamps with one capsule, put it in front of a Yamaha HS80M and did a Measurement using a Sine Sweep in Room EQ Wizard. I then exchanged only the capsule and did another measurement. This is a screenshot of the two measurements:

The frequency response looks quite similar from this zoom level, but the levels are off. (Of course the frequency response is heavily influenced by the speaker, the room, etc.)

Is it normal for two capsules of the same model to have such level differences?

Do I just set the preamp levels different to compensate this?

Answer 1

No, it is not normal for two capsules of the same model to have such a level difference. A few tenths of dB would be acceptable, unless you have ordered factory paired capsules (which you should do if you intent is to use them in a stereo setup) which should match more closely.

Using the preamp to compensate this will not not give optimum results, especially for a stereo setup, although it can be a temporary workaround.

As the tests you have been doing seem to indicate that this issue come neither from the preamp or the cable from the capsule to the preamp, I would try to get these capsules checked by an appropriate service center if I were you.