LDC issue in Fig.8 & Omni (but fine in Cardioid)

[alexdingley]

I have two AT4050/CM5 mics, and I love them to death. I use them in cardiod pattern almost ALL of the time, but I recently tried fig.8 on them, and one of them seems to have a really noisy issue when in Fig.8. The problem continues (on that mic) when in Omni. That mic works fine in Cardioid, but is unusable (though it still passes signal) in Fig.8/Omni modes. The other 4050 is fine in all 3 patterns.

In fig.8 / omni, this mic emits a constant low-freq rumble (sounds like persistent wind & almost like rustling leaves + there are loud electrical pops).

If this is a capsule issue (with the “rear” diaphragm), I suppose it would need to be sent in for support (I've already emailed AT support to see what the bench fees are), but if this is a circuit issue, I wonder if there's a cap/resistor/etc that could fail that would cause this problem. If anyone on here is a particularly savvy mic/capsule troubleshooter, would you mind letting me know what your next step tests/investigations would be?

[Scodiddly]

Probably an issue with the backside, as that capsule (and the associated circuitry) is only used in non-cardioid modes.

The super high impedance section, the part the capsule sees, is usually pretty hard to measure in any meaningful way. AT official repair will probably just replace assemblies until the problem goes away. I'd probably poke around with an ESR meter on all the big capacitors and do a magnifying glass inspection for questionable connections and solder joints. Try gently tugging on the wire(s) that connect the capsule to the circuit; if it breaks right off then there's your problem.

[digitaldrummer]

when I've had a mic that sounds like you describe, it's usually been a bad capsule (or in this case the rear side of the capsule). You could try putting the mic in a bag of rice or sealed in a bag with silica gel (desiccant) packs if you have them. If it's moisture (and a lot of time that's what kills them) it might help but it might not. If not, you'd have to replace the capsule (which likely means sending it back to AT). Also make sure you store mics with the silica gel packs (and that they are in a zipped pouch or some other mostly airtight container) and it will help prevent damage to the capsules.

note - if you use rice be really careful to just set it in the bag - don't disturb the rice since it can be a little dusty or powdery and you don't want that on the diaphragm either.

[Nick Sevilla]

It's one of two issues:

1. There is a bad capacitor in the circuit section regarding the backplane diaphragm.

2. The backplane diaphragm has gone bad.

Either way, I recommend you have it serviced by the company.

https://www.audio-technica.com/en-us/su ... air-center