Shure SM81

[Emmathom]

Hi guys !
I thought about something... when I (gently) blow on the capsule's vents (so 90° of axis) it does the same noise as when I shake the mic : could the "wind" generated by the movement be the cause of this noise ?

So I replace the capsule by a 56pF and... bingo ! no noise at all when I shake the mic !
This capsule is very sensitive to "air displacement" (as most of the SDC capsules - and even LDC)
Issue fixed ! Mic for sell in a while...

 

[Voyager10]

What did you do to fix the problem? Was there a mechanical problem with the capsule connection?

 

[Emmathom]

What did you do to fix the problem? Was there a mechanical problem with the capsule connection?

Hi @Voyager10 !
No mechanical issue with the capsule.
I did nothing special (see post #21) the noise was coming from "air pressure" to capsule's vents when I shaked it !
I move it quite fast > "wind" is generated > it hits the vents > it makes low noise (as when you blow on the vents)

 

[Voyager10]

OK, thanks. So if you put the mic in a plastic bag, so no 'wind', there's no noise when you shake it?

 

[Emmathom]

Not even so... I'm quite sure it's about "air pressure" to the vents. The mic is fully quite when resting and even when moving gently. Plus the "noise" (very low*) is the same as a blow on the capsule-vents, so...
*very low implies why the "noise" disappears with high-pass filter engaged (-6dB@100Hz)...

 

[Emmathom]

In conclusion I would say that at a purchase price almost equal to that of a WA84 (400€ SM81 vs 350€ WA84) the manufacturing quality of the SM81 is far, far ahead! As I explained this microphone was acquired in 1990 and was first used in the worst conditions for about ten years without ever breaking down.
To me Shure is a great brand above all suspicion. An american company (my 1990 mic is of course made in USA) at same reliability level as german's (or austrian's)

 

[ricardo]

SM81 is one of 2 cardioids with the most extended LF of any available ... a true free-field -3dB @ 50Hz. Hence it will be more susceptible to wind noise & also movement than lesser models.

But capacitor mikes NEED to have their LF limited cos the 1G/capsule capacitance noise goes through the roof at VLF.

Some of your problem may be the extended LF of the SM81 capsule.

But the LF cut switch in the 'OFF' position should still have a roll-off eg below 20-30Hz. Worth checking this is still in place with the filter 'OFF'. This might be a shorted electrolytic problem.

 

[emrr]

Same noise as posted by @Emmathom in his first post?

“Noise” is such a broad concept that simply mentioning the word is not enough to determine the root cause.

different, but could be air movement related. Something not sealed as it should be, etc.

 

[Emmathom]

Guys, it's air movement coming thru the vents to hit the diaphragm. That's all.
I never noticed it before because I never tested the mic by moving it in a such manner.
Just try to (even softly) blow on your sdc cardio rear vents and I'm sure you'll tell me it does the same thing (or move the mic fast enough to generate air pressure)
As far as I'm I'm concerned the subject is closed ...
Thank you all for your help

 

[Barry Hufker]

When I listened to the noise sample, the first thing that came to my mind was "wind noise" from being waved. I didn't post anything because I feared my explanation was too simple and that I was missing something. It's wind noise...