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Hi all,

I'm finally getting around to spending some time with REW. The Coronavirus pandemic has me unable to work, so I've got some time on my hands. Unfortunately, my EMM-6 mic seems to have some issues. The output from the mic is dropping to the level of the noise floor below 300hz. Parts express has agreed to take it back, but I just wanted to make sure I haven't missed anything that might be causing this beyond a defective mic.

I have used two different usb audio interfaces, a focusrite itrack solo and a M-Audio usb fasttrack. With the focusrite, I used the onboard phantom power, with the M-Audio, I used a Rolls standalone phantom power unit. I level matched my subs and speakers usin an Extech 407735 meter as well.

The mic just produces the same output as it does with no sound playing for any signal below approximately 300hz. With 106db of headroom post spl calibration in REW, and playing the "subwoofer" test signal at 75db (verified by the extech, slow response c weighting), I see the equivalent reading of no sound playing, ie the ambient level of my living space. This is roughly 55db and equates to around -40db on the meters in rew. When I do the same procedure with the main speaker level test signal, I get 75db, same as measured by my meter. The measurement graphs reflect this with the output below 300hz at approximately the level of the noise floor of the mic / ambient levels.

Is there anything I might be missing? Can I make some useful practice attempts using the ac output from my extech meter into my usb audio interface and get anything useful? Is it even worth the effort or should I just wait until the replacement mic comes in?
 

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Since you tried two interfaces, that would suggest the mic is the problem. However, it seems to me that a mic would either work or it wouldn’t.

I’d try tapping on the head of the mic and see what you hear through the speakers. You would normally get something below 300 Hz through the speakers and sub. If so that would confirm if the mic is working as it should.

Regards,
Wayne A. Pflughaupt
 
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