mic measurement without audio output - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #1 of 4 Old 08-02-16, 03:10 PM Thread Starter
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mic measurement without audio output

Hello,

I would like to measure my loudspeakers (frequency response) but I face some difficulties. They are planar (dipole) loudspeakers so I expected some phase cancellation < 500 Hz but the freq. response looked too good to be true so I got suspicious. I did a new measurement with speakers disconneced and I got a non-flat frequency response:

mic measurement without audio output-zoomed_out.png

zoomed in:

mic measurement without audio output-zoomed_in.png

I would expect a level / flat line as there is no sound. I'm wondering what could be the cause of this non-flat line? The mic is a MCE-2000 electret and I connected the ground wire that is twisted around the signal wire to the mic housing as a shield. I added an extra aluminium foil shield around the mic cable and connected that to the mic housing but it makes no difference.

Could it be the mic wire? Or my pc soundcard? I did a soundcard callibration by connecting mic-in and speaker-out (loop) and it showed a flat frequency repsonse between 10 Hz and 20 kHz. I put the mic (input) sensitivity slide in my volume control at max. setting as the mic is powered by the soundcard and the signal tends to be weak. (no seperate power supply for the mic)

Regards, John
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post #2 of 4 Old 08-02-16, 03:54 PM Thread Starter
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Re: mic measurement without audio output

Hello again,

I did another freq. measurement, with input (mic) level at max sensitivity setting. The "Make a measurement" window reads: "Level OK -25,8 dB". This is the result: (no sound, just mic connected) I see a peak at 50 Hz and a lot of variations in output between 60 and 100 dB.

mic measurement without audio output-another.png
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post #3 of 4 Old 08-02-16, 04:59 PM
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Re: mic measurement without audio output


Quote:
response looked too good to be true so I got suspicious.
The reason your response looks so good is that you have the vertical scale at 280 dB. That would make even the Grand Canyon look like the Great Plains! See here:

Getting Graphs Ready to Post

Regards,
Wayne




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post #4 of 4 Old 08-02-16, 06:29 PM Thread Starter
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Re: mic measurement without audio output

Hi,

thanks for your help. I did a new measurement, I placed the mic in between my headphone and I adjusted the vertical scale. I still see a peak at 50 Hz as usual.

mic measurement without audio output-new.png

Regards
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